Sumi, D, Kojima, C, and Goto, K. Impact of endurance exercise in hypoxia on muscle damage, inflammatory and performance responses. J Strength Cond Res 32(4): 1053-1062, 2018-This study evaluated muscle damage and inflammatory and performance responses after high-intensity endurance exercise in moderate hypoxia among endurance athletes. Nine trained endurance athletes completed 2 different trials on different days: exercise under moderate hypoxia (H trial, FiO2 = 14.5%) and normoxia (N trial, FiO2 = 20.9%). They performed interval exercises (10 × 3-minute running at 95% of V[Combining Dot Above]O2max with 60-second of active rest at 60% of V[Combining Dot Above]O2max) followed by 30-minute of continuous running at 85% of V[Combining Dot Above]O2max under either hypoxic or normoxic conditions. Venous blood samples were collected 4 times: before exercise, 0, 60, and 120-minute after exercise. The time to exhaustion (TTE) during running at 90% of V[Combining Dot Above]O2max was also determined to evaluate endurance capacity 120-minute after the training session. The H trial induced a significantly greater exercise-induced elevation in the blood lactate concentration than did the N trial (p = 0.02), whereas the elevation in the exercise-induced myoglobin concentration (muscle damage marker) was significantly greater in the N trial than in the H trial (p = 0.005). There was no significant difference in plasma interleukin-6 (inflammatory marker) concentration between the H and N trials. The TTE was shorter in the N trial (613 ± 65 seconds) than in the H trial (783 ± 107 seconds, p = 0.02). In conclusion, among endurance athletes, endurance exercise under moderate hypoxic conditions did not facilitate an exercise-induced muscle damage response or cause a further reduction in the endurance capacity compared with equivalent exercise under normoxic conditions.

Iron is essential for providing oxygen to working muscles during exercise, and iron deficiency leads to decreased exercise capacity during endurance events. However, the mechanism of iron deficiency among endurance athletes remains unclear. In this study, we compared iron status between two periods involving different training regimens. Sixteen female long-distance runners participated. Over a seven-month period, fasting blood samples were collected during their regular training period (LOW; middle of February) and during an intensified training period (INT; late of August) to determine blood hematological, iron, and inflammatory parameters. Three-day food diaries were also assessed. Body weight and lean body mass did not differ significantly between LOW and INT, while body fat and body fat percentage were significantly lower in INT (p < 0.05). Blood hemoglobin, serum ferritin, total protein, and iron levels, total iron-binding capacity, and transferrin saturation did not differ significantly between the two periods. Serum hepcidin levels were significantly higher during INT than LOW (p < 0.05). Carbohydrate and iron intakes from the daily diet were significantly higher during INT than LOW (p < 0.05). In conclusion, an elevated hepcidin level was observed during an intensified training period in long-distance runners, despite an apparently adequate daily intake of iron.

BackgroundExercise-induced disturbance of acid-base balance and accumulation of extracellular potassium (K+) are suggested to elicit fatigue. Exercise under hypoxic conditions may augment exercise-induced alterations of these two factors compared with exercise under normoxia. In the present study, we investigated acid-base balance and potassium kinetics in response to exercise under moderate hypoxic conditions in endurance athletes.MethodsNine trained middle-to-long distance athletes [maximal oxygen uptake (VO2max) 57.2 ± 1.0 mL/kg/min] completed two different trials on different days, consisting of exercise in moderate hypoxia [fraction of inspired oxygen (FiO2) = 14.5%, H trial] and exercise in normoxia (FiO2 = 20.9%, N trial). They performed interval endurance exercise (8 × 4 min pedaling at 80% of VO2max alternated with 2-min intervals of active rest at 40% of VO2max) under hypoxic or normoxic conditions. Venous blood samples were obtained to determine blood lactate, pH, bicarbonate ion, and K+ concentrations before exercise, during exercise, and after exercise.ResultsThe blood lactate concentrations increased significantly with exercise in both trials. Exercise-induced blood lactate elevations were significantly greater in the N trial than in the H trial at all time points (P = 0.012). Bicarbonate ion concentrations (P = 0.001) and blood pH (P = 0.019) during exercise and post-exercise periods were significantly lower in the N trial than in the H trial. A significantly greater exercise-induced elevation in blood K+ concentration was produced in the N trial than in the H trial during exercise and immediately after exercise (P = 0.03).ConclusionsHigh-intensity interval exercise on a cycle ergometer under moderate hypoxic conditions did not elicit a decrease in blood pH or elevation in K+ levels compared with an equivalent level of exercise under normoxic conditions.

Purpose To investigate the carbohydrate metabolism, acid–base balance, and potassium kinetics in response to exercise in moderate hypoxia among endurance athletes. Methods Nine trained endurance athletes [maximal oxygen uptake (VO 2max ): 62.5 ± 1.2 mL/kg/min] completed two different trials on different days: either exercise in moderate hypoxia [fraction of inspired oxygen (FiO 2 ) = 14.5%, HYPO] or exercise in normoxia (FiO 2 = 20.9%, NOR). They performed a high-intensity interval-type endurance exercise consisting of 10 × 3 min runs at 90% of VO 2max with 60 s of running (active rest) at 50% of VO 2max between sets in hypoxia (HYPO) or normoxia (NOR). Venous blood samples were obtained before exercise and during the post-exercise. The subjects consumed 13 C-labeled glucose immediately before exercise, and we collected expired gas samples during exercise to determine the 13 C-excretion (calculated as 13 CO 2 / 12 CO 2 ). Results The running velocities were significantly lower in HYPO (15.0 ± 0.2 km/h) than in NOR (16.4 ± 0.3 km/h, P < 0.0001). Despite the lower running velocity, we found a significantly greater exercise-induced blood lactate elevation in HYPO compared with in NOR ( P = 0.002). The bicarbonate ion concentration ( P = 0.002) and blood pH ( P = 0.002) were significantly lower in HYPO than in NOR. There were no significant differences between the two trials regarding the exercise-induced blood potassium elevation ( P = 0.87) or 13 C-excretion (HYPO, 0.21 ± 0.02 mmol⋅39 min; NOR, 0.14 ± 0.03 mmol⋅39 min; P = 0.10). Conclusion Endurance exercise in moderate hypoxia elicited a decline in blood pH. However, it did not augment the exercise-induced blood K + elevation or exogenous glucose oxidation ( 13 C-excretion) compared with the equivalent exercise in normoxia among endurance athletes. The findings suggest that endurance exercise in moderate hypoxia causes greater metabolic stress and similar exercise-induced elevation of blood K + and exogenous glucose oxidation compared with the same exercise in normoxia, despite lower mechanical stress (i.e., lower running velocity).

The present study was designed to determine the effect of 5 consecutive days of repeated sprint training under hypoxia on anaerobic performance and energy substances. Nineteen male sprinters performed repeated sprints for 5 consecutive days under a hypoxic (HYPO; fraction of inspired oxygen [FO], 14.5%) or normoxic (NOR; FO, 20.9%) condition. Before and after the training period, 10-s maximal sprint, repeated sprint ability (5×6-s sprints), 30-s maximal sprint, and maximal oxygen uptake (VO) tests were conducted. Muscle glycogen and PCr contents were evaluated using carbon magnetic resonance spectroscopy (C-MRS) and phosphorus magnetic resonance spectroscopy (P-MRS), respectively. The HYPO group showed significant increases in power output during the 10-s maximal sprint (P=0.004) and repeated sprint test (P=0.004), whereas the NOR group showed no significant change after the training period. Muscle glycogen and PCr contents increased significantly in both groups (P<0.05, respectively). However, relative increases were not significantly different between groups. These findings indicated that 5 consecutive days of repeated sprint training under hypoxic conditions increased maximal power output in competitive sprinters. Furthermore, short-term sprint training significantly augmented muscle glycogen and PCr contents with little added benefit from training in hypoxia.