This is the published version. Copyright 1985 Wayne State University Press.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 community. 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
