Abstract
This study investigated neuromuscular adaptations of the knee extensors after 8 weeks
of plyometric training. 23 subjects were randomly assigned to an intervention group
and a control group. We measured isometric maximum voluntary torque (iMVT), rate of
torque development (RTD) and impulse (IMP) over different time intervals. The neural
drive to muscles was estimated with the interpolated twitch technique and normalized
root mean square of the EMG signal. Contractile properties, H reflexes as well as
jump height in squat jump (SJ) and countermovement jump (CMJ) were evaluated. Neuromuscular
testing was performed at 2 knee angles, i. e., 80° and 45° (0°=full extension). The
iMVT at 80° knee flexion was 23.1 N · m (95% CI: 0.1–46.1 N · m, P=0.049) higher at post-test for the intervention group compared with controls. The
same was true for RTD and IMP in the time interval 0–50 ms [308.7 N · m · s−1 (95% CI: 28.8–588.6 N · m · s−1, P=0.033) and 0.32 N · m · s (95% CI: 0.05–0.60 N · m · s, P=0.026), respectively]. These changes were accompanied by enhanced neural drive to
the quadriceps muscle. Jump height in SJ and CMJ was higher at post-test for the intervention
group compared with controls. Parameters at 45° knee flexion, contractile properties
and evoked potentials did not differ between groups. Although hypertrophic changes
were not measured, data suggest that the training regime probably induced mainly neural
adaptations that were specifically related to the knee angle. The strength gains at
80° knee flexion likely contributed to the enhanced jump height in SJ and CMJ.
Key words
maximal voluntary strength - explosive voluntary strength - voluntary activation -
angular specificity
