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.
