BackgroundThis study determined the effect of repeated sprint training in hypoxia (RSH) in female athletes.MethodsThirty-two college female athletes performed repeated cycling sprints of two sets of 10 × 7-s sprints with a 30-s rest between sprints twice per week for 4 weeks under either normoxic conditions (RSN group; FiO2, 20.9%; n = 16) or hypoxic conditions (RSH group; FiO2, 14.5%; n = 16). The repeated sprint ability (10 × 7-s sprints) and maximal oxygen uptake () were determined before and after the training period.ResultsAfter training, when compared to pre-values, the mean power output was higher in all sprints during the repeated sprint test in the RSH group but only for the second half of the sprints in the RSN group (P ≤ 0.05). The percentage increases in peak and mean power output between before and after the training period were significantly greater in the RSH group than in the RSN group (peak power output, 5.0 ± 0.7% vs. 1.5 ± 0.9%, respectively; mean power output, 9.7 ± 0.9% vs. 6.0 ± 0.8%, respectively; P < 0.05). did not change significantly after the training period in either group.ConclusionFour weeks of RSH further enhanced the peak and mean power output during repeated sprint test compared with RSN.

PurposeThis study aimed to examine the effect of applying BFR during rest periods of repeated cycling sprints on muscle oxygenation.MethodsSeven active males performed 5 × 10-s maximal pedaling efforts with 40-s passive rest, with or without BFR application during rest period. BFR was applied for 30 s between sprints (between 5 and 35 s into rest) through a pneumatic pressure cuff inflated at 140 mmHg. Vastus lateralis muscle oxygenation was monitored using near-infrared spectroscopy. In addition, blood lactate concentration and heart rate were also evaluated.ResultsThe BFR trial showed significantly lower oxyhemoglobin (oxy-Hb) and tissue saturation (StO2) levels than the CON trial (P &lt; 0.05). However, power output and blood lactate concentration did not significantly differ between the two trials (P &gt; 0.05).ConclusionApplying BFR during rest periods of repeated cycling sprints decreased muscle oxygenation of active musculature, without interfering with power output during sprints.

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.