Peripheral impairments cause a progressive age-related loss of strength and velocity-dependent power in the dorsiflexors

Abstract

Muscle power is more functionally relevant than static muscle strength, particularly with aging. However, the effect of age on power derived from isotonic contractions has been studied sparingly, and it has not been studied at all in subjects >75 yr of age. Thus the purpose was to investigate the magnitude and causes of age-related losses in isotonic power among 13 young (26 yr), 13 old (65 yr), and 13 very old (84 yr) men. Six different loads were employed to create velocity-torque and power-torque relationships. Dorsiflexor cross-sectional area was assessed via magnetic resonance imaging for the calculation of specific power. Electromyographic signals of the tibialis anterior and soleus muscles were recorded to assess agonist activation and antagonist coactivation, respectively. Despite similar contractile masses and levels of voluntary drive and antagonist co-activation, power was significantly impaired in the old vs. young (∼25%), and in the very old relative to both the young (∼60%) and old (∼40%). The novel results punctuate two important considerations for studies concerned with the effect of age on the neuromuscular system. First, the decreased ability of muscles from old men to produce power in the presence of reasonably well-preserved strength indicates the utility of studying isotonic contractions. Second, the precipitous decline in many measures between the seventh and ninth decades underscores the benefit of testing more than one group of aged subjects to improve our understanding of rates of change in key variables.

The influence on sarcopenia of muscle quality and quantity derived from magnetic resonance imaging and neuromuscular properties

“…Thus, at the whole muscle level, in the present study, both old groups were weaker but the intrinsic contractile properties of the contractile muscle mass, at least for torque generation, appears to be essentially intact. In contrast, McNeil et al (2007) found a decrease in normalized strength in their very old age group of men who were older (~5 years) than the upper age group of men in our study. In that prior study, the very old men were found to have decreased strength values, but not significantly different muscle CSA which accounted for the difference Fig.…”

“…4), Schwenzer et al (2009) reported 6 % lower MTR values for healthy old (~65 years) versus young participants in the TA. Thus, MTR may be a sensitive measure of MQ and the functional declines to follow, as MTR depicts a decrease in MPQ in the eighth decade of life, but a decrease in normalized strength was not found in this muscle until the ninth decade of life (McNeil et al 2007). Results from the present study also highlight that sarcopenia cannot be explained by a single process but is the result of a number of contributing factors that perhaps converge due to reduced compensatory abilities in each factor by the eighth decade.…”

“…This process could be one of the extrinsic changes to whole muscle affecting MQ (Doherty 2003), but the possible relationship between loss of MUs and MQ has not been explored systematically. In separate studies, MU loss was related to strength loss for only a very old (~80 years) group of subjects (McNeil et al 2005b), but muscle cross-sectional area quantified from magnetic resonance imaging (MRI) showed no relationship between amount of muscle tissue and strength when comparing young with older subjects (McNeil et al 2007). This supports that age-related alterations in MQ rather than only muscle quantity are related to functional declines.…”

Effects of aging and sex on voluntary activation and peak relaxation rate of human elbow flexors studied with motor cortical stimulation

“…Among the major secondary findings was an age-related decrease of maximal torque which achieved statistical significance in men but just failed to do so in women (P 00.06). For both sexes, elbow flexor strength was reasonably wellmaintained until the eighth decade at which point it began to decline somewhat rapidly (Table 2), which is similar to previous findings of other muscle groups (e.g., Kallman et al 1990;McNeil et al 2007;Vandervoort and McComas 1986). Fig.…”

Modulation of reflex responses in activated ankle dorsiflexors differs in healthy young and elderly subjects

“…The age-related decline in motor function (Enoka et al 2003;McNeil et al 2007;Nardone et al 1995;Stelmach et al 1989;Woollacott 1998, 1999) is not only associated with alterations affecting the muscular (McNeil et al 2007) but also the neural system (Enoka et al 2003). During voluntary contractions and responses to sudden perturbations of a limb or whole body, motor neurone activity is modulated by both the descending input and sensory feedback (Nielsen 2004).…”