Changes in Lower Extremity Biomechanics Due to a Short-Term Fatigue Protocol

Context: Noncontact anterior cruciate ligament injury has been reported to occur during the later stages of a game when fatigue is most likely present. Few researchers have focused on progressive changes in lower extremity biomechanics that occur throughout fatiguing. Objective: To evaluate the effects of a sequential fatigue protocol on lower extremity biomechanics during a sidestep-cutting task (SS). Design: Controlled laboratory study. Setting: Laboratory. Patients or Other Participants: Eighteen uninjured female collegiate soccer players (age 19.2 ± 0.9 years, height = 1.66 ± 0.5 m, mass 61.6 ± 5.1 kg) volunteered. Intervention(s): The independent variable was fatigue level, with 3 levels (prefatigue, 50% fatigue, and 100% fatigue). Using 3-dimensional motion capture, we assessed lower extremity biomechanics during the SS. Participants alternated between a fatigue protocol that solicited different muscle groups and mimicked actual sport situations and unanticipated SS trials. The process was repeated until fatigue was attained. Main Outcome Measure(s): Dependent variables were hip- and knee-flexion and abduction angles and internal moments measured at initial contact and peak stance and defined as measures obtained between 0% and 50% of stance phase. Results: Knee-flexion angle decreased from prefatigue (-17 degrees ± 5 degrees) to 50% fatigue (-16 degrees ± 6 degrees) and to 100% fatigue (-14 degrees ± 4 degrees) (F2,34 = 5.112, P = .004). Knee flexion at peak stance increased from prefatigue (-52.9 degrees ± 5.6 degrees) to 50% fatigue (-56.1 degrees ± 7.2 degrees) but decreased from 50% to 100% fatigue (-50.5 degrees ± 7.1 degrees) (F2,34 = 8.282, P = 001). Knee-adduction moment at peak stance increased from prefatigue (0.49 ± 0.23 Nm/kgm) to 50% fatigue (0.55 ± 0.25 Nm/kgm) but decreased from 50% to 100% fatigue (0.37 ± 0.24) (F 2,34 = 3.755, P = 03). Hip-flexion angle increased from prefatigue (45.4 degrees ± 10.9 degrees) to 50% fatigue (46.2 degrees ± 11.2 degrees) but decreased from 50% to 100% fatigue (40.9 degrees ± 11.3 degrees) (F2,34 = 6.542, P= .004). Hip flexion at peak stance increased from prefatigue (49.8 degrees ± 9.9 degrees) to 50% fatigue (52.9 degrees ± 12.1 degrees) but decreased from 50% to 100% fatigue (46.3 degrees ± 12.9 degrees) (F 2,34 = 8.639, P = 001). Hip-abduction angle at initial contact decreased from prefatigue (-13.8 degrees ± 6.6 degrees) to 50% fatigue (-9.1 degrees ± 6.5 degrees) and to 100% fatigue (-7.8 degrees ± 6.5 degrees) (F2,34 = 11.228, P = .001). Hip-adduction moment decreased from prefatigue (0.14 ± 0.13 Nm/kgm) to 50% fatigue (0.08 ± 0.13 Nm/kgm) and to 100% fatigue (0.06 ± 0.05 Nm/ kg) (F2,34 = 5.767, P = .007). Conclusions: The detrimental effects of fatigue on sagittal and frontal mechanics of the hip and knee were visible at 50% of the participants\u27 maximal fatigue and became more marked at 100% fatigue. Anterior cruciate ligament injury-prevention programs should emphasize feedback on proper mechanics throughout an entire practice and not only at the beginning of practice

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

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

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

Perceived severity and management of low back pain in adult dancers in the United States

This is an accepted manuscript of an article published by J. Michael Ryan Publishing Inc. in Journal of Dance Medicine & Science (in press). The accepted version of the publication may differ from the final published version.Introduction: Low back pain (LBP) lifetime prevalence in dancers reportedly ranges from 17%-88%. LBP can have negative secondary consequences on dancers’ lives and careers. Still, how LBP impacts dancer function and medical care-seeking behaviors, and whether these issues differ across dance genres, is understudied. Materials and Methods: 289 ballet, modern, and hip-hop dancers and teachers (median age=20.3 years; range:18-69) in the United States age 18 years and older completed an online 24 question survey assessing LBP related self-reported injury history, impact on their lives, and management strategies. We defined LBP as occurrence of acute or chronic pain in the lumbar or sacral regions of the back. Results: 257 participants (88.9% of 289 total) reported at least one instance of LBP during their lifetime and 220 participants reported LBP in the prior four weeks. Of these 220, 72 (32.7%) had LBP severe enough to limit their activities of daily living. Of the 213 who had LBP and danced during that time, 89 (41.8%) reported that LBP limited their dancing. Pain intensity (median:4 on a 0-10 scale, IQR:3.0) and LBP prevalence were similar across dance genres. Dancers sought multiple medical professionals, most often chiropractors (n=94, 33.8%), medical doctors (n=77, 27.7%), and physiotherapists (n=60, 21.6%). 90 dancers (35.0% of those with LBP) never sought medical care for their LBP at all. Dancers who did seek care reported higher pain intensities (median:4, IQR:3.8) than those who did not (median:3, IQR:3.0). Conclusion: Overall, most participants did suffer from LBP. LBP negatively impacts dancers’ everyday activities and dancing. Pain intensity and loss of function may impact care-seeking. Our findings highlight the need for all dance stakeholders to educate dancers about their health, provide resources for dancer healthcare, and proactively create an environment that supports injury reporting behaviors in dancers

Spinal counts, impact, and partnering movements in ballet, modern, and hip hop dance: A YouTube video analysis study

This is an accepted manuscript of an article due to be published by J. Michael Ryan Publishing Inc. The accepted version of the publication may differ from the final published version.Introduction: Dancers have self-reported a link between spinal extension movements and low back pain (LBP). Researchers have not reported the total number or frequency that spinal movements occur in ballet, modern, or hip-hop dance classes or performances. The purpose of this study was to report the number of spinal movements dancers are exposed to in different dance environments. Materials and Methods: We analyzed 65 dance videos on YouTube.com for dance movements within seven dance environments: ballet class and performance, modern class and performance, and hip-hop breaking, cyphers (large groups), and battles (“1v1sTwo reviewers recorded counts of spinal (spinal flexion, extension, lateral flexion, and rotation), impact (jumps, leaps, and falls), and partnering movements (lifts, catches, and leans). Data analyses were processed in Jamovi (the jamovi project, Sydney, Australia). We reported movement totals, percentages, frequency, ranges, means with standard deviations (SD), and medians with interquartile range (IQR). We calculated significant differences using Mann-Whitney U tests. Results: Video length ranged from 3 to 141 minutes (mean±SD: 38.4±38.3, range: 138). The average spinal extension movements ranged from 2±0.8 to 7±9.6 movements per minute across genres. Modern dance class had the most spinal flexion (89±53.6), rotation (60±40.8), and lateral flexion (74±20.7) movements. Ballet performance had the most spinal extension movements (77±69.8), jumps (74±48), and leaps (19±18.2). Hip-hop breaking had the highest number of falling movements (2±2.3). Partnering movements were only present in ballet performance, modern dance performance, and hip-hop breaking environments. Conclusions: Movements that increase LBP occur often in all three dance genres. Dancers can expect frequent exposure to spinal extension movements; therefore, we recommend strengthening back and core musculature for all dancers. We recommend that ballet dancers also strengthen their lower extremity muscles. For modern dancers, we recommend strengthening their obliques. For hip-hop dancers, we recommend increasing muscular power and muscular endurance