Vascular dysfunction and the age-related decline in critical power.

Abstract

Ageing results in lower exercise tolerance, manifested as decreased critical power (CP). We examined whether the age-related decrease in CP occurs independently of changes in muscle mass and whether it is related to impaired vascular function. Ten older (63.1±2.5 years) and 10 younger (24.4±4.0 years) physically active volunteers participated. Physical activity was measured with accelerometry. Leg muscle mass was quantified with dual X-ray absorptiometry. The CP and maximum power during a graded exercise test (PGXT ) of single-leg knee-extension exercise were determined over the course of four visits. During a fifth visit, vascular function of the leg was assessed with passive leg movement (PLM) hyperaemia and leg blood flow and vascular conductance during knee-extension exercise at 10W, 20W, slightly below CP (90% CP) and PGXT . Despite not differing in leg lean mass (P=0.901) and physical activity (e.g., steps per day, P=0.735), older subjects had ∼30% lower mass-specific CP (old=3.20±0.94Wkg-1 vs. young=4.60±0.87Wkg-1 ; P<0.001). The PLM-induced hyperaemia and leg blood flow and/or conductance were blunted in the old at 20W, 90% CP and PGXT (P<0.05). When normalized for leg muscle mass, CP was strongly correlated with PLM-induced hyperaemia (R2 =0.52; P<0.001) and vascular conductance during knee-extension exercise at 20W (R2 =0.34; P=0.014) and 90% CP (R2 =0.39; P=0.004). In conclusion, the age-related decline in CP is not only an issue of muscle quantity, but also of impaired muscle quality that corresponds to impaired vascular function.