The relationships between physical capacity and biomechanical plasticity in old adults during level and incline walking

Old versus young adults exhibit increased hip and decreased ankle joint mechanical output during level and incline walking. This distal-to-proximal redistribution of joint torques and powers is now a well-established age-related gait adaptation and has been termed biomechanical plasticity. The effect of physical capacity, which varies greatly in old adults, on this gait adaptation remains unclear. For example, high capacity old adults (i.e. those with fast walking speeds) might either retain a more youthful gait strategy or adopt larger magnitudes of plasticity in order to walk well. The purpose of this study was to quantify the relationships between physical capacity and biomechanical plasticity in old adults during level and incline walking. We conducted 3D gait analyses on 32 old adults (>70 yrs) as they walked over level ground and up a 10° incline at self-selected speeds. We used motion capture (Qualisys AB) and force platforms (AMTI) to collect kinematic and ground reaction force data, respectively. To measure physical capacity, we used the SF-36 Physical Component score and to define biomechanical plasticity we created ratios of hip extensor to ankle plantarflexor peak torques, angular impulses, peak positive powers, and work. We conducted correlation analyses between SF-36 PC scores and the biomechanical plasticity ratios. Positive relationships existed between SF-36 PC scores and all biomechanical plasticity ratios during level walking. Similar results were observed during incline walking, however only three of these four relationships reached statistical significance. Our results suggest that old adults of higher physical capacities exhibit larger magnitudes of biomechanical plasticity.
Listed In: Biomechanics, Gait

Muscle and tendon adaptation in young and older adult athletes: A combined longitudinal and cross sectional investigation

This study examined triceps surae muscle strength and tendon stiffness in young adult elite sprinters and jumpers over one season, in order to detect potential discordance between muscle and tendon adaptation due to training. Furthermore, we examined the effect of habitual training on triceps surae muscle-tendon unit (MTU) mechanical properties in young and older athletes, using a cross-sectional design. Eleven healthy younger elite sprinters and jumpers, 12 master athletes, 12 recreationally active young controls and one young elite athlete, 10 months after unilateral Achilles tendon reconstruction participated. All young athletes underwent regular measurements over one season. Triceps surae muscle strength and tendon stiffness of both legs were analysed using dynamometry and ultrasonography synchronously. Within one season, similar patterns of relative changes in muscle strength and tendon stiffness were seen in the young elite athletes. For the tendon reconstruction athlete, the affected leg showed no increases in muscle strength or tendon stiffness over one season, and remarkably lower muscle strength but similar tendon stiffness compared to the non-affected leg. Healthy young elite athletes showed higher muscle strength and tendon stiffness than both other subject groups, with no differences between young controls and master athletes. Our results provide evidence for training-induced concordant adaptation of muscle and tendon over one season within healthy young elite athletes. Achilles tendon rupture and reconstruction may be a major risk factor for irreversible discordance within the triceps surae MTU. Finally, habitual athletics training over the lifespan may effectively counteract age-related decreases in muscle strength and tendon stiffness.
Listed In: Biomechanics, Sports Science

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