The effect of ramp slope on determination of aerobic parameters from the ramp exercise test. Med. Sci. Sports Exercise, Vol. 14, No. 5, pp. 339-343, 1982. We have previously demonstrated that the four parameters of aerobic function (maximal oxygen uptake (muVO2), VO2 at the anaerobic threshold (theta an), the time constant for VO2 kinetics (tau VO2), and work efficiency (eta)) may all be determined reliably from a single test in which the work rate increases continuously at a constant rate, i.e., ramp. That study, however, utilized a single ramp slope of 50 W X min-1, which may not be appropriate for subjects with very low or very high work tolerances. We therefore studied the effect of different ramp slopes on the determination of these parameters. Ramp slopes of 20, 30, 50, and 100 W X min-1 were generated on a cycle ergometer, and each was assigned randomly to 14 healthy subjects. Ventilatory and gas exchange variables were measured breath-by-breath utilizing on-line digital computation. Ramp slopes of 20, 30, and 50 W X min-1 yielded the same values for each aerobic parameter. The 100 W X min-1 ramp yielded muVO2 and eta an values that were the same as those found for the other ramp slopes, but tau VO2 and eta could not be discerned validly from this ramp slope. We conclude that valid assessment of the four parameters of aerobic function is possible with ramp slopes between 20 and 50 W X min-1; no further information on the parameters is to be gained by prolonging the tests with ramps slower than 20 W X min-1.