As part of a joint project concerned with the various physiological and biomechanical aspects of hand activities with the final goal of reducing the number and severity of injuries to the hand, the relationships of some physiological parameters to exertion level and fatigue were studied. Four men were tested on two occasions. The exertion levels for static grip were 10, 20, 30, 50, and 75% of each subject's maximum voluntary contraction (MVC) strength. Electrocardiogram findings, blood pressure, forearm blood flow rate, and the electromyographical activity of the finger flexor muscles were recorded. Normalized heart rate increased linearly with exertion levels and these increases were significant at all levels except the 10% MVC. Normalized mean arterial blood pressure increased linearly and significantly with exertion levels. The normalized blood flow increased linearly to about 13% of each person's MVC strength, decreasing linearly above that level of exertion. Normalized vascular resistance to blood flow decreased linearly to about 17% MVC and increased linearly thereafter. Decreases were significant from 10 to 30% MVC. The strain gauge plethysmography proved to be reliable and accurate as a noninvasive blood flow analysis tool.
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