We accept a definition of synergy introduced by Nikolai Bernstein and develop it for various actions, from those involving the whole body to those involving a single muscle. Furthermore, we use two major theoretical developments in the field of motor control—the idea of hierarchical control with spatial referent coordinates and the uncontrolled manifold hypothesis—to discuss recent studies of synergies within spaces of individual motor units (MUs) recorded within a single muscle. During the accurate finger force production tasks, MUs within hand extrinsic muscles form robust groups, with parallel scaling of the firing frequencies. The loading factors at individual MUs within each of the two main groups link them to the reciprocal and coactivation commands. Furthermore, groups are recruited in a task-specific way with gains that covary to stabilize muscle force. Such force-stabilizing synergies are seen in MUs recorded in the agonist and antagonist muscles but not in the spaces of MUs combined over the two muscles. These observations reflect inherent trade-offs between synergies at different levels of a control hierarchy. MU-based synergies do not show effects of hand dominance, whereas such effects are seen in multifinger synergies. Involuntary, reflex-based, force changes are stabilized by intramuscle synergies but not by multifinger synergies. These observations suggest that multifinger (multimuscle synergies) are based primarily on supraspinal circuitry, whereas intramuscle synergies reflect spinal circuitry. Studies of intra- and multimuscle synergies promise a powerful tool for exploring changes in spinal and supraspinal circuitry across patient populations.
Mark L. Latash, Shirin Madarshahian, and Joseph M. Ricotta
Chris J. Alfiero, Ann F. Brown, Youngmin Chun, Alexandra Holmes, and Joshua P. Bailey
The purpose of this study was to investigate the effects of foot positioning and lean mass on jumping and landing mechanics in collegiate dancers. Thirteen dancers performed 3 unilateral and bilateral vertical jumps with feet in neutral and turnout positions. Dual-energy x-ray absorptiometry scans, jump height, vertical stiffness, and joint stiffness were assessed for relationships between foot positions. Jump heights were greater in right compared with left limb (P = .029) and neutral compared with turnout (P = .020) during unilateral jumping. In unilateral landing, knee stiffness was greater in turnout compared with neutral (P = .004) during the loading phase. Jump height (P < .001) was significantly increased, and vertical stiffness (P = .003) was significantly decreased during bilateral jumping in neutral compared with turnout. Significantly increased hip stiffness during the attenuation phase was observed in neutral compared with turnout (P = .006). Left-limb lean mass was significantly less than the right limb (P < .05). Adjustments for bilateral jumping were focused on hip stiffness, whereas there was a slight shift to knee strategy for unilateral jump.
Rodrigo Ghedini Gheller, Rafael Lima Kons, Juliano Dal Pupo, and Daniele Detanico
The aim of this systematic review was to investigate the effect of specific sprint and vertical jump training interventions on transfer of speed–power parameters. The data search was carried out in three electronic databases (PubMed, SCOPUS, and SPORTDiscus), and 28 articles were selected (13 on vertical jump training and 15 on sprint training). We followed the PRISMA criteria for the construction of this systematic review and used the Physiotherapy Evidence Database (PEDro) scale to assess the quality of all studies. It included studies with a male population (athletes and nonathletes, n = 512) from 18 to 30 years old who performed a vertical jump or sprint training intervention. The effect size was calculated from the values of means and SDs pre- and posttraining intervention. The percentage changes and transfer of training effect were calculated for vertical jump training and sprint training through measures of vertical jump and sprint performance. The results indicated that both training interventions (vertical jump training and sprint training) induced improvements in vertical jump and linear sprint performance as well as transfer of training to speed–power performance. However, vertical jump training produced greater specific and training transfer effects on linear sprint than sprint training (untrained skill). It was concluded that vertical jump training and sprint training were effective in increasing specific actions of vertical jump and linear sprint performance, respectively; however, vertical jump training was shown to be a superior alternative due to the higher transfer rate.
Lee T. Atkins, Michael Lowrey, Sarah Reagor, Kirsten Walker, and Dhalston Cage
Research indicates that increasing trunk flexion may optimize patellofemoral joint loading. However, this postural change could cause an excessive Achilles tendon force (ATF) and injury risk during movement. This study aimed to examine the effects of increasing trunk flexion during stair ascent on ATF, ankle biomechanics, and vertical ground reaction force in females. Twenty asymptomatic females (age: 23.4 [2.5] y; height: 1.6 [0.8] m; mass: 63.0 [12.2] kg) ascended stairs using their self-selected and flexed trunk postures. Compared with the self-selected trunk condition, decreases were observed for peak ATF (mean differences [MD] = 0.14 N/kg; 95% confidence interval [CI], 0.06 to 0.23; Cohen d = −1.2; P = .003), average rate of ATF development (MD = 0.25 N/kg/s; 95% CI, 0.07 to 0.43; Cohen d = −0.9; P = .010), ankle plantar flexion moment (MD = 0.08 N·m/kg; 95% CI, 0.03 to 0.13; Cohen d = −1.1; P = .005), and vertical ground reaction force (MD = 38.6 N/kg; 95% CI, 20.3 to 56.90; Cohen d = −1.8; P < .001). Increasing trunk flexion did not increase ATF. Instead, this postural change was associated with a decreased ATF rate and magnitude and may benefit individuals with painful Achilles tendinopathy.
Carlos Alix-Fages, Jozo Grgic, Pablo Jiménez-Martínez, Eneko Baz-Valle, and Carlos Balsalobre-Fernández
The purpose of the present systematic review and meta-analysis was to explore the effects of mental fatigue on upper and lower body strength endurance. Searches for studies were performed in the PubMed/MEDLINE and Web of Science databases. We included studies that compared the effects of a demanding cognitive task (set to induce mental fatigue) with a control condition on strength endurance in dynamic resistance exercise (i.e., expressed as the number of performed repetitions at a given load). The data reported in the included studies were pooled in a random-effects meta-analysis of standardized mean differences. Seven studies were included in the review. We found that mental fatigue significantly reduced the number of performed repetitions for upper body exercises (standardized mean difference: −0.41; 95% confidence interval [−0.70, −0.12]; p = .006; I2 = 0%). Mental fatigue also significantly reduced the number of performed repetitions in the analysis for lower body exercises (standardized mean difference: −0.39; 95% confidence interval [−0.75, −0.04]; p = .03; I2 = 0%). Our results showed that performing a demanding cognitive task—which induces mental fatigue—impairs strength endurance performance. Collectively, our findings suggest that exposure to cognitive tasks that may induce mental fatigue should be minimized before strength endurance-based resistance exercise sessions.
Jacob Benzinger, Jeff R. Crane, Angela M. Coppola, and David J. Hancock
Schools can support physical education (PE) among students with mobility disabilities (SMDs). However, previous research has indicated that people and resources in the school environment have served as facilitators and barriers to engaging SMDs in PE. Thus, the purpose of this pragmatic, qualitative study was to explore physical educators’ perceptions and experiences of teaching SMDs to learn how to develop a PE environment supportive of SMDs. Eleven K-8 PE teachers who taught SMDs engaged in semistructured interviews. A thematic analysis revealed three themes describing facilitators and barriers of a supportive PE environment for SMDs: (a) teacher planning, (b) students in the PE environment, and (c) resources and support. These findings provide context to PE environments for SMDs and highlight a need for increased communication and collaboration with students with or without mobility disabilities, training or professional development for PE teachers to develop skills for adapted PE, and financial and personnel support.
Michal Vagner, Daniel J. Cleather, Petr Kubový, Vladimír Hojka, and Petr Stastny
Contemporary descriptions of motor control suggest that variability in movement can be indicative of skilled or unskilled performance. Here we used principal component analysis to study the kicking performance of elite and sub-elite soldiers who were highly familiar with the skill in order to compare the variability in the first and second principal components. The subjects kicked a force plate under a range of loaded conditions, and their movement was recorded using optical motion capture. The first principal component explained >92% of the variability across all kinematic variables when analyzed separately for each condition, and both groups and explained more of the variation in the movement of the elite group. There was more variation in the loading coefficient of the first principal component for the sub-elite group. In contrast, for the second principal component, there was more variation in the loading coefficient for the elite group, and the relative magnitude of the variation was greater than for the first principal component for both groups. These results suggest that the first principal component represented the most fundamental movement pattern, and there was less variation in this mode for the elite group. In addition, more of the variability was explained by the hip than the knee angle entered when both variables were entered into the same PCA, which suggests that the movement is driven by the hip.
Kevin Andrew Richards, Scott McNamara, Alyssa M. Trad, Lauren Hill, and Sarena Abdallah
School administrators represent key agents of socialization for teachers within their schools, including adapted physical educators who design and implement instruction for youth with disabilities, often across multiple school sites. The purpose of this study was to understand how adapted physical educators navigate and build relationships with administrators in the schools where they teach. Data were collected through semistructured interviews with 24 adapted physical educators from the U.S. state of California and analyzed using a multiphase approach. Analysis suggested both the importance of and challenges with building effective relationships with administrators. Themes included the following: (a) Administrators do not understand adapted physical education, which impacts programs and students; (b) the importance of relationship building in cultivating principal support; and (c) relationship development requires intentionality, but results in trust and motivation. Results are discussed using role socialization theory, and recommendations for the preparation of both adapted physical educators and school principals are discussed.
ZáNean McClain and Daniel W. Tindall
Diego Augusto Santos Silva and Carolina Fernandes da Silva
Brazil is a country member of the Para Report Card, and Brazilian researchers have frequently published information on physical activity of children and adolescents. The current study aimed to analyze the policies for the promotion of adapted physical activity to Brazilian children and adolescents with disabilities. Official government information on adapted physical activity was analyzed from the official websites. Policies were analyzed based on the Para Report Card benchmarks, and after that we used the principles of SWOT (strengths, weaknesses, opportunities, and threats) to analyze the information. Adapted physical activity is not the main focus of any of the many policies to promote physical activity for children and adolescents. Based on the Para Report Card initiative, the score for this indicator in Brazil is D. Brazil needs to develop specific policies to promote physical activity adapted to the pediatric population with disabilities.