Early studies suggested that the effects of varying length of work period (TW) and duration of rest period (TR) are additive when TW and TR alternate and are constant within experimental conditions. Recent investigations indicate that the joint effect of these variables on performance depends on the ratio TW:TR. this ratio effect is not predicted by functions traditionally used to describe theoretical massing and distribution effects. Parabolic functions were suggested and were shown to describe reminiscence data adequately. College students were given 30 min, of rotary pursuit practice with 10- or 30-sec work periods alternating with 5-, 10-, or 30-sec rest intervals (n = 30 per group). Predictions that work and rest variables would have orthogonal effects while final performance levels could be described as a parabolic function of the ratio TW:TR were confirmed.