The plantar flexors play a critical role in gait by aiding in moving the body forward. The function of the plantar flexor muscles, like many other muscle groups, decreases with age, resulting in plantar flexor weakness. Plantar flexor function is also affected by neurological impairment, like stroke. In order to quantify an individual’s level of plantar flexor function, the maximum plantar flexion moment during the stance phase of gait can be evaluated via a gait analysis. However, gait analysis software and equipment is expensive and not always clinically-feasible. Instead, clinicians usually evaluate a patient’s level of plantar flexor weakness via common clinical tests, such as isometric muscle testing and the single-leg heel rise test. It has not yet been determined if measures of plantar flexor strength from either of these clinical tests are related to plantar flexor function during gait. Thus, the purpose of this study was to determine if there is a relationship between clinical and gait measures of plantar flexor strength and function. To accomplish this purpose, three populations were chosen: young, healthy individuals (n = 15); older, healthy individuals (n = 10); and individuals post-stroke (n = 8). Subjects underwent three different tests: (1) a gait analysis, (2) isometric muscle testing of the plantar flexors, and (3) a single-leg heel rise test. For individuals post-stroke, the single-leg heel rise test was modified (i.e. laying-down and seated versions of the test) as this population could not perform the test standing. The absolute maximum plantar flexion moment during the gait analysis, maximum isometric plantar flexion torque during isometric muscle testing, and total work, average heel rise height, and maximum plantar flexion moment during the single-leg heel rise test were calculated for each subject. Percent differences and positive, one-tailed Pearson correlation analyses were conducted between gait and clinical measures of plantar flexor function and strength. Maximum plantar flexion moment from the single-leg heel rise test was the clinical measure with the strongest relationship to the absolute maximum plantar flexion moment during gait as the absolute average percent difference between these measures was less than 10% for young and older, healthy individuals. Furthermore, there was nearly a significant correlation (r = 0.512, p = 0.051) and a significant, moderate correlation (r = 0.647, p = 0.043) for young and older, healthy individuals, respectively. Significant, moderate correlations to the absolute maximum plantar flexion moment during gait were also found with total work done during the single-leg heel rise test and with maximum isometric plantar flexion torque for older, healthy individuals. This study’s findings provide an initial understanding of the relationship between plantar flexor function during gait and plantar flexor strength and, ultimately, lays a foundation for facilitating the clinical evaluation of plantar flexor strength in a manner that relates to plantar flexor function during gait.
gait analysis; isometric muscle testing; single-leg heel rise test; young, healthy individuals; older, healthy individuals; individuals post-stroke