History Dependency of Muscle Strength Recovery from a Fatiguing Intermittent Task

Abstract

Muscle fatigue and recovery are complex processes influencing muscle force generation capacity. While fatigue reduces this capacity, muscle recovery acts to restore the unfatigued muscle state. Many factors can potentially affect muscle recovery, among these may be a task dependency of recovery following an exercise. However, little has been reported regarding the history dependency of recovery after fatiguing contractions. Recently, we investigated the dependency of the fatigue process on cycle time during low to moderate exertion levels of intermittent muscle contraction (Rashedi & Nussbaum, 2016). A dependency of localized muscle fatigue on cycle time was shown, even though there was a consistent level of overall physical demand. It was concluded that the difference in fatigue development might be related to recovery processes occurring during execution of the intermittent task. In the present study, we focused on the potential effect of contraction history on post-fatigue recovery. Based on the expected dependency of recovery to task demands during exercise, it was hypothesized that post-fatigue recovery will also be affected by the history of exercise-induced muscle fatigue. We examined the dependency of muscle recovery subsequent to four different histories of fatiguing muscle contractions, imposed using two cycle times (30 and 60 sec) during low to moderate levels (15% and 25% of maximum voluntary contraction (MVC)) of intermittent static exertions involving index finger abduction. All participants completed the intermittent contractions, in all four conditions, for 1 hour, and MVCs were obtained at fixed intervals during 1 hour of post-exercise recovery (i.e., at 0.2, 5, 10, 30, and 60 minutes). There was a clear and statistically-significant dependency of muscle recovery rate on the muscle capacity state existing immediately after fatiguing exercise. This dependency did not appear to be modified by either the cycle time or exertion level leading to that state. Similar results were found in the study of Iguchi et al. (2008), wherein the authors compared recovery between two different exertion histories while fatiguing muscles to the same level, though recovery was only monitored for 5 minutes. These results imply that the post-exercise rate of recovery is primarily influenced by the post-exercise muscle state. Such evidence may help improve existing models of muscle recovery (Rashedi & Nussbaum, 2015b), facilitating more accurate predictions of localized muscle fatigue development (Rashedi & Nussbaum, 2015a), and thereby helping to enhance muscle performance and reduce the risk of injury