Static and Dynamic Exertion: A Psychophysical Similarity and Dissimilarity

Abstract

At about the same time and apparently quite independently, Borg (see Borg, 1962; Borg & Dahlström, 1959, 1960) and J. C. Stevens and Mack (1959) began studies of how perceived exertion depends on the physical level of performance. Borg and his associates concentrated on dynamic exercise (e.g., cycling), Stevens and his collaborators on static exercise (e.g., handgrip squeezing, curling). Both kinds of exercise turned out to obey the power law of S.S. Stevens (1957, 1975) with very nearly identical exponents (1.6–1.7). This means that perceived exertion always grows as an accelerating function of physical level, so that the closer one approaches maximal exertion the faster the sense of exertion increases — probably helping to protect against straining, and paradoxically enabling greater amounts of work to be done. Perceived exertion also grows over time, given a constant physical level of performance. Here the psychophysical properties of dynamic and static exercise diverge. For example, perceived level of cycling builds up considerably more slowly than does perceived level of handgrip squeezing and, unlike static handgripping, its growth rate depends on the level sustained. These differences show themselves in the slopes of the hyperbolic functions (the so-called Grosse-Lordemann and Müller curves) relating physical level to the duration beyond which the exertion cannot be further sustained.