The effect of HIT exercise on plasma volume and plasma viscosity

PURPOSE: High intensity interval training (HIT) is an exercise model that has been seen to cause similar muscle adaptations and improvements in exercise performance to traditional exercise models. This study aimed to examine the effects of low-volume HIT exercise on a hemorheological parameter, the plasma viscosity. METHODS: Ten healthy male subjects (25.80(3.39) years) randomly performed either a HIT exercise protocol (2-min warm up at 8 km/h, 5 2-min bouts at 90% maximal heart rate, separated by 2-min at 8 km/h, finished with another 2-min period at 8 km/h) or an aerobic (AER) exercise (60’ running at 55% VO2max). Blood samples were drawn before and after exercise, and after 30-minute recovery. Plasma viscosity, hematocrit, fibrinogen, total proteins, triglycerides, total cholesterol and glucose levels were analyzed. Plasma volume loss was calculated from changes in hemoglobin and hematocrit. RESULTS: Plasma viscosity rose after HIT (p<0.05) but did not after AER (p>0.05) while hematocrit rose after both exercises. Plasma volume lowered more after HIT (-6.35(3.47) %) than after AER (-3.11(2.49) %) (p=0.045). Total-proteins (p<0.001), triglycerides (p=0.013), total-cholesterol (p<0.001) and glucose (p=0.001) concentrations increased after HIT. After AER exercise no statistically significant differences were found in plasma constituents concentrations (p>0.05). CONCLUSIONS: A session of low-volume HIT promotes a loss in plasma volume enough to cause a significant increment of plasma constituents concentrations and, therefore, a mild transient rise in plasma viscosity.