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The effect of endurance interval training (IT) on hematocrit (Ht), hemoglobin (Hb), and estimated plasma-volume variation (PVV) in response to maximal exercise was studied in 15 male subjects (21.1 ± 1.1 y; control group n = 6, and training group, n = 9). The training group participated in interval training 3 times a week for 7 wk. A maximal graded test (GXT) was performed to determine maximal aerobic power (MAP) and maximal aerobic speed (MAS) both before and after the training program. To determine Ht, Hb concentration, and lactate concentrations, blood was collected at rest, at the end of GXT, and after 10 and 30 min of recovery. MAP and MAS increased significantly (P < .05) after training only in training group. Hematocrit determined at rest was significantly lower in the training group than in the control group after the training period (P < .05). IT induced a significant increase of estimated PVV at rest for training group (P < .05), whereas there were no changes for control group. Hence, significant relationships were observed after training between PVV determined at the end of the maximal test and MAS (r = .60, P < .05) and MAP (r = .76, P < .05) only for training group. In conclusion, 7 wk of IT led to a significant increase in plasma volume that possibly contributed to the observed increase of aerobic fitness (MAP and MAS).

Ben Abderrahman, Prioux, and Zouhal are with the Movement, Sport, and Health Sciences Laboratory, Rennes 2 University, Rennes, France. Chamari is with “Sport Performance Optimization,” National Center of Medicine and Science in Sport, Tunis, Tunisia. Ben Ounis and Tabka are with the Laboratory of Cardiovascular, Respiratory, Metabolic, and Hormonal Adaptations to Muscle Exercise, Faculty of Medicine Ibn El Jazzar, Sousse, Tunisia.