Abstract
[Purpose]Hemodynamic function is a parameter indicating oxygen delivery and utilization capacity and is an important determinant of exercise performance. The present study aimed to determine whether intermittent hypoxic training (IHT) ameliorates hemodynamic function and exercise performance in competitive swimmers.[Methods]Twenty competitive swimmers (10 men, 10 women) volunteered to participate in the study. Participants were divided into the normoxic training (NT) group and the hypoxic training (HT) group and were subjected to training in a simulated altitude of 3000 m. We evaluated hemodynamic function profiles over 30 min of submaximal exercise on a bicycle and exercise performance before and after 6 weeks of training, which involved continuous exercise at 80% maximal heart rate (HRmax) for 30 min and interval exercise at 90% of HRmax measured before training for 30 min (ten rounds comprising 2 min of exercise followed by 1 min of rest each round).[Results]Significant changes in oxygen consumption (decrease) and end-diastolic volume (increase) were observed only in the HT group. Heart rate (HR), cardiac output (CO), and ejection fraction (EF) were significantly reduced in both groups, but the reduction rates of HR and CO were greater in the HT group than in the NT group. Exercise performance measures, including maximal oxygen consumption and 400-m time trial, were significantly increased only in the HT group.[Conclusion]Our findings suggested that 6 weeks of IHT, which involved high-intensity continuous and interval exercise, can effectively improve exercise performance by enhancing hemodynamic function in competitive swimmers.
Highlights
Since the Olympic Games were held at a high altitude in Mexico City in 1968, the usefulness of exercise training at altitude or under hypoxia for the enhancement of athletic performance has received considerable attention among athletes, coaches, and sports scientists[1,2]
Athletic performance is related to various parameters that can be altered by diversiform training methods at high altitude or under hypoxic conditions; these parameters include erythropoiesis, exercise economy, capillary density, hemodynamic function, and acid-base response in skeletal muscles[2,3]
The intermittent hypoxic training (IHT) does not improve exercise performance by increasing oxygen transportation capacity via erythropoiesis, which is characterized by increased red cell count and hemoglobin mass[7]
Summary
Since the Olympic Games were held at a high altitude in Mexico City in 1968, the usefulness of exercise training at altitude or under hypoxia for the enhancement of athletic performance has received considerable attention among athletes, coaches, and sports scientists[1,2]. Athletic performance is related to various parameters that can be altered by diversiform training methods at high altitude or under hypoxic conditions; these parameters include erythropoiesis, exercise economy, capillary density, hemodynamic function, and acid-base response in skeletal muscles[2,3]. Intermittent hypoxic training (IHT) using artificial equipment has become an increasingly popular altitude/hypoxic practice; in this method, athletes live at or near sea level but undergo at training at 2,000 to 3,000 m to simulate hypobaric or normobaric hypoxic conditions[3,4,5]. Very interestingly, previous studies suggested that short-term exposure to hypoxic conditions combined with high-intensity exercise training improves athletic performance by enhancing the metabolic (i.e. blood lactate level, glycolytic enzyme and glucose transport, and acid-base regulation) and oxygen utilization capacity[2,4,7,8].
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