Impact of protein and carbohydrate supplementation on plasma volume expansion and thermoregulatory adaptation by aerobic training in older men

We examined whether protein-carbohydrate (CHO) supplementation immediately after exercise each day during aerobic training facilitated plasma volume (PV) expansion and thermoregulatory and cardiovascular adaptations in older men. Fourteen moderately active older men [68 ± 5 (SD) yr] were divided into two groups so as to have no significant differences in anthropometric measures, PV, and peak oxygen consumption rate (V̇O_2peak). Each group was provided with a mixture of protein and CHO (3.2 kcal, 0.18 g protein/kg body wt, Pro-CHO, n = 7) or a non-protein and low-calorie placebo (0.5 kcal, 0 g protein/kg body wt, CNT, n = 7) immediately after cycling exercise (60-75% V̇O_2peak, 60 min/day, 3 days/wk) each day for 8 wk at ∼19°C ambient temperature (T_a) and ∼43% relative humidity (RH). Before and after training, we measured PV, cardiac stroke volume (SV), and esophageal temperature (T_es) during 20-min exercise at 60% of pretraining V̇O_2peak at 30°C T_a and 50% RH. Moreover, we determined the sensitivity of the chest sweat rate (ΔSR/ΔTes) and forearm vascular conductance (ΔFVC/ ΔT_es) in response to increased T_es during exercise. After training, PV increased by ∼6% in Pro-CHO (P < 0.001), with an ∼10% increase in SV during exercise (P < 0.001), but not in CNT (P > 0.07). ΔFVC/ΔT_es increased by 80% and ΔSR/ΔT_es by 18% in Pro-CHO (both P < 0.01) but not in CNT (P > 0.07). Moreover, we found a significant interactive effect of group X training on PV, SV, and ΔFVC/ΔT_es (all P < 0.02) but with no significant effect of group (P > 0.4), suggesting that the supplement enhanced these responses to aerobic training. Thus postexercise protein-CHO supplementation during training caused PV expansion and facilitated thermoregulatory and cardiovascular adaptations, possibly providing a new training regimen for older men.