Hyperoxia enhances self-paced exercise performance to a greater extent in cool than hot conditions.

NEW FINDINGS: What is the central question of this study? Hyperoxia enhances endurance performance by increasing O2 availability to locomotor muscles. We investigated whether hyperoxia can also improve prolonged self-paced exercise in conditions of elevated thermal and cardiovascular strain. What is the main finding and its importance? Hyperoxia improved self-paced exercise performance in hot and cool conditions. However, the extent of the improvement (increased work rate relative to normoxia) was greater in cool conditions. This suggests that the development of thermal and cardiovascular strain during prolonged self-paced exercise under heat stress might attenuate the hyperoxia-mediated increase in O2 delivery to locomotor muscles. ABSTRACT: The aim of this study was to determine whether breathing hyperoxic gas when self-paced exercise performance is impaired under heat stress enhances power output. Nine well-trained male cyclists performed four 40 min cycling time trials: two at 18°C (COOL) and two at 35°C (HOT). For the first 30 min, participants breathed ambient air, and for the remaining 10 min normoxic (fraction of inspired O2 0.21; NOR) or hyperoxic (fraction of inspired O2 0.45; HYPER) air. During the first 30 min of the time trials, power output was lower in the HOT (∼250 W) compared with COOL (∼273 W) conditions (P < 0.05). In the final 10 min, power output was higher in HOT-HYPER (264 ± 25 W) than in HOT-NOR (244 ± 31 W; P = 0.008) and in COOL-HYPER (315 ± 28 W) than in COOL-NOR (284 ± 25 W; P < 0.001). The increase in absolute power output in COOL-HYPER was greater than in HOT-HYPER (∼12 W; P = 0.057), as was normalized power output (∼30%; P < 0.001). The peripheral capillary percentage oxygen saturation increased in HOT-HYPER and COOL-HYPER (P < 0.05), with COOL-HYPER being higher than HOT-HYPER (P < 0.01). Heart rate was higher during the HOT compared with COOL trials (P < 0.01), as were mean skin temperature (P < 0.001) and peak rectal temperature (HOT, ∼39.5°C and COOL, ∼38.9°C; P < 0.01). Thermal discomfort was also higher in the HOT compared with COOL (P < 0.01), whereas ratings of perceived exertion were similar (P > 0.05). Hyperoxia enhanced performance during the final 25% of a 40 min time trial in both HOT and COOL conditions compared with normoxia. However, the attenuated increase in absolute and normalized power output noted in the HOT condition suggests that heat stress might mitigate the influence of hyperoxia.

Live high, train low - influence on resting and post-exercise hepcidin levels.

The post-exercise hepcidin response during prolonged (>2 weeks) hypoxic exposure is not well understood. We compared plasma hepcidin levels 3 h after exercise [6 × 1000 m at 90% of maximal aerobic running velocity (vVO2max )] performed in normoxia and normobaric hypoxia (3000 m simulate altitude) 1 week before, and during 14 days of normobaric hypoxia [196.2 ± 25.6 h (median: 200.8 h; range: 154.3-234.8 h) at 3000 m simulated altitude] in 10 well-trained distance runners (six males, four females). Venous blood was also analyzed for hepcidin after 2 days of normobaric hypoxia. Hemoglobin mass (Hbmass ) was measured via CO rebreathing 1 week before and after 14 days of hypoxia. Hepcidin was suppressed after 2 (Cohen's d = -2.3, 95% confidence interval: [-2.9, -1.6]) and 14 days of normobaric hypoxia (d = -1.6 [-2.6, -0.6]). Hepcidin increased from baseline, 3 h post-exercise in normoxia (d = 0.8 [0.2, 1.3]) and hypoxia (d = 0.6 [0.3, 1.0]), both before and after exposure (normoxia: d = 0.7 [0.3, 1.2]; hypoxia: d = 1.3 [0.4, 2.3]). In conclusion, 2 weeks of normobaric hypoxia suppressed resting hepcidin levels, but did not alter the post-exercise response in either normoxia or hypoxia, compared with the pre-exposure response.

Physical Demands of Sprinting in Professional Road Cycling.

The aim of this study was to quantify the demands of road competitions ending with sprints in male professional cycling. 17 races finished with top-5 results from 6 male road professional cyclists (age, 27.0±3.8 years; height, 1.76±0.03 m; weight, 71.7±1.1 kg) were analysed. SRM power meters were used to monitor power output, cadence and speed. Data were averaged over the entire race, different durations prior to the sprint (60, 10, 5 and 1 min) and during the actual sprint. Variations in power during the final 10 min of the race were quantified using exposure variation analysis. This observational study was conducted in the field to maximize the ecological validity of the results. Power, cadence and speed were statistically different between various phases of the race (p<0.001), increasing from 316±43 W, 95±4 rpm and 50.5±3.3 km·h(-1) in the last 10 min, to 487±58 W, 102±6 rpm and 55.4±4.7 km·h(-1) in the last min prior to the sprint. Peak power during the sprint was 17.4±1.7 W·kg(-1). Exposure variation analysis revealed a significantly greater number of short-duration high-intensity efforts in the final 5 min of the race, compared with the penultimate 5 min (p=0.010). These findings quantify the power output requirements associated with high-level sprinting in men's professional road cycling and highlight the need for both aerobic and anaerobic fitness.

Pacing, the missing piece of the puzzle to high-intensity interval training.

This study examined physiological and perceptual responses to matched work high-intensity interval training using all-out and 2 even-paced methodologies. 15 trained male cyclists performed 3 interval sessions of three 3-min efforts with 3 min of active recovery between efforts. The initial interval session was completed using all-out pacing, with the following 2 sessions being completed with computer- and athlete-controlled pacing in a randomised and semi-counterbalanced manner. Computer- and athlete-controlled intervals were completed at the mean power from the corresponding interval during the all-out trial. Oxygen consumption and ratings of perceived exertion were recorded during each effort. 20 min following each session, participants completed a 4-km time trial and provided sessional rating of perceived exertion. Oxygen consumption was greater during all-out (54.1±6.6 ml.kg(-1).min(-1); p<0.01) and athlete-controlled (53.0±5.8 ml.kg(-1).min(-1); p<0.01) compared with computer-controlled (51.5±5.7 ml.kg(-1).min(-1)). Total time ≥85% maximal oxygen consumption was greater during all-out compared to both even-paced efforts. Sessional ratings of perceived exertion were greater after all-out compared to both even-paced sessions. Mean 4-km power output was lower after all-out compared with both even paced intervals. Distribution of pace throughout high-intensity interval training can influence perceptual and metabolic stress along with subsequent performance and should be considered during the prescription of such training.

Muscle oxygenation and blood volume reliability during continuous and intermittent running.

The reliability of near infrared spectroscopy derived tissue oxygenation index (TOI) and total haemoglobin concentration (tHb) were examined during continuous (CR) and interval (INT) running. In a repeated measures design, 10 subjects twice performed 30 min of CR at 70% of their peak treadmill velocity, followed by 10 bouts of INT at 100%. Between trial reliability of mean and amplitude changes in TOI and tHb during CR were determined. Muscle de-oxygenation and re-oxygenation rates during INT were calculated using 3 analytical methods; i) linear modelling, ii) minimum and maximum values during work/rest intervals, and iii) mean values during work/rest intervals. Reliability was assessed using coefficient of variation (CV; %). During CR, mean TOI was more reliable (3.5%) compared with TOI amplitude change (34.7%), while mean tHb (12%) was similar to both absolute (9.2%) and relative (10.2%) amplitude changes. During INT, de-oxygenation rates analysed via linear modelling produced the lowest CV (7.2%), while analysis using min-max values produced the lowest CV (9.3%) for re-oxygenation rates. In conclusion, while the variables demonstrated CVs lower than reported changes in training-induced adaptations and/or differences between athletes and controls (23- 450%), practitioners are encouraged to consider the advantages/disadvantages of each method when performing their analysis.

Pack hike test finishing time for Australian firefighters: pass rates and correlates of performance.

The pack hike test (PHT, 4.83 km hike wearing a 20.4-kg load) was devised to determine the job readiness of USA wildland firefighters. This study measured PHT performance in a sample of Australian firefighters who currently perform the PHT (career land management firefighters, LMFF) and those who do not (suburban/regional volunteer firefighters, VFF). The study also investigated the relationships between firefighters' PHT performance and their performance across a range of fitness tests for both groups. Twenty LMFF and eighteen age-, body mass-, and height-matched VFF attempted the PHT, and a series of muscular endurance, power, strength and cardiorespiratory fitness tests. Bivariate correlations between the participants' PHT finishing time and their performance in a suite of different fitness tests were determined using Pearson's product moment correlation coefficient. The mean PHT finishing time for LMFF (42.2 ± 2.8 min) was 9 ± 14% faster (p = 0.001) than for VFF (46.1 ± 3.6 min). The pass rate (the percentage of participants who completed the PHT in under 45 min) for LMFF (90%) was greater than that of VFF (39%, p = 0.001). For LMFF, VO(2peak) in L min(-1)(r = -0.66, p = 0.001) and the duration they could sustain a grip 'force' of 25 kg (r = -0.69, p = 0.001) were strongly correlated with PHT finishing time. For VFF, VO(2peak) in mL kg(-1) min(-1)(r = -0.75, p = 0.002) and the duration they could hold a 1.2-m bar attached to 45.5 kg in a 'hose spray position' (r = -0.69, p = 0.004) were strongly correlated with PHT finishing time. This study shows that PHT fitness-screening could severely limit the number of VFF eligible for duty, compromising workforce numbers and highlights the need for specific and valid firefighter fitness standards. The results also demonstrate the strong relationships between PHT performance and firefighters' cardiorespiratory fitness and local muscular endurance. Those preparing for the PHT should focus their training on these fitness components in the weeks and months prior to undertaking the PHT.

Examining pacing profiles in elite female road cyclists using exposure variation analysis.

OBJECTIVE: In this study, the amplitude and time distribution of power output in a variety of competitive cycling events through the use of a new mathematical analysis was examined: exposure variation analysis (EVA). DESIGN: Descriptive field study. SETTING: Various professional road cycling events, including; a 5-day-eight-stage tour race, a 1-day World Cup event and the Australian National Individual Time Trial Championships. PARTICIPANTS: 9 elite female cyclists (mean (SD), mass = 57.8 (3.4) kg, height = 167.3 (2.8) cm, Vo(2)peak = 63.2 (5.2) ml kg(-1) min(-1)). INTERVENTIONS: None. MAIN OUTCOME MEASUREMENTS: The variation in power output and the quantification of the total time and acute time spent at various exercise intensities during competitive professional cycling were examined. Predefined levels of exercise intensity that elicited first ventilation threshold, second ventilation threshold and maximal aerobic power were determined from a graded exercise test performed before the events and compared with power output during each event. RESULTS: EVA exposed that power output during the time trial was highly variable (EVA(SD) = 2.81 (0.33)) but more evenly distributed than the circuit/criterium (4.23 (0.31)) and road race events (4.81 (0.96)). CONCLUSION: EVA may be useful for illustrating variations in the amplitude and time distribution of power output during cycling events. The specific race format influenced not only the overall time spent in various power bands, but also the acute time spent at these exercise intensities.

Effect of a 5-min cold-water immersion recovery on exercise performance in the heat.

BACKGROUND: This study examined the effect of a 5-min cold-water immersion (14 degrees C) recovery intervention on repeated cycling performance in the heat. METHODS: 10 male cyclists performed two bouts of a 25-min constant-paced (254 (22) W) cycling session followed by a 4-km time trial in hot conditions (35 degrees C, 40% relative humidity). The two bouts were separated by either 15 min of seated recovery in the heat (control) or the same condition with 5-min cold-water immersion (5th-10th minute), using a counterbalanced cross-over design (CP(1)TT(1) --> CWI or CON --> CP(2)TT(2)). Rectal temperature was measured immediately before and after both the constant-paced sessions and 4-km timed trials. Cycling economy and Vo(2) were measured during the constant-paced sessions, and the average power output and completion times were recorded for each time trial. RESULTS: Compared with control, rectal temperature was significantly lower (0.5 (0.4) degrees C) in cold-water immersion before CP(2) until the end of the second 4-km timed trial. However, the increase in rectal temperature (0.5 (0.2) degrees C) during CP(2) was not significantly different between conditions. During the second 4-km timed trial, power output was significantly greater in cold-water immersion (327.9 (55.7) W) compared with control (288.0 (58.8) W), leading to a faster completion time in cold-water immersion (6.1 (0.3) min) compared with control (6.4 (0.5) min). Economy and Vo(2) were not influenced by the cold-water immersion recovery intervention. CONCLUSION: 5-min cold-water immersion recovery significantly lowered rectal temperature and maintained endurance performance during subsequent high-intensity exercise. These data indicate that repeated exercise performance in heat may be improved when a short period of cold-water immersion is applied during the recovery period.

Muscle deoxygenation during repeated sprint running: Effect of active vs. passive recovery.

The purpose of this study was to compare the effect of active (AR) versus passive recovery (PR) on muscle deoxygenation during short repeated maximal running. Ten male team sport athletes (26.9+/-3.7y) performed 6 repeated maximal 4-s sprints interspersed with 21 s of either AR (2 m.s (-1)) or PR (standing) on a non-motorized treadmill. Mean running speed (AvSp (mean)), percentage speed decrement (Sp%Dec), oxygen uptake (V O (2)), deoxyhemoglobin (HHb) and blood lactate ([La] (b)) were computed for each recovery condition. Compared to PR, AvSp (mean) was lower (3.79+/-0.28 vs. 4.09+/-0.32m.s (-1); P<0.001) and Sp%Dec higher (7.2+/-3.7 vs. 3.2+/-0.1.3%; P<0.001) for AR. Mean V O (2) (3.64+/-0.44 vs. 2.91+/-0.47L.min (-1), P<0.001), HHb (94.4+/-16.8 vs. 83.4+/-4.8% of HHb during the first sprint, P=0.02) and [La] (b) (13.5+/-2.5 vs. 12.7+/-2.2 mmol.l (-1), P=0.03) were significantly higher during AR compared to PR. In conclusion, during run-based repeated sprinting, AR was associated with reduced repeated sprint ability and higher muscle deoxygenation.

Influence of starting strategy on cycling time trial performance in the heat.

The purpose of this study was to determine the influence of starting strategy on time trial performance in the heat. Eleven endurance trained male cyclists (30+/-5 years, 79.5+/-4.6 kg, VO(2max) 58.5+/-5.0 ml x kg x (-1) min(-1)) performed four 20-km time trials in the heat (32.7+/-0.7 degrees C and 55% relative humidity). The first time trial was completed at a self-selected pace (SPTT). During the following time trials, subjects performed the initial 2.5-km at power outputs 10% above (10% ATT), 10% below (10% BTT) or equal (ETT) to that of the average power during the initial 2.5-km of the self-selected trial; the remaining 17.5-km was self-paced. Throughout each time trial, power output, rectal temperature, skin temperature, heat storage, pain intensity and thermal sensation were taken. Despite significantly (P<0.05) greater power outputs for 10% BTT (273+/-45W) compared with the ETT (267+/-48W) and 10% ATT (265+/-41W) during the final 17.5-km, overall 20-km performance time was not significantly different amongst trials. There were no differences in any of the other measured variables between trials. These data show that varying starting power by +/-10% did not affect 20 km time trial performance in the heat.

Accuracy of the Velotron ergometer and SRM power meter.

The purpose of this study was to determine the accuracy of the Velotron cycle ergometer and the SRM power meter using a dynamic calibration rig over a range of exercise protocols commonly applied in laboratory settings. These trials included two sustained constant power trials (250 W and 414 W), two incremental power trials and three high-intensity interval power trials. To further compare the two systems, 15 subjects performed three dynamic 30 km performance time trials. The Velotron and SRM displayed accurate measurements of power during both constant power trials (<1% error). However, during high-intensity interval trials the Velotron and SRM were found to be less accurate (3.0%, CI=1.6-4.5% and -2.6%, CI=-3.2--2.0% error, respectively). During the dynamic 30 km time trials, power measured by the Velotron was 3.7+/-1.9% (CI=2.9-4.8%) greater than that measured by the SRM. In conclusion, the accuracy of the Velotron cycle ergometer and the SRM power meter appears to be dependent on the type of test being performed. Furthermore, as each power monitoring system measures power at various positions (i.e. bottom bracket vs. rear wheel), caution should be taken when comparing power across the two systems, particularly when power is variable.

Effect of cold water immersion on postexercise parasympathetic reactivation.

The aim of the present study was to assess the effect of cold water immersion (CWI) on postexercise parasympathetic reactivation. Ten male cyclists (age, 29 +/- 6 yr) performed two repeated supramaximal cycling exercises (SE(1) and SE(2)) interspersed with a 20-min passive recovery period, during which they were randomly assigned to either 5 min of CWI in 14 degrees C or a control (N) condition where they sat in an environmental chamber (35.0 +/- 0.3 degrees C and 40.0 +/- 3.0% relative humidity). Rectal temperature (T(re)) and beat-to-beat heart rate (HR) were recorded continuously. The time constant of HR recovery (HRRtau) and a time (30-s) varying vagal-related HR variability (HRV) index (rMSSD(30s)) were assessed during the 6-min period immediately following exercise. Resting vagal-related HRV indexes were calculated during 3-min periods 2 min before and 3 min after SE(1) and SE(2). Results showed no effect of CWI on T(re) (P = 0.29), SE performance (P = 0.76), and HRRtau (P = 0.61). In contrast, all vagal-related HRV indexes were decreased after SE(1) (P < 0.001) and tended to decrease even further after SE(2) under N condition but not with CWI. When compared with the N condition, CWI increased HRV indexes before (P < 0.05) and rMSSD(30s) after (P < 0.05) SE(2). Our study shows that CWI can significantly restore the impaired vagal-related HRV indexes observed after supramaximal exercise. CWI may serve as a simple and effective means to accelerate parasympathetic reactivation during the immediate period following supramaximal exercise.

Reliability of power output during dynamic cycling.

The aims of the present study were to determine the influence of familiarization on the reliability of power output during a dynamic 30-km cycling trial and to determine the test-retest reliability following a 6-week period. Nine trained male cyclists performed five self-paced 30-km cycling trials, which contained three 250-m sprints and three 1-km sprints. The first three of these trials were performed in consecutive weeks (Week 1, Week 2 and Week 3), while the latter two trials were consecutively conducted 6 wk following (Week 9 and Week 10). Subjects were instructed to complete each sprint, as well as the entire trial in the least time possible. Reproducibility in average power output over the entire 30-km trial for Week 2 and 3 alone (coefficient of variation, CV = 2.4 %, intra-class correlation coefficient, ICC = 0.93) was better than for Week 1 and 2 (CV = 5.5 %, ICC = 0.77) and Week 9 and 10 alone (CV = 5.3 %, ICC = 0.57). These results indicate that high reliability during a dynamic 30-km cycling trial may be obtained after a single familiarization trial when subsequent trials are performed within 7 days. However, if cyclists do not perform trials for six weeks, the same level of reliability is not maintained.

Core temperature and hydration status during an Ironman triathlon.

BACKGROUND: Numerous laboratory based studies have documented that aggressive hydration strategies (approximately 1-2 litres/h) are required to minimise a rise in core temperature and minimise the deleterious effects of hyperthermia on performance. However, field data on the relations between hydration level, core body temperature, and performance are rare. OBJECTIVE: To measure core temperature (Tcore) in triathletes during a 226 km Ironman triathlon, and to compare Tcore with markers of hydration status after the event. METHOD: Before and immediately after the 2004 Ironman Western Australia event (mean (SD) ambient temperature 23.3 (1.9) degrees C (range 19-26 degrees C) and 60 (14)% relative humidity (44-87%)) body mass, plasma concentrations of sodium ([Na+]), potassium ([K+]), and chloride ([Cl-]), and urine specific gravity were measured in 10 well trained triathletes. Tcore was measured intermittently during the event using an ingestible pill telemetry system, and heart rate was measured throughout. RESULTS: Mean (SD) performance time in the Ironman triathlon was 611 (49) minutes; heart rate was 143 (9) beats/min (83 (6)% of maximum) and Tcore was 38.1 (0.3) degrees C. Body mass significantly declined during the race by 2.3 (1.2) kg (-3.0 (1.5)%; p < 0.05), whereas urine specific gravity significantly increased (1.011 (0.005) to 1.0170 (0.008) g/ml; p < 0.05) and plasma [Na+], [K+], and [Cl-] did not change. Changes in body mass were not related to finishing Tcore (r = -0.16), plasma [Na+] (r = 0.31), or urine specific gravity (r = -0.37). CONCLUSION: In contrast with previous laboratory based studies examining the influence of hypohydration on performance, a body mass loss of up to 3% was found to be tolerated by well trained triathletes during an Ironman competition in warm conditions without any evidence of thermoregulatory failure.