Sarah A. Roelker, Elena J. Caruthers, Rachel K. Hall, Nicholas C. Pelz, Ajit M.W. Chaudhari and Robert A. Siston
Two optimization techniques, static optimization (SO) and computed muscle control (CMC), are often used in OpenSim to estimate the muscle activations and forces responsible for movement. Although differences between SO and CMC muscle function have been reported, the accuracy of each technique and the combined effect of optimization and model choice on simulated muscle function is unclear. The purpose of this study was to quantitatively compare the SO and CMC estimates of muscle activations and forces during gait with the experimental data in the Gait2392 and Full Body Running models. In OpenSim (version 3.1), muscle function during gait was estimated using SO and CMC in 6 subjects in each model and validated against experimental muscle activations and joint torques. Experimental and simulated activation agreement was sensitive to optimization technique for the soleus and tibialis anterior. Knee extension torque error was greater with CMC than SO. Muscle forces, activations, and co-contraction indices tended to be higher with CMC and more sensitive to model choice. CMC’s inclusion of passive muscle forces, muscle activation-contraction dynamics, and a proportional-derivative controller to track kinematics contributes to these differences. Model and optimization technique choices should be validated using experimental activations collected simultaneously with the data used to generate the simulation.
Robert J. Gregor
Prasanna Sritharan, Luke G. Perraton, Mario A. Munoz, Peter Pivonka and Adam L. Bryant
This study compared lower-limb muscle function, defined as the contributions of muscles to center-of-mass support and braking, during a single-leg hopping task in anterior cruciate ligament-reconstructed (ACLR) individuals and uninjured controls. In total, 65 ACLR individuals and 32 controls underwent a standardized anticipated single-leg forward hop. Kinematics and ground reaction force data were input into musculoskeletal models to calculate muscle forces and to quantify muscle function by decomposing the vertical (support) and fore-aft (braking) ground reaction force components into contributions by individual lower-limb muscles. Four major muscles, the vasti, soleus, gluteus medius, and gluteus maximus, were primarily involved in support and braking in both ACLR and uninjured groups. However, although the ACLR group demonstrated lower peak forces for these muscles (all Ps < .001, except gluteus maximus, P = .767), magnitude differences in these muscles’ contributions to support and braking were not significant. ACLR individuals demonstrated higher erector spinae (P = .012) and hamstrings forces (P = .085) to maintain a straighter, stiffer landing posture with more forward lumbar flexion. This altered landing posture may have enabled the ACLR group to achieve similar muscle function to controls, despite muscle force deficits. Our findings may benefit rehabilitation and the development of interventions to enable faster and safer return to sport.
Alison Schinkel-Ivy, Vicki Komisar and Carolyn A. Duncan
Investigating balance reactions following continuous, multidirectional, support surface perturbations is essential for improving our understanding of balance control in moving environments. Segmental motions are often incorporated into rapid balance reactions following external perturbations to balance, although the effects of these motions during complex, continuous perturbations have not been assessed. This study aimed to quantify the contributions of body segments (ie, trunk, head, upper extremity, and lower extremity) to the control of center-of-mass (COM) movement during continuous, multidirectional, support surface perturbations. Three-dimensional, whole-body kinematics were captured while 10 participants experienced 5 minutes of perturbations. Anteroposterior, mediolateral, and vertical COM position and velocity were calculated using a full-body model and 7 models with reduced numbers of segments, which were compared with the full-body model. With removal of body segments, errors relative to the full-body model increased, while relationship strength decreased. The inclusion of body segments appeared to affect COM measures, particularly COM velocity. Findings suggest that the body segments may provide a means of improving the control of COM motion, primarily its velocity, during continuous, multidirectional perturbations, and constitute a step toward improving our understanding of how the limbs contribute to balance control in moving environments.
Thomas D. Raedeke, Victoria Blom and Göran Kenttä
This study evaluated the relationship of perfectionism and self-perceptions with burnout and life satisfaction in aesthetic performers (N = 254) recruited in Sweden. Cluster analysis revealed four groups: perfectionistic with maladaptive self-perceptions, perfectionistic (parent-driven) with maladaptive self-perceptions, achievement-oriented with adaptive self-perceptions, and nonperfectionistic with adaptive self-perceptions. Performers in both maladaptive clusters reported characteristics suggesting they were perfectionistic compared to their peers. They also reported relatively high contingent self-worth and low basic self-esteem. In contrast, those in the nonperfectionistic with adaptive self-perceptions cluster scored relatively low on perfectionism and reported relatively high basic self-esteem and low contingent self-worth. The performers in the achievement-oriented with adaptive self-perceptions cluster reported average scores across most variables, moderately high personal standards, and higher basic self-esteem compared with contingent self-worth. Overall, performers in both maladaptive clusters reported the highest burnout and lowest life satisfaction. Study findings underscore the importance of perfectionism and self-perceptions when considering burnout and life satisfaction.
Chantelle Zimmer, Janice Causgrove Dunn and Nicholas L. Holt
Children with developmental coordination disorder (DCD) may experience stress in physical activity contexts due to emphasis on their poor motor skills. The purpose of this study was to explore the lived experiences of children at risk for DCD in physical education in order to develop a deeper understanding about what they experience as stress and how they cope with it. Using interpretative phenomenological analysis, six children in Grades 4–6 participated in two semistructured interviews. A motivational (and developmental) stress and coping theory informed interpretation of the three themes that described the children’s experiences: (a) they hurt me—psychological and physical harm sustained from peers, (b) it’s hard for me—difficulties encountered in activities, and (c) I have to—pressure to meet the teacher’s demands. Although the children at risk for DCD were confronted with various stressors in physical education, they coped more adaptively when social support was provided.