Inter-individual variability in peripheral oxygen saturation and repeated sprint performance in hypoxia: an observational study of highly-trained subjects.

Individual variations in peripheral oxygen saturation (SpO2) during repeated sprints in hypoxia and their impact on exercise performance remain unclear despite fixed external hypoxic stimuli (inspired oxygen fraction: FiO2). This study examined SpO2 individual variations during repeated sprints in hypoxia and their impact on exercise performance. Thirteen highly-trained sprint runners performed 10 × 10-s cycle sprints with 30-s passive recoveries in normobaric hypoxia (FiO2: 0.150). Mean power output (MPO), post-sprint SpO2, and heart rate for each sprint were assessed. Sprint decrement score (Sdec), evaluating fatigue development, was calculated using MPO variables. Participants were categorized into a high saturation group (HiSat, n = 7) or a low saturation group (LowSat, n = 6) based on their mean post-sprint SpO2 (measured 10-15 s after each sprint). Individual mean post-sprint SpO2 ranged from 91.6% to 82.2%. Mean post-sprint SpO2 was significantly higher (P < 0.001, d = 1.54) in HiSat (89.1% ± 1.5%) than LowSat (84.7% ± 1.6%). A significantly larger decrease in Sdec (P = 0.008, d = 1.68) occurred in LowSat (-22.3% ± 2.3%) compared to HiSat (-17.9% ± 2.5%). MPO (P = 0.342 d = 0.55) and heart rate (P = 0.225 d = 0.67) did not differ between groups. There was a significant correlation (r = 0.61; P = 0.028) between SpO2 and Sdec. In highly-trained sprint runners, individual responses to hypoxia varied widely and significantly affected repeated sprint ability, with greater decreases in SpO2 associated with larger performance alterations (i.e., larger decrease in Sdec).

Differential patterns of sweat and blood lactate concentration response during incremental exercise in varied ambient temperatures: A pilot study.

Blood lactate concentration during exercise is a reliable indicator of energy metabolism and endurance performance. Lactate is also present in sweat, and sweating plays an important role in thermoregulation, especially in hot conditions. Recently, wearable sensors have enabled the real-time and noninvasive measurement of sweat lactate concentration, potentially serving as an alternative indicator of blood lactate response. However, the evidence regarding the relationship between sweat and blood lactate responses during incremental exercise in hot conditions is lacking. In a randomized cross-over design, six highly trained male runners completed two incremental treadmill tests under normal (20°C/50%RH) or hot (30°C/50%RH) conditions. The tests include 3-min running stages and 1-min recovery, starting at 12 km/h and increasing by 1 km/h at each stage. Blood and sweat lactate concentrations were measured at each stage to determine blood and sweat lactate thresholds (LT). Blood lactate concentrations were higher under hot conditions (p < 0.01), but there was no difference in the response pattern or velocity at blood LT between conditions. Significant early increase (p < 0.01) in sweat lactate and low velocity at sweat LT (p < 0.05) were observed under hot conditions. A significant correlation between blood and sweat lactate concentrations was found under normal conditions (p < 0.001) but not under hot conditions, and no significant correlations were observed between the velocity at blood and sweat LT. In conclusion, sweat lactate concentration does not consistently reflect blood lactate concentration during incremental exercise.

Performance, Metabolic, and Neuromuscular Consequences of Repeated Wingates in Hypoxia and Normoxia: A Pilot Study.

BACKGROUND: Compared with normoxia, repeated short (5-10 s) sprints (>10 efforts) with incomplete recovery (≤30 s) in hypoxia likely cause substantial performance reduction accompanied by larger metabolic disturbances and magnitude of neuromuscular fatigue. However, the effects of hypoxia on performance of repeated long (30 s) "all-out" efforts with near complete recovery (4.5 min) and resulting metabolic and neuromuscular adjustments remain unclear. PURPOSE: The intention was to compare acute performance, metabolic, and neuromuscular responses across repeated Wingates between hypoxia and normoxia. METHODS: On separate visits, 6 male participants performed 4 × 30-second Wingate efforts with 4.5-minute recovery in either hypoxia (fraction of inspired oxygen: 0.145) or normoxia. Responses to exercise (muscle and arterial oxygenation trends, heart rate, and blood lactate concentration) and the integrity of neuromuscular function in the knee extensors were assessed for each exercise bout. RESULTS: Mean (P = .80) and peak (P = .92) power outputs, muscle oxygenation (P = .88), blood lactate concentration (P = .72), and perceptual responses (all Ps > .05) were not different between conditions. Arterial oxygen saturation was significantly lower, and heart rate higher, in hypoxia versus normoxia (P < .001). Maximal voluntary contraction force and peripheral fatigue indices (peak twitch force and doublets at low and high frequencies) decreased across efforts (all Ps < .001) irrespective of conditions (all Ps > .05). CONCLUSION: Despite heightened arterial hypoxemia and cardiovascular solicitation, hypoxic exposure during 4 repeated 30-second Wingate efforts had no effect on performance and accompanying metabolic and neuromuscular adjustments.

No Influence of Acute Moderate Normobaric Hypoxia on Performance and Blood Lactate Concentration Responses to Repeated Wingates.

BACKGROUND: Training in hypoxia versus normoxia often induces larger physiological adaptations, while this does not always translate into additional performance benefits. A possible explanation is a reduced oxygen flux, negatively affecting training intensity and/or volume (decreasing training stimulus). Repeated Wingates (RW) in normoxia is an efficient training strategy for improving both physiological parameters and exercise capacity. However, it remains unclear whether the addition of hypoxia has a detrimental effect on RW performance. PURPOSE: To test the hypothesis that acute moderate hypoxia exposure has no detrimental effect on RW, while both metabolic and perceptual responses would be slightly higher. METHODS: On separate days, 7 male university sprinters performed 3 × 30-s Wingate efforts with 4.5-min passive recovery in either hypoxia (FiO2: 0.145) or normoxia (FiO2: 0.209). Arterial oxygen saturation was assessed before the first Wingate effort, while blood lactate concentration and ratings of perceived exertion were measured after each bout. RESULTS: Mean (P = .92) and peak (P = .63) power outputs, total work (P = .98), and the percentage decrement score (P = .25) were similar between conditions. Arterial oxygen saturation was significantly lower in hypoxia versus normoxia (92.0% [2.8%] vs 98.1% [0.4%], P < .01), whereas blood lactate concentration (P = .78) and ratings of perceived exertion (P = .51) did not differ between conditions. CONCLUSION: In sprinters, acute exposure to moderate hypoxia had no detrimental effect on RW performance and associated metabolic and perceptual responses.

Short-Term Repeated Wingate Training in Hypoxia and Normoxia in Sprinters.

Repeated Wingate efforts (RW) represent an effective training strategy for improving exercise capacity. Living low-training high altitude/hypoxic training methods, that upregulate muscle adaptations, are increasingly popular. However, the benefits of RW training in hypoxia compared to normoxia on performance and accompanying physiological adaptations remain largely undetermined. Our intention was to test the hypothesis that RW training in hypoxia provides additional performance benefits and more favorable physiological responses than equivalent training in normoxia. Twelve male runners (university sprinters) completed six RW training sessions (3 × 30-s Wingate "all-out" efforts with 4.5-min recovery) in either hypoxia (FiO2: 0.145, n = 6) or normoxia (FiO2: 0.209, n = 6) over 2 weeks. Before and after the intervention, participants underwent a RW performance test (3 × 30-s Wingate "all-out" efforts with 4.5-min recovery). Peak power output, mean power output, and total work for the three exercise bouts were determined. A capillary blood sample was taken for analyzing blood lactate concentration (BLa) 3 min after each of the three efforts. Peak power output (+ 11.3 ± 23.0%, p = 0.001), mean power output (+ 6.6 ± 6.8%, p = 0.001), and total work (+ 6.3 ± 5.4% p = 0.016) significantly increased from pre- to post-training, independently of condition. The time × group × interval interaction was significant (p = 0.05) for BLa. Compared to Pre-tests, BLa values during post-test were higher (+ 8.7 ± 10.3%) after about 2 in the normoxic group, although statistical significance was not reached (p = 0.08). Contrastingly, BLa values were lower (albeit not significantly) during post- compared to pre-tests after bout 2 (-9.3 ± 8.6%; p = 0.08) and bout 3 (-9.1 ± 10.7%; p = 0.09) in the hypoxic group. In conclusion, six RW training sessions over 2 weeks significantly improved RW performance, while training in hypoxia had no additional benefit over normoxia. However, accompanying BLa responses tended to be lower in the hypoxic group, while an opposite pattern was observed in the normoxic group. This indicates that different glycolytic and/or oxidative pathway adaptations were probably at play.

Palladium-catalyzed highly regio- and stereoselective synthesis of 4-alkylidene-4H-3,1-benzoxazines from N-acyl-o-alkynylanilines.

The highly regio- and stereoselective 6-exo-dig mode cyclization of N-acyl-o-alkynylanilines producing 4-alkylidene-3,1-benzoxazines occurred unpredictably by use of a proper catalyst [Pd(OAc)(2)] and an effective additive (acetic acid) under suitable reaction conditions.