Reliability, Variability and Minimal Detectable Change of the Isometric Mid-Thigh Pull in Adolescent Dancers.

INTRODUCTION: The importance and potential benefits of muscular strength in the adolescent's development for health and fitness has been demonstrated in the literature. Maximal muscular strength and its assessment, however, is not a primary assessment criterium in the selection of young talented dancers. METHODS: The present study evaluated the within- and between session reliability, variability, and minimal detectable change (MDC) of the isometric mid-thigh pull (IMTP). Thirty-five participants (female n = 17) participated in 2 identical assessments on the same day with 4-hour break in between. Three 3-second IMTP were performed, and the mean peak force value was used for the analyses. RESULTS: Within-session the ICC indicated excellent reliability (ICC = .99, 95% CI: 0.98-0.99). Between-session reliability was excellent (ICC = .98, 95% CI: 0.95-0.99). The standard error of measurement was 4% (48 N), the minimum detectable change was 12% (134 N) and the CV was 3%. There were no within-session statistically significant differences, but statistically significant differences between-session were observed (P < .001). Limits of agreement ranged from -121 N (95% CI -186 to -56 N) to 307 N (95% CI 243-372 N). CONCLUSION: The observed results demonstrated excellent within- and between sessions reliability, low variability, and an MDC of 12%. The consistency of the within-session scores suggest that peak force data may be obtained with single try efforts. The statistically significant difference in the means of the retest session, however, suggests that the time of the day or the time since entrained awakening may be affecting performance in adolescent dancers. The results of the current study indicate that the IMTP is a reliable assessment tool for maximal muscular strength in adolescent dancers.

The Relationship of Year Group and Sex on Injury Incidence and Countermovement Jump in Adolescent Ballet Dancers: A Cross-Sectional Analysis.

INTRODUCTION: Pre-professional ballet training involves long training hours from an early age that could influence young dancers' physical performance and injury incidence. This cross-sectional analysis investigated the relationship of year group and sex with countermovement jump and injury incidence (primary outcome) in adolescent ballet dancers at a pre-professional dance school.
Method: Countermovement jump (CMJ) height was recorded at the start of the academic year for 179 participants (M = 68, F = 111) spread across eight year-groups. Injury etiology and incidence was prospectively recorded over a 6-month period (September through February) by the medical team using a time-loss definition.
Results: Between-subject statistically significant differences were reported for sex [F(1, 153) = 101.46; p < 0.001], year group [F(7, 153) = 12.57; p < 0.001], and sex*year group [F(7, 153) = 9.22; p < 0.001]. Mean CMJ across the year groups ranged between 24.7 to 41.3 cm for males and 23.5 to 25.1 cm for females. Injury incidence per dancer was 0.84 (CI: 0.13, 1.56) and injury incidence per 1,000 hours of dance was 1.94 (CI: 1.63, 2.25). No statistically significant differences between sexes or year groups were reported for injury incidence per 1,000 dance hours and time-loss. Hours dancing was statistically significantly positively associated with CMJ (r = .481, p < 0.05) and negatively associated with injury incidence (r = -.253, p < 0.05) for males; for females it was positively associated with time-loss (r = .254, p < 0.05).
Conclusion: Even though CMJ was cross-sectionally monitored, the expected increased physical abilities in males as they grew older and progressed through their training was observed. Females did not indicate a similar increase in their physical ability, but they seemed to become more susceptible to injuries as they grow older. The lack of this speculative physiological development for the females may be associated with the ballet-only approach in their training. The use of CMJ as an injury screening tool may be limited, however, it could still be used as a tool to monitor physiological and fundamental motor skill development of adolescent dancers, as jumping is an integral part of ballet.

Neuromuscular Training in Pre-Professional Ballet Dancers: A Feasibility Randomized Controlled Trial.

INTRODUCTION: It is well documented that there is high prevalence of injuries in pre-professional and professional ballet dancers. Current evidence from high in quality and quantity research on in- jury prevention in sport indicates that interventions can reduce injury risks by 30% to 50%. Injury prevention research in dance is limited. The aim of this study was to assess the feasibility (adherence, fidelity, and practicality) of a randomized controlled trial for the utilization of neuromuscular training in pre-professional ballet dancers.
Methods: A convenience sample of 22 pre-professional ballet dancers were randomized into an intervention and control group. The intervention group took part in a neuromuscular-based training workout, five times per week before the ballet class, for 10 weeks. The intervention was an adaptation of the FIFA 11+, an injury prevention intervention and is called 11+ Dance. The intervention consisted of low intensity bodyweight exercises that lasted 20 to 30 minutes performed daily.
Results: Intervention adherence was 38% ± 8%, with higher participation at the beginning of the study. Attendance for post-testing was low 45% and 36% for the intervention and control group, respectively, mainly due to injury. There were no adverse effects reported, however, the participants reported delayed onset muscle soreness at the beginning of the intervention, indicating that there may be a potential training effect. Fear of muscle hypertrophy and fatigue were also reported as reasons for attrition. The repeated measures ANOVA revealed statistically non-significant differences for the countermovement jump F(1, 9) = 0.36, p = 0.564, η² p= 0.04; reactive strength index F(1, 7) = 0.02, p = 0.885, η² p= 0.003; and the isometric mid-thigh pull F(1, 12) = 0.002, p = 0.967, η² p= 0.000.
Conclusion: The results of the study, together with the feedback from the participants, suggest that some protocol modifications are necessary for the feasibility of a randomized controlled trial in a pre-professional setting. The current trial has produced valuable information for the intervention frequency and load prescription.

Effect of Vitamin D on Muscle Function and Injury in Elite Adolescent Dancers: A Randomized Double-Blind Study.

PURPOSE: A number of studies have noted low levels of vitamin D in dancers, and this has been associated with increased risk of injuries and decreased muscle-strength indices. The aim of the present study was to examine whether vitamin D supplementation over a 4-mo period can improve muscle function and injury incidence. METHODS: A total of 84 participants volunteered; exclusion criteria and dropout (19%) reduced the cohort to 67 participants (females = 29 and males = 38; 17-19 y). Participants were randomly assigned to either an intervention or placebo group (2∶1 ratio). All provided a venous blood sample before and after the 4-mo study period. The intervention group received 120,000 IU vitamin D to be taken over a 1-wk period, and the placebo group received the same number of inert pills. Participants completed a series of muscle function tests before and after the monitoring period. Injury incidence was recorded by the independent health team at the school. RESULTS: Preintervention, 6% of the cohort were vitamin D deficient, 81% were insufficient, and 13% had sufficient levels; postintervention, 53% were insufficient and 47% were sufficient. The intervention group reported a significant increase in serum 25(OH)D3 (57%; P < .00) and isometric strength (7.8%; P = .022) but not muscle power. There was a significant association between traumatic injury occurrence for the intervention and control groups (10.9% vs 31.8%; P < .02). CONCLUSION: Vitamin D supplementation decreased the numbers of deficient and insufficient participants in this cohort. The intervention group reported a small significant increase in muscle strength that was negatively associated with traumatic injury occurrence.

The effect of ankle bracing on peak mediolateral ground reaction force during cutting maneuvers in collegiate male basketball players.

The literature suggests that one-third of ankle injuries sustained during a collegiate basketball season are due to the poor execution of dynamic cutting movements, leading to increased mediolateral force being placed on the unstable ankle. The objective of the present study was to examine the effect of ankle bracing on peak mediolateral ground reaction forces (PMGRF) during sidestep cutting motions in collegiate basketball players. Ten male collegiate basketball players, with no previous history of ankle trauma, performed sidestep cutting motions past a static defensive opponent at speeds between 4.5 and 5.5 meters per second under 2 different conditions, with and without ankle bracing. Peak mediolateral ground reaction force was recorded (as a unit of body weight) for each subject in both bracing and control conditions. The application of an Aircast brace significantly (P = 0.01) reduced peak mediolateral forces during cutting maneuvers compared with no brace. Results suggest that the application of an Aircast ankle brace significantly reduces PMGRF during cutting maneuvers around a static defensive opponent.

A comparison of two stretching modalities on lower-limb range of motion measurements in recreational dancers.

Most stretching techniques are designed to place a "stress" on the musculoskeletal unit that will increase its resting length and range of motion (ROM). Twenty-four adolescent dancers participated in a 6-week intervention program that compared low-intensity stretching (Microstretching) with moderate-intensity static stretching on active and passive ranges of motion. Microstretching is a new modality that reduces the possibility of the parasympathetic system being activated. Repeated measures analysis indicated changes in ROM over the intervention period (p < 0.05), with the Microstretching group demonstrating greater increases in passive and active ROM than the static stretch group (p < 0.01); there was no noted bilateral differences in ROM. The results from this study agree with past studies that have found that stretching increases the compliance of any given muscle and therefore increases the range of motion. One main finding of the present study was that throughout a 6-week training program very-low-intensity stretching had a greater positive effect on lower-limb ROM than moderate-intensity static stretching. The most interesting aspect of the study was the greater increase in active ROM compared to passive ROM by the Microstretching group. This suggests that adaptation has occurred within the muscle itself to a greater extent than in structures of the hip joint. Practical application for this technique suggests it is beneficial as a postexercise modality that potentially has a restorative component.