Differential contributions of fatigue‐induced strength loss and slowing of angular velocity to power loss following repeated maximal shortening contractions

Abstract

The purpose of this study was to investigate the relationship between fatigue‐induced reductions in isometric torque and isotonic power and to quantify the extent to which the decreases in angular velocity and dynamic torque can explain the power loss immediately following an isotonic fatiguing task and throughout recovery in seven young males and six young females. All measurements were performed with both legs. For dorsiflexion, fatigue‐related time‐course changes in isometric maximal voluntary contraction (MVC) torque, angular velocity, dynamic torque, and power production following repeated maximal isotonic contractions (load: 20% MVC) were investigated before, immediately after, and 1, 2, 5 and 10 min after a fatiguing task. There were no relationships between the fatigue‐related reductions in isometric MVC torque and peak power at any timepoint, suggesting that fatigue‐induced reductions in isometric MVC torque does not entirely reflect fatigue‐induced changes in dynamic performance. The relative contribution of fatigue‐related reduction in dynamic torque on power loss was greater immediately following the task, and lower throughout recovery than the corresponding decrease in angular velocity. Thus, power loss immediately following the task was more strongly related to the decline in dynamic torque; however, this relationship shifted throughout recovery to a greater dependence on slowing of angular velocity for power loss.

Isometric versus isotonic contractions: Sex differences in the fatigability and recovery of isometric strength and high‐velocity contractile parameters

“…Similar to fatigability, recovery of muscle function was also similar between sexes. In support of recent studies (Akagi et al, 2020; Krüger et al, 2019), fatigue‐ and recovery‐related responses in maximal strength did not correspond with changes in power, thus is it important for future work to consider these measures and their physiological contributors independently. The present work indicates that sex differences in fatigability for the plantar flexors may not be as prominent as other commonly examined muscle groups.…”

“…Isometric strength and isotonic power recovered differently after isotonic exercise as the latter showed a quicker rate of recovery. As suggested by Krüger et al (2019) and demonstrated by Akagi et al (2020), fatigue‐induced changes in isometric strength and power should not be considered interchangeable as they follow different timelines and likely reflect at least some unique physiological processes. Similar to Akagi et al (2020), relative changes in isometric strength were not correlated with power at any timepoint.…”

“…As suggested by Krüger et al (2019) and demonstrated by Akagi et al (2020), fatigue‐induced changes in isometric strength and power should not be considered interchangeable as they follow different timelines and likely reflect at least some unique physiological processes. Similar to Akagi et al (2020), relative changes in isometric strength were not correlated with power at any timepoint. As expected, percent changes in OPT T , OPT V , and RVD were strongly correlated with the change in power during recovery after both fatiguing protocols, but RTD and RER MG were moderately correlated with changes in power only after isometric fatigue.…”

“…There is far less evidence for the fatigue‐ and recovery‐related response of power. Further, there are divergent decrements in power and isometric strength after fatiguing isotonic contractions (Akagi et al, 2020; Cheng & Rice, 2005; Krüger et al, 2019). It was recently shown that the fatigue‐induced reduction in isometric strength was not associated with the reduction in power during isotonic contractions (Akagi et al, 2020).…”

“…Further, there are divergent decrements in power and isometric strength after fatiguing isotonic contractions (Akagi et al, 2020; Cheng & Rice, 2005; Krüger et al, 2019). It was recently shown that the fatigue‐induced reduction in isometric strength was not associated with the reduction in power during isotonic contractions (Akagi et al, 2020). Thus, it is warranted to investigate power and isometric strength as standalone performance measures to better understand fatigue‐ and recovery‐related sex differences in muscle function.…”