Reduced Cardiac Load During Aerobic Eccentric Exercise in Healthy Older Adults

Abstract

Aerobic eccentric exercise (i.e. downhill walking) is energetically less demanding (reduced VO2) than exercise conducted on a neutral gradient. The impact of eccentric exercise on the cardiovascular constituents of the oxygen cascade has not been established. PURPOSE: To determine the responses of cardiac output (Q); heart rate (HR); stroke volume (SV); systolic (SBP), diastolic (DBP), and mean arterial (MAP) blood pressure in healthy older adults during a single bout of aerobic exercise (treadmill walking) on either a neutral (LW) or downhill (DW) gradient. METHODS: Fifteen healthy adults (age 68 ± 4 yr; height 1.69 ± 0.08 m; weight 74.7 ± 8.0 kg) completed two bouts of treadmill walking at a self-selected walking speed (SSWS). Both LW and the DW lasted 15 min. Blood pressure (SBP, DBP and MAP), HR, and SV were estimated on a beat-to-beat basis using an arterial volume clamp applied to the middle finger of each subjects left hand, and infrared plethysmography. All variables were subsequently averaged over 5 min blocks. Respiratory gases were collected during the final 3 min of each bout. Whole body total peripheral resistance (TPR) and arteriovenous oxygen difference (a - vO2 diff) were estimated. Statistical significance was set at P < 0.05. RESULTS: Oxygen consumption was 2.94 mL·min-1·kg-1 (P < 0.0001) lower during DW than LW. Cardiac output was lower during each 5 min interval compared to LW, this was the result of a mean 9.9 mL·beat-1 reduction in SV as there were no differences in HR. Systolic blood pressure was significantly lower (10 mmHg) during DW, there were no differences in either DBP or MAP between the conditions. Total peripheral resistance was 2.11 mmHg higher during DW, and a - vO2 diff was 1.4 mL·L (P < 0.0001) lower during DW. CONCLUSIONS: Healthy older adults required 25% less oxygen to walk at the same speed on a negative gradient as opposed to a neutral gradient. As a result the cardiac load was reduced. The reduction in Q was entirely attributable to lower SV as HR was not different between the two conditions. Potential endothelial changes and the reduced metabolic demand of DW are responsible for the differences in TPR and a - vO2 diff respectively. With appropriate familiarisation downhill walking represents an alternative form of exercise which induces reduced cardiac strain suitable for higher-risk populations.