Chang Y, Liu CC, Tsaih PL, Shields RK; Department of Physical Therapy, Chang Gung University, Tao-Yuan, Taiwan.

PURPOSE: Stepping is a common program in cardiovascular rehabilitation and lower extremities strength training. In order to get the maximum training effect without inducing substantial fatigue, a sensitive monitoring fatigue index is important. Several monitoring fatigue indexes such as heart rate (HR), Rating of Perceived exertion (RPE), and surface electromyography (sEMG) are common in different clinical and research settings. However, the relations among these indexes are not well established. The purpose of this study was to investigate the changes of RPE, HR, and EMG after fatiguing from stepping exercise. SUBJECTS: Ten healthy adults (4 male and 6 female) participated with informed consents. All subjects had no previous history of cardiovascular disease, CNS and low extremity neuromuscular disease. METHODS: The Subjects performed right bare foot stepping on a 23 cm-high-curb at constant speed until the score of RPE reached 20 which means the load was very hard. The left foot was in an AFO to prevent plantar flexion and ensure all the effort of stepping was made by the right foot. RPE, HR, and sEMG of Rectus Femoris (RF) were recorded every minute during stepping and 30 minutes after recovery. The knee extension force was recorded before, after stepping and 30 minutes after recovery. Root-mean-scquare (RMS) of sEMG and the median frequency (MF) of power spectrum were calculated for statistical analyses. ANALYSIS: One way repeated measure ANOVA was performed on RPE, HR, RMS, and MF (SAS 6.0). The alpha level was set at 0.05. Time plots were performed to evaluate the pattern of changes in these four indexes. RESULTS: The knee extension force showed a significant decrease (p < 0.05) after stepping but the amount of decrement was not extensive (<50%). The RPE and HR decreased significantly after stepping and the time plot showed a parallel decrease during stepping (p < 0.05). The RMS and MF did not significantly change after stepping (p > 0.05) and subjects’ plot demonstrated that there were two directions of changes among subjects. After 30 minutes of recovery, all the parameters returned even though the averaged knee extension force was slightly lower than pre-stepping status (p > 0.05). CONCLUSIONS: The perceived fatigue is consistent with the change of HR but inconsistent with the neuromuscular fatigue. Stepping exercise for lower extremity strength training may not be optimal if RPE or HR is used as the stopping criteria. FUNDING SOURCE: Chang Gung University, Taiwan, CMRP1350. richard-shields@uiowa.edu.

Copyright 2004 by the American Physical Therapy Association

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