This study examined the impact of heat acclimation on improving exercise performance in cool and hot environments. Twelve trained cyclists performed tests of maximal aerobic power (VO2max), time-trial performance, and lactate threshold, in both cool [13°C, 30% relative humidity (RH)] and hot (38°C, 30% RH) environments before and after a 10-day heat acclimation (∼50% VO2max in 40°C) program. The hot and cool condition VO2max and lactate threshold tests were both preceded by either warm (41°C) water or thermoneutral (34°C) water immersion to induce hyperthermia (0.8-1.0°C) or sustain normothermia, respectively. Eight matched control subjects completed the same exercise tests in the same environments before and after 10 days of identical exercise in a cool (13°C) environment. Heat acclimation increased VO2max by 5% in cool (66.8 ± 2.1 vs. 70.2 ± 2.3 ml·kg(-1)·min(-1), P = 0.004) and by 8% in hot (55.1 ± 2.5 vs. 59.6 ± 2.0 ml·kg(-1)·min(-1), P = 0.007) conditions. Heat acclimation improved time-trial performance by 6% in cool (879.8 ± 48.5 vs. 934.7 ± 50.9 kJ, P = 0.005) and by 8% in hot (718.7 ± 42.3 vs. 776.2 ± 50.9 kJ, P = 0.014) conditions. Heat acclimation increased power output at lactate threshold by 5% in cool (3.88 ± 0.82 vs. 4.09 ± 0.76 W/kg, P = 0.002) and by 5% in hot (3.45 ± 0.80 vs. 3.60 ± 0.79 W/kg, P < 0.001) conditions. Heat acclimation increased plasma volume (6.5 ± 1.5%) and maximal cardiac output in cool and hot conditions (9.1 ± 3.4% and 4.5 ± 4.6%, respectively). The control group had no changes in VO2max, time-trial performance, lactate threshold, or any physiological parameters. These data demonstrate that heat acclimation improves aerobic exercise performance in temperate-cool conditions and provide the scientific basis for employing heat acclimation to augment physical training programs.

Reactive hyperaemia is the increase in blood flow following arterial occlusion. The exact mechanisms mediating this response in skin are not fully understood. The purpose of this study was to investigate the individual and combined contributions of (1) sensory nerves and large-conductance calcium activated potassium (BK Ca ) channels, and (2) nitric oxide (NO) and prostanoids to cutaneous reactive hyperaemia. Laser-Doppler flowmetry was used to measure skin blood flow in a total of 18 subjects. Peak blood flow (BF) was defined as the highest blood flow value after release of the pressure cuff. Total hyperaemic response was calculated by taking the area under the curve (AUC) of the hyperaemic response minus baseline. Infusates were perfused through forearm skin using microdialysis in four sites. In the sensory nerve/BK Ca protocol:

The aim of this study was to explore heat acclimation effects on cutaneous vascular responses and sweating to local ACh infusions and local heating. We also sought to examine whether heat acclimation altered maximal skin blood flow. ACh (1, 10, and 100 mM) was infused in 20 highly trained cyclists via microdialysis before and after a 10-day heat acclimation program [two 45-min exercise bouts at 50% maximal O2 uptake (V̇o2max) in 40°C ( n = 12)] or control conditions [two 45-min exercise bouts at 50% V̇o2max in 13°C ( n = 8)]. Skin blood flow was monitored via laser-Doppler flowmetry (LDF), and cutaneous vascular conductance (CVC) was calculated as LDF ÷ mean arterial pressure. Sweat rate was measured by resistance hygrometry. Maximal brachial artery blood flow (forearm blood flow) was obtained by heating the contralateral forearm in a water spray device and measured by Doppler ultrasound. Heat acclimation increased %CVCmax responses to 1, 10, and 100 mM ACh (43.5 ± 3.4 vs. 52.6 ± 2.6% CVCmax, 67.7 ± 3.4 vs. 78.0 ± 3.0% CVCmax, and 81.0 ± 3.8 vs. 88.5 ± 1.1% CVCmax, respectively, all P < 0.05). Maximal forearm blood flow remained unchanged after heat acclimation (290.9 ± 12.7 vs. 269.9 ± 23.6 ml/min). The experimental group showed significant increases in sweating responses to 10 and 100 mM ACh (0.21 ± 0.03 vs. 0.31 ± 0.03 mg·cm−2·min−1 and 0.45 ± 0.05 vs. 0.67 ± 0.06 mg·cm−2·min−1, respectively, all P < 0.05), but not to 1 mM ACh (0.13 ± 0.02 vs. 0.18 ± 0.02 mg·cm−2·min−1, P = 0.147). No differences in any of the variables were found in the control group. Heat acclimation in highly trained subjects induced local adaptations within the skin microcirculation and sweat gland apparatus. Furthermore, maximal skin blood flow was not altered by heat acclimation, demonstrating that the observed changes were attributable to improvement in cutaneous vascular function and not to structural changes that limit maximal vasodilator capacity.

Obesity is a widespread and growing problem worldwide and is among the most important health challenges of the 21st century. 1 Exercise is an important component in the prevention and treatment of obesity and, thus, an accurate assessment of the patient's cardiorespiratory fitness (CRF) level to determine optimal workout intensities, exercise modes, and exercise routines is critical. 2 Moreover, a proper quantification and interpretation of CRF is important for assessing who has low CRF, underlying comorbidities, and increased disease risk.Peak oxygen uptake ( o 2 peak ) is routinely measured as a means of evaluating CRF by exercise physiologists, allied health-care providers, epidemiologists, Background: The quantifi cation and interpretation of cardiorespiratory fi tness (CRF) in obesity is important for adequately assessing cardiovascular conditioning , underlying comorbidities, and properly evaluating disease risk. We retrospectively compared peak oxygen uptake ( O 2 peak) (ie, CRF) in absolute terms, and relative terms (% predicted) using three currently suggested prediction equations (Equations R, W, and G). Methods: There were 19 nonobese and 66 obese participants. Subjects underwent hydrostatic weighing and incremental cycling to exhaustion. Subject characteristics were analyzed by independent t test, and % predicted O 2 peak by a two-way analysis of variance (group and equation) with repeated measures on one factor (equation). Results: O 2 peak (L/min) was not different between nonobese and obese adults (2.35 Ϯ 0.80 [SD] vs2.39 Ϯ 0.68 L/min). O 2 peak was higher ( P , .02) relative to body mass and lean body mass in the nonobese (34 Ϯ 8 mL/min/kg vs 22 Ϯ 5 mL/min/kg, 42 Ϯ 9 mL/min/lean body mass vs 37 Ϯ 6 mL/min/lean body mass). Cardiorespiratory fi tness assessed as % predicted was not different in the nonobese and obese (91% Ϯ 17% predicted vs 95% Ϯ 15% predicted) using Equation R, while using Equation W and G, CRF was lower ( P , .05) but within normal limits in the obese (94 Ϯ 15 vs 87 Ϯ 11; 101% Ϯ 17% predicted vs 90% Ϯ 12% predicted, respectively), depending somewhat on sex. Conclusions: Traditional methods of reporting O 2 peak do not allow adequate assessment and quantifi cation of CRF in obese adults. Predicted O 2 peak does allow a normalized evaluation of CRF in the obese, although care must be taken in selecting the most appropriate prediction equation, especially in women. In general, otherwise healthy obese are not grossly deconditioned as is commonly believed, although CRF may be slightly higher in nonobese subjects depending on the uniqueness of the prediction equation. CHEST 2012; 141(4):1031-1039Abbreviations: CRF 5 cardiorespiratory fi tness; LBM 5 lean body mass; MW 5 measured weight; PW 5 predicted weight; o 2 5 oxygen uptake; o 2 peak 5 peak oxygen uptake.

Automated detection of CAD by AC and NC MPS demonstrated similar sensitivity, specificity, and normalcy rates. Some gender differences were noted for AC normal limits.

There are differences in myocardial-perfusion quantification, diagnostic performance, and degree of automation of software packages.

No abstract

Lorenzo S, Minson CT, Babb TG, Halliwill JR. Lactate threshold predicting time-trial performance: impact of heat and acclimation. J Appl Physiol 111: 221-227, 2011. First published April 28, 2011 doi:10.1152/japplphysiol.00334.2011The relationship between exercise performance and lactate and ventilatory thresholds under two distinct environmental conditions is unknown. We examined the relationships between six lactate threshold methods (blood-and ventilation-based) and exercise performance in cyclists in hot and cool environments. Twelve cyclists performed a lactate threshold test, a maximal O2 uptake (V O2max) test, and a 1-h time trial in hot (38°C) and cool (13°C) conditions, before and after heat acclimation. Eight control subjects completed the same tests before and after 10 days of identical exercise in a cool environment. The highest correlations were observed with the blood-based lactate indexes; however, even the indirect ventilation-based indexes were well correlated with mean power during the time trial. Averaged bias was 15.4 Ϯ 3.6 W higher for the ventilation-than the blood-based measures (P Ͻ 0.05). The bias of blood-based measures in the hot condition was increased: the time trial was overestimated by 37.7 Ϯ 3.6 W compared with only 24.1 Ϯ 3.2 W in the cool condition (P Ͻ 0.05). Acclimation had no effect on the bias of the blood-based indexes (P ϭ 0.51) but exacerbated the overestimation by some ventilation-based indexes by an additional 34.5 Ϯ 14.1 W (P Ͻ 0.05). Blood-based methods to determine lactate threshold show less bias and smaller variance than ventilation-based methods when predicting time-trial performance in cool environments. Of the blood-based methods, the inflection point between steady-state lactate and rising lactate (INFL) was the best method to predict time-trial performance. Lastly, in the hot condition, ventilation-based predictions are less accurate after heat acclimation, while blood-based predictions remain valid in both environments after heat acclimation. heat stress; heat acclimation; heat acclimatization; critical power; endurance exercise SEVERAL PHYSIOLOGICAL PARAMETERS, namely, maximal O 2 uptake (V O 2max ), lactate threshold, ventilatory threshold, fraction of slow-twitch fibers, and running economy, are known to be related to (or predictive of) endurance exercise performance (12,13,19). As the margins for success in athletic competition are often quite small, coaches, athletes, and physiologists have long been interested in assessing an individual athlete's lactate or ventilatory threshold, in an effort to use such information to design more effective training plans, optimize an athlete's performance, or make race-day predictions. The terms "lactate threshold" and "ventilatory threshold" have generally been used to define the highest work rate or O 2 uptake (V O 2 ) at which athletes can maintain their efforts over a specified time frame. To the best of our knowledge, no study has focused on simultaneously determining the accuracy of lactate threshold vs. ventila...