Abstract

Aging results in lower exercise tolerance, manifested as decreased Critical Power (PCRIT). Aging is also associated with reduced physical activity, decreased muscle mass, and altered muscle blood flow, all of which may contribute to the age-related decrease in PCRIT. Purpose: The purpose of this study was to determine if the age-related decrease in PCRIT occurs independently of changes in physical activity and muscle mass and if it is related to impaired muscle blood flow. Methods: 10 Old (63.1 ± 2.5 years, 5 female and 5 male) and 10 Young (24.4 ± 4.0 years, 5 female and 5 male) physically active volunteers enrolled in this study. Physical activity was measured with accelerometry. Leg muscle mass was quantified with dual x-ray absorptiometry (DEXA). PCRIT and the maximum power achieved during a graded exercise test (PGXT) during single-leg knee extension exercise were determined over the course of 4 visits. On the fifth visit, vascular function of the leg was assessed with the passive leg movement (PLM) hyperemia. Subsequently, subjects performed knee extension exercise at 10 watts (W), 20 W, 90% PCRIT, and 100% PGXT while blood flow and blood pressure were measured at the femoral artery for each intensity. Results: Young and Old subjects did not differ in daily step count (Old = 13001.1  2464.0 vs Young = 13527.0  3213.8 steps, P = 0.735) or in leg lean mass (9.06  0.62 g/kg, P = 0.901). The Old subjects had a lower mass-specific PCRIT (Old = 3.20  0.94 vs Young = 4.60  0.87 W/kg, P = 0.004), vascular function (mass-specific Passive Leg Movement (PLM): Old = 79.4  38.3 vs Young = 128.8  34.9 ml/min/kg, P = 0.010) and leg blood flow at 90% PCRIT (mass-specific: Old = 378  122 vs Young = 522  124 ml/min/kg, P = 0.014) and 100% PGXT (mass-specific: Old = 391  109 vs Young = 544  136 ml/min/kg, P = 0.013). When normalized for leg muscle mass, PCRIT was strongly correlated to peak leg blood flow in response to PLM (R2 = 0.53; P < 0.001) and leg blood flow during knee extension exercise at 90% PCRIT (R2 = 0.36; P = 0.007). Conclusion: The age-related decline in PCRIT is associated with major decreases in muscle endurance and is correlated with concomitant reductions in vascular function in healthy active adults. Future research should determine if interventions known to improve vascular function can ameliorate exercise tolerance in Old adults.

Degree

College and Department

Life Sciences; Exercise Sciences

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