Contractile properties of elderly human triceps surae.

Maximal electrically evoked and voluntary contractions of the triceps surae were repeatedly measured over several weeks in 13 elderly men, mean age 69.6 +/- 1.3 years. All subjects were found to be tolerant of supramaximal single twitch stimuli from the first occasion of measurement onwards and were habituated to supramaximal tetanic stimulation at frequencies of 10 and 20 Hz after three occasions of measurement. There was a significant increase in maximal voluntary contraction between the first and second occasions of measurement, but thereafter it remained unchanged. The coefficient of variation for maximal twitch and tetanic tensions and MVC were 12.5, 9.0 and 8.3%, respectively. Comparison with previously reported data showed that elderly muscle had an increased time-to-peak twitch tension development (148 +/- 15 ms) compared with young subjects (113 +/- 11 ms). The respective half relaxation times were 99 +/- 13 and 78 +/- 4 ms. Maximal tetanic tensions at frequencies of 10 and 20 Hz were significantly lower in the elderly men, 520 +/- 168 and 716 +/- 193 N respectively compared with 742 +/- 133 and 1,162 +/- 199 N respectively in the young subjects. A 2-min test involving repeated tetanisation of the triceps surae showed that though the absolute loss of tension was the same the relative loss was greater in the older than the younger men. It is concluded that muscle function in the elderly can be reliably assessed. The results suggest that the triceps surae of the elderly are weaker, more slowly contracting and show a greater relative force loss, when subjected to a standard "fatigue' test procedure, than young triceps surae.