Neuromuscular function in different stages of sarcopenia

This study applied the screening tool developed by the European Working Group on Sarcopenia in Older People (EWGSOP) on seniors aged over 65 years and concurrently tested various  laboratory-based indices of neuromuscular function. Twenty-four healthy and independent living older adults (9 men, 15 women) with a mean age of 79.1 ± 5.8 years participated. Based on gait speed, handgrip strength and muscle mass all subjects were categorized into one of the three conceptual sarcopenia stages (pre-sarcopenia, sarcopenia, severe sarcopenia). Maximal strength of dorsiflexors in the left legwas measured and voluntary activationwas assessed by the interpolated twitch technique. In addition, isometric evoked contractile properties were recorded. Skeletal muscle mass was assessed by ultrasound from nine sites. There were roughly equal number of subjects in each sarcopenic category, and age was not different among the 3 groups. There were no differences in handgrip strength and skeletal muscle mass index among the 3 groups. Gait speed was significantly slower (p b 0.01) in the severe sarcopenic subjects compared to the pre-sarcopenic group. With no differences in voluntary activation among the groups, the maximal voluntary contractions (MVCs) for severe sarcopenic subjects were 29% lower (p=0.02) and with 19% slower (p=0.02) voluntary rates of torque development (RTD) compared to sarcopenic subjects. Furthermore, the severe  group was 34% lower (p=0.04) with 36% slower (p=0.02) RTD compared to pre-sarcopenic subjects. Peak twitch tension was 54% lower (p b 0.01) in the severe group compared with the pre-sarcopenic group. Maximal twitch RTD were 40% (p = 0.03) slower for the severe group compared to the sarcopenia group, and 51% slower (p = 0.03) compared with the pre-sarcopenia group, but when normalized to peak torques there were no statistical differences. The laboratory tests found neuromuscular differences among the 3 groups which generally supported the classification scheme and helped to illustrate some key factors that could explain differences in functional capacities. These initial findings support the assumption that this categorization is relevant for identifying older adultswith different neuromuscular properties. However, further studies are needed to provide more insight into the specific neuromuscular changes in the three sarcopenia stages, and how these changes relate to functional capacity. Such studies could ultimately contribute to identifying optimal interventions to improve neuromuscular functioning.
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