Abstract
This study aimed to determine the effect of eccentric (ECC)
velocity of the down phase of a jump squat (JSQ) on JSQ
performance during the concentric (CON) upward phase under
60% and 70% loads of one repetition maximum (1RM). The
subjects were ten university rugby players who took part in both
experiments: 1) ECC velocity of 2 seconds (ECC2s), and 2)
individual maximum velocity (ECCmax) under 60% and 70%
loads of 1RM squat. Measurements were made of jumping height,
mean and peak velocity, power, and force exerted during the CON
phase. For 60%1RM, peak velocity, mean and peak power, and the
mean force exerted by the ECCmax squat was significantly higher
than by the ECC2s squat. No significant difference was seen in
jump height, mean velocity or peak force. For 70%1RM, the mean
velocity and mean power of the ECCmax squat was significantly
higher than the ECC2s squat. No significant differences were
observed in jumping height, peak velocity, peak power, mean
or peak force between the two squat conditions. Individual
differences were, however, observed in the effect of ECC velocity
on CON performance. ECCmax also varied according to the
individual. It appears that subjects with higher ECCmax values
had the potential to increase their CON velocity or jump height;
on the other hand, those with low ECCmax would not be expected
to achieve improved performance.
https://ror.org/01rwx7470 
