Countermovement Jump Assessment for Athlete Neuromuscular Fatigue Monitoring
Date
2014-08-29
Authors
Gathercole, Robert
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Neuromuscular (NM) fatigue can be defined as an exercise-induced decrease in skill-based performance and/or capacity that originates within the NM system (i.e. between activation of the primary motor cortex to the performance of the contractile apparatus (Bigland-Ritchie, 1981)) (Boyas & Guével, 2011). NM fatigue is a fundamental component of athlete training and competition, required for both optimal adaptation and performance. However, in the short-term, NM fatigue can decrease performance and increase injury risk, whilst its accumulation can produce long-term deleterious performance and health consequences. Consequently, athlete fatigue monitoring is recommended for precise management of athlete training adaptation and recovery practices. Regular NM function measurement is a key component of athlete fatigue monitoring; still the best means of assessing fatigue-induced effects on NM function is presently unclear. A broader understanding of the most suitable NM testing methods, and associated NM constructs, would therefore be of value to sport practitioners. As elaborated below, this dissertation aimed to first identify the most suitable NM function test, and then develop the testing technique to better determine the NM responses associated with acute fatigue, an accumulation of exercise stress (i.e. accumulated fatigue), and post-exercise recovery. A secondary aim was to provide a greater understanding of the NM responses elicited by fatiguing exercise.
First, the suitability of four NM function tests (e.g. countermovement jump (CMJ), squat jump (SJ), drop jump (DJ), 20-m sprint (SPRINT)) for the regular measurement of NM fatigue was examined. Assessment of test repeatability (mean coefficient of variation for various measures of force, velocity, power, impulse and flight time; SPRINT: 1.2%; CMJ: 3.0%; SJ: 3.5%; DJ: 4.8%) and sensitivity to NM fatigue (substantial post-exercise changes observed up to; SPRINT: 0-hr post; SJ: 24-hr post; CMJ & DJ: 72-hr post) revealed the CMJ test to be the most suitable, with it highly repeatable and sensitive to fatigue-induced changes immediately following fatiguing exercise and during post-exercise recovery. Subsequent investigations further explored the use of CMJ testing for NM fatigue detection.
Second, CMJ responses to acute NM fatigue and during post-exercise recovery were examined in recreational athletes. As part of this process, two analytic approaches, anticipated to decrease measurement error and improve test sensitivity through the examination of CMJ mechanics, were utilised. Fatiguing exercise resulted in a biphasic recovery profile. Immediate decreases were evident in most CMJ variables (i.e. small-to-moderate changes), followed by mechanical changes indicative of NM fatigue (i.e. small changes in CMJ time- and rate-based variables) at 72-hour. Observation of mechanical changes at 72-hour, supported the use of the two adopted CMJ analytic approaches.
Third, the developed methodology was used with elite snowboard-cross athletes to examine fatigue- and training-induced changes in NM function. Compared to concentric CMJ variables (i.e. peak/mean power/force/velocity), mechanical CMJ changes were more marked following both the fatiguing protocol (ES: moderate-to-large vs. small-to-moderate) and the 19-week training block (large-to-extremely large vs. small-to-very large). The more apparent mechanical changes observed in this highly-trained population (vs. the recreational athletes in Chapter 3) indicated that CMJ mechanical analysis may be of particular value in athlete populations.
Fourth, the CMJ testing techniques were used to examine NM changes associated with accumulated fatigue (i.e. an accumulation of exercise and/or non-exercise stress) in a highly-trained population. Alongside increased training loads and decreased wellness, substantial changes in CMJ mechanics (e.g. time to peak force, force at zero velocity) and jump outcome (e.g. flight time, peak displacement) were observed, thereby supporting the inclusion of mechanical CMJ assessment for the monitoring of accumulated NM fatigue effects.
This series of investigations support the use of CMJ testing for athlete NM fatigue monitoring, and highlight that NM fatigue can manifest as alterations in the mechanical strategies used to accomplish a task. These changes appear evident in response to acute fatigue (Chapters 3 and 4), alongside increases in training load (Chapters 4 and 5) and during post-exercise recovery (Chapter 3). Practitioners should therefore incorporate analyses of CMJ mechanics to provide a more comprehensive assessment of fatigue- and training-induced changes in NM function.
Description
Keywords
Neuromuscular fatigue, Athlete monitoring, Countermovement jump