This study aimed to determine whether subject-specific individual muscle models for the ankle plantar flexors could be obtained from single joint isometric and isovelocity maximum torque measurements in combination with a model of plantar flexion. Maximum plantar flexion torque measurements were taken on one subject at six knee angles spanning full flexion to full extension. A planar three-segment (foot, shank and thigh), two-muscle (soleus and gastrocnemius) model of plantar flexion was developed. Seven parameters per muscle were determined by minimizing a weighted root mean square difference (wRMSD) between the model output and the experimental torque data. Valid individual muscle models were obtained using experimental data from only two knee angles giving a wRMSD score of 16 N m, with values ranging from 11 to 17 N m for each of the six knee angles. The robustness of the methodology was confirmed through repeating the optimization with perturbed experimental torques (±20%) and segment lengths (±10%) resulting in wRMSD scores of between 13 and 20 N m. Hence, good representations of maximum torque can be achieved from subject-specific individual muscle models determined from single joint maximum torque measurements. The proposed methodology could be applied to muscle-driven models of human movement with the potential to improve their validity.
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Filipe Conceição, Mark A. King, Maurice R. Yeadon, Martin G.C. Lewis, and Stephanie E. Forrester
Lewis King, Sarah Jane Cullen, Jean McArdle, Adrian McGoldrick, Jennifer Pugh, Giles Warrington, and Ciara Losty
The purpose of this study was to explore the sources of stress reported by professional jockeys. In total, 15 jockeys participated in semistructured interviews that included apprentice, conditional, and senior jockeys. Reflexive thematic analysis was used to analyze qualitative data that included inductive and deductive approaches. Jockeys reported a wide range of stress sources. Four core themes were identified and categorized as competitive (current form or being in a slump, pressure, horse, injury, opponents, tactical, and race day), racing industry (weight, workload, travel demands, injury concerns, suspension, and facilities), interpersonal (trainer, other jockeys, expectations of others, support networks, and communication), and career stressors (career uncertainty, career opportunities, and transitions). The findings highlight unique stressors to the jockey population, as well as stressors common with other athlete groups. Practical applied recommendations and future research directions are provided.
Barbara C. Belyea, Ethan Lewis, Zachary Gabor, Jill Jackson, and Deborah L. King
Context: Lower-extremity landing mechanics have been implicated as a contributing factor in knee pain and injury, yet cost-effective and clinically accessible methods for evaluating movement mechanics are limited. The identification of valid, reliable, and readily accessible technology to assess lower-extremity alignment could be an important tool for clinicians, coaches, and strength and conditioning specialists. Objective: To examine the validity and reliability of using a handheld tablet and movement-analysis application (app) for assessing lower-extremity alignment during a drop vertical-jump task. Design: Concurrent validation. Setting: Laboratory. Participants: 22 healthy college-age subjects (11 women and 11 men, mean age 21 ± 1.4 y, mean height 1.73 ± 0.12 m, mean mass 71 ± 13 kg) with no lower-extremity pathology that prevented safe landing from a drop jump. Intervention: Subjects performed 6 drop vertical jumps that were recorded simultaneously using a 3-dimensional (3D) motion-capture system and a handheld tablet. Main Outcomes Measures: Angles on the tablet were calculated using a motion-analysis app and from the 3D motion-capture system using Visual 3D. Hip and knee angles were measured and compared between both systems. Results: Significant correlations between the tablet and 3D measures for select frontal- and sagittal-plane ranges of motion and angles at maximum knee flexion (MKF) ranged from r = .48 (P = .036) for frontal-plane knee angle at MKF to r = .77 (P < .001) for knee flexion at MKF. Conclusion: Results of this study suggest that a handheld tablet and app may be a reliable method for assessing select lower-extremity joint alignments during drop vertical jumps, but this technology should not be used to measure absolute joint angles. However, sports medicine specialists could use a handheld tablet to reliably record and evaluate lower-extremity movement patterns on the field or in the clinic.
Martin G.C. Lewis, Mark A. King, Maurice R. Yeadon, and Filipe Conceição
This study determines whether maximal voluntary ankle plantar flexor torque could be more accurately represented using a torque generator that is a function of both knee and ankle kinematics. Isovelocity and isometric ankle plantar flexor torques were measured on a single participant for knee joint angles of 111° to 169° (approximately full extension) using a Contrex MJ dynamometer. Maximal voluntary torque was represented by a 19-parameter two-joint function of ankle and knee joint angles and angular velocities with the parameters determined by minimizing a weighted root mean square difference between measured torques and the two-joint function. The weighted root mean square difference between the two-joint function and the measured torques was 10 N-m or 3% of maximum torque. The two-joint function was a more accurate representation of maximal voluntary ankle plantar flexor torques than an existing single-joint function where differences of 19% of maximum torque were found. It is concluded that when the knee is flexed by more than 40°, a two-joint representation is necessary.
Lewis King, SarahJane Cullen, Jean McArdle, Adrian McGoldrick, Jennifer Pugh, Giles Warrington, and Ciara Losty
A large proportion of jockeys report symptoms associated with mental health difficulties (MHDs), yet most do not seek help from professional mental health support services. Due to the paucity of literature in this field, this study sought to explore jockeys’ barriers to, and facilitators of, help-seeking for MHDs. Twelve jockeys participated in semistructured interviews, subsequently analyzed via reflexive thematic analysis. Barriers to help-seeking included the negative perceptions of others (stigma and career implications), cultural norms (masculinity and self-reliance), and low mental health literacy (not knowing where to seek help, minimization of MHDs, negative perceptions of treatment, and recognizing symptoms). Facilitators to help-seeking included education (exposure to psychological support at a younger age), social support (from professionals, jockeys, family, and friends), and media campaigns (high-profile disclosures from jockeys). Findings are consistent with barrier and facilitator studies among general and athletic populations. Applied recommendations and future research considerations are presented throughout the manuscript.