RESEARCH ARTICLE - APPLICATION
Effectiveness of various isometric exercises at improving
bone strength in cortical regions prone to distal tibial stress
fractures
C.S. Florio
Department of Mechanical and Industrial
Engineering, New Jersey Institute of
Technology, University Heights, Newark,
NJ 07102, USA
Correspondence
C. S. Florio, Department of Mechanical
and Industrial Engineering, New Jersey
Institute of Technology, University
Heights, Newark, NJ 07102, USA.
Email: cxf6791@njit.edu
Funding information
Zonta International Foundation
Abstract
A computational model was used to compare the local bone strengthening
effectiveness of various isometric exercises that may reduce the likelihood of
distal tibial stress fractures. The developed model predicts local endosteal and
periosteal cortical accretion and resorption based on relative local and global
measures of the tibial stress state and its surface variation. Using a
multisegment 3‐dimensional leg model, tibia shape adaptations due to 33 com-
binations of hip, knee, and ankle joint angles and the direction of a single or
sequential series of generated isometric resultant forces were predicted. The
maximum stress at a common fracture‐prone region in each optimized geome-
try was compared under likely stress fracture‐inducing midstance jogging con-
ditions. No direct correlations were found between stress reductions over an
initially uniform circular hollow cylindrical geometry under these critical
design conditions and the exercise‐based sets of active muscles, joint angles,
or individual muscle force and local stress magnitudes. Additionally, typically
favorable increases in cross‐sectional geometric measures did not guarantee
stress decreases at these locations. Instead, tibial stress distributions under the
exercise conditions best predicted strengthening ability. Exercises producing
larger anterior distal stresses created optimized tibia shapes that better resisted
the high midstance jogging bending stresses. Bent leg configurations generating
anteriorly directed or inferiorly directed resultant forces created favorable adap-
tations. None of the studied loads produced by a straight leg was significantly
advantageous. These predictions and the insight gained can provide prelimi-
nary guidance in the screening and development of targeted bone strengthen-
ing techniques for those susceptible to distal tibial stress fractures.
KEYWORDS
computational modeling, parametric study, shape optimization, strength adaptation, stress fractures
1 | INTRODUCTION
Distal tibial stress fractures are common among military recruits, runners, and those with jobs involving repeated
weight‐bearing loads. Such fractures often occur in otherwise healthy adults and young adults with nonosteoporotic
Received: 12 November 2017 Revised: 25 February 2018 Accepted: 25 February 2018
DOI: 10.1002/cnm.2976
Int J Numer Meth Biomed Engng. 2018;34:e2976.
https://doi.org/10.1002/cnm.2976
Copyright © 2018 John Wiley & Sons, Ltd.wileyonlinelibrary.com/journal/cnm 1of17
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