OBJECTIVE: To determine the effect of very high stimulation frequency (150 and 200 Hz) with wide pulse duration versus 50 Hz with wide pulse duration on stimulated force and fatigue of quadriceps femoris in healthy participants. METHODS: Thirty-four healthy participants underwent fatigue test using three stimulation frequency conditions (50, 150, and 200 Hz) with pulse duration of 0.9 ms. Normalized force values at the end of each fatigue protocol and curve fitting patterns were compared among stimulated frequencies. RESULTS: Very high stimulation frequency (150 and 200 Hz) conditions showed a trend of having more decline in normalized stimulated force during fatigue test compared to a low stimulation frequency at 50 Hz. However, the difference was not statistically significant. Responder group showed the same slope of a linear fitting pattern, implying the same pattern of muscle fatigue among three stimulation frequency conditions (−3.32 in 50 Hz, −2.88 in 150 Hz, and −3.14 in 200 Hz, respectively). CONCLUSION: There were high inter-subject variations in the response to different frequency stimulation conditions. However, very high stimulation frequency generated the same fatigue pattern as the low stimulation frequency in the responder group. Further research is needed to explore the mechanism involved.
Electric Stimulation ; Fatigue* ; Healthy Volunteers* ; Muscle Contraction ; Muscle Fatigue ; Quadriceps Muscle

OBJECTIVE: To describe scapular upward rotation during passive humeral abduction in individuals with hemiplegia post-stroke compared to normal subjects. METHODS: Twenty-five individuals with hemiplegia post-stroke and 25 age- and gender-matched normal subjects voluntarily participated in this study. Scapular upward rotation during resting and passive humeral abduction at 30°, 60°, 90°, 120°, and 150° were measured using a digital inclinometer. RESULTS: In both groups, scapular upward rotation significantly increased as humeral abduction increased (p<0.001). Scapular upward rotation was significantly less in the hemiplegic group compared to that in the control at 90° (p=0.002), 120° (p<0.001), and 150° of humeral abduction (p<0.001). The mean difference in scapular upward rotation between these two groups ranged from 6.3° to 11.38°. CONCLUSION: Passive humeral abductions ranging from 90° to 150° can significantly alter scapular upward rotation in individuals with hemiplegia post-stroke compared to those of matched normal subjects. The magnitude of reduction of the scapular upward rotation may potentially lead to the development of hemiplegic shoulder pain after prolonged repetitive passive movement. Scapular upward rotation should be incorporated during passive humeral abduction in individuals with hemiplegia post-stroke, especially when the humeral is moved beyond 90° of humeral abduction. Combined movements of scapular and humeral will help maintain the relative movement between the scapula and humerus. However, further longitudinal study in patients with shoulder pain post-stroke is needed to confirm these findings.
Hemiplegia ; Humans ; Humerus ; Longitudinal Studies ; Range of Motion, Articular ; Scapula ; Shoulder ; Shoulder Pain ; Stroke