Validity of double- and single-leg vertical jumps as tests of leg extensor muscle function

The purpose of this research was to determine if 5 weeks of resistance training for the shoulder and hip flexor muscles produces improvements in vertical jumping (VJ) performance. Twenty-eight men were assessed on tests of shoulder power, leg extensor muscle function, and VJ performance using jumps performed from a standing position, a 3-stride run-up, and double- and single-leg takeoffs. A shoulder and hip flexor training group (n = 14) improved significantly more than a nontraining control group (n = 12) in shoulder power and 2 VJ performance tests, but not in the tests of leg extensor muscle function. It was concluded that the arm swing and free-leg drive significantly influence VJ performance and, therefore, VJ tests are not valid for assessment of leg extensor muscle function.