muscle strength


Background: Approximately 33% of the adult population in the United States is considered obese (28), which increases the risk of comorbidities such as osteoarthritis (OA) (34). The most notable feature of OA is the loss of articular cartilage within a joint, resulting in pain and physical disability (3). The association between obesity and OA is due to a combination of mechanical and metabolic factors (3). Greater weight from obesity adds stress to articular cartilage in weight-bearing joints, and contributes to cartilage breakdown (21). Previous studies have demonstrated an association between gait biomechanics and OA in older populations (15, 25), but data are lacking in young obese individuals without OA. Young obese compared to normal weight adults have lesser knee flexion excursion (KFE) (31), and greater vertical loading rates (vLR) during gait (30, 31). However, the source of aberrant gait mechanics in obese adults is unclear, and could be related to impaired shock attenuation from weakened musculature in the lower extremity. Obese young adults have deficits in quadriceps function after normalizing to fat-free mass, and walk slower compared to normal weight young adults. RTD was moderately associated with KEM at habitual gait speed, and KEM was also lesser in obese compared to normal weight adults. The lesser KEM in the obese group suggests that obese young adults walk with a quadriceps avoidance gait, which may contribute to knee OA development. Exercise interventions targeting RTD may be useful for improving walking mechanics in obese adults.
Listed In: Biomechanics, Gait, Orthopedic Research

Matching participants for triceps surae muscle-tendon unit mechanical properties eliminates age-related differences in drop jump performance

In the current study, we aimed to determine if differences in drop jump height or motor task execution strategy between young and middle-aged adults exist, when triceps surae MTU capacities (muscle strength and tendon stiffness) were matched. The triceps surae MTU biomechanical properties of 29 middle-aged and 26 younger adults were assessed during isometric voluntary ankle plantarflexion contractions of the dominant leg using a custom-made dynamometer and ultrasonography simultaneously. The 12 young adults with the lowest triceps surae muscle strength and the 12 middle-aged adults with the greatest muscle strength then completed a series of drop jumps from different heights. Ground contact time, average vertical ground reaction force, average mechanical power and jumping height were recorded. Younger and middle-aged adults attained comparable jumping heights independent of the drop jump height. There were significant age effects on ground contact time and average vertical ground reaction force during ground contact phase, with the middle-aged adults showing higher ground contact times but lower forces, leading to a significant age effect on mechanical power. Significant correlations were found between triceps surae MTU capacities and drop jump height. The results of the current study demonstrate that when triceps surae MTU capacities are matched, young and middle-aged adults show comparable performance of a jumping task, despite having different motor strategies. Finally, the results suggest that neuromuscular factors other than maximum isometric strength and tendon stiffness may influence motor task execution strategy during jumping.
Listed In: Biomechanics, Sports Science