Lower Extremity Horizontal Work but Not Vertical Power Predicts Lower Extremity Injury in Female Collegiate Dancers

Dancers often perform powerful and explosive movements that require adequate lower extremity (LE) activity in horizontal and vertical directions. We examined whether these measures were interrelated and whether they predicted LE injury status in dancers using binary logistic regressions and receiver operator characteristic (ROC) curve analyses. Forty-three collegiate female dancers (18 +/- 0.7 years; 162.6 +/- 5.9 cm; 59.4 +/- 7.1 kg) performed single leg hop (SLH, m) and vertical jump (VJ, cm) tests. Single leg hop and VJ distances were used to calculate SLH norm (as a % of body height) and vertical power (vPower, watts). Lower extremity injuries and dance exposure hours (DEhrs) were recorded for 16 weeks. Dancers had 51 injuries resulting in a 3.7/1,000 DEhr injury incidence rate (95% confidence interval [CI]: 2.7-4.7). Twenty dancers were injured, whereas 23 remained injury free. Injured dancers had significantly lower SLH norm than noninjured dancers (t = 2.7, p = 0.009, 85.2 +/- 11.2% vs. 76.8 +/- 8.4%, respectively), but vPower was similar (t = 0.6, p = 0.53, injured = 2,632.0 +/- 442.9 watts, noninjured = 2,722.7 +/- 480.0 watts). SLH norm, but not vPower significantly predicted injury status chi(2)(1,43) = 5.9, p = 0.02. Specifically, an SLH norm cut-off value of 78.2% identified dancers at injury risk (area under the curve = 0.73, SE = 0.08, p = 0.01, 95% CI = 0.57-0.89, sensitivity = 0.75, specificity = 0.70). However, vPower was not able to identify dancers at risk (p = 0.36). vPower had moderate relationships with SLH norm (r = 0.31, p = 0.04). Compared with injured dancers, noninjured dancers had greater SLH norm but similar vPower. Only SLH norm predicted injury status in female collegiate dancers. Thus, the SLH test may possibly predict LE injury risk in dancers. Strength and conditioning coaches can prospectively use baseline SLH test screenings to identify dancers whose SLH is less than 78.2% of their height because these dancers may have increased probability of LE injury risk. Coaches can then include horizontal direction exercises when designing training programs and examine whether these programs reduce LE injury risk in female collegiate dancers.