Self-Directed Oral Vitamin D Supplementation in Professional Ballet Dancers: A Randomized Controlled Trial Pilot Study.

Inadequate levels of vitamin D may lead to poor performance in professional dancers. Therefore, dietary supplementation may be essential in this population. This longitudinal pilot study to a randomized controlled trial assessed dancer compliance with self-directed oral vitamin D supplementation. Seventy-one dancers, 41 females and 30 males with a mean age of 31.1 years, were recruited from The Royal Ballet, London. Baseline serum 25(OH)D levels were measured and dancers were interviewed, examined, and provided with oral supplements for the winter period, November 2011 to March 2012. Dancers with normal serum 25(OH)D levels were provided with maintenance supplements (1,000 IU/ day) and those with insufficient or deficient serum 25(OH)D levels were given a loading dose of 60,000 IU weekly for 2 and 6 weeks, respectively. Serum 25(OH) D levels were measured at 1 and 2 years and dancers were sampled for compliance with instructions. Mean compliance during loading and maintenance was 86% and 50%, respectively. Mean serum 25(OH)D levels at start and end of the study period were 79.3 ± 31.6 nmol/L and 78.68 ± 19.8 nmol/L, respectively. Only one-third of dancers with insufficient (N = 5) and deficient (N = 5) serum vitamin D levels improved to normal values. It is concluded that professional ballet dancers demonstrate good compliance with self-directed loading doses of vitamin D supplementation but poor compliance with maintenance doses. Poor maintenance compliance may have accounted for the low rates of serum vitamin D level improvement among dancers with insufficient or deficient levels.

Gluteal muscle activation during the isometric phase of squatting exercises with and without a Swiss ball.

OBJECTIVES: Growing evidence supports hip muscle activation and strengthening exercise prescription to prevent and treat various lower limb injuries. Common prescriptions include single-legged and double-legged squatting, with and without a Swiss ball. We aimed to establish the effect of varying forms of squatting exercises on gluteal muscle activation. DESIGN AND SETTING: Observational laboratory study. PARTICIPANTS: Nineteen (11 male) healthy participants (28.4 +/- 2.7 years old) were compared using one-way repeated measures analysis of variance. MAIN OUTCOME MEASURES: Surface electromyography (EMG) measures of gluteus medius (GMed) and gluteus maximus (GMax) during the isometric phase of single-legged and double-legged squatting, with and without a Swiss ball. RESULTS: A greater percentage of maximal voluntary contraction (%MVC) during single-legged squatting was found compared to double-legged squatting for GMed (42 versus 9%MVC, p < 0.001) and GMax (35 versus 14%MVC, p < 0.001). Additionally, the Swiss ball increased GMax activity (42 versus 35%MVC, p = 0.026) and demonstrated a trend toward increased GMed activity (46 versus 42%MVC, p = 0.075) during the single-legged squat. CONCLUSIONS: These results indicate single-legged squatting may be more appropriate than double-legged squatting to facilitate strength gains of GMed and GMax. Additionally, the Swiss ball may be a useful adjunct to target gluteal muscle strengthening during single-legged squatting.