Reports of severe paralytic poliomyelitis apparently precipitated by strenuous exertion have appeared in the literature. Russell,1 in England, studied statistically two series of poliomyelitis cases: one of 44 cases and an additional series of 100 cases.2 He concluded that exercise during the preparalytic stage greatly increases the danger of paralysis, and that bed rest considerably reduces it. Hargreaves,3 who studied 30 cases in Cornwall, and Horstmann,4 who studied 411 cases chiefly from California and North Carolina, have presented data to support his view. However, they could find no evidence that activity before the preparalytic stage influenced paralysis, or that activity at any stage affected the severity of bulbar paralysis. The present study was undertaken in New York State in July 1949. Its purpose was to determine whether, with certain changes in study technique, the severity of poliomyelitis could be ascribed largely to the extent of physical