Dynamic exercise in man as influenced by experimental restriction of blood flow in the working muscles

Abstract

The effects of reduced muscle perfusion pressure on dynamic exercise performance and cardiovascular and respiratory functions were investigated. Eight subjects were studied during supine cycle ergometry at stepwise increasing workloads until exhaustion with and without the legs exposed to a supra-atmospheric pressure of 50 mmHg (Leg Positive Pressure, LPP), a novel and convenient means of reducing the perfusion pressure in the working muscles. In the LPP condition exercise performance was reduced by 40% which, judging from assessments of perceived exertion, was due to premature muscle fatigue, indicating local or overall underperfusion of the working muscles. At any given work load, the arterial pressure response was considerably stronger during LPP than in the control condition. LPP also caused greater increases in blood lactate concentration and pulmonary ventilation, the differences from control increasing with the work load. Furthermore, the ventilatory equivalent for O2 at a given work load was markedly higher in the LPP than in the control condition, while exercise-induced decreases in end-tidal PCO2 were considerably exaggerated by LPP. The augmented pressor response during flow-restricted exercise, together with the strong ventilatory response which was out of proportion to overall O2 uptake, suggests increased activation of muscle chemoreflexes by accumulation of metabolic end products, the increased pressor response tending to reduce the local flow error in the working muscles.

Erratum to: Lactate concentrations in human skeletal muscle biopsy, microdialysate and venous blood during dynamic exercise under blood flow restriction

“…The hypothesis that microdialysate lactate concentrations increase with stepwise increments in blood flow restriction was based on previous studies in which ante-cubital vein [5] and femoral vein [7] lactate concentrations were found to increase with increasing degrees of blood flow restriction, and this was confirmed in the present study.…”

“…We used the model introduced by Eiken and Bjurstedt [5] in which it is possible to reduce blood flow during one-legged bicycle exercise in a controlled fashion by applying supra-atmospheric pressure over the lower body. With 50 mmHg applied, exercise blood flow is reduced by 15-20% [7].…”

“…An experimental model designed to mimic the blood flow restriction encountered in patients with peripheral arterial occlusive disease has been described previously [5]. In this model muscle ischaemia is induced by the application of positive pressure over a working leg.…”

Increasing blood flow to exercising muscle attenuates systemic cardiovascular responses during dynamic exercise in humans

“…Neural mechanisms also act to increase cardiac output (CO) and to redistribute blood flow from inactive regions to support the increase in skeletal muscle flow. This neural cardiovascular regulation is thought to be mediated by central command (41), as well as by feedback transmitted via afferent nerves (group III and IV fibers), innervating the working skeletal muscles, which are sensitive to mechanical (the so-called muscle mechanoreflex) and metabolic changes (the so-called muscle metaboreflex) (26,33,34,37,42), and are modulated via the arterial and cardiopulmonary baroreflexes (23,41,42).Reducing the blood flow to working muscles during dynamic exercise causes accumulation of metabolites within the active muscles and evokes muscle metaboreflex-mediated increases in sympathetic nerve activity, heart rate (HR), and systemic blood pressure (1,5,12,19,29,30,35,42). In addition, the reduced blood flow and resultant accumulation of metabolites would cause muscle fatigue so that recruitment of additional motor units would be required to perform the same amount of work, and thus central command would be increased (12,14,19,30).…”

“…Reducing the blood flow to working muscles during dynamic exercise causes accumulation of metabolites within the active muscles and evokes muscle metaboreflex-mediated increases in sympathetic nerve activity, heart rate (HR), and systemic blood pressure (1,5,12,19,29,30,35,42). In addition, the reduced blood flow and resultant accumulation of metabolites would cause muscle fatigue so that recruitment of additional motor units would be required to perform the same amount of work, and thus central command would be increased (12,14,19,30).…”