1. We tested the hypothesis that afferent nerves from working muscles are important in determining the heart rate and blood pressure responses to brief maximal static exercise.
2. In twenty human subjects, the heart rate and arterial blood pressure reponses to a brief maximal manual hand grip were studies before and after axillary nerve anaesthesia or to maximal one-leg knee extension before and after epidural anaesthesia at L3-L4. Maximal knee extension could not be acomplished without performing a 'Valsalva-like' manoeuvre, but during handgrip it was possible to avoid the use of muscles other than those directly involved in the contraction. Heart rate and blood pressure were also monitored during a Valsalva manoeuvre of a similar duration to the maximal voluntary contractions (4s).
3. During handgrip with normal breathing, axillary nerve anaesthesia reduced the heart rate response but had no effect on the blood pressure response.
4. During Valsalva manoeuvre, blood pressure increased but heart rate remained stable as long as expiratory pressure was maintained. During one-leg knee extension, epidural anaesthesia reduced the blood pressure responce; however, the reduction in blood pressure was probably due to a reduction in the simultaneously performed 'Valsalva-like' manoeuvre.
5. The results of this study suggests that afferent input from the working muscles is of importance for the heart rate responces to brief static muscle contractions. That such influence may be important for the blood pressure responce remains unproven.