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Seong-won Han, Andrew Sawatsky, Azim Jinha and Walter Herzog

Vastus medialis (VM) weakness is thought to alter patellar tracking, thereby changing the loading of the patellofemoral joint (PFJ), resulting in patellofemoral pain. However, it is challenging to measure VM force and weakness in human studies, nor is it possible to measure the associated mechanical changes in the PFJ. To obtain fundamental insight into VM weakness and its effects on PFJ mechanics, the authors determined PFJ loading in the presence of experimentally simulated VM weakness. Skeletally mature New Zealand White rabbits were used (n = 6), and the vastus lateralis, VM, and rectus femoris were stimulated individually through 3 custom-built nerve cuff electrodes. Muscle torque and PFJ pressure distribution were measured while activating all muscles simultaneously, or when the vastus lateralis and rectus femoris were activated, while VM was not, to simulate a quadriceps muscle strength imbalance. For a given muscular joint torque, peak pressures were greater and joint contact areas were smaller when simulating VM weakness compared with the condition where all muscles were activated simultaneously. The results in the rabbit model support that VM weakness results in altered PFJ loading, which may cause patellofemoral pain, often associated with a strength imbalance of the knee extensor muscle group.

Open access

Jim Potvin

Open access

Robert J. Gregor

Open access

Walter Herzog

Open access

James A. Ashton-Miller and Ronald F. Zernicke

Open access

Tobias Lundgren, Gustaf Reinebo, Markus Näslund and Thomas Parling

Despite the growing popularity of mindfulness and acceptance-based performance enhancement methods in applied sport psychology, evidence for their efficacy is scarce. The purpose of the current study is to test the feasibility and effect of a psychological training program based on Acceptance and Commitment Training (ACT) developed for ice hockey players. A controlled group feasibility designed study was conducted and included 21 elite male ice hockey players. The ACT program consisted of four, once a week, sessions with homework assignments between sessions. The results showed significant increase in psychological flexibility for the players in the training group. The outcome was positive for all feasibility measures. Participants found the psychological training program important to them as ice hockey players and helpful in their ice hockey development. Desirably, future studies should include objective performance data as outcome measure to foster more valid evidence for performance enhancement methods in applied sport psychology.

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Yuko Kuramatsu, Yuji Yamamoto and Shin-Ichi Izumi

This study investigated the sensorimotor strategies for dynamic balance control in individuals with stroke by restricting sensory input that might influence task accomplishment. Sit-to-stand movements were performed with restricted vision by participants with hemiparesis and healthy controls. The authors evaluated the variability in the position of participants’ center of mass and velocity, and the center-of-pressure position, in each orthogonal direction at the lift-off point. When vision was restricted, the variability in the mediolateral center-of-pressure position decreased significantly in individuals with hemiparesis, but not in healthy controls. Participants with hemiparesis adopted strategies that explicitly differed from those used by healthy individuals. Variability may be decreased in the direction that most requires accuracy. Individuals with hemiparesis have been reported to have asymmetrical balance deficits, and that meant they had to prioritize mediolateral motion control to prevent falling. This study suggests that individuals with hemiparesis adopt strategies appropriate to their characteristics.

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Joseph Hamill

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Mhairi K. MacLean and Daniel P. Ferris

The authors tested 4 young healthy subjects walking with a powered knee exoskeleton to determine if it could reduce the metabolic cost of locomotion. Subjects walked with a backpack loaded and unloaded, on a treadmill with inclinations of 0° and 15°, and outdoors with varied natural terrain. Participants walked at a self-selected speed (average 1.0 m/s) for all conditions, except incline treadmill walking (average 0.5 m/s). The authors hypothesized that the knee exoskeleton would reduce the metabolic cost of walking uphill and with a load compared with walking without the exoskeleton. The knee exoskeleton reduced metabolic cost by 4.2% in the 15° incline with the backpack load. All other conditions had an increase in metabolic cost when using the knee exoskeleton compared with not using the exoskeleton. There was more variation in metabolic cost over the outdoor walking course with the knee exoskeleton than without it. Our findings indicate that powered assistance at the knee is more likely to decrease the metabolic cost of walking in uphill conditions and during loaded walking rather than in level conditions without a backpack load. Differences in positive mechanical work demand at the knee for varying conditions may explain the differences in metabolic benefit from the exoskeleton.