Ambient temperature influences metabolic substrate oxidation curves during running and cycling in healthy men.

Fat oxidation in cold environments and carbohydrate (CHO) use in hot environments are increased during exercise at steady-state submaximal workloads. However, the influence of cold and heat on fat and CHO oxidation curves remain unknown. We therefore examined the influence of a cold and warm ambient temperature on fat and CHO oxidation across a wide range of exercise intensities during treadmill and cycle ergometer exercise. Nine, young, healthy, male subjects completed four trials, during which they performed an incremental peak oxygen consumption (⩒O2peak) test on a cycle ergometer or treadmill in a 4.6°C or 34.1°C environment. Substrate oxidation, maximal fat oxidation rate (MFO), and exercise intensity where MFO occurs (Fatmax) were assessed via indirect calorimetry. MFO was significantly greater in the cold vs. warm during the treadmill exercise (0.66 ± 0.31 vs. 0.43 ± 0.23 g min-1; p = 0.02) but not during cycling (0.45 ± 0.24 vs. 0.29 ± 0.11 g min-1; p = 0.076). MFO was also greater during treadmill vs. cycling exercise, irrespective of ambient temperature (0.57 g min-1 vs. 0.37 g min-1; p = 0.04). Fatmax was greater in the cold vs. warm for both treadmill (57 ± 20 vs. 37 ± 17%⩒O2peak; p = 0.025) and cycling (62 ± 28 vs. 36 ± 13%⩒O2peak; p = 0.003). Multiple, linear, mixed-effects regressions revealed a strong influence of ambient temperature on substrate oxidation. We demonstrated that exercising in a cold environment increases MFO and Fatmax, predominantly during treadmill exercise. These results validate the implication of ambient temperature on energy metabolism over a wide range of exercise intensities.

Effect of a Simulated Mine Rescue on Physiological Variables and Heat Strain of Mine Rescue Workers.

OBJECTIVE: To describe physiological responses of mine rescuers during a simulated mine emergency. METHODS: Body-worn monitors (n = 74) and core temperature (Tc) capsules (n = 54) assessed heart rate (HR), respiration rate (RR), energy expenditure (EE), oxygen consumption ((Equation is included in full-text article.)), Tc and skin temperature (Tskin), by team position and task. A multivariate analysis was performed with team positions, tasks, and measures as factors. RESULTS: HRmean and HRpeak were 78.6% and 94.5%, respectively, of predicted maximum heart rate. Arduous labor tasks elicited higher HR, RR, and (Equation is included in full-text article.)than casualty care. Captains exhibited lower HRmean, HRpeak, RR, RRpeak, (Equation is included in full-text article.), Tc, and Tskin compared with other positions. Tc mean exceeded 38.6 °C (n = 14 recorded Tc >39 °C). CONCLUSIONS: Captains' physical loading and heat stress were lowest. Nonetheless, all tasks and positions induced high physical load and heat strain.

Evaluation of the running-based anaerobic sprint test as a measure of repeated sprint ability in collegiate-level soccer players.

Repeated sprint ability (RSA) refers to an individual's ability to perform maximal sprints of short duration in succession with little recovery between sprints. The running-based anaerobic sprint test (RAST) has been adapted from the Wingate anaerobic test (WAnT) protocol as a tool to assess RSA and anaerobic power. The purpose of this study was to evaluate the relationship between performance variables and physiological responses obtained during the RAST and the WAnT using 8 collegiate-level soccer players. Participants performed a single trial of both the WAnT and the RAST. Breath-by-breath gas exchange was monitored throughout each trial, and blood lactate (BL) measures were recorded postexercise. The oxygen uptake (VO2) profile suggested that the RAST required greater contributions from aerobic metabolism although there was no difference in VO2peak (p < 0.05). Peak BL values were also similar between the RAST and the WAnT (p < 0.05). Neither peak physiological values nor performance variables (peak and mean power) were significantly correlated between protocols. The weak association in physiological responses indicates that different combinations of metabolic contributions exist between protocols, suggesting that individual performances on each test are not related in collegiate soccer players. Further studies on these relationships with players of other competitive levels and team sport athletes are warranted.

Occurrence of fatigue induced by a whole-body vibration session is not frequency dependent.

The aim of this study was to determine whether neuromuscular adaptations (magnitude and location) induced by isometric exercise performed on an oscillating platform are dependent on whole-body vibration (WBV) frequency. Eleven young men performed 4 separate fatigue sessions of static squatting exercise at 3 frequencies of WBV (V20, V40, and V60) and 1 session without vibration (V0). Isometric torque and electromyographic activity of the vastus lateralis, rectus femoris, and biceps femoris were recorded during maximal voluntary and evoked contractions of the knee extensor muscles before and after each fatigue session to examine both peripheral and central adaptations. Isometric torque decreased significantly after each of the 4 frequency sessions (V0: -9.4 ± 6.1%, p = 0.003; V20: -8.1 ± 9.9%, p = 0.010; V40: -11.9 ± 12.7%, p = 0.011; and V60: -7.8 ± 9.2%, p = 0.001, respectively), but this reduction was not significantly different between frequencies. The torque produced by evoked contraction significantly decreased from pre-exercise values after each session (V0: -14.9 ± 15.6%, p = 0.012; V20: -15.8 ± 16.4%, p = 0.010; V40: -21.0 ± 14.3%, p = 0.004; and V60: -17.3 ± 11.6%, p = 0.005, respectively); however, there was no effect of vibration frequency. In both conditions, the maximal voluntary contraction torque reduction observed was mainly attributable to peripheral fatigue and was not because of central modifications of the neuromuscular system. The present study demonstrates that the frequency of vibration does not significantly influence the magnitude and location of neuromuscular fatigue, suggesting that adding WBV to static squat exercise (on a vertically oscillating platform) does not provide an additional training stimulus.

Mechanical efficiency of treadmill running exercise: effect of anaerobic-energy contribution at various speeds.

OBJECTIVES: Mechanical efficiency (ME) describes the ratio between mechanical (PMECH) and metabolic (PMET) power. The purpose of the study was to include an estimation of anaerobic energy expenditure (AnE) into the quantification of PMET using the accumulated oxygen deficit (AOD) and to examine its effect on the value of ME in treadmill running at submaximal, maximal, and supramaximal running speeds. METHODS: Participants (N = 11) underwent a graded maximal exercise test to determine velocity at peak oxygen uptake (vVO2peak). On 4 separate occasions, subjects ran for 6 min at speeds corresponding to 50%, 70%, 90%, and 110% of vVO2peak. During each testing session, PMET was measured from pulmonary oxygen uptake (VO2p) using open-circuit spirometry and was quantified in 2 ways: from VO2p and an estimate of AnE (from the AOD method) and from VO2p only. PMECH was determined from kinematic analyses. RESULTS: ME at 50%, 70%, 90%, and 110% of vVO2peak was 59.9% ± 11.9%, 55.4% ± 12.2%, 51.5% ± 6.8%, and 52.9% ± 7.5%, respectively, when AnE was included in the calculation of PMET. The exclusion of AnE yielded significantly greater values of ME at all speeds: 62.9% ± 11.4%, 62.4% ± 12.6%, 55.1% ± 6.2%, and 64.2% ± 8.4%; P = .001 (for 50%, 70%, 90%, and 110% of vVO2peak, respectively). CONCLUSIONS: The data suggest that an estimate of AnE should be considered in the computation of PMET when determining ME of treadmill running, as its exclusion leads to overestimations of ME values.