Muscle oxygenation maintained during repeated-sprints despite inspiratory muscle loading

A high work of breathing can compromise limb oxygen delivery during sustained high-intensity exercise. However, it is unclear if the same is true for intermittent sprint exercise. This project examined the effect of adding an inspiratory load on locomotor muscle tissue reoxygenation during repeated-sprint exercise. Ten healthy males completed three experiment sessions of ten 10-s sprints, separated by 30-s of passive rest on a cycle ergometer. The first two sessions were “all-out’ efforts performed without (CTRL) or with inspiratory loading (INSP) in a randomised and counterbalanced order. The third experiment session (MATCH) consisted of ten 10-s work-matched intervals. Tissue saturation index (TSI) and deoxy-haemoglobin (HHb) of the vastus lateralis and sixth intercostal space was monitored with near-infrared spectroscopy. Vastus lateralis reoxygenation (ΔReoxy) was calculated as the difference from peak HHb (sprint) to nadir HHb (recovery). Total mechanical work completed was similar between INSP and CTRL (effect size: -0.18, 90% confidence limit ±0.43), and differences in vastus lateralis TSI during the sprint (-0.01 ±0.33) and recovery (-0.08 ±0.50) phases were unclear. There was also no meaningful difference in ΔReoxy (0.21 ±0.37). Intercostal HHb was higher in the INSP session compared to CTRL (0.42 ±0.34), whilst the difference was unclear for TSI (-0.01 ±0.33). During MATCH exercise, differences in vastus lateralis TSI were unclear compared to INSP for both sprint (0.10 ±0.30) and recovery (-0.09 ±0.48) phases, and there was no meaningful difference in ΔReoxy (-0.25 ±0.55). Intercostal TSI was higher during MATCH compared to INSP (0.95 ±0.53), whereas HHb was lower (-1.09 ±0.33). The lack of difference in ΔReoxy between INSP and CTRL suggests that for intermittent sprint exercise, the metabolic O₂ demands of both the respiratory and locomotor muscles can be met. Additionally, the similarity of the MATCH suggests that ΔReoxy was maximal in all exercise conditions.

Respiratory muscle oxygenation is not impacted by hypoxia during repeated-sprint exercise

This study aimed to investigate whether exercise hyperpnoea contributes to an impairment of locomotor muscle oxygenation and performance during repeated-sprint exercise in normoxia and hypoxia. Subjects performed ten 10-s sprints, separated by 30 s of passive rest while breathing either a normoxic (21% O₂) or hypoxic (15% O₂) gas mixture. Muscle oxygenation of the vastus lateralis and intercostal muscles was examined with near-infrared spectroscopy. Sprint and recovery vastus lateralis deoxyhaemoglobin was elevated in hypoxia by 9.2% (90% confidence interval 0.2 to 18.0) and 14.1% (90% CL 4.9 to 23.3%) compared to normoxia, respectively. There were no clear differences in respiratory muscle deoxyhaemoglobin (-0.1%, 90% CL -2.9 to 0.9%) or oxyhaemoglobin (0.9%, 90% CL -0.8 to 2.6%) between conditions. Maintenance of respiratory muscle oxygenation may contribute to the rise of vastus lateralis deoxyhaemoglobin in hypoxia during intermittent sprint cycling. This manuscript presents data which extends the fact that oxygen competition could be a limiting factor of exercise capacity.

Influence of averaging method on muscle deoxygenation interpretation during repeated-sprint exercise

Near-infrared spectroscopy (NIRS) is a common tool used to study oxygen availability and utilization during repeated-sprint exercise. However, there are inconsistent methods of smoothing and determining peaks and nadirs from the NIRS signal, which make interpretation and comparisons between studies difficult. To examine the effects of averaging method on deoxyhaemoglobin concentration ([HHb]) trends, nine males performed ten 10-s sprints, with 30 seconds of recovery, and six analysis methods were used for determining peaks and nadirs in the [HHb] signal. First, means were calculated over predetermined windows in the last 5 and 2 seconds of each sprint and recovery period. Second, moving 5-seconds and 2-seconds averages were also applied, and peaks/nadirs were determined for each 40-seconds sprint/recovery cycle. Third, a Butterworth filter was used to smooth the signal, and the resulting signal output was used to determine peaks and nadirs from predetermined time points and a rolling approach. Correlation and residual analysis showed that the Butterworth filter attenuated the "noise" in the signal, while maintaining the integrity of the raw data (r = .9892; mean standardized residual -9.71 × 10³  ± 3.80). Means derived from predetermined windows, irrespective of length and data smoothing, underestimated the magnitude of peak and nadir [HHb] compared to a rolling mean approach. Consequently, sprint-induced metabolic changes (inferred from Δ[HHb]) were underestimated. Based on these results, we suggest using a digital filter to smooth NIRS data, rather than an arithmetic mean, and a rolling approach to determine peaks and nadirs for accurate interpretation of muscle oxygenation trends.

The Critical Power Model as a Potential Tool for Anti-doping

Existing doping detection strategies rely on direct and indirect biochemical measurement methods focused on detecting banned substances, their metabolites, or biomarkers related to their use. However, the goal of doping is to improve performance, and yet evidence from performance data is not considered by these strategies. The emergence of portable sensors for measuring exercise intensities and of player tracking technologies may enable the widespread collection of performance data. How these data should be used for doping detection is an open question. Herein, we review the basis by which performance models could be used for doping detection, followed by critically reviewing the potential of the critical power (CP) model as a prototypical performance model that could be used in this regard. Performance models are mathematical representations of performance data specific to the athlete. Some models feature parameters with physiological interpretations, changes to which may provide clues regarding the specific doping method. The CP model is a simple model of the power-duration curve and features two physiologically interpretable parameters, CP and W′. We argue that the CP model could be useful for doping detection mainly based on the predictable sensitivities of its parameters to ergogenic aids and other performance-enhancing interventions. However, our argument is counterbalanced by the existence of important limitations and unresolved questions that need to be addressed before the model is used for doping detection. We conclude by providing a simple worked example showing how it could be used and propose recommendations for its implementation.

Prediction of Critical Power and W' in Hypoxia: Application to Work-Balance Modelling

Purpose: Develop a prediction equation for critical power (CP) and work above CP (W′) in hypoxia for use in the work-balance (WBAL′) model.

Methods: Nine trained male cyclists completed cycling time trials (TT; 12, 7, and 3 min) to determine CP and W′ at five altitudes (250, 1,250, 2,250, 3,250, and 4,250 m). Least squares regression was used to predict CP and W′ at altitude. A high-intensity intermittent test (HIIT) was performed at 250 and 2,250 m. Actual and predicted CP and W′ were used to compute W′ during HIIT using differential (WBALdiff′) and integral (WBALint′) forms of the WBAL′ model.

Results: CP decreased at altitude (P < 0.001) as described by 3rd order polynomial function (R² = 0.99). W′ decreased at 4,250 m only (P < 0.001). A double-linear function characterized the effect of altitude on W′ (R² = 0.99). There was no significant effect of parameter input (actual vs. predicted CP and W′) on modelled WBAL′ at 2,250 m (P = 0.24). WBALdiff′ returned higher values than WBALint′ throughout HIIT (P < 0.001). During HIIT, WBALdiff′ was not different to 0 kJ at completion, at 250 m (0.7 ± 2.0 kJ; P = 0.33) and 2,250 m (−1.3 ± 3.5 kJ; P = 0.30). However, WBALint′ was lower than 0 kJ at 250 m (−0.9 ± 1.3 kJ; P = 0.058) and 2,250 m (−2.8 ± 2.8 kJ; P = 0.02).

Conclusion: The altitude prediction equations for CP and W′ developed in this study are suitable for use with the WBAL′ model in acute hypoxia. This enables the application of WBAL′ modelling to training prescription and competition analysis at altitude.

Ventilatory acclimatisation is beneficial for high-intensity exercise at altitude in elite cyclists

AIM

The aim of this study was to examine the relationship between ventilatory adaptation and performance during altitude training at 2700 m.

METHODS

Seven elite cyclists (age: 21.2 ± 1.1 yr, body mass: 69.9 ± 5.6 kg, height 176.3 ± 4.9 cm) participated in this study. A hypoxic ventilatory response (HVR) test and a submaximal exercise test were performed at sea level prior to the training camp and again after 15 d at altitude (ALT15). Ventilation (VE), end-tidal carbon-dioxide partial pressure (PETCO2) and oxyhaemoglobin saturation via pulse oximetry (SpO2) were measured at rest and during submaximal cycling at 250 W. A hill climb (HC) performance test was conducted at sea level and after 14 d at altitude (ALT14) using a road of similar length (5.5-6 km) and gradient (4.8-5.3%). Power output was measured using SRM cranks. Average HC power at ALT14 was normalised to sea level power (HC%). Multiple regression was used to identify significant predictors of performance at altitude.

RESULTS

At ALT15, there was a significant increase in resting VE (10.3 ± 1.9 vs. 12.2 ± 2.4 L·min(-1)) and HVR (0.34 ± 0.24 vs. 0.71 ± 0.49 L·min(-1)·%(-1)), while PETCO2 (38.4 ± 2.3 vs. 32.1 ± 3.3 mmHg) and SpO2 (97.9 ± 0.7 vs. 94.0 ± 1.7%) were reduced (P < .05). Multiple regression revealed ΔHVR and exercise VE at altitude as significant predictors of HC% (adjusted r(2) = 0.913; P = 0.003).

CONCLUSIONS

Ventilatory acclimatisation occurred during a 2 wk altitude training camp in elite cyclists and a higher HVR was associated with better performance at altitude, relative to sea level. These results suggest that ventilatory acclimatisation is beneficial for cycling performance at altitude.

The effect of intermittent hypobaric hypoxic exposure and sea level training on submaximal economy in well-trained swimmers and runners

To evaluate the effect of intermittent hypobaric hypoxia combined with sea level training on exercise economy, 23 well-trained athletes (13 swimmers, 10 runners) were assigned to either hypobaric hypoxia (simulated altitude of 4,000-5,500 m) or normobaric normoxia (0-500 m) in a randomized, double-blind design. Both groups rested in a hypobaric chamber 3 h/day, 5 days/wk for 4 wk. Submaximal economy was measured twice before (Pre) and after (Post) the treatment period using sport-specific protocols. Economy was estimated both from the relationship between oxygen uptake (V(.-)o2) and speed, and from the absolute V(.-)o2 at each speed using sport-specific protocols. V(.-)o2 was measured during the last 60 s of each (3-4 min) stage using Douglas bags. Ventilation (V(.-)E), heart rate (HR), and capillary lactate concentration ([La(-)]) were measured during each stage. Velocity at maximal V(.-)o2 (velocity at V(.-)o2max) was used as a functional indicator of changes in economy. The average V(.-)o2 for a given speed of the Pre values was used for Post test comparison using a two-way, repeated-measures ANOVA. Typical error of measurement of V(.-)o2 was 4.7% (95% confidence limits 3.6-7.1), 3.6% (2.8-5.4), and 4.2% (3.2-6.9) for speeds 1, 2, and 3, respectively. There was no change in economy within or between groups (ANOVA interaction P = 0.28, P = 0.23, and P = 0.93 for speeds 1, 2, and 3). No differences in submaximal HR, [La-], Ve, or velocity at V(.-)o2(max) were found between groups. It is concluded that 4 wk of intermittent hypobaric hypoxia did not improve submaximal economy in this group of well-trained athletes.

Performance of runners and swimmers after four weeks of intermittent hypobaric hypoxic exposure plus sea level training

This double-blind, randomized, placebo-controlled trial examined the effects of 4 wk of resting exposure to intermittent hypobaric hypoxia (IHE, 3 h/day, 5 days/wk at 4,000-5,500 m) or normoxia combined with training at sea level on performance and maximal oxygen transport in athletes. Twenty-three trained swimmers and runners completed duplicate baseline time trials (100/400-m swims, or 3-km run) and measures for maximal oxygen uptake (VO(2max)), ventilation (VE(max)), and heart rate (HR(max)) and the oxygen uptake at the ventilatory threshold (VO(2) at VT) during incremental treadmill or swimming flume tests. Subjects were matched for sex, sport, performance, and training status and divided randomly between hypobaric hypoxia (Hypo, n = 11) and normobaric normoxia (Norm, n = 12) groups. All tests were repeated within the first (Post1) and third weeks (Post2) after the intervention. Time-trial performance did not improve in either group. We could not detect a significant difference between groups for a change in VO(2max), VE(max), HR(max), or VO(2) at VT after the intervention (group x test interaction P = 0.31, 0.24, 0.26, and 0.12, respectively). When runners and swimmers were considered separately, Hypo swimmers appeared to increase VO(2max) (+6.2%, interaction P = 0.07) at Post2 following a precompetition taper and increased VO(2) at VT (+8.9 and +12.1%, interaction P = 0.007 and 0.006, at Post1 and Post2). We conclude that this "dose" of IHE was not sufficient to improve performance or oxygen transport in this heterogeneous group of athletes. Whether there are potential benefits of this regimen for specific sports or training/tapering strategies may require further study.

Intermittent hypobaric hypoxia exposure does not cause sustained alterations in autonomic control of blood pressure in young athletes

Intermittent hypoxia (IH), which refers to the discontinuous use of hypoxia to reproduce some key features of altitude acclimatization, is commonly used in athletes to improve their performance. However, variations of IH are also used as a model for sleep apnea, causing sustained sympathoexcitation and hypertension in animals and, thus, raising concerns over the safety of this model. We tested the hypothesis that chronic IH at rest alters autonomic control of arterial pressure in healthy trained individuals. Twenty-two young athletes (11 men and 11 women) were randomly assigned to hypobaric hypoxia (simulated altitude of 4,000-5,500 m) or normoxia (500 m) in a double-blind and placebo-controlled design. Both groups rested in a hypobaric chamber for 3 h/day, 5 days/wk for 4 wk. In the sitting position, resting hemodynamics, including heart rate (HR), blood pressure (BP), cardiac output (Q(c), C(2)H(2) rebreathing), stroke volume (SV = Q(c)/HR), and total peripheral resistance (TPR = mean BP/Q(c)), were measured, dynamic cardiovascular regulation was assessed by spectral and transfer function analysis of cardiovascular variability, and cardiac-vagal baroreflex function was evaluated by a Valsalva maneuver, twice before and 3 days after the last chamber exposure. We found no significant differences in HR, BP, Q(c), SV, TPR, cardiovascular variability, or cardiac-vagal baroreflex function between the groups at any time. These results suggest that exposure to intermittent hypobaric hypoxia for 4 wk does not cause sustained alterations in autonomic control of BP in young athletes. In contrast to animal studies, we found no secondary evidence for sustained physiologically significant sympathoexcitation in this model.

Interspersed normoxia during live high, train low interventions reverses an early reduction in muscle Na+, K +ATPase activity in well-trained athletes

Hypoxia and exercise each modulate muscle Na(+), K(+)ATPase activity. We investigated the effects on muscle Na(+), K(+)ATPase activity of only 5 nights of live high, train low hypoxia (LHTL), 20 nights consecutive (LHTLc) versus intermittent LHTL (LHTLi), and acute sprint exercise. Thirty-three athletes were assigned to control (CON, n = 11), 20-nights LHTLc (n = 12) or 20-nights LHTLi (4 x 5-nights LHTL interspersed with 2-nights CON, n = 10) groups. LHTLc and LHTLi slept at a simulated altitude of 2,650 m (F(I)O(2) 0.1627) and lived and trained by day under normoxic conditions; CON lived, trained, and slept in normoxia. A quadriceps muscle biopsy was taken at rest and immediately after standardised sprint exercise, before (Pre) and after 5-nights (d5) and 20-nights (Post) LHTL interventions and analysed for Na(+), K(+)ATPase maximal activity (3-O-MFPase) and content ([(3)H]-ouabain binding). After only 5-nights LHTLc, muscle 3-O-MFPase activity declined by 2% (P < 0.05). In LHTLc, 3-O-MFPase activity remained below Pre after 20 nights. In contrast, in LHTLi, this small initial decrease was reversed after 20 nights, with restoration of 3-O-MFPase activity to Pre-intervention levels. Plasma [K(+)] was unaltered by any LHTL. After acute sprint exercise 3-O-MFPase activity was reduced (12.9 +/- 4.0%, P < 0.05), but [(3)H]-ouabain binding was unchanged. In conclusion, maximal Na(+), K(+)ATPase activity declined after only 5-nights LHTL, but the inclusion of additional interspersed normoxic nights reversed this effect, despite athletes receiving the same amount of hypoxic exposure. There were no effects of consecutive or intermittent nightly LHTL on the acute decrease in Na(+), K(+)ATPase activity with sprint exercise effects or on plasma [K(+)] during exercise.

Increased serum erythropoietin but not red cell production after 4 wk of intermittent hypobaric hypoxia (4,000-5,500 m)

This study tested the hypothesis that athletes exposed to 4 wk of intermittent hypobaric hypoxia exposure (3 h/day, 5 days/wk at 4,000-5,500 m) or double-blind placebo increase their red blood cell volume (RCV) and hemoglobin mass (Hbmass) secondary to an increase in erythropoietin (EPO). Twenty-three collegiate level athletes were measured before (Pre) and after (Post) the intervention for RCV via Evans blue (EB) dye and in duplicate for Hbmass using CO rebreathing. Hematological indexes including EPO, soluble transferrin receptor, and reticulocyte parameters were measured on 8-10 occasions spanning the intervention. The subjects were randomly divided among hypobaric hypoxia (Hypo, n = 11) and normoxic (Norm, n = 12) groups. Apart from doubling EPO concentration 3 h after hypoxia there was no increase in any of the measures for either Hypo or Norm groups. The mean change in RCV from Pre to Post for the Hypo group was 2.3% (95% confidence limits = -4.8 to 9.5%) and for the Norm group was -0.2% (-5.7 to 5.3%). The corresponding changes in Hbmass were 1.0% (-1.3 to 3.3%) for Hypo and -0.3% (-2.6 to 3.1%) for Norm. There was good agreement between blood volume (BV) from EB and CO: EB BV = 1.03 x CO BV + 142, r2 = 0.85, P < 0.0001. Overall, evidence from four independent techniques (RCV, Hbmass, reticulocyte parameters, and soluble transferrin receptor) suggests that intermittent hypobaric hypoxia exposure did not accelerate erythropoiesis despite the increase in serum EPO.

Sleep disturbance at simulated altitude indicated by stratified respiratory disturbance index but not hypoxic ventilatory response

At high altitudes, the clinically defined respiratory disturbance index (RDI) and high hypoxic ventilatory response (HVR) have been associated with diminished sleep quality. Increased RDI has also been observed in some athletes sleeping at simulated moderate altitude. In this study, we investigated relationships between the HVR of 14 trained male endurance cyclists with variable RDI and sleep quality responses to simulated moderate altitude. Blood oxygen saturation (SpO2%), heart rate, RDI, arousal rate, awakenings, sleep efficiency, rapid eye movement (REM) sleep, non-REM sleep stages 1, 2 and slow wave sleep as percentages of total sleep time (%TST) were measured for two nights at normoxia of 600 m and one night at a simulated altitude of 2,650 m. HVR and RDI were not significantly correlated with sleep stage, arousal rate or awakening response to nocturnal simulated altitude. SpO2 was inversely correlated with total RDI (r = -0.69, P = 0.004) at simulated altitude and with the change in arousal rate from normoxia (r = -0.65, P = 0.02). REM sleep response to simulated altitude correlated with the change, relative to normoxia, in arousal (r = -0.63, P = 0.04) and heart rate (r = -0.61, P = 0.04). When stratified, those athletes at altitude with RDI >20 h(-1) (n = 4) and those with <10 h(-1) (n = 10) exhibited no difference in HVR but the former had larger falls in SpO2 (P = 0.05) and more arousals (P = 0.03). Neither RDI (without stratification) nor HVR were sufficiently sensitive to explain any deterioration in REM sleep or arousal increase. However, the stratified RDI provides a basis for determining potential sleep disturbance in athletes at simulated moderate altitude.

Sleep in athletes undertaking protocols of exposure to nocturnal simulated altitude at 2650 m

A popular method to attempt to enhance performance is for athletes to sleep at natural or simulated moderate altitude (SMA) when training daily near sea level. Based on our previous observation of periodic breathing in athletes sleeping at SMA, we hypothesised that athletes' sleep quality would also suffer with hypoxia. Using two typical protocols of nocturnal SMA (2650 m), we examined the effect on the sleep physiology of 14 male endurance-trained athletes. The selected protocols were Consecutive (15 successive exposure nights) and Intermittent (3x 5 successive exposure nights, interspersed with 2 normoxic nights) and athletes were randomly assigned to follow either one. We monitored sleep for two successive nights under baseline conditions (B; normoxia, 600 m) and then at weekly intervals (nights 1, 8 and 15 (N1, N8 and N15, respectively)) of the protocols. Since there was no significant difference in response between the protocols being followed (based on n=7, for each group) we are unable to support a preference for either one, although the likelihood of a Type II error must be acknowledged. For all athletes (n=14), respiratory disturbance and arousal responses between B and N1, although large in magnitude, were highly individual and not statistically significant. However, SpO2 decreased at N1 versus B (p<0.001) and remained lower on N8 (p<0.001) and N15 (p<0.001), not returning to baseline level. Compared to B, arousals were more frequent on N8 (p=0.02) and N15 (p=0.01). The percent of rapid eye movement sleep (REM) increased from N1 to N8 (p=0.03) and N15 (p=0.01). Overall, sleeping at 2650 m causes sleep disturbance in susceptible athletes, yet there was some improvement in REM sleep over the study duration.

Hypoxic ventilatory response is correlated with increased submaximal exercise ventilation after live high, train low

This study tested the hypothesis that live high, train low (LHTL) would increase submaximal exercise ventilation (V(E)) in normoxia, and the increase would be related to enhanced hypoxic ventilatory response (HVR). Thirty-three cyclists/triathletes were divided into three groups: 20 consecutive nights of hypoxia (LHTLc, n = 12), 20 nights of intermittent hypoxia (4x5-night 'blocks' of hypoxia interspersed by two nights of normoxia, LHTLi, n = 10), or control (CON, n = 11). LHTLc and LHTLi slept 8-10 h per night in normobaric hypoxia (2,650 m), and CON slept under ambient conditions (600 m). Resting, isocapnic HVR (DeltaV(E)/Deltablood oxygen saturation) was measured in normoxia before (PRE) and after 15 nights (N15) hypoxia. Submaximal cycle ergometry was conducted PRE and after 4, 10, and 19 nights of hypoxia (N4, N10, and N19 respectively). Mean submaximal exercise V(E) was increased (P < 0.05) from PRE to N4 in LHTLc [74.4 (5.1) vs 80.0 (8.4) l min(-1); mean (SD)] and in LHTLi [69.0 (7.5) vs 76.9 (7.3) l min(-1)] and remained elevated in both groups thereafter, with no changes observed in CON at any time. Prior to LHTL, submaximal V(E) was not correlated with HVR, but this relationship was significant at N4 (r = 0.49, P = 0.03) and N19 (r = 0.77, P < 0.0001). Additionally, the increases in submaximal V(E) and HVR from PRE to N15-N19 were correlated (r = 0.51, P = 0.02) for the pooled data of LHTLc and LHTLi. These results suggest that enhanced hypoxic chemosensitivity contributes to increased exercise V(E) in normoxia following LHTL.

Effects of live high, train low hypoxic exposure on lactate metabolism in trained humans

We determined the effect of 20 nights of live high, train low (LHTL) hypoxic exposure on lactate kinetics, monocarboxylate lactate transporter proteins (MCT1 and MCT4), and muscle in vitro buffering capacity (βm) in 29 well-trained cyclists and triathletes. Subjects were divided into one of three groups: 20 consecutive nights of hypoxic exposure (LHTLc), 20 nights of intermittent hypoxic exposure [four 5-night blocks of hypoxia, each interspersed with 2 nights of normoxia (LHTLi)], or control (Con). Rates of lactate appearance (Ra), disappearance (Rd), and oxidation (Rox) were determined from a primed, continuous infusion of l-[U-14C]lactic acid tracer during 90 min of steady-state exercise [60 min at 65% peak O2 uptake (V̇o2 peak) followed by 30 min at 85% V̇o2 peak]. A resting muscle biopsy was taken before and after 20 nights of LHTL for the determination of βm and MCT1 and MCT4 protein abundance. Ra during the first 60 min of exercise was not different between groups. During the last 25 min of exercise at 85% V̇o2 peak, Ra was higher compared with exercise at 65% of V̇o2 peak and was decreased in LHTLc ( P < 0.05) compared with the other groups. Rd followed a similar pattern to Ra. Although Rox was significantly increased during exercise at 85% compared with 65% of V̇o2 peak, there were no differences between the three groups or across trials. There was no effect of hypoxic exposure on βm or MCT1 and MCT4 protein abundance. We conclude that 20 consecutive nights of hypoxia exposure decreased whole body Ra during intense exercise in well-trained athletes. However, muscle markers of lactate metabolism and pH regulation were unchanged by the LHTL intervention.

Changes in performance, maximal oxygen uptake and maximal accumulated oxygen deficit after 5, 10 and 15 days of live high:train low altitude exposure

Nineteen well-trained cyclists (14 males and 5 females, mean initial .VO(2max) 62.3 ml kg(-1 )min(-1)) completed a multistage cycle ergometer test to determine maximal mean power output in 4 min (MMPO(4min)), maximal oxygen uptake (.VO(2max)) and maximal accumulated oxygen deficit (MAOD). The athletes were divided into three groups, each of which completed 5, 10 or 15 days of both a control condition (C) and live high:train low altitude exposure (LHTL). The C groups lived and trained at the ambient altitude of 610 m. The LHTL groups spent 8-10 h night(-1) in normobaric hypoxia at a simulated altitude of 2,650 m, and trained at the ambient altitude of 610 m. The changes to MMPO(4min), .VO(2max) and MAOD in response to LHTL altitude exposure were not significantly different for the 5-, 10- and 15-day treatment periods. For the pooled data from all three treatment periods, there were significant increases in MMPO(4min) [mean (SD) 5.15 (0.83) W kg(-1) vs 5.34 (0.78) W kg(-1)] and MAOD [50.1 (14.2) ml kg(-1) vs 54.9 (13.1) ml kg(-1)] in the LHTL athletes between pre- and post-altitude exposure. There were no significant changes in MMPO(4min) [5.09 (0.76) W kg(-1) vs 5.16 (0.86) W kg(-1)] or MAOD [50.5 (14.1) ml kg(-1) vs 49.1 (13.0) ml kg(-1)] in the C athletes over the corresponding period. There were significant increases in .VO(2max) in the athletes during both the LHTL [63.2 (9.0) ml kg(-1 )min(-1) vs 64.1 (9.0) ml kg(-1 )min(-1)] and C [62.0 (8.6) ml kg(-1 )min(-1) vs 63.4 (9.2) ml kg(-1 )min(-1)] conditions. In these athletes, there was no difference in the impact of 5, 10 or 15 days of LHTL on the increases observed in MMPO(4min), .VO(2max) or MAOD; and LHTL increased MMPO(4min) and MAOD more than training at low altitude alone.

Living high-training low increases hypoxic ventilatory response of well-trained endurance athletes

This study determined whether "living high-training low" (LHTL)-simulated altitude exposure increased the hypoxic ventilatory response (HVR) in well-trained endurance athletes. Thirty-three cyclists/triathletes were divided into three groups: 20 consecutive nights of hypoxic exposure (LHTLc, n = 12), 20 nights of intermittent hypoxic exposure (four 5-night blocks of hypoxia, each interspersed with 2 nights of normoxia, LHTLi, n = 10), or control (Con, n = 11). LHTLc and LHTLi slept 8-10 h/day overnight in normobaric hypoxia (approximately 2,650 m); Con slept under ambient conditions (600 m). Resting, isocapnic HVR (DeltaVE/DeltaSp(O(2)), where VE is minute ventilation and Sp(O(2)) is blood O(2) saturation) was measured in normoxia before hypoxia (Pre), after 1, 3, 10, and 15 nights of exposure (N1, N3, N10, and N15, respectively), and 2 nights after the exposure night 20 (Post). Before each HVR test, end-tidal PCO(2) (PET(CO(2))) and VE were measured during room air breathing at rest. HVR (l. min(-1). %(-1)) was higher (P < 0.05) in LHTLc than in Con at N1 (0.56 +/- 0.32 vs. 0.28 +/- 0.16), N3 (0.69 +/- 0.30 vs. 0.36 +/- 0.24), N10 (0.79 +/- 0.36 vs. 0.34 +/- 0.14), N15 (1.00 +/- 0.38 vs. 0.36 +/- 0.23), and Post (0.79 +/- 0.37 vs. 0.36 +/- 0.26). HVR at N15 was higher (P < 0.05) in LHTLi (0.67 +/- 0.33) than in Con and in LHTLc than in LHTLi. PET(CO(2)) was depressed in LHTLc and LHTLi compared with Con at all points after hypoxia (P < 0.05). No significant differences were observed for VE at any point. We conclude that LHTL increases HVR in endurance athletes in a time-dependent manner and decreases PET(CO(2)) in normoxia, without change in VE. Thus endurance athletes sleeping in mild hypoxia may experience changes to the respiratory control system.