Lifelong physical activity and blood flow to active muscles: sufficient supply to meet the demand

Abstract

Despite many efforts over the past ∼40 years to determine the influence of ageing on exercise hyperaemia, fundamental questions remain regarding (1) the interactive influences of primary ageing and physical activity level and (2) whether or not attenuated blood flow and vascular conductance responses at a given work rate have metabolic or functional consequences (Proctor & Parker, 2006). Nowhere have these questions been more comprehensively addressed than in a study published in the current issue of The Journal of Physiology. In this study (Mortensen et al. 2012), Mortensen and colleagues at the Copenhagen Muscle Research Centre examined exercise-and pharmacologically-induced leg vascular and metabolic responses in three groups of men: young, lifelong sedentary, and lifelong physically active older men. They report that, during single leg knee extensor exercise at the same submaximal work rate, both sedentary and physically active older men exhibited blunted vasodilator responses compared with younger men. Similarly, leg blood flow during exercise was significantly (sedentary) or on average (physically active) lower in both groups of older men. However, in the sedentary older men, attenuated leg vascular responses were associated with greater lactate release ( Fig. 3 in their paper), while similarly attenuated vascular responses in the lifelong active men were not. These findings provide evidence to suggest that lower blood flow to exercising leg muscles in sedentary older men may be associated with impaired local aerobic metabolism. Therefore, despite similar vasodilator and blood flow responses to dynamic exercise between the two older groups, the extent to which these responses are sufficient to meet the metabolic demand appear to differ depending on lifelong physical activity.While the use of isolated leg ergometry models (e.g. knee extensor and stationary cycling) offer the advantage of measuring arterial inflow and assessing local vascular and metabolic responses within a well-defined group of muscles, it is important to note that whole limb blood flow and arterial-venous differences tell us little about the distribution of blood flow within the active limb(s). As seen in Fig. 3 of their paper, local noradrenaline release induced by tyramine lowered blood flow and vascular conductance but augmented (a-v) O 2 difference in the exercising leg of sedentary older men despite unaltered legV O2 and lactate release. Taken together, these findings suggest that tyramine-induced constriction in the exercising leg of sedentary older men may be occurring to a greater extent within less metabolically active regions. These findings are in contrast to the younger and lifelong active older men who exhibited unaltered vascular and metabolic responses to tyramine. Collectively, these findings suggest that blood flow may be less effectively distributed within the exercising leg of sedentary, but not lifelong active, older men. Moreover, a less effective distribution of blood flow in the exercising leg of sedentary older men...

Impaired modulation of postjunctional α1‐ but not α2‐adrenergic vasoconstriction in contracting forearm muscle of postmenopausal women

“…However, whether the functional distribution of post‐junctional alpha‐adrenergic receptors of the female human forearm is similar to the male mouse cremaster or gluteus maximus skeletal muscle remains inconclusive. Lastly, it is possible that blood flow may be less effectively distributed within the exercising muscle of PMW, which could possibly result from attenuated vasoconstriction within less metabolically active regions and/or impaired dilatation within active muscle fibres (Proctor & Moore, ).…”

Leg vascular and skeletal muscle mitochondrial adaptations to aerobic high‐intensity exercise training are enhanced in the early postmenopausal phase

“…). The finding that O 2 uptake and lactate release were similar in the two groups of women prior to training suggests that the matching of O 2 delivery and oxidative metabolism was not affected by the menopausal transition (Proctor & Moore, ). This preserved capacity of the circulation to deliver O 2 to meet the O 2 demand of the contracting muscles despite a marked reduction in vascular function, as assessed by arterial ACh and epoprostenol infusion, in the present group of postmenopausal women (Nyberg et al .…”

Potentiation of cGMP signaling increases oxygen delivery and oxidative metabolism in contracting skeletal muscle of older but not young humans

“… 2012 ) but the mechanisms underlying the altered regulation of exercise hyperemia have not been resolved (Proctor and Parker 2006 ). Furthermore, to what extent a reduced blood flow and O 2 delivery to contracting skeletal muscle of older individuals have metabolic and functional consequences remain unclear (Proctor and Moore 2012 ). Blood flow to skeletal muscle is determined by perfusion pressure and vascular tone of which the latter is the result of the balance between vasoconstrictor and vasodilator signaling pathways in vascular smooth muscle cells (VSMC).…”