In exercising muscle, interstitial metabolites accumulate and stimulate mus
cle afferents. This evokes the muscle metaborflex and raises arterial blood
pressure (BP). In this report, we examined the effects of tension generati
on on muscle metabolites and BP during ischemic forearm exercise in humans.
Heart rate (HR), BP, P-i, H2PO4- and pH (P-31-NMR spectroscopy) data were
collected in 10 normal healthy men (age 23 +/- 1 yr) during rhythmic handgr
ip exercise. After baseline measurements, the subjects performed rhythmic h
andgrip for 2 min. At 2 min, a 250-mmHg occlusion cuff was inflated, and is
chemic handgrip exercise was continued until near fatigue (Borg 19). Measur
ements were continued for an additional 30 s of ischemia. This protocol was
performed at 15, 30, 45, and 60% of the subjects' maximum voluntary contra
ction (MVC) in random order. As tension increased, the time to fatigue decr
eased. In addition, mean arterial pressure and HR were higher at 60% MVC th
an at any of the other lower tensions. The NMR data showed significantly gr
eater increases in H2PO4-, P-i, and H+ at 60% than at 15 and 30% MVC. There
fore, despite the subjects working to the same perceived effort level, a gr
eater reflex response (represented by BP and HR data) was elicited at 60% M
VC than at any of the other ischemic tensions. These data are consistent wi
th the hypothesis that, as tension increases, factors aside from insufficie
nt blood flow contribute to the work effect on muscle metabolites and the m
agnitude of the reflex response.