Attenuated exercise induced hyperaemia with age: mechanistic insight from passive limb movement

The influence of age on the central and peripheral contributors to exercise‐induced hyperaemia is unclear. Utilizing a reductionist approach, we compared the peripheral and central haemodynamic responses to passive limb movement (exercise without an increase in metabolism) in 11 old (71 ± 9 years of age s.d.) and 11 young (24 ± 2 years of age) healthy subjects. Cardiac output (CO), heart rate (HR), stroke volume (SV), mean arterial pressure (MAP), and femoral blood flow of the passively moved and control legs were evaluated second‐by‐second during 2 min of passive knee extension at a rate of 1 Hz. Compared to the young, the old group exhibited a significantly attenuated increase in HR (7 ± 4%vs. 13 ± 7%s.d.), CO (10 ± 6%vs. 18 ± 8%) and femoral blood flow in the passively moved (123 ± 55%vs. 194 ± 57%) and control legs (47 ± 43%vs. 77 ± 96%). In addition, the change in vascular conductance in the passively moving limb was also significantly attenuated in the old (2.4 ± 1.2 ml min−1 mmHg−1) compared to the young (4.3 ± 1.7 ml min−1 mmHg−1). In both groups all main central and peripheral changes that occurred at the onset of passive knee extension were transient, lasting only 45 s. In a paradigm where metabolism does not play a role, these data reveal that both central and peripheral haemodynamic mechanisms are likely to be responsible for the 30% reduction in exercise‐induced hyperaemia with age. The preponderance of evidence has revealed that aged humans have a 20–30% reduction in skeletal muscle blood flow during rest and exercise; however, the mechanisms behind these reductions are unclear. We compared the peripheral and central haemodynamic responses to passive limb movement (exercise without an increase in metabolism) in young and old healthy subjects. Our data show that the older subjects have an attenuated cardiac output and peripheral blood flow response to passive exercise. The reduction in blood flow is similar to that observed during active exercise, which, due to the current paradigm, cannot be explained by metabolic differences. Elucidating the mechanisms responsible for attenuated hyperaemia during exercise in the elderly population will help us understand the factors associated with their exercise and mobility limitations.