ABSTRACT
In a study of the human response to exercise, a subject was asked to squeeze an object in the hand with maximum voluntary force for 4 s.Within two heartbeats of starting the exercise, heart rate had increased from 68 min1 to 80 min1. Mean arterial pressure increased from 98 to 110 mmHg by the end of the 4 s.Afferent input from the muscles of the arm was then blocked by injections of local anaesthetic into the axillary and radial nerves, and the study repeated.The heart rate increased less, from 68 to 72 min1 by the second beat; blood pressure increased from 96 to 102 mmHg by the end of the 4 s effort. a. How could the heart rate be monitored so accurately that it was possibly to detect an
increase within two beats of starting the exercise? b. Which branch of the autonomic nervous system is more likely to account for a change in
heart rate in under 2 s? c. What can be inferred from the reduced cardiac response to static exercise after muscle
afferent block by local anaesthetic? d. What types of muscle receptor might mediate the exercise pressor response? e. Did afferent blockade completely block the tachycardia at the onset of exercise? How might
the result be interpreted?
