July 14, 2016

Nick Clarke1,2, Jonathan P. Farthing1, Joel L. Lanovaz1 & Joel R. Krentz1

1 College of Kinesiology, University of Saskatchewan, Saskatoon, SK, Canada.
2 Canadian Sport Institute Pacific, Victoria, BC, Canada.

The importance of monitoring and maintaining the balance between training stimulus and recovery in all athletes is vital to optimize positive adaptation. However, the combative nature and unpredictable stress imposed on an individual Canadian football player presents a unique monitoring challenge especially when interpreting fatigue measures.

The ability to generate explosive force within fractions of a second is seen as a vital determinant of performance in Canadian football. For this reason monitoring alterations in a maximal countermovement jump (CMJ) as an indicator of neuromuscular fatigue (NMF) is popular in professional settings. However, when considering the high injury rates within collision-based team sports compared with other team sports such as soccer, the likelihood and practicality of being able to regularly use maximal CMJ protocols to assess NMF is far from ideal. A need for an alternative and less taxing NMF monitoring tool is therefore evident.

A potential solution to practical NMF monitoring in collision-based team sports may be the assessment of balance (postural sway). By assessing the effects of a fatiguing game simulation on the balance of collegiate Canadian football players the purpose of this study was to evaluate postural sway as a potential tool for monitoring NMF in collision-based team sports.

Fifteen male Canadian Football players were recruited. Indirect NMF measures (postural sway and CMJ) were performed immediately before and after a simulated Canadian football Game (G-Sim). Peak isometric knee extensor torque of a maximal voluntary contraction (MVC) and an electrically evoked maximal contraction (involuntary) were also collected pre and post G-Sim as direct NMF measures.

Significant declines in MVC were observed immediately post G-Sim (-15.3%) with no change in the electrically evoked contraction (i.e. signals sent voluntarily from the brain to knee extensor were compromised after G-Sim confirming the presence of NMF). These direct results were accompanied by significant reductions in CMJ takeoff velocity and peak power (-6.9% and -6.5%) as well as a significantly larger area covered by the center of pressure trajectory (95.2%) during a 60s postural sway task (i.e. increased instability). In other words, the G-Sim produced NMF and the indirect measures were effected negatively.

Our results confirm that monitoring peak power of a CMJ is the most useful tool in identifying NMF in collision-based team sport players. In addition however, when the collection of a maximal CMJ is hampered by injury, postural sway may be an alternative, less taxing monitoring tool which is also sensitive to NMF.

The relevance of this to all health, fitness and sport professionals is that regardless of clientele or fitness status a measure of fatigue can be assessed through monitoring balance. As long as clear baseline values are established and remembering that postural sway is not directly related to performance (unlike the CMJ), trends of balance monitoring have the potential to aid in the tricky “balancing” act between increasing training loads/stimulus and adequate recovery (dose vs response).

This article is a summary of an article published in Applied Physiology, Nutrition & Metabolism. If you intend citing any information in this article, please consult the original article and cite that source. This summary was written for the Canadian Society for Exercise Physiology and it has been reviewed by the CSEP Knowledge Translation Committee.

Original Article

Clarke N, Farthing J, Lanovaz J, Krentz J. Direct and indirect measurement of neuromuscular fatigue in Canadian football players. Applied Physiology, Nutrition, and Metabolism; 2015, 40:464-473, dx.doi.org/10.1139/apnm-2014-0465