The Relationship between Lean Mass and Contractile Properties of the Quadriceps in Elderly and Young Adults.

BACKGROUND Aging is associated with a loss of muscle mass (sarcopenia) and function. The twitch torque evoked by supramaximal electrical stimulation of peripheral nerves has been frequently used to analyse age-related modulations at the skeletal muscle level, such as changes in muscle mass. However, only one study has investigated the association between twitch contractile properties and skeletal muscle mass. A significant positive correlation between cross-sectional area and twitch parameters was found for the plantar flexors in young adults when using supramaximal doublet stimulation. It remains unclear whether this relationship exists for the quadriceps in elderly and young subjects when using single and doublet stimulation. OBJECTIVE The aim of the present study was to investigate the relationship between the lean mass of the thigh and evoked twitch properties of the quadriceps using single and doublet stimulation in two age groups. METHODS Fifteen young (aged 25.3 ± 3.6 years) and 15 elderly (aged 69.6 ± 3.1 years) subjects were recruited to participate in this study. The lean mass of the thigh was measured by dual-energy X-ray absorptiometry. Supramaximal single and doublet electrical stimulation was used to assess the contractile properties of the quadriceps. RESULTS We observed no significant associations between lean mass and contractile properties when using single stimulation. Significant positive correlations were shown between lean mass and peak twitch torque evoked by doublet stimulation in young (r = 0.56; p = 0.030) and elderly (r = 0.54; p = 0.040) subjects. The analysis of twitch time and slope parameters demonstrated no significant correlations with lean mass. CONCLUSION The peak twitch torque evoked by doublet electrical stimulation seems to be an appropriate measure to assess modulations in muscle mass in elderly and young subjects. The use of supramaximal single stimulation and the analysis of time and slope parameters may not be recommended for estimating changes in muscle mass. Consequently, the occurrence of muscle mass loss with aging can be identified from the twitch torque signal induced by doublet stimulation, which is a simple and favorable way to estimate sarcopenia.