Abstract
Intense exercise training can induce low concentrations of hemoglobin, which may be followed by maladaptation. Therefore, it is important for athletes to prevent low concentrations of hemoglobin during intense exercise training. In this study, we explored whether different protocols of intermittent hypoxic exposure (IHE, normobaric hypoxia, 14.5% O2) could prevent the exercise training-induced reduction in hemoglobin concentration in rats. Six-week-old male Sprague-Dawley rats were subjected to progressive intense treadmill exercise training over three weeks followed by three weeks of training with IHE after exercise. IHE lasted either 1 h, 2 h, or 1 h + 1 h (separated by a 3-h interval) after the exercise sessions. Hematological parameters, including hemoglobin concentration [(Hb)], red blood cells (RBCs), and hematocrit (Hct), and both renal and serum erythropoietin (EPO) were examined. We found that intense exercise training significantly reduced [Hb], RBCs, Hct, food intake and body weight (P < 0.01). Analysis of reticulocyte hemoglobin content (CHr) and reticulocyte counts in the serum of the rats suggested that this reduction was not due to iron deficiency or other cofounding factors. The addition of IHE after the intense exercise training sessions significantly alleviated the reduction in [Hb], RBCs, and Hct (P < 0.05) without an obvious impact on either food intake or body weight (P > 0.05). Increase in reticulocyte count in the rats from the IHE groups (P < 0.05 or P < 0.01) suggests that IHE promotes erythropoiesis to increase the hemoglobin concentration. Furthermore, the addition of IHE after the intense exercise training sessions also significantly increased the concentration of renal EPO (P < 0.05), although the increase of the serum EPO level was statistically insignificant (P > 0.05). The different IHE protocols were similarly effective at increasing renal EPO and preventing the training-induced decreases in [Hb], RBCs, and Hct. Collectively, this study suggests that IHE may be used as a new strategy to prevent intense exercise training-induced reductions in [Hb], and deserves future exploration in athletes.
Highlights
Sport training is a process of carefully applied stress-adaptation (Lorenz and Morrison, 2015; Haugen et al, 2019)
From the second week, the average daily food intake of rats in the exercise control (EC) group was significantly lower than that in the sedentary control (SC) group (P < 0.01) (Table 1); from the 3nd week, the body weight of rats in the EC group was significantly lower than that in the SC group (P < 0.05, Table 2). These data suggested that the food intake and body weight of the rats in the EC group could have been affected by low concentrations of hemoglobin
To exclude the possibility that low concentrations of hemoglobin in the EC group was caused by cofounding factors such as water intake or manipulation stress, the reticulocyte counts of the rats which can reflects the erythropoietic activity of the bone marrow were examined (Cline and Berlin, 1963; Riley et al, 2001)
Summary
Sport training is a process of carefully applied stress-adaptation (Lorenz and Morrison, 2015; Haugen et al, 2019). Providing stress at the optimal level that an athlete can endure will lead to improvements in physical function and performance (Lorenz and Morrison, 2015; Haugen et al, 2019). Seeking appropriate monitoring, nutritional, and rehabilitation strategies during periods of intense exercise training is critical to help athletes to avoid excessive stress, and to improve physical function and performance. It has been accepted that a 10% decrease in hemoglobin concentration [(Hb)] can be a practical indicator to predict maladaptation caused by intense exercise training, this state can result from plasma dilution, which frequently occurs early in prolonged training process (Zhao, 2003; Sheng, 2006). It is important to avoid low concentrations of hemoglobin by promoting the synthesis of Hb through appropriate strategies
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