Muscle Strength Asymmetries of the Lower Limbs and Trunk in Ballet Dancers.

BACKGROUND: Ballet dancers are expected to use their bodies symmetrically during training, because dance movements are performed on both sides. However, there is a general belief that ballet training encourages the use of one side of the body more than the other. Frequent repetition of a particular exercise can lead to body asymmetries and musculoskeletal injuries. The aim of this cross-sectional study was to investigate the presence of lower limbs and trunk muscle strength asymmetries in ballet dancers and secondly to assess whether there is a difference between professional dancers and ballet students. METHODS: Ballet students (n=19) and professional ballet dancers (n=23) performed maximal voluntary isometric contractions of the trunk (flexion, extension, lateral flexion), hip (flexion, extension, adduction, abduction, external and internal rotation), knee (flexion, extension) and ankle (flexion, extension) on isometric dynamometer. RESULTS: The results showed that the percentage of ballet dancers with contralateral muscle strength asymmetries >10% ranged from 22.5% (ballet students) to 31.6% (professional dancers). The percentage of ballet dancers deviating by >10% from the normative maximum torque agonist/antagonist ratio ranged from 56.5% to 100%. A statistically significant difference between ballet students and professional ballet dancers was found in the trunk flexion/extension ratio (t(40) = -3 .55; p = 0.001; d = 0.55). CONCLUSION: This study revealed strength asymmetries in the lower limbs and trunk in ballet dancers, both professionals and students. Further research is needed to develop appropriate complementary exercise to address and eliminate asymmetries in muscle strength in ballet dancers.

Responsiveness of Isokinetic Dynamometry in Patients with Osteoarthritis after Knee and Hip Arthroplasty: A Prospective Repeated-Measures Cohort Study.

Functional assessments are crucial for the evaluation of rehabilitation after total knee (TKA) and hip (THA) arthroplasty. Muscle strength, a key determinant of physical function (PF), is often measured with isokinetic dynamometry (ID), which is considered the gold standard. However, studies lack evaluations of responsiveness-the ability to detect changes over time. This study aims to determine the responsiveness of ID in measuring PF in TKA and THA rehabilitation-is muscle strength a valid indicator for assessing improvement in rehabilitation processes? The pre- and post-surgery PF of 20 osteoarthritis patients (age 55-82) was assessed, using ID, performance-based and self-reported measures. Responsiveness was evaluated by comparing the observed relationship of changes in ID and PF scores with the a priori defined expected relationship of change scores. While the performance-based and self-reported measures showed significant improvements post-surgery (Cohen's d [0.42, 1.05] p < 0.05), ID showed no significant differences. Moderate correlations were found between changes in some ID parameters and selected functional tests (r ≈|0.5|, p < 0.05). Responsiveness was solely found for the peak torque of knee extension at 180°/s on the operated side. Responsiveness is an often-overlooked psychometric property of outcome measurements. The findings suggest that ID may not be fully responsive to the construct of PF after TKA and THA, raising questions about its role and usefulness in this context and the need for more appropriate assessment methods.

Body asymmetries as risk factors for musculoskeletal injuries in dancesport, hip-hop and ballet dancers?

OBJECTIVES: The study aimed to determine the incidence and expression of body asymmetries in dancers of three different dance styles: dancesport (n = 14), hip-hop (n = 21) and ballet (n = 20) and to examine how body asymmetries (muscle strength and power, stability and range of motion) are associated with musculoskeletal injuries occurring over the past 12 months. DESIGN: Cross-sectional and retrospective study. METHODS: Maximal isometric voluntary contraction was measured for trunk, hip, knee and ankle movements. Participants performed a single leg stance, unilateral landing, weight bearing symmetry, squat and countermovement jump on force platforms. Passive range of motion was measured for hip, knee and ankle with two-arm goniometer or digital inclinometer (hip flexion, extension and rotations). A retrospective questionnaire was used to collect data on musculoskeletal injuries occurring in the last 12 months. RESULTS: Different dance styles were associated with different body asymmetries, including strength asymmetries (hip flexion and external rotation), agonist/antagonist asymmetries (trunk flexion/extension, hip abduction/adduction, ankle dorsi/plantar flexion) and hip adduction and internal rotation range of motion asymmetries. Moreover, strength asymmetries of hip flexion, adduction and abduction/adduction as well as stability asymmetries were associated with the total number of musculoskeletal injuries. CONCLUSIONS: The incidence of body asymmetries (> 10%) in dancesport, hip-hop and ballet dancers was confirmed, as well as the association of some asymmetries with self-reported injuries occurring over the last 12 months. The cause-effect relationship should be clarified by further studies.