Lower extremity hypermobility, but not core muscle endurance influences balance in female collegiate dancers

Background Dance is a physically demanding activity, with almost 70% of all injuries in dancers occurring in the lower extremity (LE). Prior researchers report that muscle function (e.g. muscle endurance) and anatomical factors (e.g. hypermobility) affect physical performance (e.g. balance) and can subsequently influence LE injury risk. Specifically, lesser core muscle endurance, balance deficits, and greater hypermobility are related to increased LE injury risk. However, the potentials interrelationships among these factors in dancers remain unclear. Purpose The purposes of this study were to examine the relationships among core muscle endurance, balance, and LE hypermobility, and determine the relative contributions of core muscle endurance and LE hypermobility as predictors of balance in female collegiate dancers. Study Design Cross-sectional Methods Core muscle endurance was evaluated using the combined average anterior, left, and right lateral plank test time scores(s). LE hypermobility was measured using the LE-specific Beighton hypermobility measure, defining hypermobility if both legs had greater than 10 ° knee hyperextension. Balance was measured via the composite anterior, posterolateral, and posteromedial Star Excursion Balance Test (SEBT) reach distances (normalized to leg length) in 15 female healthy collegiate dancers (18.3 + 0.5yrs, 165.5 + 6.9cm, 63.7 + 12.1kg). Point-biserial-correlation-coefficients examined relationships and a linear regression examined whether core endurance and hypermobility predicted balance (p<.05). Results LE hypermobility (Yes; n = 3, No; n = 12) and balance (87.2 + 8.3% leg length) were positively correlated r(14)=.67, (p=.01). However, core endurance (103.9 + 50.6 s) and balance were not correlated r(14)=.32, (p=.26). LE hypermobility status predicted 36.9% of the variance in balance scores (p=.01). Conclusion LE hypermobility, but not core muscle endurance may be related to balance in female collegiate dancers. While LE hypermobility status influenced balance in the female collegiate dancers, how this LE hypermobility status affects their longitudinal injury risk as their careers progress needs further study. Overall, the current findings suggest that rather than using isolated core endurance-centric training, clinicians may encourage dancers to use training programs that incorporate multiple muscles - in order to improve their balance, and possibly reduce their LE injury risk

A comparison of knee muscle activation and knee joint stiffness between female dancers and basketball players during drop jumps

"This dissertation compared knee muscle activation of the lateral gastrocnemius, medial and lateral hamstrings, and lateral quadriceps (LG, MH, LH, and LQ) and knee joint stiffness(KJS) between female dancers(D) and basketball players(B) during the initial landing of a double-leg drop jump. The purpose was to examine possible neuromechanical strategies dancers employ that might protect them from Anterior Cruciate Ligament (ACL) injuries during a potentially high ACL-injury risk activity. Fifty-five females (D=35, 20.7+2.3yrs, 164.3+6.7cm,62.2+1.9kg, B=20,20.1+2.0yrs, 170.5+6.1cm,72.6+11.4kg) performed 5 double-leg drop jumps from a 45cm box. Muscle activity was recorded via surface electromyography (sEMG). A force plate and three-dimensional electromagnetic tracking system were used to record kinetic and kinematic data and calculate KJS (ratio of change in sagittal knee moment to sagittal knee flexion angle from ground contact to maximum knee flexion). sEMG data were normalized to maximum volitional isometric contractions(%MVIC), and joint moments to body weight (Nm/kg). Separate 2x4 ANOVAs compared D and B on muscle onsets (ms) and mean RMS amplitudes (%MVIC) before (PRE=150 ms) and after (POST=50 ms) ground contact. A one-way ANOVA examined group differences in KJS (Nm/kg°), with a stepwise regression model examining prediction of KJS. No significant group differences were observed in muscle onsets (D=133.4+53.2ms, B=121.6+50.2ms;P=.22), activation amplitudes (PRE: D=28.1+8.7%MVIC, B=27.7+10.5%MVIC;P=.60; POST: D=51+17.3%MVIC, B=49.6+21.4%MVIC;P=.78), or KJS (D=.0163+.009Nm/kg°, B=.0185+.011Nm/kg°;P=.44). Due to recruitment challenges the proposed full complement of participants (N=70;D=35,B=35) was not achieved. Moderate effect sizes (ES) between-groups indicated a trend towards higher muscle activation levels in dancers in MH both pre (34vs.26%MVIC;ES=.55) and post (38vs.25%MVIC;ES=.41) contact, and in LG post contact (45vs.35%MVIC;ES=.33). The exception was LQPOST (90vs.109%MVIC;ES=.30) where dancers had a tendency for lower muscle activation levels. Prelanding muscle activation amplitudes and group membership were not able to predict changes in KJS. These results suggest that the lack of findings may in-part be due to low statistical power. Further, although KJS did not differ between groups, between-group effect sizes noted in LGPOST, MHPRE, POST, and LQPOST suggest possible differences in neuromechanical strategies over other lower extremity joints. Additional research is necessary to determine possible ACL-injury protective mechanisms employed by dancers during other high ACL-injury risk activities."--Abstract from author supplied metadata

Multifactorial Exercise Intervention Decreases Falls Risk in High-risk and Low-risk Older Adults

Background: Each year, 1 in 4 people over the age of 65 years of age will experience a fall. It is important to identify and address modifiable risk factors that are associated with falls in adults at high and low risk for falls. Hypothesis: Falls risk improves in both high-risk and low-risk participants with the implementation of Stay Active and Independent for Life (SAIL). Study Design: Cohort study Level of Evidence: Level 3. Methods: Seventy-eight older adults (age, 70.9 ± 5.1 years) were included in this study and categorized into high risk and low risk for falling based on the falls risk score from the Physiological Profile Assessment. High risk was defined as having a preintervention falls risk score >1, whereas low risk was defined as having a preintervention falls risk score <1. Both groups had the same 10-week intervention. A multivariate analysis of covariance was used to compare differences pre- and postintervention, using preintervention falls risk score as covariate. Results: Results showed that regardless of preintervention falls risk, participants showed significant improvements in right and left knee extensor strength and sit-to-stand after participation in the 10-week SAIL program. Also, noteworthy is that 15 participants who were considered at high risk for falling preintervention were considered low risk for falling postintervention. Conclusion: The positive outcomes noted on modifiable risk factors suggest SAIL can be beneficial for decreasing falls risk in older adults, regardless of risk of falling, using a multifactorial exercise intervention. Our results also showed that it was possible for participants not only to improve falls risk but to improve to such a degree that they change from high risk to low risk of falling. Clinical Relevance: Our results demonstrated that SAIL was effective in improving overall fall risk after a 10-week intervention. Targeted community-based interventions for the aging population can bring physical health benefits that can decrease falls risk

Blood lactate and heart rate responses between active and passive recovery modes over a 15-minute recovery period in female dancers after Kathak dance

Introduction: Dance is physically demanding and results in blood lactate (BL) accumulation and elevated Heart Rate (HR). Researchers recommend using either Active Recovery (AR; eg, low-to-moderate intensity-exercise) or Passive Recovery (PR; eg, complete rest) modes after activity. We compared BL and HR responses between AR or PR over a 15-minute recovery period following a Kathak dance. Methods: Twelve female dancers (31.0 ± 6.0 years; 161.5 ± 4.9 cm; 55.5 ± 5.8 kg) performed 2 dance testing sessions (Day 1 = AR, Day 2 = PR) 48 hours apart. Each session started with a 10-minute warm up followed by dancers performing four 2-minute stages of Kathak dance, with three 1-minute periods between stages where we recorded HR and their Rate of Perceived Exertion (RPE:scale = 6-20) to match the intensity of both sessions. Post-dance, we recorded dancers’ BL and HR at 1, 3, 5, 10, and 15 minutes while they recovered via AR or PR. Separate 2(mode) × (time) Repeated-Measures-ANOVA followed by simple-main-effects testing and adjusted Bonferroni-pairwise-comparisons examined differences in BL and HR responses across modes and time(α = .05). Results: Dancers’ HR and RPE were similar across sessions. No mode × time interaction existed in BL ( F4,8 = 3.6, P = .06). BL levels were similar across modes ( F1,2 = 0.5, P = .5). BL levels reduced over time ( F4,8 = 6.0, P = .02), but Bonferroni-comparisons did not reveal any pairwise differences. In HR a significant mode*time interaction ( F4,36 = 11.0, P = .01, η2 = .55) was observed. Both Active and Passive recovery modes achieved absolute HR levels by 15 minutes, with PR mode stabilizing within 5 minutes. Conclusions: Over a 15-minute recovery period after Kathak dance, dancers’ BL and HR responses were similar across time in both AR and PR, with HR being higher in AR. Dancers’ HR remained similar from 1 to 3 minute post dance recovery and then dropped over time. Thus, dancers can rest up to 3 minutes and still maintain the same elevated HR. Overall, dancers can choose either AR or PR as their recovery mode based on their individual preferences

Fit to dance survey: a comparison with dancesport injuries

The Fit to Dance survey has been conducted twice previously, in 1993 and 2002, without dancesport participants. The purpose of this present online survey was to supplement a comparison of dancesport against the earlier results. The current study had a greater percentage of male respondents than previous studies (43% vs 24% and 26%). The dancesport participants were older (28% at 40+ yrs vs 3% and 1%) and more likely to have normal (69% vs 57%) to overweight BMI (18% vs 2%). Dancesport participants spent more time in various non-dancing conditioning activities than previous surveys (5.2 ± 3.9 hrs SD vs 1.9 ± 2.5 and 2.2 ± 2.7). Muscles and joints were the most common type of injury in all the surveys. The knee was the top injury site in this survey, with lower back in previous surveys. The main perceived cause of injury was repetitive movements, whereas fatigue and overwork were cited in the previous surveys. Physiotherapists were the most common type of medical professionals from whom the dancers sought treatment for their injuries in all surveys. The first survey included recommendations that the present survey results agree with, including: dancers should be physically fit, dancers should warm up and cool down, dancers should never have to work in unsuitable environments, and dancers should receive immediate high-quality treatment for injuries

Female Collegiate Dancers’ Physical Fitness across Their Four-Year Programs: A Prospective Analysis

Dance is physically demanding, requiring physical fitness (PF) that includes upper body, lower body, core fitness, and balance for successful performance. Whether PF changes as dancers advance from when they enter (freshmen) to when they graduate from their collegiate program (seniors) is unclear. We prospectively compared collegiate dancers’ freshman-to-senior PF. We recorded PF in regard to upper body strength endurance (push-ups), core strength endurance (front, left-side, right-side, and extensor plank hold times), lower body power (single leg hop—SLH—distances % height; Leg Symmetry Index: LSI = higher/lower × 100, %), and balance (anterior reach balance, % leg length, LL; LSI balance = higher/lower × 100, %) in 23 female collegiate dancers (freshman age = 18.2 ± 0.6 years). Repeated measures ANOVAs (p ≤ 0.05) were used to compare measures from freshman to senior years. Across their collegiate programs, dancers’ PF remained unchanged. Specifically, their upper body strength endurance push-up numbers (p = 0.93), their core strength endurance plank times (left: p = 0.44, right: p = 0.67, front: p = 0.60, p = 0.22), their SLH distances (left: p = 0.44, right: p = 0.85), and their symmetry (p = 0.16) stayed similar. Also, dancers’ right leg (p = 0.08) and left leg balance (p = 0.06) remained similar, with better balance symmetry (p < 0.001) in seniors. Overall, dancers’ PF did not change across their collegiate programs. Thus, female dancers’ freshman PF may be an adequate baseline reference measure when devising rehabilitation programs and determining readiness-to-return-to-activity post injury

Electromyographic comparison of grand battement devant at the barre, in the center, and traveling.

This study examined utilization of the trunk and lower extremity muscles during grand battement devant in three conditions: at the barre (supported stationary condition in 1st position), in the center (unsupported stationary condition in 1st position), and traveling through space. Forty dancers (age 30.0 ± 13.0 yrs, height 1.63 ± 0.06 m, weight 59.0 ± 7.4 kg, and 13.9 ± 13.3 yrs of training in ballet and/or modern dance) volunteered and were placed in three skill level groups: beginner (n = 12), intermediate (n = 14), and advanced (n = 14). Dancers executed five grand battement devant in each of the three conditions in randomized order. We examined muscle activation bilaterally in eight muscles (abdominals, abductor hallucis, erector spinae, gastrocnemius, gluteus maximus, hamstrings, quadriceps, and tibialis anterior) using surface electromyography, a three-dimensional video biomechanical tracking system to identify events, and force plates. All data were analyzed in four events: stance, initiation, peak, and end. Analysis was done using a linear mixed effects regression model with condition, event, muscle, level, and side as the fixed effects, and subject as the random effect. There were significant effects for muscle x event x condition (p<0.01) and for level x side x muscle (p<0.01). Muscle use varied according to the combination of event and condition that was executed, and these differences were also influenced by the level of training of the dancer and the side of the body used. It is recommended that dance educators consider the importance of allocating sufficient time to each of the three conditions (barre, center, and traveling) to ensure development of a variety of motor strategies and muscle activation levels for dance practice