Reproducibility and criterion validity of data derived from a flywheel resistance exercise system

BACKGROUND: Flywheel (FW) load represents a new trend among resistance exercise (RE) modalities; however, protocols and acquisition systems to measure FW-RE parameters are not yet fully researched and developed. OBJECTIVE: To assess the reproducibility and criterion validity of a prototype FW-RE acquisition system. METHODS: Thirty-eight student volunteers completed the low-row FW testings with a test-retest break of 1 week. Force (F), power (P) and velocity (v) parameters were simultaneously collected using a prototype FW acquisition system and a load cell (LC), respectively. Paired samples t-test was used to determine differences between test-retest and inter-devices results. The analysis included Pearson's correlation (r), standard error of measurement (SEM), smallest real difference (SRD) and Bland-Altman plots. In addition, for reproducibility purposes, ICC and smallest real difference (SRD) were calculated. RESULTS: An excellent correlation was found between FW and LC parameters (r= 0.971-0.997). The FW acquisition system provided us with significantly higher values among F and P parameters for men and women. The testing protocol that was used has shown good-to-excellent reproducibility for FW acquisition system in men (ICC = 0.771-0.985) and women (ICC = 0.773-948), respectively. Both men and women performed better during the retest. SEM and SRD values were higher for women (4.4-22.7%) compared to men (4.9-10.5%). CONCLUSIONS: The FW device and acquisition system described in this study has shown adequate criterion validity and good-to-excellent reproducibility of mechanical RE parameters for sports-diagnostic purposes. However, a familiarization session is necessary to obtain true measurements of a performance when using the FW based assessement in women.