On the assessment of lower-limb muscular power capability

Purpose: This study assessed the reliability and validity of different methods used to estimate lower-limb muscular power capability based on mechanical variables. For this purpose, vertical jumping was compared with isokinetic knee extensions and with power tests used by practitioners. Methods: Four groups of subjects (N = 106) were tested in different conditions. Group-I performed countermovement vertical jumps (CMJ) on a force plate followed by left and right knee extensions on an isokinetic device at 120, 180 and 240 deg·s^-1. Group-II performed CMJ trials followed by 20-m sprints, hand-reach jumps and 1RM leg-press testing. Group-III carried out squat jumps (SJ) in addition to CMJ trials. Finally, Group-IV performed the CMJ test and was retested twice after a short inter-session interval (1-4 days) and after a long one (4.5-5 months). The Pearson correlation was used to assess the validity and reliability of CMJ (p ≤ 0.01, **). Results: Mean peak power during CMJ was correlated with sprint time (r = -0.882**) and leg-press 1 RM (r = 0.797**), but less with peak hand-reach height (r = 0.695; p ≤ 0.05). Isokinetic knee extension power showed also a significant correlation with CMJ power, but its strength depended on the angular velocity (Isok-120 r = 0.702**; Isok-180 r = 0.737**; Isok-240 r = 0.599**). Test-retests showed a strong correlation after a short interval (r = 0.915**) and after a long one (r = 0.890**). Using the SJ technique did not have any effect on reliability (r = 0.914**). Conclusions: CMJ matches other methods used for testing lower-limb power capability. It is highly reliable and it allows a valid assessment of muscular power. Since CMJ is also simple and accurate to perform, it is the recommended method.