Quadriceps Strength and Jumping Efficiency in Dancers

Abstract

Body composition, isometric quadriceps muscle force output, EMG activity during isometric and SSC activity, and flexibility were assessed in female dancers (n = 11) and physically active controls (n = 11) to investigate quadriceps muscle strength and electromyographic (EMG) activity during isometric and stretch-shortening cycle (SSC) activity in dancers. The dancers had less body fat (21.4% ± 2.8 vs 25.6% ± 3.7, p < 0.01) and were more flexible in the straight-leg raise, ankle plantar flexion and dorsiflexion, elbow flexion and extension and sit-and-reach tests (all p < 0.01) than the controls. The dancers generated greater quadriceps muscle force output during a 5 second maximal voluntary isometric contraction (peak force: 458.9N ± 91.4 vs 327.9N ± 78.2, p < 0.01), but did not jump significantly higher than the controls (37.6 ± 5.5 vs 35.9 ± 3.9 cm, respectively). The dancers generated similar force output to the controls, but with less relative EMG activity, during the squat (p < 0.01), counter-movement (p < 0.05), and drop (p < 0.05) SSC jumps. The dancers had greater quadriceps muscle strength than the controls, but did not jump significantly higher. They used less of their maximum EMG during the jump tests, and hence less of their maximal possible muscle recruitment when jumping than the controls. This may be due to the dancers subconsciously sacrificing their jump height for aesthetics, to training-induced differences in whole limb muscle recruitment patterns, or to training-induced or genetic differences in the elastic components of the dancers’ compared to the controls’ lower limb musculotendinous tissue.