Force-velocity relationship during isometric and isotonic fatiguing contractions

Force-velocity relationship during isometric and isotonic fatiguing contractions Fatiguing contractions change the force-velocity relationship, but assessment of this relationship in fatigue has usually been obtained after isometric contractions. We studied fatigue due to isometric or isotonic contractions, by assessment of the force-velocity relationship while the contractions maintaining fatigue were continued. This approach allowed determination of the force-velocity relationship during a steady condition of fatigue. We used the in situ rat medial gastrocnemius muscle, a physiologically relevant preparation. Intermittent (1s-1) stimulation at 170 Hz for 100 ms resulted in decreased isometric force to about 35 % of initial or decreased peak velocity of shortening in dynamic contractions to about 45% of initial. Dynamic contractions resulted in a transient initial increase in velocity, followed by a rapid decline until a reasonable steady level was maintained. Data were fit to the classic Hill equation for determination of the force-velocity relationship. Isometric and dynamic contractions resulted in similar decreases in maximal isometric force and peak power. Only Vmax was different between the types of contraction (p<0.005) with greater decrease in Vmax during isotonic contractions to 171.7{plus minus}7.3 mms-1 than during isometric contractions to 208.8 mms-1. Curvature was decreased substantially in both types of contraction: a/Po changed from 0.45{plus minus}0.04 to 0.71{plus minus}0.11 during isometric contractions and from 0.51{plus minus}0.04 to 0.85{plus minus}0.18 during isotonic contractions. Recovery was incomplete 45 min after stopping the intermittent contractions. At this time, recovery of low frequency isometric force was substantially less after isometric contractions, implicating force during intermittent contractions as a determining factor with this measure of fatigue. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Applied Physiology The American Physiological Society

Force-velocity relationship during isometric and isotonic fatiguing contractions

Journal of Applied Physiology Dec 19, 2017

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ISSN
8750-7587
eISSN
1522-1601
D.O.I.
10.1152/japplphysiol.01119.2017
Publisher site
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Abstract

Fatiguing contractions change the force-velocity relationship, but assessment of this relationship in fatigue has usually been obtained after isometric contractions. We studied fatigue due to isometric or isotonic contractions, by assessment of the force-velocity relationship while the contractions maintaining fatigue were continued. This approach allowed determination of the force-velocity relationship during a steady condition of fatigue. We used the in situ rat medial gastrocnemius muscle, a physiologically relevant preparation. Intermittent (1s-1) stimulation at 170 Hz for 100 ms resulted in decreased isometric force to about 35 % of initial or decreased peak velocity of shortening in dynamic contractions to about 45% of initial. Dynamic contractions resulted in a transient initial increase in velocity, followed by a rapid decline until a reasonable steady level was maintained. Data were fit to the classic Hill equation for determination of the force-velocity relationship. Isometric and dynamic contractions resulted in similar decreases in maximal isometric force and peak power. Only Vmax was different between the types of contraction (p<0.005) with greater decrease in Vmax during isotonic contractions to 171.7{plus minus}7.3 mms-1 than during isometric contractions to 208.8 mms-1. Curvature was decreased substantially in both types of contraction: a/Po changed from 0.45{plus minus}0.04 to 0.71{plus minus}0.11 during isometric contractions and from 0.51{plus minus}0.04 to 0.85{plus minus}0.18 during isotonic contractions. Recovery was incomplete 45 min after stopping the intermittent contractions. At this time, recovery of low frequency isometric force was substantially less after isometric contractions, implicating force during intermittent contractions as a determining factor with this measure of fatigue.

Journal

Journal of Applied PhysiologyThe American Physiological Society

Published: Dec 19, 2017

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