Is the magnitude of acute post-exercise hypotension mediated by exercise intensity or total work done?

The purpose of this study was to investigate the effects of exercise intensity on the magnitude of acute post-exercise hypotension while controlling for total work done over the exercise bout. Seven normotensive physically active males aged 28 ± 6 years (mean ± SD) completed four experimental trials, a no exercise control, 30 min of semi-recumbent cycling at 70% (INT), cycling for 30 min at 40% (SMOD) and cycling at 40% for a time which corresponded to the same total work done as in the intense trial (LMOD). Blood pressure (BP), heart rate, stroke volume, cardiac output, total peripheral resistance, core body temperature and forearm skin and limb blood flow were measured prior to and for 20 min following the exercise bout. Post-exercise summary statistics were compared between trials with a one-factor general linear model. The change in systolic BP, averaged over the 20-min post-exercise period was significantly lower only following the INT (−5 ± 3 mm Hg) and LMOD exercise (−1 ± 7 mm Hg) compared to values in control (P < 0.04). The changes in systolic BP and MAP following INT and LMOD were not significantly different from each other (P > 0.05). Similar results were obtained when the minimum values of these variables recorded during the post-exercise period were compared. Mean changes in cardiac output (1.9 ± 0.3 l min⁻¹) and total peripheral resistance (−3 ± 1 mm Hg l⁻¹ min⁻¹) after INT exercise were also different from those in CON (P < 0.0005). The acute post-exercise reduction in BP was clinically similar following high intensity short duration exercise and moderate intensity longer duration exercise that was matched for total work done.     

Effects of pedal frequency on estimated muscle microvascular O2 extraction

An increase in muscle contraction frequency could limit muscle blood flow compromising the matching of and muscle oxygen uptake This study examined the effects of pedal cadence on skeletal muscle oxygenation at low, moderate and peak exercise. Nine healthy subjects [24.7±6.3 years (SD)] performed incremental cycling exercise at 60 and 100 rpm. Pulmonary was measured breath-by-breath and vastus lateralis oxygenation was determined by near-infrared spectroscopy (NIRS). The deoxyhemoglobin signal ([HHb]) from NIRS was used to estimate microvascular O₂ extraction (i.e., [HHb] ∝ ). The and [HHb] for low, moderate and at peak exercise were determined. The at 60 rpm (low=0.64±0.13, moderate=2.03±0.38 and peak=3.39±0.84 l/min) were lower (P<0.01) than at 100 rpm (1.29±0.23, 2.14±0.39 and 3.54±0.88 l/min, respectively). There was a progressive increase in [HHb] from low to peak exercise. However, there was no significant difference (ANOVA, P=0.94) for the 60 (in μM, low=24.0±9.5, moderate=30.5±13.8 and peak=36.7±16.5) and 100 contractions/min (in μM, low=25.7±11.6, moderate=32.1±14.0 and peak=35.4±16.5). We conclude that vastus lateralis O₂ extraction was similar at 60 and 100 cpm, suggesting that the in the microcirculation was not altered and, presumably, no impairment of occurred with the increase in pedal frequency.     

The influence of acute and 23 days of intermittent hypoxic exposures on the exercise-induced forehead sweating response

The effect of acute and 23 days of intermittent exposures to normobaric hypoxia on the forehead sweating response during steady-state exercise was investigated. Eight endurance athletes slept in a normobaric hypoxic room for a minimum of 8 h per day at a simulated altitude equivalent to 2,700 m for 23 days (sleep high–train low regimen). Peak oxygen uptake and peak work rate (WR_peak) were determined under normoxic (20.9%O₂) and hypoxic (13.5%O₂) conditions prior to (pre-IHE), and immediately after (post-IHE) the intermittent hypoxic exposures (IHE). Also, each subject performed three 30-min cycle-ergometry bouts: (1) normoxic exercise at 50% WR_peak attained in normoxia (control trial; CT); (2) hypoxic exercise at 50% WR_peak attained in hypoxia (hypoxic relative trial; HRT) and (3) hypoxic exercise at the same absolute work rate as in CT (hypoxic absolute trial; HAT). Exposure to hypoxia induced a 33 and 37% decrease (P < 0.001) in pre-IHE and post-IHE, respectively. Despite similar relative oxygen uptake during HAT pre-IHE and post-IHE, the ratings of perceived whole-body exertion decreased substantially (P < 0.05) post-IHE. Pre-IHE the sweat secretion on the forehead was greater (P < 0.01) in the HAT (2.60 (0.80) mg cm⁻² min⁻¹) compared to the other two trials (CT = 1.87 (1.09) mg cm⁻² min⁻¹; HRT = 1.57 (0.82) mg cm⁻² min⁻¹) despite a similar exercise-induced elevation in body temperatures, resulting in an augmented (P < 0.01) gain of the sweating response The augmented and during the HAT were no longer evident post-IHE. Thus, it appears that exercise sweating on the forehead is potentiated by acute exposure to hypoxia, an effect which can be abolished by 23 days of intermittent hypoxic exposures.     

The influence of fatigue-induced increase in relative work rate on temperature regulation during exercise

Heat-loss responses during steady-load exercise are affected by an increase in relative work rate induced by muscle ischaemia or hypoxaemia. The present study investigated whether progressive increases in perception of exertion and relative oxygen uptake which occur during prolonged steady-load exercise as a result of progressively increased peripheral fatigue, might also affect the regulation of heat loss responses and hence the exercise-induced increase in mean body temperature. Ten male subjects first performed a ramp-test to exhaustion on a cycle ergometer to evaluate their initial peak oxygen uptake (Control ). On a separate day, 120 min of cycling at constant power output corresponding to 60% of Control was performed in thermoneutral environment (Ta = 23°C, RH = 50%, wind speed = 5 m s⁻¹). This was immediately followed by another maximal performance test (Fatigue ). During prolonged exercise, median (range) rating of perceived exertion for whole-body (RPE_wb) increased (P < 0.01) from initial 3.5 (1–5) to 5.5 (5–9) at the end of exercise. Fatigue and peak power output were 9 (5) and 10 (5)% lower (P < 0.01) when compared to control values. At the onset of exercise, heat production, mechanical efficiency, heat loss and mean body temperature increased towards asymptotic values, thereafter remained constant throughout the 120 min exercise, despite the concomitant progressive increase in relative work rate, as reflected in increased RPE_wb and relative oxygen uptake. It is thus concluded that the increase in relative work rate induced predominantly by peripheral muscle fatigue affects neither the level of increase in mean body temperature nor the regulation of heat loss responses during prolonged steady-load exercise.     

Energy cost and energy sources of a ballet dance exercise in female adolescents with different technical ability

This study evaluated energy cost and energy sources of a ballet exercise (grand adage) in young female dancers with different technical ability, and then related the energy sources to the subject’s and anaerobic threshold (IAT). Twenty-five dancers (13–16 years) were divided into two different technical ability groups: low-level (n = 13) and high-level (n = 12). The overall energy requirement of dance exercise (VO_2eq) was obtained by adding the amount of VO₂ during exercise above resting (aerobic source or VO_2ex) to the VO₂ up to the fast component of recovery (anaerobic alactic source or VO_2al) and to the energy equivalent of peak blood lactate accumulation (anaerobic lactic source or ) of recovery. VO_2eq of exercise amounted to 81 ± 10 and 94 ± 9 ml kg⁻¹ in low-level and high-level groups, respectively. VO_2ex represented the higher fraction (65 ± 4% and 77 ± 5%) in low-level and high-level groups, respectively, of VO_2eq in both the groups. In the low-level group the remaining fractions were: 23 ± 2 % for VO_2al and 12 ± 1% for . In high-level group the remaining fractions were: 18 ± 2 % for VO_2al and 4 ± 1% for . Between two groups, significant differences were found in VO_2ex (P < 0.01), (P < 0.01), and VO_2al (P < 0.05). IAT was 55 and 60% of for low-level and high-level dancers, respectively. Low-level dancers performed more exercise above IAT than high-level. For these reasons, it should be better to define exercise intensity according to the IAT parameter and not only to      

The effects of training intensity on muscle buffer capacity in females

We examined changes in muscle buffer capacity (βm_{in vitro}), and the lactate threshold (LT) after 5 weeks of high-intensity interval training (INT) above the LT or moderate-intensity continuous training (CON) just below the LT. Prior to and immediately after training, 16 female subjects performed a graded exercise test to determine and the LT, followed 2 days later by a resting muscle biopsy from the vastus lateralis muscle to determine βm_{in vitro}. Following baseline testing, the subjects were randomly placed into the INT (n=8) or CON training group (n=8). Subjects then performed 5 weeks of cycle training (3 days per week), performing either high-intensity INT (6–10×2 min at 120–140% LT with 1 min rest) or moderate-intensity CON (80–95% LT) training. Total training volume was matched between the two groups. After the training period, both groups had significant improvements in (12–14%; P<0.05) and the LT (7–10%; P<0.05), with no significant differences between groups. The INT group, however, had significantly greater improvements in βm_{in vitro} (25%; 123±5–153±7 μmol H⁺·g muscle dm⁻¹·pH⁻¹; P<0.05) than the CON group (2%; 130±12–133±7 μmol H⁺·g muscle dm⁻¹·pH⁻¹, P>0.05). Our results show that when matched for training volume, high-intensity interval training above the LT results in similar improvements in and the LT, but greater improvements in βm_{in vitro} than moderate-intensity continuous training below the LT. This suggests that training intensity is an important determinant of changes to βm_{in vitro}.     

Safe cooling limits from exercise-induced hyperthermia

We evaluated the cooling rate of hyperthermic subjects, as measured by three estimates of deep core temperatures (esophageal, rectal and aural canal temperatures), during immersion in a range of water temperatures. The objective of the study was to compare the three indices of core temperature and define safe cooling limits when using rectal temperature to avoid the development of hypothermia. On 4 separate days, seven subjects (four males, three females) exercised for 45.4±4.1 min at 65% at an ambient temperature of 39°C, RH: 36.5%, until rectal temperature (T _re) increased to 40.0°C (39.5°C for two subjects). Following exercise, the subjects were immersed in a circulated water bath controlled at 2, 8, 14 and 20°C until T _re returned to 37.5°C. When T _re reached normothermia during the cooling period (37.5±0.05°C), both esophageal (T _es) (35.6±1.3°C) and aural canal (T _ac) (35.9±0.9°C) temperatures were approaching or reaching hypothermia, particularly during immersion in 2°C water (T _es=34.5±1.2°C). On the basis of the heat loss data, the heat gained during the exercise was fully eliminated after 5.4±1.5, 7.9±2.9, 10.4±3.8 and 13.1±2.8 min of immersion in 2, 8, 14 and 20°C water, respectively, with the coldest water showing a significantly faster cooling rate. During the immersion in 2°C water, a decrease of only 1.5°C in T _re resulted in the elimination of 100% of the heat gained during exercise without causing hypothermia. This study would therefore support cooling the core temperature of hyperthermic subjects to a rectal temperature between 37.8°C (during immersion in water >10°C) and 38.6°C (during immersion in water <10°C) to eliminate the heat gained during exercise without causing hypothermia.     

Comparison of muscle buffer capacity and repeated-sprint ability of untrained, endurance-trained and team-sport athletes

We measured the muscle buffer capacity (βm) and repeated-sprint ability (RSA) of young females, who were either team-sport athletes (n=7), endurance trained (n=6) or untrained but physically active (n=8). All subjects performed a graded exercise test to determine followed 2 days later by a cycle test of RSA (5×6 s, every 30 s). Resting muscle samples (Vastus lateralis) were taken to determine βm. The team-sport group had a significantly higher βm than either the endurance-trained or the untrained groups (181±27 vs. 148±11 vs. 122±32 μmol H⁺ g dm⁻¹ pH⁻¹ respectively; P<0.05). The team-sport group also completed significantly more relative total work (299±27 vs. 263±31 vs. 223±21 J kg⁻¹, respectively; P<0.05) and absolute total work (18.2±1.6 vs. 14.6±2.4 vs. 13.0±1.9 kJ, respectively; P<0.05) than the endurance-trained or untrained groups during the RSA test. The team-sport group also had a greater post-exercise blood lactate concentration, but not blood pH. There was a significant correlation between βm and RSA (r = 0.67; P<0.05). Our findings show that young females competing in team sports have a larger βm than either endurance-trained or untrained females. This may be the result of the intermittent, high-intensity activity during training and the match play of team-sport athletes. The team-sport athletes also had a greater RSA than either the endurance-trained or untrained subjects. The greater total work by team-sport athletes was predominantly due to a better performance during the early sprints of the repeated-sprint bout.     

Body temperature and its effect on leukocyte mobilization, cytokines and markers of neutrophil activation during and after exercise

We investigated the influence of rectal temperature on the immune system during and after exercise. Ten well-trained male cyclists completed exercise trials (90 min cycling at 60% time trial) on three separate occasions: once in 18°C and twice in 32°C. Twenty minutes after the trials in 32°C, the cyclists sat for ∼20 min in cold water (14°C) on one occasion, whereas on another occasion they sat at room temperature. Rectal temperature increased significantly during cycling in both conditions, and was significantly higher after cycling in 32°C than in 18°C (P < 0.05). Leukocyte counts increased significantly during cycling but did not differ between the conditions. The concentrations of serum interleukin (IL)-6, IL-8 and IL-10, plasma catecholamines, granulocyte-colony stimulating factor, myeloperoxidase and calprotectin increased significantly following cycling in both conditions. The concentrations of serum IL-8 (25%), IL-10 (120%), IL-1 receptor antagonist (70%), tumour necrosis factor-α (17%), plasma myeloperoxidase (26%) and norepinephrine (130%) were significantly higher after cycling in 32°C than in 18°C. During recovery from exercise in 32°C, rectal temperature was significantly lower in response to sitting in cold water than at room temperature. However, immune changes during 90 min of recovery did not differ significantly between sitting in cold water and at room temperature. The greater rise in rectal temperature during exercise in 32°C increased the concentrations of serum IL-8, IL-10, IL-1ra, TNF-α and plasma myeloperoxidase, whereas the greater decline in rectal temperature during cold water immersion after exercise did not affect immune responses.     

Sex-related differences in evaporative heat loss: the importance of metabolic heat production

We evaluated the hypothesis that different rates of metabolic heat production between sexes, during exercise at the same percentage of maximum oxygen consumption give proportional differences in evaporative heat loss. Seven males and seven females, exercised at 41.3 ± 2.7% for 60-min at 40°C and 30% relative humidity. Whole-body direct air calorimetry measured rate of whole-body evaporative heat loss while metabolic heat production was measured by indirect calorimetry. was greater in males (243 ± 18 W m⁻²) relative to females (201 ± 4 W m⁻²) (P ≤ 0.05) throughout exercise. This was paralleled by a greater at end-exercise in males (207 ± 51 W m⁻²) relative to females (180 ± 3 W m⁻²) (P ≤ 0.05). Differences in metabolic heat production between sexes during exercise at a fixed percentage of give differences in evaporative heat loss. To compare thermoregulatory function between sexes, differences in metabolic heat production must therefore be accounted for.     

Physiological responses to nordic walking, walking and jogging

The goal of this study was to evaluate the physiological responses during incremental field tests (FT) in nordic walking (NW), walking (W) and jogging (J). Fifteen healthy middle-aged women participated in three FT. Heart rate (HR) and oxygen uptake were monitored continuously by portable analyzers. Capillary blood lactate (La) was analyzed at rest and after every stage of the FT. The disciplines showed differences during stage 1.8 and 2.1 m s⁻¹ for between NW and W (P < 0.05). The maximum value was measured at 1.8 m s⁻¹ (8%). In accordance with La, was higher in NW compared with W during all stages (P < 0.05) and even higher in NW compared with J during 2.1 and 2.4 m s⁻¹. While there were higher HR for NW and W at 2.4 m s⁻¹ than in J (P < 0.01), there were increases for HR at fixed values of 2 (La2) and 4 (La4) mmol l⁻¹ lactate for J compared with NW and W (P < 0.01). Although the speed of NW was slower than that of W at La2 and La4 (P < 0.05), there were no differences for the HR and the Our results demonstrate that metabolic responses are a helpful instrument to assess the intensity during bipedal exercise. As NW speed at submaximal lactate levels is lower than in W and J, W and J test measures of HR and are not suitable for NW training recommendations. Additionally, the formed by performing NW is not as high as previously reported.     

Reproducibility of relationships between human ventilation, its components and oesophageal temperature during incremental exercise

For human exercise at intensities greater than ~70 to 85% of maximal levels of exertion, ventilation (V _E) increases proportionately to core temperature (T _C) following distinct T _C thresholds. This suggested T _C in humans could be a modulator of exercise-induced ventilation. This study tested the reproducibility of relationships between oesophageal temperature (T _oes), ventilation and its components during incremental exercise. On two nonconsecutive days, at an ambient temperature of 22.1±0.3°C and RH of 45±5%, seven untrained adult males of normal physique pedaled on a seated cycle ergometer in an incremental exercise protocol from rest to the point of exhaustion. In each exercise session, ventilatory equivalents for oxygen consumption and carbon dioxide production plus the components of V _E, tidal volume (V _T) and frequency of respiration (ƒ), were expressed as a function of T _oes. Results indicated the reproducibility criteria of Bland and Altman were met for the relationships between T _oes and both and as well as for relationships between T _oes and each of V _T and f. Intraclass correlation coefficients (R) for between-trial T _oes thresholds for (R=0.91, P<0.05) and (R=0.88, P<0.05) were also high and significant. In both trials, after T _oes increased by ~0.3°C, V _T demonstrated a distinct plateau point at a reproducible T _oes (R=0.93, P<0.05) and ƒ demonstrated a distinct and reproducible T _oes threshold (R=0.84, P<0.05). In conclusion, the results illustrate that for humans, ventilation has a significant and reproducible relationship with core temperature during incremental exercise.     

Power output during women’s World Cup road cycle racing

Little information exists on the power output demands of competitive women’s road cycle racing. The purpose of our investigation was to document the power output generated by elite female road cyclists who achieved success in FLAT and HILLY World Cup races. Power output data were collected from 27 top-20 World Cup finishes (19 FLAT and 8 HILLY) achieved by 15 nationally ranked cyclists (mean ± SD; age: 24.1±4.0 years; body mass: 57.9±3.6 kg; height: 168.7±5.6 cm; 63.6±2.4 mL kg⁻¹ min⁻¹; peak power during graded exercise test (GXT_{peak power}): 310±25 W). The GXT determined GXT_{peak power}, lactate threshold (LT) and anaerobic threshold (AT). Bicycles were fitted with SRM powermeters, which recorded power (W), cadence (rpm), distance (km) and speed (km h⁻¹). Racing data were analysed to establish time in power output and metabolic threshold bands and maximal mean power (MMP) over different durations. When compared to HILLY, FLAT were raced at a similar cadence (75±8 vs. 75±4 rpm, P=0.93) but higher speed (37.6±2.6 vs. 33.9±2.7 km h⁻¹, P=0.008) and power output (192±21 vs. 169±17 W, P=0.04; 3.3±0.3 vs. 3.0±0.4 W kg⁻¹, P=0.04). During FLAT races, riders spent significantly more time above 500 W, while greater race time was spent between 100 and 300 W (LT-AT) for HILLY races, with higher MMPs for 180–300 s. Racing terrain influenced the power output profiles of our internationally competitive female road cyclists. These data are the first to define the unique power output requirements associated with placing well in both flat and hilly women’s World Cup cycling events.     

Core temperature differences between males and females during intermittent exercise: physical considerations

We examined differences in dynamic heat balance between males and females during intermittent exercise. Six males (M) and six females (F) performed three 30-min bouts of exercise (Ex1, Ex2, Ex3) at a constant rate of metabolic heat production () of ~500 W separated by three 15-min periods of inactive recovery. Rate of total heat loss () was measured by direct calorimetry, while was determined by indirect calorimetry. Esophageal (T _es) was measured continuously. Exercise at a constant of ~500 W, was paralleled by a similar between sexes at the end of Ex1 (M: 462 ± 30 W, F: 442 ± 9 W, p = 0.117), Ex2 (M: 468 ± 28 W, F: 508 ± 18 W, p = 0.343), and Ex3 (M: 469 ± 17 W, F: 465 ± 13 W, p = 0.657). Consequently, changes in body heat content were comparable after Ex1 (M: 218 ± 21 kJ, F: 287 ± 35 kJ, p = 0.134), Ex2 (M: 109 ± 18 kJ, F: 158 ± 29 kJ, p = 0.179), and Ex3 (M: 92 ± 19 kJ, F: 156 ± 35 kJ, p = 0.136). However, females had greater overall increases in T _es at the end of Ex3 (M: 0.55 ± 0.25°C, F: 0.97 ± 0.26°C, p ≤ 0.05). Differences in core temperature between sexes appear to be solely related to differences in physical characteristics, and not due to concurrent differences in whole-body thermoregulatory responses.     

High-frequency fatigue after alpine slalom skiing

The purpose of this study was to determine the effect of crank length and cadence on mechanical efficiency in hand cycling. Eight wheelchair dependent, high performance athletes completed four 4-min submaximal exercise bouts at a constant power output of 90 W over the different experimental conditions (crank length, pedal rate) using a sports hand bike (Draft, Godmanchester, UK). Two different crank lengths (180 and 220 mm) were tested at two different cadences (70 and 85 rev min⁻¹) using the synchronous mode of cranking. Physiological measures of oxygen uptake minute ventilation, blood lactate (B[La]), heart rate (HR), rate of perceived exertion (RPE) were recorded, gross (GE) and net (NE) efficiency were calculated. A two-way ANOVA with repeated measures was applied to determine the effects of crank length, cadence and their interaction on these physiological measures. Both GE and NE were significantly higher and significantly lower for the 180 mm crank (P < 0.05). No significant main effect was found for cadence on the physiological measures (P > 0.05). Likewise, no interactions between crank length and pedal rate were found. There was however, a trend observed with HR and B[La] often lower with the 180 mm crank, indicating lower physiological stress. The RPE data supported this finding, with a tendency for lower ratings with the 180 mm crank (9 ± 2 vs. 10 ± 3). The short crank length when used at 85 rev min⁻¹ was found to be the most efficient (GE 21.4 ± 3.1%). In conclusion, crank length has a significant effect on ME in hand cycling. A shorter crank length of 180 mm was found to be more efficient than the 220 mm, regardless of pedal rate during hand cycling.     

Effects of exercise intensity and duration on fat metabolism in trained and untrained older males

Advancing age is associated with changes in fat and carbohydrate (CHO) metabolism, which is considered a risk factor for cardiovascular disease and diabetes. The effects of exercise intensity and duration on fat and CHO metabolism in elderly male subjects were investigated in the present study. Seven trained (63.7 ± 4.7 years) and six untrained (63.5 ± 4.5 years) healthy males performed three 30 min trials on a cycle ergometer at 50, 60 and 70% and two other trials at 60 and 70% in which the total energy expenditure was equal to that for 30 min at 50% Respiratory measures were undertaken throughout the exercise and blood samples taken before and immediately after each trial. Statistical analyses revealed a significant effect of exercise intensity on fat oxidation when the exercise durations were equated as well as when the energy expenditure was held constant for the three trials, though no training effect was noted. Total carbohydrate oxidation increased significantly with exercise intensity (P < 0.05) and with training. Significantly higher levels of non-esterified free fatty acid (NEFA) and glycerol were observed for trained compared with untrained though not for B-hydroxybutyrate (3-OH) or insulin. No differences in NEFA, glycerol, 3-OH were evident for increases in exercise intensity. Carbohydrate and fat oxidation are significantly affected by exercise intensity in elderly males, although only CHO oxidation is influenced by training. Furthermore, training-induced increases in the availability of NEFA and glycerol are not associated with an increase in fat oxidation, rather an increase in CHO oxidation.     

The effects of β1-adrenergic blockade on cardiovascular oxygen flow in normoxic and hypoxic humans at exercise

At exercise steady state, the lower the arterial oxygen saturation (SaO₂), the lower the O₂ return A linear relationship between these variables was demonstrated. Our conjecture is that this relationship describes a condition of predominant sympathetic activation, from which it is hypothesized that selective 1-adrenergic blockade (BB) would reduce O₂ delivery and To test this hypothesis, we studied the effects of BB on and in exercising humans in normoxia and hypoxia. O₂ consumption cardiac output heart rate, SaO₂ and haemoglobin concentration were measured on six subjects (age 25.5±2.4 years, mass 78.1±9.0 kg) in normoxia and hypoxia (inspired O₂ fraction of 0.11) at rest and steady-state exercises of 50, 100, and 150 W without (C) and with BB with metoprolol. Arterial O₂ concentration (CaO₂), and were then computed. Heart rate, higher in hypoxia than in normoxia, decreased with BB. At each was higher in hypoxia than in normoxia. With BB, it decreased during intense exercise in normoxia, at rest, and during light exercise in hypoxia. SaO₂ and CaO₂ were unaffected by BB. The changes under BB were parallel to those in was unaffected by exercise in normoxia. In hypoxia the slope of the relationship between and was lower than 1, indicating a reduction of with increasing workload. was a linear function of SaO₂ both in C and in BB. The line for BB was flatter than and below that for C. The resting in normoxia, lower than the corresponding exercise values, lied on the BB line. These results agree with the tested hypothesis. The two observed relationships between and SaO₂ apply to conditions of predominant sympathetic or vagal activation, respectively. Moving from one line to the other implies resetting of the cardiovascular regulation.     

Determination of the maximal fat oxidation point in obese children and adolescents: validity of methods to assess maximal aerobic power

We aimed to examine the interchangeability of techniques used to assess maximal oxygen consumption () and maximal aerobic power (MAP) employed to express the maximal fat oxidation point in obese children and adolescents. Rate of fat oxidation were measured in 24 obese subjects (13.0 ± 2.4 years; Body Mass Index 30.2 ± 6.3 kg m⁻²) who performed a five 4-min stages submaximal incremental cycling exercise. A second cycling exercise was performed to measure . Results are those of the 20 children who achieved the criterion of RER (>1.02) to assess the attainment of . Although correlations between results obtained by different methods were strong, Bland–Altman plots showed little agreement between the maximal fat oxidation point expressed as a percentage of measured and as % estimated according to ACSM guidelines (underestimation : −5.9%) or using the predictive equations of Wasserman (−13.9%). Despite a mean underestimation of 1.4% several values were out of the limits of agreement when comparing measured MAP and Theoretical MAP. Estimations of lead to underestimations of the maximal fat oxidation point.     

Effect of posture on high-intensity constant-load cycling performance in men and women

The time sustained during a graded cycle exercise is ~10% longer in an upright compared with a supine posture. However, during constant-load cycling this effect is unknown. Therefore, we tested the postural effect on the performance of high-intensity constant-load cycling. Twenty-two active subjects (11 men, 11 women) performed two graded tests (one upright, one supine), and of those 22, 10 subjects (5 men, 5 women) performed three high-intensity constant-load tests (one upright, two supine). To test the postural effect on performance at the same absolute intensity, during the upright and one of the supine constant-load tests subjects cycled at 80% of the peak power output achieved during the upright graded test. To test the postural effect on performance at the same relative intensities, during the second supine test subjects cycled at 80% of the peak power output achieved during the supine graded test. Exercise time on the graded and absolute intensity constant-load tests for all subjects was greater (P<0.05) in the upright compared with supine posture (17.9±3.5 vs. 16.1±3.1 min for graded; 13.2±8.7 vs. 5.2±1.9 min for constant-load). This postural effect at the same absolute intensity was larger in men (19.4±8.5 upright vs. 6.6±1.6 supine, P<0.001) than women (7.1±2 upright vs. 3.9±1.4 supine, P>0.05) and it was correlated (P<0.05) with both the difference in between positions during the first minute of exercise (r=0.67) and the height of the subjects (r=0.72). In conclusion, there is a very large postural effect on performance during constant-load cycling exercise and this effect is significantly larger in men than women.     

No effect of skin temperature on human ventilation response to hypercapnia during light exercise with a normothermic core temperature

Hyperthermia potentiates the influence of CO₂ on pulmonary ventilation ( [(V)\dot]_\textE \dot{V}_{\text{E}} ). It remains to be resolved how skin and core temperatures contribute to the elevated exercise ventilation response to CO₂. This study was conducted to assess the influences of mean skin temperature ( [`(T)]<sub>\textSK</sub> \overline{T}_{\text{SK}} ) and end-tidal PCO<sub>2</sub> (P<sub>ET</sub>CO<sub>2</sub>) on [(V)\dot]<sub>\textE</sub> \dot{V}_{\text{E}} during submaximal exercise with a normothermic esophageal temperature (T <sub>ES</sub>). Five males and three females who were 1.76 ± 0.11 m tall (mean ± SD), 75.8 ± 15.6 kg in weight and 22.0 ± 2.2 years of age performed three 1 h exercise trials in a climatic chamber with the relative humidity (RH) held at 31.5 ± 9.5% and the ambient temperature (T <sub>AMB</sub>) maintained at one of 25, 30, or 35°C. In each trial, the volunteer breathed eucapnic air for 5 min during a rest period and subsequently cycle ergometer exercised at 50 W until T <sub>ES</sub> stabilized at ~37.1 ± 0.4°C. Once T <sub>ES</sub> stabilized in each trial, the volunteer breathed hypercapnic air twice for ~5 min with P<sub>ET</sub>CO<sub>2</sub> elevated by approximately +4 or +7.5 mmHg. The significantly (P < 0.05) different increases of P<sub>ET</sub>CO<sub>2</sub> of +4.20 ± 0.49 and +7.40 ± 0.51 mmHg gave proportionately larger increases in [(V)\dot]<sub>\textE</sub> \dot{V}_{\text{E}} of 10.9 ± 3.6 and 15.2 ± 3.6 L min<sup>−1</sup> (P = 0.001). This hypercapnia-induced hyperventilation was uninfluenced by varying the [`(T)]_\textSK \overline{T}_{\text{SK}} to three significantly different levels (P < 0.001) of 33.2 ± 1.2°C, to 34.5 ± 0.8°C to 36.4 ± 0.5°C. In conclusion, the results support that skin temperature between ~33 and ~36°C has neither effect on pulmonary ventilation nor on hypercapnia-induced hyperventilation during a light exercise with a normothermic core temperature.