Differences in Jump Height and Reactive Strength Index-Modified in Dancers and Non-dancers Performing the Vertical Jump from Two Positions

Differences in Jump Height and Reactive Strength Index-Modified in Dancers and Non-dancers Performing the Vertical Jump from Two Positions

The vertical jump (VJ), the gold standard for assessing leg power, is most commonly performed from a squat stance (SS). However, dancers often initiate jumps/leaps from a plié, externally rotated from the hip or “turned out” (TO). Testing dancers from a SS may not indicate activity specific power. This study’s purpose was to determine differences in jump height and leg explosiveness, as measured by reactive strength index-modified (RSI-mod) when performed from TO and SS positions in dancers and non-dancers. Thus far, five healthy participants who are physically active at least ten hours/week have been studied; three dancers, having at least four years of ballet training (19.3+2.1 yrs, 66.7+11.7 kg, 1.70 +0.05 m), and two non-dancers (24.5+3.5 yrs, 71.0+2.5 kg, 1.70+0.03 m). Post warm-up, participants performed three jumps from both TO and SS conditions. Time to take-off was determined as the time difference between the beginning of the eccentric lowering phase and take-off. Jump height was measured with a Vertec. RSI-mod was calculated as jump height/time to take-off. Preliminary results show dancers jumped higher TO vs. SS (18.83+3.55 vs. 18.33+4.37 in), and non-dancers jumped higher SS vs. TO (18.25+5.30 vs. 17.75+5.30 in). RSI-mod was higher for TO than SS for dancers (0.70+0.18 vs 0.64+0.23), and similar for SS vs. TO for non-dancers (0.41+0.11 vs .40+0.08). Dancers appear to have greater leg power overall than non-dancers, and generate more power in the TO vs. SS condition as indicated by higher jump heights and RSI-mod. Testing dancers from a TO position improves VJ performance.