Physical, Physiological, and Dietary Comparisons Between Marine Corps Forces Special Operations Command Critical Skills Operators and Enablers

Physical, Physiological, and Dietary Comparisons Between Marine Corps Forces Special Operations... Abstract Introduction Tactical demands of a Marine Corps Forces Special Operations Command (MARSOC) Critical Skills Operator (CSO) require high levels of physical performance. During combat deployments, teams of CSOs are supplemented with enablers who specialize in mission-specific tasks. MARSOC CSOs and enablers serve alongside each other in extreme combat environments, often enduring the same physical demands, but the selection process for each group is very different. The purpose of this observational study was to quantify the physical, physiological, and dietary differences of MARSOC CSOs and enablers, as this may have a direct impact on tactical performance and provide important information to shape future research. Materials and Methods Fat free mass (FFM), fat mass (FM), fat mass index (FMI), fat free mass index (FFMI), anaerobic power (AP), anaerobic capacity (AC), aerobic capacity (VO2max), knee flexion (KF), knee extension (KE), trunk extension (TE), and trunk flexion (TF) isokinetic strength were collected. Dietary intake was collected using automated self-administered 24-hr dietary recalls (ASA24) for a subgroup of subjects. Results Testing on 164 male CSOs (age: 27.5 ± 3.8 yr, height: 178.7 ± 6.5 cm, mass: 85.7 ± 9.1 kg, and 7.6 ± 2.9 yr of military service) and 51 male enablers (age: 27.8 ± 5.4 yr, height: 178.4 ± 8.5 cm, mass: 83.8 ± 11.8 kg, and 7.9 ± 5.4 yr of military service) showed there were no significant differences for age, height, mass, or years of military service. (p> 0.05). CSOs demonstrated greater physiological performance in AP (W/kg) (p= 0.020), AC (W/kg) (p = 0.001), and VO2max (ml/kg/min) (p = 0.018). There were no significant differences in FM and FFM (p > 0.05), however CSOs demonstrated significantly higher FFMI (p = 0.011). CSOs also demonstrated greater KF (%BW) (p = 0.001), KE (%BW) (p = 0.001), TE (%BW) (p = 0.010), and TF (%BW) (p = 0.016). No differences in energy or macronutrient intake were observed in the subgroup. Conclusions MARSOC CSOs demonstrated significantly greater FFMI, AP, AC, VO2max, KF, KE, TE, and TF compared with enablers. Dietary intake was consistent between groups, but fueling concerns were identified for all personnel in the subgroup. These findings suggest the need for future studies to examine what physiological and strength thresholds are necessary to operate effectively as a member of a MSOT and determine the relationship between specific performance deficits and risk of injury. In addition, the integration of nutrition strategies that augment and optimize the performance of both CSOs and enablers may be beneficial. INTRODUCTION U.S. Special Operations Forces (SOF) have a challenging occupation, often requiring personnel to perform at their maximal physical and physiological capacity.1 SOF are assigned to specialized military missions, requiring variable and unpredictable levels of strength, power, and endurance, while also presenting unique metabolic challenges, including matching nutrient needs with fuel demands.2,3 SOF operations, or tasks within an operation can range from long-duration, low intensity, aerobic based tasks, to short-duration, high-intensity anaerobic tasks. These wide variations in task demand require multifaceted strength, power, and endurance capabilities in conjunction with sufficient nutritional intake to fuel periods of high-intensity and/or extended moderate intensity physical activity.4,5 In addition to task performance improvements, high levels of aerobic fitness and strength correlate with reduced risk of musculoskeletal injury.6–8 Reducing the incidence of musculoskeletal injury in SOF is critical to ensure tactical readiness and availability for deployment.9 The United States Marine Corps Forces Special Operations Command (MARSOC) deploy Marine Special Operations Teams (MSOTs) that consist of Critical Skills Operators (CSOs) and enablers. CSOs are highly trained in combat skills and tactics in order to complete a wide variety of complex military operations. Enablers supplement CSOs during deployments and operations by providing specialized skill sets ranging from medical care, to intelligence and communications.10 As a MSOT, CSOs and enablers operate alongside each other in tactical situations, often enduring the same physical task demands. Although CSOs and enablers deploy as a unit, the selection process and training of CSOs and enablers are very different. The assessment and training to become a CSO are exhaustive, requiring high levels of tactical and physical performance, while an enablers’ selection is primarily based on military occupational specialty and less on physical or tactical performance. Regardless, performance deficiencies among enablers have a similar impact on force readiness and MSOT capability. CSOs and enablers are both critical components of an MSOT and absence or inefficient performance due to suboptimal physical conditioning or injury may be detrimental to special operations missions by reducing the overall capability of a MSOT. Therefore, the purpose of this observational study was to quantify the differences in physical, physiological, and dietary characteristics between MARSOC CSOs and enablers as this may have a direct impact on the tactical capability of a MSOT. This information will help identify team specific weaknesses and provide data that will assist in the advancement of training programs and selection processes to help improve overall MSOT performance and the prevention of injuries. METHODS Subjects A total of 164 male CSOs (age: 27.5 ± 3.8 yr, height: 178.7 ± 6.5 cm, mass: 85.7 ± 9.1 kg, and 7.6 ± 2.9 yr of military service) and 51 male enablers (age: 27.8 ± 5.4 yr, height: 178.4 ± 8.5 cm, mass: 83.8 ± 11.8 kg, and 7.9 ± 5.4 yr of military service) were recruited to the study (Table I). Inclusion criteria included clearance for full and unrestricted participation in physical and tactical training, and no history of musculoskeletal injury within the past month that led to training cessation or medical treatment. Subjects were also asked to limit any strenuous physical training, avoid caffeine, nicotine, and alcoholic beverages 24 h prior to testing. The study was approved by the University of Kentucky’s Institutional Review Board. Written informed consent was obtained from each subject prior to participation in the study. Table I. Subject Characteristics   CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD  Age (years)  164  27.5  3.8  51  27.8  5.4  0.720  Height (cm)  164  178.7  6.5  51  178.4  8.5  0.809  Mass (kg)  164  85.7  9.1  51  83.8  11.8  0.229  Years of service  162  7.6  2.9  51  7.9  5.4  0.867    CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD  Age (years)  164  27.5  3.8  51  27.8  5.4  0.720  Height (cm)  164  178.7  6.5  51  178.4  8.5  0.809  Mass (kg)  164  85.7  9.1  51  83.8  11.8  0.229  Years of service  162  7.6  2.9  51  7.9  5.4  0.867  Table I. Subject Characteristics   CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD  Age (years)  164  27.5  3.8  51  27.8  5.4  0.720  Height (cm)  164  178.7  6.5  51  178.4  8.5  0.809  Mass (kg)  164  85.7  9.1  51  83.8  11.8  0.229  Years of service  162  7.6  2.9  51  7.9  5.4  0.867    CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD  Age (years)  164  27.5  3.8  51  27.8  5.4  0.720  Height (cm)  164  178.7  6.5  51  178.4  8.5  0.809  Mass (kg)  164  85.7  9.1  51  83.8  11.8  0.229  Years of service  162  7.6  2.9  51  7.9  5.4  0.867  Study Design This study was an observational analysis. Subjects completed a 1-d laboratory protocol that consisted of an all-encompassing performance assessment. A subgroup completed a 24 h dietary recall. All laboratory assessment categories were completed in the following order: anthropometrics, anaerobic performance, strength, dietary assessment, and aerobic capacity. Anthropometrics Average height from two measurements was taken barefoot using a wall stadiometer (Doran Scales, Inc, Batavia, IL, USA). Body mass (kg), fat free mass (FFM), and fat mass (FM) were estimated using Bod Pod (Bod Pod Body Composition System, Cosmed, Chicago, IL, USA). Fat mass index (FMI) and fat free mass index (FFMI) were calculated from fat mass and fat free mass Bod Pod measurements and height measurements (FMI = fat mass [kg]/height [m2]; FFMI = fat free mass [kg]/height [m2]). FMI and FFMI are height-normalized indices of body composition.11 The Bod Pod was calibrated according to factory recommendations the day of each testing session. Anaerobic Performance Peak power (anaerobic power – AP) and mean power (anaerobic capacity – AC) were measured using a VeloTron cycling ergometer (RacerMate, Seattle, WA, USA) during a Wingate protocol. Seat and handlebar position were adjusted to ensure a comfortable position and 10o flexion of the knee during full extension. Following a 5-min warm up (125 W), subjects completed a 30-s Wingate protocol (9.0% body weight braking torque). Subjects were instructed to pedal as hard and as fast as they could against the applied resistance for the length of the test, all while maintaining a seated position and front handgrip position. Verbal encouragement was provided by the investigators. AP and average AC were analyzed in absolute units (W) as well as relative to body weight (W/kg). Aerobic Capacity Maximal oxygen uptake (VO2max) was assessed using a metabolic gas analyzer (TrueOne 2400, ParvoMedics, Sandy, UT, USA) during a modified Astrand treadmill protocol to volitional exhaustion. The treadmill protocol was based on a variation of the protocol designed by Astrand.12 Heart rate data were collected with a heart rate monitor (Polar USA, Lake Success, NY, USA) and blood lactate was assessed with a portable lactate analyzer (Lactate Pro, Arkray, Inc, Kyoto Japan). The speed for the test was selected according to the subject’s most recent self-reported three mile run time, and incline was increased 2% every 3 min until volitional exhaustion. Strength Isokinetic strength of the knee and trunk was assessed using an isokinetic dynamometer (Biodex Medical Systems, Inc., Shirley, NY, USA). Knee extension/flexion strength and trunk extension/flexion strength were measured during a concentric/concentric protocol at 60°/s with submaximal and maximal practice repetitions. The test consisted of five maximal strength repetitions (100% max effort) with verbal encouragement from the investigators. Strength was determined by the average of five repetitions, and analyzed in absolute units (Nm) as well as relative to body weight (%BW). Diet Assessment A subgroup (CSOs = 27, enablers = 22) reported their dietary intake via the Automated Self-Administered 24-h (ASA24) dietary recall system on a computer. Before data collection, subjects were provided detailed instruction by investigators on how to complete the recall survey. Following familiarization, they completed the 24-h dietary recall survey during the laboratory testing session. Statistical Analysis Data were assessed for normality via histogram plots and Shapiro–Wilk tests. Independent samples t-tests were used for normally distributed data. Mann–Whitney U tests were used for data that were not normally distributed. Data are presented as mean ± standard deviation (SD). All physiological performance and absolute strength data were analyzed collectively and presented as percentage of CSOs and enablers in the 0–25th, 25–50th, 50–75th, and 75–100th percentiles. Fisher’s exact tests were used to analyze the association between the percentage of CSOs and enablers in each percentile. Data were also analyzed and presented relative to a normal distribution curve. SPSS Statistics for Windows (SPSS Inc., Chicago, IL, USA) version 23 was used for all analyses. Significance was set at p< 0.05. RESULTS Laboratory Assessments Descriptive data for both groups are presented in Table I. There were no significant differences for age, height, mass, or years of military service between CSOs and enablers (p> 0.05). Physiological and strength laboratory data relative to mass are presented in Table II. There were no significant differences in FM, FFM, and FMI (p > 0.05), however, CSOs had significantly greater FFMI than enablers (p= 0.011). CSOs demonstrated significantly greater physiological performance than enablers in AP (W/kg) (p = 0.020), AC (W/kg) (p = 0.001), VO2max (ml/kg/min) (p = 0.018), and VO2 (ml/kg/min) @LT (p = 0.007). There were no significant differences in VO2max% @LT (p > 0.05). CSOs also demonstrated greater KF (%BW) (p = 0.001), KE (%BW) (p = 0.001), TE (%BW) (p = 0.010), and TF (%BW) (p = 0.016). Table II. Physiological and Strength Measures   CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD    Physiological   Fat free mass (kg)  163  71.1  7.1  49  68.8  9.4  0.067   Fat mass (kg)  163  14.7  5.0  49  15.3  6.2  0.474   Fat free mass index  163  22.2  1.6  49  21.5  1.8  0.011*   Fat mass index  163  4.6  1.5  49  4.8  1.9  0.474   Anaerobic power (W/kg)  162  13.0  0.6  46  12.7  0.8  0.020*   Anaerobic power (W)  162  1121.4  150.7  46  1089.3  190.6  0.232   Anaerobic capacity (W/kg)  162  9.1  0.8  46  8.5  1.0  0.001*   Anaerobic capacity (W)  162  785.1  94.4  46  731.2  134.1  0.003*   VO2max (ml/kg/min)  134  49.6  4.5  46  47.7  4.4  0.018*   VO2max (l/min)  134  4.1  0.4  46  3.9  0.5  0.001*   VO2max% @LT  134  90.3  3.9  46  89.7  4.4  0.350   VO2 (ml/kg/min) @LT  134  44.7  3.9  46  42.8  4.5  0.007*   VO2 (l/min) @LT  134  3.8  0.3  46  3.5  0.5  0.001*  Strength   Knee flexion (%BW)  154  140.9  23.0  43  125.4  25.8  0.001*   Knee flexion (Nm)  154  121.0  23.8  43  105.0  25.2  0.001*   Knee extension (%BW)  155  266.8  45.8  43  239.1  53.4  0.001*   Knee extension (Nm)  155  229.0  46.9  43  201.3  53.4  0.001*   Trunk extension (%BW)  152  407.8  77.5  43  374.6  65.6  0.010*   Trunk extension (Nm)  152  348.9  76.7  43  313.9  65.5  0.018*   Trunk flexion (%BW)  153  242.1  39.6  43  224.9  48.8  0.016*   Trunk flexion (Nm)  153  207.5  41.0  43  190.0  52.3  0.034*    CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD    Physiological   Fat free mass (kg)  163  71.1  7.1  49  68.8  9.4  0.067   Fat mass (kg)  163  14.7  5.0  49  15.3  6.2  0.474   Fat free mass index  163  22.2  1.6  49  21.5  1.8  0.011*   Fat mass index  163  4.6  1.5  49  4.8  1.9  0.474   Anaerobic power (W/kg)  162  13.0  0.6  46  12.7  0.8  0.020*   Anaerobic power (W)  162  1121.4  150.7  46  1089.3  190.6  0.232   Anaerobic capacity (W/kg)  162  9.1  0.8  46  8.5  1.0  0.001*   Anaerobic capacity (W)  162  785.1  94.4  46  731.2  134.1  0.003*   VO2max (ml/kg/min)  134  49.6  4.5  46  47.7  4.4  0.018*   VO2max (l/min)  134  4.1  0.4  46  3.9  0.5  0.001*   VO2max% @LT  134  90.3  3.9  46  89.7  4.4  0.350   VO2 (ml/kg/min) @LT  134  44.7  3.9  46  42.8  4.5  0.007*   VO2 (l/min) @LT  134  3.8  0.3  46  3.5  0.5  0.001*  Strength   Knee flexion (%BW)  154  140.9  23.0  43  125.4  25.8  0.001*   Knee flexion (Nm)  154  121.0  23.8  43  105.0  25.2  0.001*   Knee extension (%BW)  155  266.8  45.8  43  239.1  53.4  0.001*   Knee extension (Nm)  155  229.0  46.9  43  201.3  53.4  0.001*   Trunk extension (%BW)  152  407.8  77.5  43  374.6  65.6  0.010*   Trunk extension (Nm)  152  348.9  76.7  43  313.9  65.5  0.018*   Trunk flexion (%BW)  153  242.1  39.6  43  224.9  48.8  0.016*   Trunk flexion (Nm)  153  207.5  41.0  43  190.0  52.3  0.034*  *Significant difference between personnel P < 0.05. kg, kilograms; W, watts; ml/kg/min, milliliters oxygen per kilogram of body weight per minute; %BW, percentage of body weight in kilograms; Nm, newton meters; LT, lactate inflection; VO2max%, percentage of VO2max (ml/kg/min). Table II. Physiological and Strength Measures   CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD    Physiological   Fat free mass (kg)  163  71.1  7.1  49  68.8  9.4  0.067   Fat mass (kg)  163  14.7  5.0  49  15.3  6.2  0.474   Fat free mass index  163  22.2  1.6  49  21.5  1.8  0.011*   Fat mass index  163  4.6  1.5  49  4.8  1.9  0.474   Anaerobic power (W/kg)  162  13.0  0.6  46  12.7  0.8  0.020*   Anaerobic power (W)  162  1121.4  150.7  46  1089.3  190.6  0.232   Anaerobic capacity (W/kg)  162  9.1  0.8  46  8.5  1.0  0.001*   Anaerobic capacity (W)  162  785.1  94.4  46  731.2  134.1  0.003*   VO2max (ml/kg/min)  134  49.6  4.5  46  47.7  4.4  0.018*   VO2max (l/min)  134  4.1  0.4  46  3.9  0.5  0.001*   VO2max% @LT  134  90.3  3.9  46  89.7  4.4  0.350   VO2 (ml/kg/min) @LT  134  44.7  3.9  46  42.8  4.5  0.007*   VO2 (l/min) @LT  134  3.8  0.3  46  3.5  0.5  0.001*  Strength   Knee flexion (%BW)  154  140.9  23.0  43  125.4  25.8  0.001*   Knee flexion (Nm)  154  121.0  23.8  43  105.0  25.2  0.001*   Knee extension (%BW)  155  266.8  45.8  43  239.1  53.4  0.001*   Knee extension (Nm)  155  229.0  46.9  43  201.3  53.4  0.001*   Trunk extension (%BW)  152  407.8  77.5  43  374.6  65.6  0.010*   Trunk extension (Nm)  152  348.9  76.7  43  313.9  65.5  0.018*   Trunk flexion (%BW)  153  242.1  39.6  43  224.9  48.8  0.016*   Trunk flexion (Nm)  153  207.5  41.0  43  190.0  52.3  0.034*    CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD    Physiological   Fat free mass (kg)  163  71.1  7.1  49  68.8  9.4  0.067   Fat mass (kg)  163  14.7  5.0  49  15.3  6.2  0.474   Fat free mass index  163  22.2  1.6  49  21.5  1.8  0.011*   Fat mass index  163  4.6  1.5  49  4.8  1.9  0.474   Anaerobic power (W/kg)  162  13.0  0.6  46  12.7  0.8  0.020*   Anaerobic power (W)  162  1121.4  150.7  46  1089.3  190.6  0.232   Anaerobic capacity (W/kg)  162  9.1  0.8  46  8.5  1.0  0.001*   Anaerobic capacity (W)  162  785.1  94.4  46  731.2  134.1  0.003*   VO2max (ml/kg/min)  134  49.6  4.5  46  47.7  4.4  0.018*   VO2max (l/min)  134  4.1  0.4  46  3.9  0.5  0.001*   VO2max% @LT  134  90.3  3.9  46  89.7  4.4  0.350   VO2 (ml/kg/min) @LT  134  44.7  3.9  46  42.8  4.5  0.007*   VO2 (l/min) @LT  134  3.8  0.3  46  3.5  0.5  0.001*  Strength   Knee flexion (%BW)  154  140.9  23.0  43  125.4  25.8  0.001*   Knee flexion (Nm)  154  121.0  23.8  43  105.0  25.2  0.001*   Knee extension (%BW)  155  266.8  45.8  43  239.1  53.4  0.001*   Knee extension (Nm)  155  229.0  46.9  43  201.3  53.4  0.001*   Trunk extension (%BW)  152  407.8  77.5  43  374.6  65.6  0.010*   Trunk extension (Nm)  152  348.9  76.7  43  313.9  65.5  0.018*   Trunk flexion (%BW)  153  242.1  39.6  43  224.9  48.8  0.016*   Trunk flexion (Nm)  153  207.5  41.0  43  190.0  52.3  0.034*  *Significant difference between personnel P < 0.05. kg, kilograms; W, watts; ml/kg/min, milliliters oxygen per kilogram of body weight per minute; %BW, percentage of body weight in kilograms; Nm, newton meters; LT, lactate inflection; VO2max%, percentage of VO2max (ml/kg/min). Physiological and absolute strength data are also presented in Table II. CSOs demonstrated significantly greater physiological performance than enablers in AC (W) (p= 0.03), VO2max (l/min) (p = 0.001), and VO2 (l/min) @LT (p= 0.001). There were no significant differences in AP (W) (p > 0.05). CSOs also demonstrated greater KF (Nm) (p = 0.001), KE (Nm) (p = 0.001), TE (Nm) (p = 0.010), and TF (Nm) (p = 0.016). Percentile distribution of physiological performance and absolute strength of CSOs and enablers are presented in (Fig. 1). Fisher’s exact tests showed that a statistically higher proportion of enablers performed in the 0–25th percentile of VO2max (p = 0.047), AP (p = 0.046), and KF (p = 0.006) compared with CSOs. There were no statistically significant differences between enablers and CSO for all other percentile groups (p > 0.05). Finally, physiological performance and absolute strength data were analyzed relative to a normal distribution curve to highlight performance and strength distribution between CSOs and enablers (Figs 2 and 3). FIGURE 1. View largeDownload slide (A) Physiological percentile distribution and (B) strength percentile distribution. FIGURE 1. View largeDownload slide (A) Physiological percentile distribution and (B) strength percentile distribution. FIGURE 2. View largeDownload slide Physiological performance normal distribution curves. FIGURE 2. View largeDownload slide Physiological performance normal distribution curves. FIGURE 3. View largeDownload slide Absolute strength normal distribution curves. FIGURE 3. View largeDownload slide Absolute strength normal distribution curves. Dietary Characteristics The dietary intake of a subgroup of CSOs and enablers is outlined in Table III. No group differences were observed in absolute energy or macronutrient intake. No group differences were observed in carbohydrate and protein intake per kilogram body weight. Carbohydrate intake per kilogram body weight for both groups (3.1 g/kg) was consistent with recommendations for participating in low intensity or skill-based activities and below the recommendation of >5 g/kg to support optimal performance during moderate to high-intensity tasks.13 Percent energy intake from fat was above the Dietary Reference Intake Acceptable Macronutrient Distribution Range (recommended 20–35% kcals from fat) in both groups.14 Table III. Dietary Intake   CSOs  Enablers  n  Mean  SD  n  Mean  SD  Kilocalories  27  2752  1073  22  2555  856.1  Carbohydrate (grams)  27  272.7  145.8  22  247.4  96.8  Carbohydrate (grams/kg)  26  3.1  1.7  21  3.1  1.3  Protein (grams)  27  154.7  98.9  22  127.6  62.1  Protein (grams/kg)  26  1.8  1.2  21  1.5  0.8  Fat (grams)  27  112.1  50.6  22  115.7  53.5  Fat (% energy)  27  36  7.5  22  39.5  8.2    CSOs  Enablers  n  Mean  SD  n  Mean  SD  Kilocalories  27  2752  1073  22  2555  856.1  Carbohydrate (grams)  27  272.7  145.8  22  247.4  96.8  Carbohydrate (grams/kg)  26  3.1  1.7  21  3.1  1.3  Protein (grams)  27  154.7  98.9  22  127.6  62.1  Protein (grams/kg)  26  1.8  1.2  21  1.5  0.8  Fat (grams)  27  112.1  50.6  22  115.7  53.5  Fat (% energy)  27  36  7.5  22  39.5  8.2  Table III. Dietary Intake   CSOs  Enablers  n  Mean  SD  n  Mean  SD  Kilocalories  27  2752  1073  22  2555  856.1  Carbohydrate (grams)  27  272.7  145.8  22  247.4  96.8  Carbohydrate (grams/kg)  26  3.1  1.7  21  3.1  1.3  Protein (grams)  27  154.7  98.9  22  127.6  62.1  Protein (grams/kg)  26  1.8  1.2  21  1.5  0.8  Fat (grams)  27  112.1  50.6  22  115.7  53.5  Fat (% energy)  27  36  7.5  22  39.5  8.2    CSOs  Enablers  n  Mean  SD  n  Mean  SD  Kilocalories  27  2752  1073  22  2555  856.1  Carbohydrate (grams)  27  272.7  145.8  22  247.4  96.8  Carbohydrate (grams/kg)  26  3.1  1.7  21  3.1  1.3  Protein (grams)  27  154.7  98.9  22  127.6  62.1  Protein (grams/kg)  26  1.8  1.2  21  1.5  0.8  Fat (grams)  27  112.1  50.6  22  115.7  53.5  Fat (% energy)  27  36  7.5  22  39.5  8.2  DISCUSSION The present study examined the differences in physical, physiological, and dietary characteristics of MARSOC CSOs and enablers. CSOs were found to have a greater fat free mass index, peak and mean anaerobic power, maximal aerobic capacity, and greater leg and trunk strength compared with enablers. Physiological and strength percentile distribution among CSOs and enablers was highly variable, with a greater percentage of enablers occupying the 0–25th percentile for all measures. Inadequate carbohydrate intake and a higher than recommended intake of energy from fat were also identified in CSOs and enablers. These findings may directly relate to the operational capability of a MSOT, highlighting overall fueling concerns and raising important questions as to how physiological and strength characteristics among CSOs and enablers affect the tactical capability of an MSOT. While we found no significant differences between key body composition variables that measure absolute fat mass and fat free mass, we did find that when these variables were normalized to height, CSOs have more lean mass and were leaner than enablers. These height-normalized indices suggest that CSOs tend to have more muscle mass for their body size, findings that may have a direct impact on strength to weight ratio and ultimately performance, especially when not required to carry a significant external load. Whereas some MSOT members may aim to gain absolute size and strength per se, both CSOs and enablers must move their own body mass, therefore it can be argued that it is just as important to optimize power to weight ratios rather than absolute power. As a part of their future training regimen, a focus on changing body composition to increase lean mass while reducing fat mass is likely to have a favorable effect on their power to weight ratio to ultimately improve performance. Physiological and strength data in the present study showed CSOs to be comparable with other US Special Operations Operators.15–17 CSOs demonstrated significantly higher overall maximal aerobic capacity and aerobic capacity at lactate threshold than enablers, an essential attribute for combat centric military occupations with many common tactical tasks requiring longer durations of moderate intensity physical activity. Individuals with higher aerobic fitness perform endurance activities at a lower fraction of their maximal aerobic capacity, for longer periods of time, fatigue less rapidly, and are at decreased risk for injury development.8,18–21 Moreover, CSOs also demonstrated significantly greater strength, peak and mean power, which are also important performance components that are often used in tactical situations that require high force and quick, explosive movements.6 Compared to CSOs, enablers present a greater likelihood of not meeting the strength and anaerobic demands of operational tasks, resulting in greater physiological strain and subsequently increasing risk of musculoskeletal injury.6,22 Specific military tasks, such as rucking or carriage loads over lengthy distance, may present critical issues for enablers, who demonstrated significantly lower aerobic capacity, power and strength than CSOs. Rucking stresses both aerobic and anaerobic pathways and places a heavy demand on the spine, lower back, and knees.7,23,24 Musculoskeletal injuries, specifically low back (pain/injuries), are a top contributor to loss of duty days on deployment and are directly related to fatigue and the mismatching of strength capability and strength demands.25 Enablers demonstrated that they are more likely to fatigue faster, and in conjunction with reduced lower extremity and trunk strength, operational tasks such as rucking may present a much higher risk of musculoskeletal injury. Given the significant performance differences between CSOs and enablers, further consideration should also address the distribution of performance between CSOs and enablers and the potential negative implications it may present on a MSOT. Overall, a greater percentage of enablers occupied the 0–25th percentile of all laboratory measures, with a statistically significant percentage of enablers in the 0–25th percentile for VO2max (p = 0.047), AP (p = 0.046), and KF (p = 0.006) (Fig. 1). The disparate range of performance between the groups is also emphasized when analyzed to a normal distribution curve (Figs 2 and 3). This uneven distribution increases the likelihood of an enabler in the lower range of performance to be paired with CSOs in the higher range of performance, potentially resulting in an unbalanced physical readiness profile of a MSOT. Tactically, this may result in higher performers taking on more tasks to make up for the weaker performers, potentially reducing the overall capability of the team. However, these novel findings still do not provide definitive data on the exact impact of mission oriented performance, but do raise important questions about what standards are necessary to operate effectively as a member of a MSOT. At this time, specific physiological and strength thresholds to successfully operate in a SOF environment do not exist, so it is beyond the scope of this study to say whether or not enablers can effectively operate as members of a MSOT. Future research should focus on the development of a needs analysis to determine what performance thresholds and occupational requirements are essential to operate effectively as a member of a MSOT. This will help determine if the significant differences in performance represent a true physical readiness gap and whether or not the implementation of additional functional training to improve overall performance is necessary. Performance thresholds would also provide important information that could help better guide the selection process for both CSOs and enablers. Given the suboptimal macronutrient intake characteristics identified in CSOs and enablers, significant nutritional modifications are required to improve body composition and address fueling requirements to support a rigorous physical training program. Absolute carbohydrate intake lower and fat intake as a percentage of energy intake exceeded the Acceptable Macronutrient Distribution Range recommendations. Inadequate carbohydrate intake has the potential to reduce the adaptations to training by limiting performance and recovery, as well as contributing to a state of chronic fatigue. Excess fat intake may negatively affect diet quality by displacing carbohydrate other nutrient-dense food and in turn decrease performance and increase the risk of injury. Access to, and utilization of MARSOC nutrition specialists to promote these nutritional modifications should be a point of emphasis for enablers and CSOs. Personalized nutrition support and education should extend beyond daily recommendation to also provide evidence based strategies to support acute fueling needs that encompass all aspects of training and deployment. These strategies, in conjunction with the utilization of MARSOC performance experts, may ultimately help bridge the performance gap between CSO’s and enablers. CONCLUSION MARSOC CSOs demonstrated significantly greater fat free mass index, power, endurance, lower extremity, and core strength compared with enablers, while nutrition fueling concerns were identified for both CSOs and enablers. Performance differences may be directly related to the rigorous selection process and training of a CSO when compared to that of an enabler. Currently, specific physiological and strength thresholds to successfully operate in a SOF environment do not exist, so it is beyond the scope of this study to say whether or not enablers can effectively operate as members of a MSOT. Future research should aim to develop a needs analysis to determine what physiological thresholds are required to effectively operate as a member of a MSOT and the validity of these measures with respect to mission-specific capabilities. Such findings may provide meaningful information that may better guide MARSOC selection processes, while also potentially leading to implementation of specific and directed training, for both CSOs and enablers. Lastly, creating a clearer performance standard for all members of a MSOT may subsequently lead to increased tactical performance and decreased injury incidence rates. Funding This work was supported by the Office of Naval Research (N00014-15-1-0069). 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Google Scholar CrossRef Search ADS PubMed  Author notes Opinions, interpretations, conclusions, and recommendations are those of the author/presenter and not necessarily endorsed by the Department of Defense, Office of Naval Research, or the U.S. Marine Corps Forces Special Operations Command © Association of Military Surgeons of the United States 2018. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Military Medicine Oxford University Press

Physical, Physiological, and Dietary Comparisons Between Marine Corps Forces Special Operations Command Critical Skills Operators and Enablers

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Abstract

Abstract Introduction Tactical demands of a Marine Corps Forces Special Operations Command (MARSOC) Critical Skills Operator (CSO) require high levels of physical performance. During combat deployments, teams of CSOs are supplemented with enablers who specialize in mission-specific tasks. MARSOC CSOs and enablers serve alongside each other in extreme combat environments, often enduring the same physical demands, but the selection process for each group is very different. The purpose of this observational study was to quantify the physical, physiological, and dietary differences of MARSOC CSOs and enablers, as this may have a direct impact on tactical performance and provide important information to shape future research. Materials and Methods Fat free mass (FFM), fat mass (FM), fat mass index (FMI), fat free mass index (FFMI), anaerobic power (AP), anaerobic capacity (AC), aerobic capacity (VO2max), knee flexion (KF), knee extension (KE), trunk extension (TE), and trunk flexion (TF) isokinetic strength were collected. Dietary intake was collected using automated self-administered 24-hr dietary recalls (ASA24) for a subgroup of subjects. Results Testing on 164 male CSOs (age: 27.5 ± 3.8 yr, height: 178.7 ± 6.5 cm, mass: 85.7 ± 9.1 kg, and 7.6 ± 2.9 yr of military service) and 51 male enablers (age: 27.8 ± 5.4 yr, height: 178.4 ± 8.5 cm, mass: 83.8 ± 11.8 kg, and 7.9 ± 5.4 yr of military service) showed there were no significant differences for age, height, mass, or years of military service. (p> 0.05). CSOs demonstrated greater physiological performance in AP (W/kg) (p= 0.020), AC (W/kg) (p = 0.001), and VO2max (ml/kg/min) (p = 0.018). There were no significant differences in FM and FFM (p > 0.05), however CSOs demonstrated significantly higher FFMI (p = 0.011). CSOs also demonstrated greater KF (%BW) (p = 0.001), KE (%BW) (p = 0.001), TE (%BW) (p = 0.010), and TF (%BW) (p = 0.016). No differences in energy or macronutrient intake were observed in the subgroup. Conclusions MARSOC CSOs demonstrated significantly greater FFMI, AP, AC, VO2max, KF, KE, TE, and TF compared with enablers. Dietary intake was consistent between groups, but fueling concerns were identified for all personnel in the subgroup. These findings suggest the need for future studies to examine what physiological and strength thresholds are necessary to operate effectively as a member of a MSOT and determine the relationship between specific performance deficits and risk of injury. In addition, the integration of nutrition strategies that augment and optimize the performance of both CSOs and enablers may be beneficial. INTRODUCTION U.S. Special Operations Forces (SOF) have a challenging occupation, often requiring personnel to perform at their maximal physical and physiological capacity.1 SOF are assigned to specialized military missions, requiring variable and unpredictable levels of strength, power, and endurance, while also presenting unique metabolic challenges, including matching nutrient needs with fuel demands.2,3 SOF operations, or tasks within an operation can range from long-duration, low intensity, aerobic based tasks, to short-duration, high-intensity anaerobic tasks. These wide variations in task demand require multifaceted strength, power, and endurance capabilities in conjunction with sufficient nutritional intake to fuel periods of high-intensity and/or extended moderate intensity physical activity.4,5 In addition to task performance improvements, high levels of aerobic fitness and strength correlate with reduced risk of musculoskeletal injury.6–8 Reducing the incidence of musculoskeletal injury in SOF is critical to ensure tactical readiness and availability for deployment.9 The United States Marine Corps Forces Special Operations Command (MARSOC) deploy Marine Special Operations Teams (MSOTs) that consist of Critical Skills Operators (CSOs) and enablers. CSOs are highly trained in combat skills and tactics in order to complete a wide variety of complex military operations. Enablers supplement CSOs during deployments and operations by providing specialized skill sets ranging from medical care, to intelligence and communications.10 As a MSOT, CSOs and enablers operate alongside each other in tactical situations, often enduring the same physical task demands. Although CSOs and enablers deploy as a unit, the selection process and training of CSOs and enablers are very different. The assessment and training to become a CSO are exhaustive, requiring high levels of tactical and physical performance, while an enablers’ selection is primarily based on military occupational specialty and less on physical or tactical performance. Regardless, performance deficiencies among enablers have a similar impact on force readiness and MSOT capability. CSOs and enablers are both critical components of an MSOT and absence or inefficient performance due to suboptimal physical conditioning or injury may be detrimental to special operations missions by reducing the overall capability of a MSOT. Therefore, the purpose of this observational study was to quantify the differences in physical, physiological, and dietary characteristics between MARSOC CSOs and enablers as this may have a direct impact on the tactical capability of a MSOT. This information will help identify team specific weaknesses and provide data that will assist in the advancement of training programs and selection processes to help improve overall MSOT performance and the prevention of injuries. METHODS Subjects A total of 164 male CSOs (age: 27.5 ± 3.8 yr, height: 178.7 ± 6.5 cm, mass: 85.7 ± 9.1 kg, and 7.6 ± 2.9 yr of military service) and 51 male enablers (age: 27.8 ± 5.4 yr, height: 178.4 ± 8.5 cm, mass: 83.8 ± 11.8 kg, and 7.9 ± 5.4 yr of military service) were recruited to the study (Table I). Inclusion criteria included clearance for full and unrestricted participation in physical and tactical training, and no history of musculoskeletal injury within the past month that led to training cessation or medical treatment. Subjects were also asked to limit any strenuous physical training, avoid caffeine, nicotine, and alcoholic beverages 24 h prior to testing. The study was approved by the University of Kentucky’s Institutional Review Board. Written informed consent was obtained from each subject prior to participation in the study. Table I. Subject Characteristics   CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD  Age (years)  164  27.5  3.8  51  27.8  5.4  0.720  Height (cm)  164  178.7  6.5  51  178.4  8.5  0.809  Mass (kg)  164  85.7  9.1  51  83.8  11.8  0.229  Years of service  162  7.6  2.9  51  7.9  5.4  0.867    CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD  Age (years)  164  27.5  3.8  51  27.8  5.4  0.720  Height (cm)  164  178.7  6.5  51  178.4  8.5  0.809  Mass (kg)  164  85.7  9.1  51  83.8  11.8  0.229  Years of service  162  7.6  2.9  51  7.9  5.4  0.867  Table I. Subject Characteristics   CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD  Age (years)  164  27.5  3.8  51  27.8  5.4  0.720  Height (cm)  164  178.7  6.5  51  178.4  8.5  0.809  Mass (kg)  164  85.7  9.1  51  83.8  11.8  0.229  Years of service  162  7.6  2.9  51  7.9  5.4  0.867    CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD  Age (years)  164  27.5  3.8  51  27.8  5.4  0.720  Height (cm)  164  178.7  6.5  51  178.4  8.5  0.809  Mass (kg)  164  85.7  9.1  51  83.8  11.8  0.229  Years of service  162  7.6  2.9  51  7.9  5.4  0.867  Study Design This study was an observational analysis. Subjects completed a 1-d laboratory protocol that consisted of an all-encompassing performance assessment. A subgroup completed a 24 h dietary recall. All laboratory assessment categories were completed in the following order: anthropometrics, anaerobic performance, strength, dietary assessment, and aerobic capacity. Anthropometrics Average height from two measurements was taken barefoot using a wall stadiometer (Doran Scales, Inc, Batavia, IL, USA). Body mass (kg), fat free mass (FFM), and fat mass (FM) were estimated using Bod Pod (Bod Pod Body Composition System, Cosmed, Chicago, IL, USA). Fat mass index (FMI) and fat free mass index (FFMI) were calculated from fat mass and fat free mass Bod Pod measurements and height measurements (FMI = fat mass [kg]/height [m2]; FFMI = fat free mass [kg]/height [m2]). FMI and FFMI are height-normalized indices of body composition.11 The Bod Pod was calibrated according to factory recommendations the day of each testing session. Anaerobic Performance Peak power (anaerobic power – AP) and mean power (anaerobic capacity – AC) were measured using a VeloTron cycling ergometer (RacerMate, Seattle, WA, USA) during a Wingate protocol. Seat and handlebar position were adjusted to ensure a comfortable position and 10o flexion of the knee during full extension. Following a 5-min warm up (125 W), subjects completed a 30-s Wingate protocol (9.0% body weight braking torque). Subjects were instructed to pedal as hard and as fast as they could against the applied resistance for the length of the test, all while maintaining a seated position and front handgrip position. Verbal encouragement was provided by the investigators. AP and average AC were analyzed in absolute units (W) as well as relative to body weight (W/kg). Aerobic Capacity Maximal oxygen uptake (VO2max) was assessed using a metabolic gas analyzer (TrueOne 2400, ParvoMedics, Sandy, UT, USA) during a modified Astrand treadmill protocol to volitional exhaustion. The treadmill protocol was based on a variation of the protocol designed by Astrand.12 Heart rate data were collected with a heart rate monitor (Polar USA, Lake Success, NY, USA) and blood lactate was assessed with a portable lactate analyzer (Lactate Pro, Arkray, Inc, Kyoto Japan). The speed for the test was selected according to the subject’s most recent self-reported three mile run time, and incline was increased 2% every 3 min until volitional exhaustion. Strength Isokinetic strength of the knee and trunk was assessed using an isokinetic dynamometer (Biodex Medical Systems, Inc., Shirley, NY, USA). Knee extension/flexion strength and trunk extension/flexion strength were measured during a concentric/concentric protocol at 60°/s with submaximal and maximal practice repetitions. The test consisted of five maximal strength repetitions (100% max effort) with verbal encouragement from the investigators. Strength was determined by the average of five repetitions, and analyzed in absolute units (Nm) as well as relative to body weight (%BW). Diet Assessment A subgroup (CSOs = 27, enablers = 22) reported their dietary intake via the Automated Self-Administered 24-h (ASA24) dietary recall system on a computer. Before data collection, subjects were provided detailed instruction by investigators on how to complete the recall survey. Following familiarization, they completed the 24-h dietary recall survey during the laboratory testing session. Statistical Analysis Data were assessed for normality via histogram plots and Shapiro–Wilk tests. Independent samples t-tests were used for normally distributed data. Mann–Whitney U tests were used for data that were not normally distributed. Data are presented as mean ± standard deviation (SD). All physiological performance and absolute strength data were analyzed collectively and presented as percentage of CSOs and enablers in the 0–25th, 25–50th, 50–75th, and 75–100th percentiles. Fisher’s exact tests were used to analyze the association between the percentage of CSOs and enablers in each percentile. Data were also analyzed and presented relative to a normal distribution curve. SPSS Statistics for Windows (SPSS Inc., Chicago, IL, USA) version 23 was used for all analyses. Significance was set at p< 0.05. RESULTS Laboratory Assessments Descriptive data for both groups are presented in Table I. There were no significant differences for age, height, mass, or years of military service between CSOs and enablers (p> 0.05). Physiological and strength laboratory data relative to mass are presented in Table II. There were no significant differences in FM, FFM, and FMI (p > 0.05), however, CSOs had significantly greater FFMI than enablers (p= 0.011). CSOs demonstrated significantly greater physiological performance than enablers in AP (W/kg) (p = 0.020), AC (W/kg) (p = 0.001), VO2max (ml/kg/min) (p = 0.018), and VO2 (ml/kg/min) @LT (p = 0.007). There were no significant differences in VO2max% @LT (p > 0.05). CSOs also demonstrated greater KF (%BW) (p = 0.001), KE (%BW) (p = 0.001), TE (%BW) (p = 0.010), and TF (%BW) (p = 0.016). Table II. Physiological and Strength Measures   CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD    Physiological   Fat free mass (kg)  163  71.1  7.1  49  68.8  9.4  0.067   Fat mass (kg)  163  14.7  5.0  49  15.3  6.2  0.474   Fat free mass index  163  22.2  1.6  49  21.5  1.8  0.011*   Fat mass index  163  4.6  1.5  49  4.8  1.9  0.474   Anaerobic power (W/kg)  162  13.0  0.6  46  12.7  0.8  0.020*   Anaerobic power (W)  162  1121.4  150.7  46  1089.3  190.6  0.232   Anaerobic capacity (W/kg)  162  9.1  0.8  46  8.5  1.0  0.001*   Anaerobic capacity (W)  162  785.1  94.4  46  731.2  134.1  0.003*   VO2max (ml/kg/min)  134  49.6  4.5  46  47.7  4.4  0.018*   VO2max (l/min)  134  4.1  0.4  46  3.9  0.5  0.001*   VO2max% @LT  134  90.3  3.9  46  89.7  4.4  0.350   VO2 (ml/kg/min) @LT  134  44.7  3.9  46  42.8  4.5  0.007*   VO2 (l/min) @LT  134  3.8  0.3  46  3.5  0.5  0.001*  Strength   Knee flexion (%BW)  154  140.9  23.0  43  125.4  25.8  0.001*   Knee flexion (Nm)  154  121.0  23.8  43  105.0  25.2  0.001*   Knee extension (%BW)  155  266.8  45.8  43  239.1  53.4  0.001*   Knee extension (Nm)  155  229.0  46.9  43  201.3  53.4  0.001*   Trunk extension (%BW)  152  407.8  77.5  43  374.6  65.6  0.010*   Trunk extension (Nm)  152  348.9  76.7  43  313.9  65.5  0.018*   Trunk flexion (%BW)  153  242.1  39.6  43  224.9  48.8  0.016*   Trunk flexion (Nm)  153  207.5  41.0  43  190.0  52.3  0.034*    CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD    Physiological   Fat free mass (kg)  163  71.1  7.1  49  68.8  9.4  0.067   Fat mass (kg)  163  14.7  5.0  49  15.3  6.2  0.474   Fat free mass index  163  22.2  1.6  49  21.5  1.8  0.011*   Fat mass index  163  4.6  1.5  49  4.8  1.9  0.474   Anaerobic power (W/kg)  162  13.0  0.6  46  12.7  0.8  0.020*   Anaerobic power (W)  162  1121.4  150.7  46  1089.3  190.6  0.232   Anaerobic capacity (W/kg)  162  9.1  0.8  46  8.5  1.0  0.001*   Anaerobic capacity (W)  162  785.1  94.4  46  731.2  134.1  0.003*   VO2max (ml/kg/min)  134  49.6  4.5  46  47.7  4.4  0.018*   VO2max (l/min)  134  4.1  0.4  46  3.9  0.5  0.001*   VO2max% @LT  134  90.3  3.9  46  89.7  4.4  0.350   VO2 (ml/kg/min) @LT  134  44.7  3.9  46  42.8  4.5  0.007*   VO2 (l/min) @LT  134  3.8  0.3  46  3.5  0.5  0.001*  Strength   Knee flexion (%BW)  154  140.9  23.0  43  125.4  25.8  0.001*   Knee flexion (Nm)  154  121.0  23.8  43  105.0  25.2  0.001*   Knee extension (%BW)  155  266.8  45.8  43  239.1  53.4  0.001*   Knee extension (Nm)  155  229.0  46.9  43  201.3  53.4  0.001*   Trunk extension (%BW)  152  407.8  77.5  43  374.6  65.6  0.010*   Trunk extension (Nm)  152  348.9  76.7  43  313.9  65.5  0.018*   Trunk flexion (%BW)  153  242.1  39.6  43  224.9  48.8  0.016*   Trunk flexion (Nm)  153  207.5  41.0  43  190.0  52.3  0.034*  *Significant difference between personnel P < 0.05. kg, kilograms; W, watts; ml/kg/min, milliliters oxygen per kilogram of body weight per minute; %BW, percentage of body weight in kilograms; Nm, newton meters; LT, lactate inflection; VO2max%, percentage of VO2max (ml/kg/min). Table II. Physiological and Strength Measures   CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD    Physiological   Fat free mass (kg)  163  71.1  7.1  49  68.8  9.4  0.067   Fat mass (kg)  163  14.7  5.0  49  15.3  6.2  0.474   Fat free mass index  163  22.2  1.6  49  21.5  1.8  0.011*   Fat mass index  163  4.6  1.5  49  4.8  1.9  0.474   Anaerobic power (W/kg)  162  13.0  0.6  46  12.7  0.8  0.020*   Anaerobic power (W)  162  1121.4  150.7  46  1089.3  190.6  0.232   Anaerobic capacity (W/kg)  162  9.1  0.8  46  8.5  1.0  0.001*   Anaerobic capacity (W)  162  785.1  94.4  46  731.2  134.1  0.003*   VO2max (ml/kg/min)  134  49.6  4.5  46  47.7  4.4  0.018*   VO2max (l/min)  134  4.1  0.4  46  3.9  0.5  0.001*   VO2max% @LT  134  90.3  3.9  46  89.7  4.4  0.350   VO2 (ml/kg/min) @LT  134  44.7  3.9  46  42.8  4.5  0.007*   VO2 (l/min) @LT  134  3.8  0.3  46  3.5  0.5  0.001*  Strength   Knee flexion (%BW)  154  140.9  23.0  43  125.4  25.8  0.001*   Knee flexion (Nm)  154  121.0  23.8  43  105.0  25.2  0.001*   Knee extension (%BW)  155  266.8  45.8  43  239.1  53.4  0.001*   Knee extension (Nm)  155  229.0  46.9  43  201.3  53.4  0.001*   Trunk extension (%BW)  152  407.8  77.5  43  374.6  65.6  0.010*   Trunk extension (Nm)  152  348.9  76.7  43  313.9  65.5  0.018*   Trunk flexion (%BW)  153  242.1  39.6  43  224.9  48.8  0.016*   Trunk flexion (Nm)  153  207.5  41.0  43  190.0  52.3  0.034*    CSOs  Enablers  p-Value  n  Mean  SD  n  Mean  SD    Physiological   Fat free mass (kg)  163  71.1  7.1  49  68.8  9.4  0.067   Fat mass (kg)  163  14.7  5.0  49  15.3  6.2  0.474   Fat free mass index  163  22.2  1.6  49  21.5  1.8  0.011*   Fat mass index  163  4.6  1.5  49  4.8  1.9  0.474   Anaerobic power (W/kg)  162  13.0  0.6  46  12.7  0.8  0.020*   Anaerobic power (W)  162  1121.4  150.7  46  1089.3  190.6  0.232   Anaerobic capacity (W/kg)  162  9.1  0.8  46  8.5  1.0  0.001*   Anaerobic capacity (W)  162  785.1  94.4  46  731.2  134.1  0.003*   VO2max (ml/kg/min)  134  49.6  4.5  46  47.7  4.4  0.018*   VO2max (l/min)  134  4.1  0.4  46  3.9  0.5  0.001*   VO2max% @LT  134  90.3  3.9  46  89.7  4.4  0.350   VO2 (ml/kg/min) @LT  134  44.7  3.9  46  42.8  4.5  0.007*   VO2 (l/min) @LT  134  3.8  0.3  46  3.5  0.5  0.001*  Strength   Knee flexion (%BW)  154  140.9  23.0  43  125.4  25.8  0.001*   Knee flexion (Nm)  154  121.0  23.8  43  105.0  25.2  0.001*   Knee extension (%BW)  155  266.8  45.8  43  239.1  53.4  0.001*   Knee extension (Nm)  155  229.0  46.9  43  201.3  53.4  0.001*   Trunk extension (%BW)  152  407.8  77.5  43  374.6  65.6  0.010*   Trunk extension (Nm)  152  348.9  76.7  43  313.9  65.5  0.018*   Trunk flexion (%BW)  153  242.1  39.6  43  224.9  48.8  0.016*   Trunk flexion (Nm)  153  207.5  41.0  43  190.0  52.3  0.034*  *Significant difference between personnel P < 0.05. kg, kilograms; W, watts; ml/kg/min, milliliters oxygen per kilogram of body weight per minute; %BW, percentage of body weight in kilograms; Nm, newton meters; LT, lactate inflection; VO2max%, percentage of VO2max (ml/kg/min). Physiological and absolute strength data are also presented in Table II. CSOs demonstrated significantly greater physiological performance than enablers in AC (W) (p= 0.03), VO2max (l/min) (p = 0.001), and VO2 (l/min) @LT (p= 0.001). There were no significant differences in AP (W) (p > 0.05). CSOs also demonstrated greater KF (Nm) (p = 0.001), KE (Nm) (p = 0.001), TE (Nm) (p = 0.010), and TF (Nm) (p = 0.016). Percentile distribution of physiological performance and absolute strength of CSOs and enablers are presented in (Fig. 1). Fisher’s exact tests showed that a statistically higher proportion of enablers performed in the 0–25th percentile of VO2max (p = 0.047), AP (p = 0.046), and KF (p = 0.006) compared with CSOs. There were no statistically significant differences between enablers and CSO for all other percentile groups (p > 0.05). Finally, physiological performance and absolute strength data were analyzed relative to a normal distribution curve to highlight performance and strength distribution between CSOs and enablers (Figs 2 and 3). FIGURE 1. View largeDownload slide (A) Physiological percentile distribution and (B) strength percentile distribution. FIGURE 1. View largeDownload slide (A) Physiological percentile distribution and (B) strength percentile distribution. FIGURE 2. View largeDownload slide Physiological performance normal distribution curves. FIGURE 2. View largeDownload slide Physiological performance normal distribution curves. FIGURE 3. View largeDownload slide Absolute strength normal distribution curves. FIGURE 3. View largeDownload slide Absolute strength normal distribution curves. Dietary Characteristics The dietary intake of a subgroup of CSOs and enablers is outlined in Table III. No group differences were observed in absolute energy or macronutrient intake. No group differences were observed in carbohydrate and protein intake per kilogram body weight. Carbohydrate intake per kilogram body weight for both groups (3.1 g/kg) was consistent with recommendations for participating in low intensity or skill-based activities and below the recommendation of >5 g/kg to support optimal performance during moderate to high-intensity tasks.13 Percent energy intake from fat was above the Dietary Reference Intake Acceptable Macronutrient Distribution Range (recommended 20–35% kcals from fat) in both groups.14 Table III. Dietary Intake   CSOs  Enablers  n  Mean  SD  n  Mean  SD  Kilocalories  27  2752  1073  22  2555  856.1  Carbohydrate (grams)  27  272.7  145.8  22  247.4  96.8  Carbohydrate (grams/kg)  26  3.1  1.7  21  3.1  1.3  Protein (grams)  27  154.7  98.9  22  127.6  62.1  Protein (grams/kg)  26  1.8  1.2  21  1.5  0.8  Fat (grams)  27  112.1  50.6  22  115.7  53.5  Fat (% energy)  27  36  7.5  22  39.5  8.2    CSOs  Enablers  n  Mean  SD  n  Mean  SD  Kilocalories  27  2752  1073  22  2555  856.1  Carbohydrate (grams)  27  272.7  145.8  22  247.4  96.8  Carbohydrate (grams/kg)  26  3.1  1.7  21  3.1  1.3  Protein (grams)  27  154.7  98.9  22  127.6  62.1  Protein (grams/kg)  26  1.8  1.2  21  1.5  0.8  Fat (grams)  27  112.1  50.6  22  115.7  53.5  Fat (% energy)  27  36  7.5  22  39.5  8.2  Table III. Dietary Intake   CSOs  Enablers  n  Mean  SD  n  Mean  SD  Kilocalories  27  2752  1073  22  2555  856.1  Carbohydrate (grams)  27  272.7  145.8  22  247.4  96.8  Carbohydrate (grams/kg)  26  3.1  1.7  21  3.1  1.3  Protein (grams)  27  154.7  98.9  22  127.6  62.1  Protein (grams/kg)  26  1.8  1.2  21  1.5  0.8  Fat (grams)  27  112.1  50.6  22  115.7  53.5  Fat (% energy)  27  36  7.5  22  39.5  8.2    CSOs  Enablers  n  Mean  SD  n  Mean  SD  Kilocalories  27  2752  1073  22  2555  856.1  Carbohydrate (grams)  27  272.7  145.8  22  247.4  96.8  Carbohydrate (grams/kg)  26  3.1  1.7  21  3.1  1.3  Protein (grams)  27  154.7  98.9  22  127.6  62.1  Protein (grams/kg)  26  1.8  1.2  21  1.5  0.8  Fat (grams)  27  112.1  50.6  22  115.7  53.5  Fat (% energy)  27  36  7.5  22  39.5  8.2  DISCUSSION The present study examined the differences in physical, physiological, and dietary characteristics of MARSOC CSOs and enablers. CSOs were found to have a greater fat free mass index, peak and mean anaerobic power, maximal aerobic capacity, and greater leg and trunk strength compared with enablers. Physiological and strength percentile distribution among CSOs and enablers was highly variable, with a greater percentage of enablers occupying the 0–25th percentile for all measures. Inadequate carbohydrate intake and a higher than recommended intake of energy from fat were also identified in CSOs and enablers. These findings may directly relate to the operational capability of a MSOT, highlighting overall fueling concerns and raising important questions as to how physiological and strength characteristics among CSOs and enablers affect the tactical capability of an MSOT. While we found no significant differences between key body composition variables that measure absolute fat mass and fat free mass, we did find that when these variables were normalized to height, CSOs have more lean mass and were leaner than enablers. These height-normalized indices suggest that CSOs tend to have more muscle mass for their body size, findings that may have a direct impact on strength to weight ratio and ultimately performance, especially when not required to carry a significant external load. Whereas some MSOT members may aim to gain absolute size and strength per se, both CSOs and enablers must move their own body mass, therefore it can be argued that it is just as important to optimize power to weight ratios rather than absolute power. As a part of their future training regimen, a focus on changing body composition to increase lean mass while reducing fat mass is likely to have a favorable effect on their power to weight ratio to ultimately improve performance. Physiological and strength data in the present study showed CSOs to be comparable with other US Special Operations Operators.15–17 CSOs demonstrated significantly higher overall maximal aerobic capacity and aerobic capacity at lactate threshold than enablers, an essential attribute for combat centric military occupations with many common tactical tasks requiring longer durations of moderate intensity physical activity. Individuals with higher aerobic fitness perform endurance activities at a lower fraction of their maximal aerobic capacity, for longer periods of time, fatigue less rapidly, and are at decreased risk for injury development.8,18–21 Moreover, CSOs also demonstrated significantly greater strength, peak and mean power, which are also important performance components that are often used in tactical situations that require high force and quick, explosive movements.6 Compared to CSOs, enablers present a greater likelihood of not meeting the strength and anaerobic demands of operational tasks, resulting in greater physiological strain and subsequently increasing risk of musculoskeletal injury.6,22 Specific military tasks, such as rucking or carriage loads over lengthy distance, may present critical issues for enablers, who demonstrated significantly lower aerobic capacity, power and strength than CSOs. Rucking stresses both aerobic and anaerobic pathways and places a heavy demand on the spine, lower back, and knees.7,23,24 Musculoskeletal injuries, specifically low back (pain/injuries), are a top contributor to loss of duty days on deployment and are directly related to fatigue and the mismatching of strength capability and strength demands.25 Enablers demonstrated that they are more likely to fatigue faster, and in conjunction with reduced lower extremity and trunk strength, operational tasks such as rucking may present a much higher risk of musculoskeletal injury. Given the significant performance differences between CSOs and enablers, further consideration should also address the distribution of performance between CSOs and enablers and the potential negative implications it may present on a MSOT. Overall, a greater percentage of enablers occupied the 0–25th percentile of all laboratory measures, with a statistically significant percentage of enablers in the 0–25th percentile for VO2max (p = 0.047), AP (p = 0.046), and KF (p = 0.006) (Fig. 1). The disparate range of performance between the groups is also emphasized when analyzed to a normal distribution curve (Figs 2 and 3). This uneven distribution increases the likelihood of an enabler in the lower range of performance to be paired with CSOs in the higher range of performance, potentially resulting in an unbalanced physical readiness profile of a MSOT. Tactically, this may result in higher performers taking on more tasks to make up for the weaker performers, potentially reducing the overall capability of the team. However, these novel findings still do not provide definitive data on the exact impact of mission oriented performance, but do raise important questions about what standards are necessary to operate effectively as a member of a MSOT. At this time, specific physiological and strength thresholds to successfully operate in a SOF environment do not exist, so it is beyond the scope of this study to say whether or not enablers can effectively operate as members of a MSOT. Future research should focus on the development of a needs analysis to determine what performance thresholds and occupational requirements are essential to operate effectively as a member of a MSOT. This will help determine if the significant differences in performance represent a true physical readiness gap and whether or not the implementation of additional functional training to improve overall performance is necessary. Performance thresholds would also provide important information that could help better guide the selection process for both CSOs and enablers. Given the suboptimal macronutrient intake characteristics identified in CSOs and enablers, significant nutritional modifications are required to improve body composition and address fueling requirements to support a rigorous physical training program. Absolute carbohydrate intake lower and fat intake as a percentage of energy intake exceeded the Acceptable Macronutrient Distribution Range recommendations. Inadequate carbohydrate intake has the potential to reduce the adaptations to training by limiting performance and recovery, as well as contributing to a state of chronic fatigue. Excess fat intake may negatively affect diet quality by displacing carbohydrate other nutrient-dense food and in turn decrease performance and increase the risk of injury. Access to, and utilization of MARSOC nutrition specialists to promote these nutritional modifications should be a point of emphasis for enablers and CSOs. Personalized nutrition support and education should extend beyond daily recommendation to also provide evidence based strategies to support acute fueling needs that encompass all aspects of training and deployment. These strategies, in conjunction with the utilization of MARSOC performance experts, may ultimately help bridge the performance gap between CSO’s and enablers. CONCLUSION MARSOC CSOs demonstrated significantly greater fat free mass index, power, endurance, lower extremity, and core strength compared with enablers, while nutrition fueling concerns were identified for both CSOs and enablers. Performance differences may be directly related to the rigorous selection process and training of a CSO when compared to that of an enabler. Currently, specific physiological and strength thresholds to successfully operate in a SOF environment do not exist, so it is beyond the scope of this study to say whether or not enablers can effectively operate as members of a MSOT. Future research should aim to develop a needs analysis to determine what physiological thresholds are required to effectively operate as a member of a MSOT and the validity of these measures with respect to mission-specific capabilities. Such findings may provide meaningful information that may better guide MARSOC selection processes, while also potentially leading to implementation of specific and directed training, for both CSOs and enablers. Lastly, creating a clearer performance standard for all members of a MSOT may subsequently lead to increased tactical performance and decreased injury incidence rates. Funding This work was supported by the Office of Naval Research (N00014-15-1-0069). 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Journal

Military MedicineOxford University Press

Published: Apr 4, 2018

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