Reliability and Repeatability of Countermovement Jump Waveforms

Abstract

Though the countermovement vertical jump (CMJ) has traditionally been used to assess lower body force and power, the force-time characteristics of the CMJ ground reaction force (GRF) waveform may be of value in predicting injury risk and assessing training readiness. Prior to evaluating the CMJ GRF waveform as a diagnostic and evaluative tool, the reliability of the waveform on a within and between day basis should be established. PURPOSE: To determine the within day and between day reliability of the CMJ GRF waveform in healthy individuals. METHODS: Twenty-five healthy (age = 21.5 ± 1.9 years), recreationally active men and women completed one familiarization and three experimental visits, a minimum of 48 hours apart. Each visit consisted of a brief, standardized warmup, two submaximal CMJs, and three maximal CMJs performed on a force plate (sample rate = 1000Hz). Each jump was separated by two minutes. To reduce the variability associated with arm swing, all jumps were performed with subjects’ hands on their hips. The CMJ GRF waveform for each jump, beginning with the minimum GRF during the counter-movement and ending at take off, was interpolated and re-sampled to a uniform length of 1000 data points. Individual within and between day reliabilities for each subject’s waveform shapes were calculated using the adjusted coefficient of multiple determination (R2a) as previously described by Kadaba et al (J Orthop Res, 7(6): 849-860, 1989). Briefly, the primary calculation of the within day reliability compared the GRF at each data point of a single jump with the mean GRF for that day at the corresponding data point. The between day reliability was calculated similarly, however, the mean GRF at each point for each day was compared to the mean GRF at that point of all three days. Data is reported as the coefficient of multiple correlation (CMC), the positive square root of the R2a. RESULTS: The CMJ waveforms were highly reliable, both on a within day (0.968 ± 0.020) and between day (0.962 ± 0.018) basis. Observed within day CMC values ranged from 0.909 – 0.993, whereas between day CMC values ranged from 0.917 – 0.994. CONCLUSION: Individual CMJ GRF waveforms are highly reliable under these test conditions. These results provide preliminary evidence that the CMJ GRF waveforms shapes may have utility as a diagnostic and evaluative tool.