Ischemic exercise and the muscle metaboreflex

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.