Fluid ingestion attenuates the decline in VO2max associated with cardiovascular drift
Ganio, Matthew Stueck
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To determine whether manipulation of cardiovascular drift (CV drift) by changing .exercise duration or by fluid ingestion is associated with altered VO2max during prolonged .exercise, VO2max was measured in 11 trained men immediately after they cycled at 60% control .VO2max for 15, 60 and 120 min with no fluid (15NF, 60NF, 120NF), or 120 min with fluid (120F). Markers of CV drift, stroke volume (SV) and heart rate (HR), were measured in 120NF and 120F at 15-, 60-, and 120-min time points. Subjects became 2.3%, 3.7%, and 0.7% dehydrated in 60NF, 120NF, and 120F. Compared to 15-min values, SV did not decline significantly after 60 min (6 ml, 4.6%, P = 0.128) but was reduced after 120 min (16 ml, 13.8%, P < 0.001) in 120NF. After 120 min, the decline in SV (3 ml, 2.1%) in 120F was significantly .less than during 120NF (P = 0.001). Compared to 15NF, VO2max was not decreased in 60NF (-1.2%, P = 1.00), but was lower in 120NF (-8.7%, P = 0.016). Fluid ingestion significantly ..reduced the decline in VO2max (-1.9%, P = 0.035). Changes in VO2max were correlated with changes in SV and HR during the preceding submaximal exercise (r = 0.47 and 0.64, SEE = 6.6 and 5.7). Manipulation of CV drift by altering exercise duration and fluid ingestion is associated .with corresponding changes in VO2max. The results provide support for the hypothesis that, under .these conditions, CV drift causes reduced VO2max.