Neuromuscular performance in a Kansas Mennonite community: age and sex effects in performance.

The effects of age and sex on six neuromuscular performance traits are studied in a cross-sectional sample of 559 members of the Goessel, Kansas Mennonite commu­ nity. Age and sex effects are assessed by stepwise polynomial regression which includes non-linear age terms up to the fourth power. Of the six traits studied only one, Hand Steadiness, fails to show a significant sex difference and only one, Trunk Flexibility, fails to show a significant non-linear trend with age. A general pattern, seen in these traits of accelerating performance decline after age 45 of up to 60%, is found to be consistent with that reported in other studies of the same traits. The consistency of this non-linear aging pattern suggests the presence of a general neuromuscular aging process. Moreover, this process appears likely to be related to a two-stage mechanism inferred from both animal and human studies involving a decline in protein synthesis and a loss of cell mass in nerve and muscle tissue. Diminished ability with regard to muscular strength and neuromuscular performance associated with advancing age is an observation which seem­ ingly h as been well documented. Pioneering investigations by Quetelet (1835) revealed declines of 35 to 40% in the strength of various muscle groups in men between the ages of 25 and 60. Later in the 19th century, large studies guided by Galton showed a pattern of decline with age that was similar for several aspects of human physiology and neuromotor per­ formance including grip strength (Ruger and Stoessiger, 1927; Elderton and Moul, 1928) and reaction time (Koga and Morant, 1923). Subsequent analyses of these phenomena have, however, been sporadic and have usually focused on only one or two aspects of human neuromuscular performance. The most extensively studied traits are muscular strength and stimulus-response characters such as reaction time. Rarely has a broad r ange of performance traits been investigated in a single popula­