Manual muscle testing with the examiner providing the resistance has long been a standard test of muscle strength. Through the use of extremities acting as levers, clinicians have been able to effectively apply resistance to all muscle groups except the ankle plantar flexors. As a result, a standing heel-rise test that uses body weight as the resistance has been substituted. The number of heel-rises that represent normal plantar-flexor "strength" and the ability of subjects to repeatedly use that "strength" remain unresolved. Because walking is an endurance task, the hypothesis tested by this study was that individuals without known weakness would be able to perform more than the standard recommended one to five standing heel-rises. The purpose of this study was to measure the number of standing heel-rises that individuals without known weakness could accomplish. Two hundred three subjects were studied for their ability to do standing heel-rises, as is done when testing plantar-flexion strength using the upright test. There were 122 male subjects and 81 female subjects, ranging in age from 20 to 59 years. Each subject was asked to do as many standing heel-rises as he or she could, with careful monitoring of body and limb alignment and of ankle motion, with specific criteria for stopping. The average number of heel-rises was 27.9 (SD = 11.1, minimum = 6, maximum = 70) for all groups and both genders, with no differences between male and female subjects. The lower 99% confidence interval was 25. A recommendation is made to change the standard of testing plantar-flexion function, when using the standing heel-rise test, to require 25 repetitions for a grade of Normal. [Lunsford BR, Perry J. The standing heel-rise test for ankle plantar flexion: criterion for normal.