ACUTE IMPROVEMENT OF VERTICAL JUMP PERFORMANCE AFTER ISOMETRIC SQUATS DEPENDS ON KNEE ANGLE AND VERTICAL JUMPING ABILITY

This study examined the acute effects of maximum isometric squats at 2 different knee angles (90 or 1408) on countermovement jump (CMJ) performance in power athletes. Fourteen national-level male track and field power athletes completed 3 main trials (2 experimental and 1 control) in a randomized and counterbalanced order 1 week apart. Countermovement jump performance was evaluated using a force-plate before and 15 seconds, 3, 6, 9, and 12 minutes after 3 sets of 3 seconds maximum isometric contractions with 1-minute rest in between, from a squat position with knee angle set at 90 or 140 degrees. Countermovement jump performance was improved compared with baseline only in the 1408 condition by 3.8 +/- 1.2% on the 12th minute of recovery (p = 0.027), whereas there was no change in CMJ height in the 908 condition. In the control condition, there was a decrease in CMJ performance over time, reaching 23.6 +/- 1.2% (p = 0.049) after 12 minutes of recovery. To determine the possible effects of baseline jump performance on subsequent CMJ performance, subjects were divided into 2 groups (high jumpers and low jumpers). The baseline CMJ values of high jumpers and low jumpers differed significantly (CMJ: 45.1 +/- 2.2 vs. 37.1 +/- 3.9 cm, respectively, p = 0.001). Countermovement jump was increased only in the high jumpers group by 5.4 +/- 1.4% (p = 0.001) and 7.4 +/- 1.2% (p = 0.001) at the knee angles of 90 and 1408, respectively. This improvement was larger at the 1408 angle (p = 0.049). Knee angle during isometric squats and vertical jumping ability are important determinants of the acute CMJ performance increase observed after a conditioning activity.