Does heat acclimation improve exercise capacity at altitude? A cross-tolerance model.

New approaches to inducing altitude acclimation in a relatively short timeframe are needed, as it is not practical for many soldiers and athletes to gain access to specialized training facilities. Acclimation to one environmental stressor could enhance adaptation to various other stressors in animals and humans. This phenomenon has been described as cross-tolerance and involves the activation of common protective pathways. The purpose of this review is to discuss possible mechanisms involved in the cross-tolerance between heat and hypoxia. Future data could potentially support the use of a cross-tolerance model as a means for military personnel to prepare for deployment to high-altitude environments, as well as for athletes competing at high altitude.

Reliability and validity of the velotron racermate cycle ergometer to measure anaerobic power.

This study assessed the reliability and validity of the Velotron Racermate™ cycle ergometer to assess anaerobic power. Men (9 cyclists and 13 recreationally-active) and women (17 recreationally-active and 1 cyclist) (age=24.7±4.2 yr) performed 2 Wingate tests on the Velotron or 3 Wingate tests (2 on the Velotron and 1 on the Monark Peak Bike) over a 7-14 day period. Peak power, mean power, minimum power, fatigue index, heart rate, and peak and minimum cadence were assessed. Results revealed significant test-retest reliability for mean power (r=0.90, p<0.01), minimum power (r=0.79, p<0.05) and peak power (r=0.70, p<0.05) with repeated bouts on the Velotron. Peak power was significantly higher (p<0.05) on the Velotron (9.95±1.39 W/kg) vs. the Monark (9.13±1.26 W/kg); however, mean power was higher (p<0.05) on the Monark (6.95±0.89 W/kg) vs. the Velotron (6.11±0.52 W/kg and 6.25±0.59 W/kg). Data reveal significant reliability for mean and peak power from the Velotron Racermate, yet multiple variables differ between the Velotron and the Monark mechanically-braked cycle ergometer.

Effect of acute caffeine ingestion on EPOC after intense resistance training.

AIM: This study investigated the effect of acute caffeine (CAF) intake on postexercise oxygen consumption (EPOC) after intense resistance training. METHODS: Fourteen strength-trained men (mean ± SD age and mass =23.1 ± 4.2 yr and 83.4 ± 13.2 kg, respectively) who were caffeine users initially completed one-repetition maximum testing (1-RM) of four exercises: bench press, leg press, lat row, and shoulder press. On each of two days separated by one week, they completed four sets of each exercise to fatigue at 70-80% 1-RM, which was preceded by ingestion of CAF (6 mg/kg) or placebo. Pre-exercise, indirect calorimetry was used to assess energy expenditure for 35 min; this was repeated for 75 min postexercise while subjects remained seated in a quiet lab. Two-way analysis of variance with repeated measures was used to examine differences in gas exchange variables across time and treatment. RESULTS: Results revealed that EPOC was significantly higher (P<0.05) with CAF (26.7 ± 4.1 L) compared to placebo (22.8 ± 3.8 L). With CAF ingestion, oxygen uptake was significantly higher (P<0.05) from 10 min pre-exercise to 70 min postexercise. Respiratory exchange ratio was significantly different (P<0.05) with CAF versus placebo. Caffeine intake increased total energy expenditure by 15% (P<0.05), but the additional calories burned was minimal (+27 kcal). CONCLUSION: Caffeine ingestion in individuals regularly completing rigorous resistance training significantly increases EPOC and energy expenditure pre-and post-exercise, yet the magnitude of this effect is relatively small.

Supramaximal testing to confirm attainment of VO2max in sedentary men and women.

Supramaximal testing is widely used to verify VO2max attainment, yet its efficacy in sedentary subjects is unknown. The aim of the study was to test this hypothesis in men and women completing maximal cycle ergometry. Fifteen sedentary subjects (age=22.4+/-3.9 year) completed incremental exercise, and returned at least 24 h later to complete constant load exercise at 105% peak work rate (Wmax). Another group of nine sedentary men and women (age=21.8+/-5 year) completed supramaximal exercise at 115% Wmax 1-1.5 h after incremental exercise. During exercise, gas exchange data and heart rate (HR) were continuously obtained. VO2max was similar (p>0.05) between incremental and supramaximal exercise in subjects in the first (32.32+/-4.81 mL/kg/min vs. 31.80+/-5.35 mL/kg/min) and second subset (40.63+/-3.61 mL/kg/min vs. 41.66+/-5.55 mL/kg/min). Maximal HR was lower (p<0.05) with supramaximal exercise, yet respiratory exchange ratio was higher (p<0.05). Test-retest reliability (r=0.81-0.89, p<0.05) for VO2max was high during repeated bouts of supramaximal testing. Findings support use of this protocol to confirm VO2max attainment in healthy, sedentary men and women completing incremental cycle ergometry.

Elucidating determinants of the plateau in oxygen consumption at VO2max.

BACKGROUND: A plateau in oxygen consumption (VO2) is the primary means of confirming that maximal oxygen uptake (VO2max) is attained during incremental exercise to fatigue. However, it is still unresolved what causes expression of a plateau in VO2 at the end of incremental exercise. OBJECTIVES: To elucidate incidence and identify determinants of the VO2 plateau in subjects of varying fitness. METHODS: Thirty subjects (mean (SD) age and VO2max 26.9 (9.8) years and 3.4 (0.8) litre/min respectively) were separated into three groups: endurance trained (ET; n = 9), recreationally active (Rec; n = 11), and strength/sprint trained (STR; n = 10). During three separate visits, subjects completed incremental treadmill exercise during which breath by breath gas exchange data were obtained. Body composition was measured using a three site skinfolds model. Force production of the knee extensors and flexors was assessed using isokinetic dynamometry. RESULTS: VO2max was significantly higher (p < 0.05) in the ET group vs STR and Rec. The change in VO2 (DeltaVO2) at VO2max was not different (p > 0.05) in the ET group (33.0 (27.3) ml/min) compared with the Rec group (30.3 (24.1) ml/min) and the STR group (44.4 (23.8) ml/min). No correlations (p > 0.05) were evident between DeltaVO2 at VO2max and VO2max (r = 0.05), fat-free mass (r = 0.12), and muscular strength (r = -0.12). CONCLUSIONS: The incidence of a plateau in VO2 at VO2max (from correlation data) is not due to factors related to training status or physical fitness of subjects, but is altered by analysis and interpretation of gas exchange data.

Is the ventilatory threshold coincident with maximal fat oxidation during submaximal exercise in women?

BACKGROUND: The purpose of this study was to detect the fraction of peak oxygen consumption (VO2peak) that elicits maximal rates of fat oxidation during submaximal treadmill exercise. It was hypothesized that this point would appear at a work rate just below the ventilatory threshold. EXPERIMENTAL DESIGN: subjects completed a protocol requiring them to exercise for 15 min on a treadmill at six different workloads, 25, 40, 55, 65, 75, and 85% VO2peak, over two separate visits. PARTICIPANTS: nine healthy, moderately-trained eumenorrheic females (age = 28.8+/-5.99 yrs, VO2peak = 47.20 +/-2.57 ml x kg(-1) x min(-1)) volunteered for the study. MEASURES: a one-way ANOVA with repeated measures was used to test for differences across exercise intensities in the metabolic variables (i.e. substrate oxidation, blood lactate concentration ([La-]), RER, and the contribution of fat to total energy expenditure). Following significant F ratios, post-hoc tests were used to detect differences between the means for various exercise intensities. RESULTS: Exercise at 75% VO2peak elicited the greatest rate of fat oxidation (4.75+/-0.49 kcal x min(-1)), and this intensity was coincident with the ventilatory threshold (76+/-7.41% VO2peak). Moreover, a significant difference (t(8) = -3.98, p<0.01) was noted between the mean ventilatory threshold and lactate threshold. CONCLUSIONS: The finding that a relatively heavy work rate elicits the highest rate of fat oxidation in an active, female population has application in exercise prescription and refutes the belief that low-intensity exercise is preferred for fat metabolism.