The effect of aging on human gastrocnemius medialis (GM) muscle architecture was evaluated by comparing morphometric measurements on 14 young (aged 27–42 yr) and on 16 older (aged 70–81 yr) physically active men, matched for height, body mass, and physical activity. GM muscle anatomic cross-sectional area (ACSA) and volume (Vol) were measured by computerized tomography, and GM fascicle length ( L_f) and pennation angle (θ) were assessed by ultrasonography. GM physiological cross-sectional area (PCSA) was calculated as the ratio of Vol/ L_f. In the elderly, ACSA and Vol were, respectively, 19.1% ( P < 0.005) and 25.4% ( P < 0.001) smaller than in the young adults. Also, L_f and θ were found to be smaller in the elderly group by 10.2% ( P < 0.01) and 13.2% ( P < 0.01), respectively. When the data for the young and elderly adults were pooled together, θ significantly correlated with ACSA ( P < 0.05). Because of the reduced Vol and L_f in the elderly group, the resulting PCSA was found to be 15.2% ( P < 0.05) smaller. In conclusion, this study demonstrates that aging significantly affects human skeletal muscle architecture. These structural alterations are expected to have implications for muscle function in old age.

For efficient prevention of falls among older adults, individuals at a high risk of falling need to be identified. In this study, we searched for muscle strength measures that best identified those individuals who would fall after a gait perturbation and those who recovered their balance. Seventeen healthy older adults performed a range of muscle strength tests. We measured maximum and rate of development of ankle plantar flexion moment, knee extension moment and whole leg push-off force, as well as maximum jump height and hand grip strength. Subsequently, their capacity to regain balance after tripping over an obstacle was determined experimentally. Seven of the participants were classified as fallers based on the tripping outcome. Maximum isometric push-off force in a leg press apparatus was the best measure to identify the fallers, as cross-validation of a discriminant model with this variable resulted in the best classification (86% sensitivity and 90% specificity). Jump height and hand grip strength were strongly correlated to leg press force (r = 0.82 and 0.59, respectively) and can also be used to identify fallers, although with slightly lower specificity. These results indicate that whole leg extension strength is associated with the ability to prevent a fall after a gait perturbation and might be used to identify the elderly at risk of falling.

Skeletal muscle contracts either by shortening or lengthening (concentrically or eccentrically, respectively); however, the two contractions substantially differ from one another in terms of mechanisms of force generation, maximum force production and energy cost. It is generally known that eccentric actions generate greater force than isometric and concentric contractions and at a lower metabolic cost. Hence, by virtue of the greater mechanical loading involved in active lengthening, eccentric resistance training (ECC RT) is assumed to produce greater hypertrophy than concentric resistance training (CON RT). Nonetheless, prevalence of either ECC RT or CON RT in inducing gains in muscle mass is still an open issue, with some studies reporting greater hypertrophy with eccentric, some with concentric and some with similar hypertrophy within both training modes. Recent observations suggest that such hypertrophic responses to lengthening vs. shortening contractions are achieved by different adaptations in muscle architecture. Whilst the changes in muscle protein synthesis in response to acute and chronic concentric and eccentric exercise bouts seem very similar, the molecular mechanisms regulating the myogenic adaptations to the two distinct loading stimuli are still incompletely understood. Thus, the present review aims to, a) critically discuss the literature on the contribution of eccentric vs. concentric loading to muscular hypertrophy and structural remodeling, and, b) clarify the molecular mechanisms that may regulate such adaptations. We conclude that, when matched for either maximum load or work, similar increase in muscle size is found between ECC and CON RT. However, such hypertrophic changes appear to be achieved through distinct structural adaptations, which may be regulated by different myogenic and molecular responses observed between lengthening and shortening contractions.