Does The Countermovement Jump Accurately Assess Lower-limb Neuromuscular Fatigue?

Abstract

Neuromuscular fatigue is monitored in athletes following intense exercise to inform future training prescription and to improve performance. Temporal analysis of the countermovement jump (CMJ) is frequently used to assess fatigue in athletes but is infrequently compared directly to low-frequency fatigue (LFF), a long-lasting fatigue typically assessed in the laboratory. LFF may be present in athletes. PURPOSE: To determine the time-course of changes in CMJ and lower limb LFF following an exhaustive cycling test and the relationship between LFF and temporal CMJ variables. METHODS: LFF and CMJ were assessed in seven active adults (24±2 years, 78±14 kg) prior to and following (0, 8, 15, 30, 60 mins and 24 and 48 hours) an incremental cycling test to exhaustion. Cycling began at 100 W and increased 25 W every 2 min until exhaustion. Temporal analysis of CMJ for peak power (PP), jump height (JH), and concentric contraction duration (CCD) were calculated from bilateral force plates. Low-frequency (10 Hz) force (F10) was elicited from transcutaneous femoral nerve stimulation prior to a maximal voluntary contraction (MVC). LFF was quantified as the F10:MVC ratio. The order of CMJ or LFF was randomized across time points. Changes in LFF and CMJ variables were assessed from two-way repeated measures analysis of variance (measure x time). RESULTS: Maximal aerobic power was 234±67 W (96±4% HRmax). A significant measure x time interaction (p<0.0001) and significant main effects of time (p=0.05) and method (p=0.02) were found. Compared to baseline, significant reductions in LFF (i.e., greater fatigue) were seen at 0-, 8-, 15- and 30-mins post-exercise (all p<0.02). No significant changes in any of the CMJ variables were observed post-exercise (p = 1.0). Furthermore, changes in LFF during exercise recovery was not correlated to changes in any of CMJ variables (r2<0.04, p>0.20), whereas all CMJ variables were significantly correlated with each other (0.22<r2<0.42, p<0.001). CONCLUSION: These results show that following exhaustive exercise, LFF persists for at least 30 mins whereas no change in CMJ performance variables were seen. These results call into question the practical utility of interpreting neuromuscular fatigue in athletes using the CMJ, even within 30 minutes of exhaustive exercise.