Increase in skeletal muscle performance during emotional stress in man.

An emotional stress arising as a result of intense mental arithmetic causes (in most subjects) an increase in blood flow through resting forearm muscle by an average of 85%. Combination of voluntary sustained handgrip contraction with mental arithmetic has shown that the duration of contraction increases by an average of 46%. This effect appears only in subjects who display an increase in blood flow as a result of mental arithmetic. A rise in muscle performance is also observed during mental arithmetic when contraction of forearm muscle is caused by direct stimulation of the motor nerve in the upper arm. Intra-arterial injection of atropine sharply reduces both the increase in blood flow through the resting muscle and the increase in muscle performance associated with mental arithmetic. Control performance (without mental arithmetic) is not altered by administration of atropine. Analysis of blood flow during muscle contraction leads to the conclusion that an increase in muscle performance during emotional stress is not dependent on an increase in muscle blood flow. The data suggest that during emotional stress the sympathetic nervous system causes metabolic changes in skeletal muscles that lead to an increase in muscle performance when oxygen deficiency exists.