Purpose: Aerobic training-induced plasma volume (PV) expansion improves thermoregulation, and carbohydrate (CHO) + whey protein supplementation enhanced the effects in older people; however, these were suggested by studies on gym-based cycling training but not on home-based interval walking training (IWT). Moreover, long-term walking training effects on PV remain unknown.
Methods: Seventeen male and 10 female subjects (~69 yr), having performed IWT for >=24 months before the study, were used. After pre-intervention measurement (PRE) of PV, plasma albumin content (Albcont), fasting glucose concentration ([Glc]f), and HbA1c, the subjects were randomly divided into two groups: CHO and Pro-CHO, either consuming CHO (22.5 g) alone or CHO (15 g) + whey protein (10 g), respectively, during additional 5-month IWT from May to November, 2009. After the additional IWT, we measured the same variables again (post-intervention measurement, POST).
Results: The baseline PV and Albcont were significantly correlated with the number of IWT days for the 12 months preceding PRE (r=0.716, P<0.001 and r=0.671, P<0.001, respectively). In POST, PV and Albcont, marginally decreased in CHO from the baselines (P=0.081 and P=0.130, respectively) with increased HbA1c (P<0.001) after correction for the baseline [Glc]f by ANCOVA, but these values remained unchanged in Pro-CHO (both, P>0.74), with significant differences in the changes between groups (P=0.020, P=0.041, and P=0.018 respectively).
Conclusion: PV was proportional to the number of IWT days for 12 months and a CHO + whey protein supplementation during the 5-month IWT prevented PV reduction for the period of no supplementation, which might be partially linked with blood glucose control mechanisms.
(C) 2017 American College of Sports Medicine