Effect of an acute period of resistance exercise on excess post-exercise oxygen consumption: implications for body mass management

Studies have shown metabolism to remain elevated for hours following resistance exercise, but none have gone beyond 16 h, nor have they followed a whole body, high intensity exercise protocol. To examine the duration of excess post-exercise oxygen consumption (EPOC) following a period of heavy resistance exercise, seven healthy men [mean (SD) age 22 (3) years, height 177 (8) cm, mass 83 (10) kg, percentage body fat 10.4 (4.2)%] engaged in a 31 min period of resistance exercise, consisting of four circuits of bench press, power cleans, and squats. Each set was performed using the subject's own predetermined ten-repetition maximum and continued until failure. Oxygen consumption ( ) measurements were obtained at consistent times (34 h pre-, 29 h pre-, 24 h pre-, 10 h pre-, 5 h pre-, immediately post-, 14 h post-, 19 h post-, 24 h post-, 38 h post-, 43 h post-, and 48 h post-exercise). Post-exercise measurements were compared to the baseline measurements made at the same time of day. The was significantly elevated (P<0.05) above baseline values at immediately post, 14, 19, and 38 h post-exercise. Mean daily values for both post-exercise days were also significantly elevated above the mean value for the baseline day. These results suggest that EPOC duration following resistance exercise extends well beyond the previously reported duration of 16 h. The duration and magnitude of the EPOC observed in this study indicates the importance of future research to examine a possible role for high intensity resistance training in a weight management program for various populations. Electronic Publication     

The effects of intensity of exercise on excess postexercise oxygen consumption and energy expenditure in moderately trained men and women

Summary This experiment investigated the effects of intensity of exercise on excess postexercise oxygen consumption (EPOC) in eight trained men and eight women. Three exercise intensities were employed 40%, 50%, and 70% of the predetermined maximal oxygen consumption (VO_2max). All ventilation measured was undertaken with a standard, calibrated, open circuit spirometry system. No differences in the 40%, 50% and 70% VO_2max trials were observed among resting levels of oxygen consumption (V0₂) for either the men or the women. The men had significantly higher resting VO₂ values being 0.31 (SEM 0.01) 1·min^–1 than did the women, 0.26 (SEM 0.01) 1·min^–1 (P < 0.05). The results indicated that there were highly significant EPOC for both the men and the women during the 3-h postexercise period when compared with resting levels and that these were dependent upon the exercise intensity employed. The duration of EPOC differed between the men and the women but increased with exercise intensity: for the men 40% – 31.2 min; 50% – 42.1 min; and 70% – 47.6 min and for the women, 40% – 26.9 min; 50% – 35.6 min; and 70% – 39.1 min. The highest EPOC, in terms of both time and energy utilised was at 70% VO_2max. The regression equation for the men, where y=O₂ in litres, and x=exercise intensity as a percentage of maximum was y=0.380x + 1.9 (r ²=0.968) and for the women is y=0.374x–0.857 (r ²=0.825). These findings would indicate that the men and the women had to exercise at the same percentage of their VO_2max to achieve the maximal benefits in terms of energy expenditure and hence body mass loss. However, it was shown that a significant EPOC can be achieved at moderate to low exercise intensities but without the same body mass loss and energy expenditure.     

Acute EPOC response in women to circuit training and treadmill exercise of matched oxygen consumption

The purpose of the study was to evaluate the effects of circuit training (CT) and treadmill exercise performed at matched rates of oxygen consumption and exercise duration on elevated post-exercise oxygen consumption (EPOC) in untrained women, while controlling for the menstrual cycle. Eight, untrained females (31.3±9.1 years; 2.04±0.26 l min^–1 estimated VO_2max; BMI=24.6±3.9 kg/m²) volunteered to participate in the study. Testing was performed during the early follicular phase for each subject to minimize hormonal variability between tests. Subjects performed two exercise sessions approximately 28 days apart. Resting, supine energy expenditure was measured for 30 min preceding exercise and for 1 h after completion of exercise. Respiratory gas exchange data were collected continuously during rest and exercise periods via indirect calorimetry. CT consisted of three sets of eight common resistance exercises. Pre-exercise and exercise oxygen consumption was not different between testing days (P>0.05). Thus, exercise conditions were appropriately matched. Analysis of EPOC data revealed that CT resulted in a significantly higher (p<0.05) oxygen uptake during the first 30 min of recovery (0.27±0.01 l min^–1 vs 0.23±0.01 l min^–1); though, at 60 min, treatment differences were not present. Mean VO₂ remained significantly higher (0.231±0.01 l min^–1) than pre-exercise measures (0.193±0.01 l min^–1) throughout the 60-min EPOC period (p<0.05). Heart rate, RPE, V_E and RER were all significantly greater during CT (p<0.05). When exercise VO₂ and exercise duration were matched, CT was associated with a greater metabolic disturbance and cost during the early phases of EPOC.     

Association between anaerobic components of the maximal accumulated oxygen deficit and 30-second Wingate test

The purpose of this study was to analyze the relationship between the anaerobiccomponents of the maximal accumulated oxygen deficit (MAOD) and of the 30-secondWingate anaerobic test (30-WAnT). Nine male physical education students performed: a)a maximal incremental exercise test; b) a supramaximal constant workload test todetermine the anaerobic components of the MAOD; and c) a 30-WAnT to measure the peakpower (PP) and mean power (MP). The fast component of the excess post-exercise oxygenconsumption and blood lactate accumulation were measured after the supramaximalconstant workload test in order to determine the contributions made by alactic(AL_MET) and lactic (LA_MET) metabolism. Significantcorrelations were found between PP and AL_MET (r=0.71; P=0.033) and betweenMP and LA_MET (r=0.72; P=0.030). The study results suggested that theanaerobic components of the MAOD and of the 30-WAnT are similarly applicable in theassessment of AL_MET and LA_MET during high-intensityexercise.     

Kinetics of oxygen uptake and recovery for supramaximal work of short duration

In order to follow the time pattern of oxygen uptake and recovery for supramaximal work of short duration, 35 male subjects (mean age 21.4 years, mean body weight 71.9 kg) pedalled a bicycle ergometer at maximal speed for 1 min. A constant frictional resistance of 5.5 kg was used, resulting in a total work output of 2890 kpm (85 revolutions, SD = 7.5). The total percent decrement in work output from the initial rate on this test was 59.7 %. The total oxygen uptake during the work averaged 2.35 l, the net oxygen recovery was 4.891, while the net work efficiency was 19.3 %. One and two component exponential curves fit the observed oxygen uptake and recovery measures with a high degree of accuracy. Comparison of the curve parameters with published data showed large differences for the post exercise oxygen recovery and the slow component of the recovery curve. The magnitude of the fast component of recovery was similar to other data. The total oxygen uptake during the test was found to be 10% lower than the maximal oxygen uptake determined on a seperate progressive step-increment test. It was shown, by curve analysis, that the maximal oxygen uptake would have been reached in approximately 2 min.     

Direct determination of local oxygen consumption of the brain cortex in vivo

Summary A method is described to determine local oxygen consumption quantitatively in the brain cortex under in vivo conditions. Local oxygen consumption is calculated from the slope of local tissue P_{O 2} decrease during a few seconds of total ischemia of the brain for each second after the stop of circulation. The decrease of tissue P_{O 2} is recorded simultaneously at several measuring sites. To be independent of oxygen chemically bound to hemoglobin, tissue P_{O 2} values are raised above 100 Torr. The calculation of local oxygen consumption for each second during the short period of ischemia showed that the O₂ consumption remains constant only for a few seconds ranging from 5 to maximally 15 s at different locations. Then O₂ consumption decreases continuously although the tissue P_{O 2} values are still above the full saturation of hemoglobin. The rate of local oxygen consumption varies considerably at different measuring sites of the superficial layers of the brain cortex (cat). The mean value amounts to 3±1.5 ml O₂/100 g tissue and minute.     

Effects of aldosterone on lipid metabolism and renal oxygen consumption in the rat

Summary The plasma level of free fatty acids (FFA) in adrenalectomized rats increases by 50% after treatment with aldosterone (2 g/100 g rat).Lipolytic activity in peripheral fat tissue is lowered after adrenalectomy and doubles after in vivo administration of aldosterone to adrenalectomized rats (measured as free fatty acid release in vitro from epididymal fat tissue).Lypolysis of adipose tissue stimulated by the in vitro presence of ACTH also increases after in vivo administration of aldosterone.Incorporation of intravenously administered label from U¹⁴C-palmitate into total extractable lipid of renal tissue is augmented 3 h after aldosterone administration to adrenalectomized rats, while no increase of the radioactivity is observed in total lipid from liver tissue. Treatment with aldosterone does not affect the total lipid content of kidney or liver in adrenalectomized rats.The oxygen consumption rate of kidney cortex slices with lactate, -hydroxybuterate or acetoacetate as substrates is lowered after in vivo administration of aldosterone to adrenalectomized rats. With succinate, however, the respiratory rate of kidney slices increases after aldosterone treatment of adrenalectomized rats, the ouabain-sensitive respiration being more affected than the ouabain-insensitive respiration. An interpretation of the O₂ consumption data implicating competition of lipid metabolism for CoA-SH is discussed.     

Effect of exercise intensity on post-exercise oxygen consumption and heart rate recovery

Purpose

There is some evidence that measures of acute post-exercise recovery are sensitive to the homeostatic stress of the preceding exercise and these measurements warrant further investigation as possible markers of training load. The current study investigated which of four different measures of metabolic and autonomic recovery was most sensitive to changes in exercise intensity.

Methods

Thirty-eight moderately trained runners completed 20-min bouts of treadmill exercise at 60, 70 and 80 % of maximal oxygen uptake (VO_2max) and four different recovery measurements were determined: the magnitude of excess post-exercise oxygen consumption (EPOC_MAG), the time constant of the oxygen consumption recovery curve (EPOCτ), heart rate recovery within 1 min (HRR_60s) and the time constant of the heart rate recovery curve (HRRτ) .

Results

Despite significant differences in exercise parameters at each exercise intensity, only EPOC_MAG showed significantly slower recovery with each increase in exercise intensity at the group level and in the majority of individuals. EPOCτ was significantly slower at 70 and 80 % of VO_2max vs. 60 % VO_2max and HRRτ was only significantly slower when comparing the 80 vs. 60 % VO_2max exercise bouts. In contrast, HRR_60s reflected faster recovery at 70 and 80 % of VO_2max than at 60 % VO_2max.

Conclusion

Of the four recovery measurements investigated, EPOC_MAG was the most sensitive to changes in exercise intensity and shows potential to reflect changes in the homeostatic stress of exercise at the group and individual level. Determining EPOC_MAG may help to interpret the homeostatic stress of laboratory-based research trials or training sessions.     

Electrostimulation improves muscle perfusion but does not affect either muscle deoxygenation or pulmonary oxygen consumption kinetics during a heavy constant-load exercise

Electromyostimulation (EMS) is commonly used as part of training programs. However, the exact effects at the muscle level are largely unknown and it has been recently hypothesized that the beneficial effect of EMS could be mediated by an improved muscle perfusion. In the present study, we investigated rates of changes in pulmonary oxygen consumption and muscle deoxygenation during a standardized exercise performed after an EMS warm-up session. We aimed at determining whether EMS could modify pulmonary O₂ uptake and muscle deoxygenation as a result of improved oxygen delivery. Nine subjects performed a 6-min heavy constant load cycling exercise bout preceded either by an EMS session (EMS) or under control conditions (CONT). and heart rate (HR) were measured while deoxy-(HHb), oxy-(HbO₂) and total haemoglobin/myoglobin (Hb_tot) relative contents were measured using near infrared spectroscopy. EMS significantly increased (P < 0.05) the Hb_tot resting level illustrating a residual hyperaemia. The EMS priming exercise did not affect either the HHb time constant (17.7 ± 14.2 s vs. 13.1 ± 2.3 s under control conditions) or the kinetics (time-constant = 18.2 ± 5.2 s vs. 15.4 ± 4.6 s under control conditions). Likewise, the other parameters were unchanged. Our results further indicated that EMS warm-up improved muscle perfusion through a residual hyperaemia. However, neither nor [HHb] kinetics were modified accordingly. These results suggest that improved O₂ delivery by residual hyperaemia induced by EMS does not accelerate the rate of aerobic metabolism during heavy exercise at least in trained subjects.     

The effect of exercise intensity and duration on salivary immunoglobulin A

Summary Two experiments were performed to examine salivary immunoglobulin A (s-IgA) responses to varying levels of exercise intensity and duration. For experiment 1, 9 college men (mean age, SD=23.56, 1.64 years) completed treadmill runs of 15, 30, and 45 min at approximately 60% of maximum oxygen consumption (VO_2max). For experiment 2, 9 other college men (mean age, SD=23.67, 2.0 years) ran for 20 min at approximately 50, 65 and 80% of VO_2max. Unstimulated salivary samples were collected before, and immediately, 1 and 2 h after the exercise. Samples were assayed for s-IgA using an enzyme-linked immunosorbent assay. Mean s-IgA levels did not change significantly (P>0.05) at any of the post-exercise collection times when compared to pre-exercise levels. The results of this investigation indicated that running at intensities of 50–80% of VO_2max and for durations of 15–45 min did not affect s-IgA levels.     

The effects of two levels of caffeine ingestion on excess postexercise oxygen consumption in untrained women

Summary The effects of two levels of caffeine ingestion (5 mg·kg ^–1, CAF1, and 10 mg·kg ^–1, CAF2) on postexercise oxygen consumption was investigated in six untrained women aged 20.5 (SEM 0.5) years. After a test to determine maximal oxygen consumption (VO_2max) each subject underwent three test sessions at 55% VO_2max either in a control condition (CON) or with the CAF1 or CAF2 dose of caffeine. During exercise, oxygen consumption was found to be significantly higher in the CAM and CAF2 trials, compared to CON (P<0.05). During the hour postexercise, oxygen consumption in CAF1 and CAF2 remained significantly higher than in CON (P<0.05). At all times throughout the exercise, free fatty acid (FFA) concentrations were significantly higher in the caffeine trials than in CON. The FFA concentrations 1 h postexercise (+ 60 min) were further elevated above resting values for all three trials. Caffeine ingestion caused the greatest elevation above resting levels being 1.89 (SEM 0.19) mmol·l^–1 and 1.96 (SEM 0.22) mmol·1^–1 for the CAF1 and CAF2 trials, respectively. This was significantly higher (P<0.0001) than the CON level which was 0.97 (SEM 0.19) mmol·l^–1. Respiratory exchange ratio (R) values became significantly lower (P<0.05) in CAF1 and CAF2 compared to CON at the onset of exercise and continued to decrease during the activity. Throughout the recovery period, R values were significantly lower for both caffeine trials compared to CON. The results of this study would suggest that caffeine is useful in significantly increasing metabolic rate above normal levels in untrained women during, as well as after, exercising at 55% VO_2max.     

Intracapillary hemoglobin oxygen saturation and oxygen consumption in different layers of the left ventricular myocardium

Summary Oxygen consumption in subendocardial and subepicardial layers of left ventricular myocardium was studied. Oxygen consumption was calculated from regional perfusion data obtained by the microsphere technique and regional O₂ extraction derived from intracapillary HbO₂ saturation (i.c. HbsO₂). I.c. HbsO₂ data were obtained cryomicrophotometrically from shock-frozen, transmural tissue specimens removed from thoracotomized dogs. Left ventricular myocardial blood flow at the time of the specimen removal was 63±9 ml/min · 100 g. The ratio of subendocardial to subepicardial blood flow was 1.27 ±0.17. Coronary sinus blood oxygen saturation was 31±2% and left ventricular oxygen consumption was 8.4±1.1 ml/min · 100 g. A mean i.c. HbsO₂ of 47±18% was obtained. 23% of all measured i.c. HbsO₂ values were lower than the respective coronary sinus value. The mean subendocardial i.c. HbsO₂ (41±19%) was significantly lower than the mean subepicardial value (53±16%). From these data a ratio of subendocardial to subepicardial oxygen consumption of 1.57 was calculated. This result is in agreement with recent hypotheses, stating that myocardial fiber shortening and energy demands in deeper layers of left ventricle exceed those of superfical layers.Supported by Deutsche Forschungsgemeinschaft and by Stiftung Volkswagenwerk     

Recovery dynamics of skeletal muscle oxygen uptake during the exercise off-transient

The time course of muscle recovery from contractions (i.e., muscle off-kinetics), measured directly at the site of O₂ exchange, i.e., in the microcirculation, is unknown. Whereas biochemical models based upon creatine kinase flux rates predict slower off- than on-transients [Kushmerick, M.J., 1998. Comp. Biochem. Physiol. B: Biochem. Mol. Biol.] whole muscle data [Krustrup, et al. J. Physiol.] suggest on–off symmetry.

Purpose

We tested the hypothesis that the slowed recovery blood flow (Qm) kinetics profile in the spinotrapezius muscle [Ferreira et al., 2006. J. Physiol.] was associated with a slowed muscle recovery compared with that seen at the onset of contractions (time constant, τ  23 s, Behnke et al., 2002. Resp. Physiol.), i.e., on–off asymmetry.

Methods

Measurements of capillary red blood cell flux and microvascular pressure of O₂ (P_O2mv) were combined to resolve the temporal profile of muscle across the moderate intensity contractions-to-rest transition.

Results

Muscle decreased from an end-contracting value of 7.7 ± 0.2 ml/100 g/min to 1.7 ± 0.1 ml/100 g/min at the end of the 3 min recovery period, which was not different from pre-stimulation . Contrary to our hypothesis, muscle in recovery began to decrease immediately (i.e., time delay <2 s) and demonstrated rapid first-order kinetics (τ, 25.5 ± 2.6 s) not different (i.e., symmetrical to) to those during the on-transient. This resulted in a systematic increase in microvascular P_O2 during the recovery from contractions.

Conclusions

The slowed Qm kinetics in recovery serves to elevate the ratio and thus microvascular P_O2. Whether this Qm response is obligatory to the rapid muscle kinetics and hence speeds the repletion of high-energy phosphates by maximizing conductive and diffusive O₂ flux is an important question that awaits resolution.     

The effect of prolonged submaximal exercise on gas exchange kinetics and ventilation during heavy exercise in humans

This study compared ventilation, gas exchange (oxygen uptake, V̇O₂) and the surface electromyogram (EMG) activity of four major lower limb muscles during heavy exercise before (Pre-Ex) and after (Post-Ex) a sustained 90-min cycling exercise at 60% V̇O_2peak. The 90-min exercise was incorporated under the hypothesis that sustained exercise would alter substrate availability in the second exercise bout causing differences in fibre recruitment patterns, gas exchange and ventilation. Nine trained male subjects [V̇O_2peak=60.2 (1.7) ml·kg⁻¹·min⁻¹] completed two identical 6-min bouts of cycling performed at high intensity [~90% V̇O_2peak; 307 (6) W, mean (SE)]. Ventilation and gas exchange were measured breath-by-breath and the EMG was recorded during the last 12 s of each minute of the two 6-min bouts. EMG signals were analysed to determine integrated EMG (iEMG) and mean power frequency (MPF). V̇O₂ at min 3 and min 6 in Post-Ex were significantly higher (i.e., +201 and 141 ml·min⁻¹, respectively, P<0.05) than in Pre-Ex but there was a ~25% decrease of the slow component, taken as the difference between min 6 and min 3 [187 (27) vs 249 (35) ml·min⁻¹, respectively, P<0.05]. The greater whole-body V̇O₂ after 3 min of exercise in Post-Ex was not accompanied by clear alterations in the iEMG and MPF of the examined leg muscles. Ventilation and heart rate were elevated (~12–16 l·min⁻¹ and ~10 beats·min⁻¹, respectively, P<0.05) as were the ratios V̇ _E/O₂ and V̇ _E/V̇CO₂ in the Post-Ex tests. It was concluded that the V̇O₂ and ventilation responses to high-intensity exercise can be altered following prolonged moderate intensity exercise in terms of increased amplitude without associated major changes in either iEMG or MPF values among conditions.     

The effect of water deprivation and hypertonic salt injection on the oxygen consumption and plasma NaCl concentration in the albino rat

Summary O₂-consumption of the whole animal was measured for rats deprived of water and food, or food only, at 27°C (for 3 days), 35°C (for 1 day), and in animals injected with NaCl solution intraperitoneally (3 ml/100 g B. W. of 3% NaCl). O₂-consumption calculated per gram body weight, decreased by about 20% compared with the control value in animals deprived of water at 27°C, but increased by about 9% in animals deprived of water at 35° C. A 15% to 40% increase in the O₂-consumption over the control value was found in the salt injected animals. Plasma NaCl concentration increased by about 5% and 10% in the animals deprived of water at 27°C and 35°C respectively; an increase of about 10% was found in the salt injected group. Rectal temperature was not affected by the experimental treatments. It is suggested that the reduction of the extracellular fluid volume for a long period might explain the observed reduction in the O₂-consumption for the animals deprived of water at 27°C.This study was partially supported by the National Council for Research and Development of Israel.     

Blood lactate accumulation in intermittent supramaximal exercise

Summary Blood lactate accumulation rate and oxygen consumption have been studied in six trained male runners, aged 20 to 30 years. Subjects ran on a treadmill at a rate representing 172±5% for four 45 s sessions, separated by 9 min rest periods. Oxygen consumption was measured throughout. Blood lactate was determined in samples taken from the ear and was measured at the end of each exercise session, and two, five and nine minutes later. After the fourth exercise session, the same measurements were made every five min for 30 min. 4 subjects repeated a single exercise of the same type, duration and intensity and the same measurements were taken. With repetitive intermittent exercise, gradual increases in blood lactate concentration ([LA]b) occurred, whereas its rate of accumulation ([LA]b) decreased. The amount of oxygen consumed during each 45 s exercise session remained unchanged for a given subject. After cessation of intermittent exercise, the half-time of blood lactate was 26 min, whereas it was only 15 min after a single exercise session. values, on the other hand, returned to normal after 15 to 20 min. All other conditions being equal, the gradual decrease in [LA]b during intermittent exercise could be explained if the lactate produced during the first exercise session is used during the second period, and/or if the diffusion space of lactate increases. The diffusion space seems to be multicompartmental on the basis of half-time values noted for [LA]b after intermittent exercise, compared with those noted after a single exercise session. The distinction between the rapid return to normal values and the more gradual return to normal blood lactate levels confirms that there is no simple and direct relationship between oxygen debt and the accumulation of blood lactate after muscular exercise. In practical terms, these results show that the calorific equivalent of lactic acid defined by Margaria et al. (1963) cannot be used in the case of intermittent exercise of supramaximal intensity.     

The oxygen supply of the rat kidney: Measurements of intrarenalpO2

Summary Using a newly developed platinum-O₂-microeletrode [30] based on the design ofSilver [37] the construction and properties of which are described,pO₂-measurements in the parenchyma of the blood-perfused and the cell-free perfused rat kidney were carried out.By continuous recording of thepO₂ during slow (150 ×min^–1) insertion of the O₂-electrode into the respiring tissue two regions of distinctly different meanpO₂-values were found. In the outer region which extends from the renal surface to a depth of about 3–4 mm (corresponding anatomically with the renal cortex) largepO₂-differences exist close to each other. In the blood-perfused kidney the maximum corticalpO₂-values lie in the range of arterialpO₂ the lowest values at about 10 Torr. In the cortex of the cell-free perfused kidney the maximumpO₂-values lie considerably below the arterialpO₂.In both the blood perfused and in the cell-free perfused kidney at centripetal movement of the O₂-electrode the cortical region of high and fluctuatingpO₂ is followed by a narrow zone (200 radial extension) of a steep decrease of the meanpO₂. At further insertion in both preparations thepO₂ remains at lowpO₂-values of ca. 10 Torr. Anatomically, this latter region of low and constantpO₂ corresponds to renal medulla and pelvis.By recording the decrease of parenchymalpO₂ after sudden stop of the perfusion attempts were made at measuring the critical local O₂-supply pressure. In the cortex of the cell-free perfused kidney critical local O₂-supply pressures between 6 and 28 Torr with a maximum abundance at 8 Torr were found.The qualitative and quantitative implications of the presented data on the conditions of parenchymal O₂-supply are discussed. The results are interpreted as an indication for the arteriovenous shunt (bypass)-diffusion of considerable amounts of oxygen, especially under the conditions of the cell-free perfusion. Furthermore, it follows from the data presented that even at high venous O₂-pressures and high meanpO₂-values in the parenchyma regions of local anoxia may exist.     

Physiological responses to intermittent and continuous exercise at the same relative intensity in older men

We investigated the physiological responses in older men to continuous (CEx) and intermittent (IEx) exercise. Nine men [70.4 (1.2) years, O_2peak: 2.21 (0.20) l min^–1; mean (SE)] completed eight exercise tests (two CEx and six IEx) on an electronically braked cycle ergometer in random order. CEx and IEx were performed at 50% and 70% O_2peak. IEx was performed using 60sE:60sR, 30sE:30sR and 15sE:15sR exercise to rest ratios. The duration of exercise was adjusted so that the total amount of work completed was the same for each exercise test. Oxygen uptake (O₂), minute ventilation (_E) and heart rate (HR) were measured at the mid-point of each exercise test. Arterialised blood samples were obtained at rest and during exercise and analysed for pH and PCO₂. At the same relative intensity (50% or 70% O_2peak), IEx resulted in a significantly lower (P<0.01) O₂, _E and HR than CEx. There were no significant differences (P>0.05) in O₂, _E and HR measured at the mid point of the three exercise to rest ratios at 50% and 70% O_2peak. pH and PCO₂ during CEx and IEx at 50% O_2peak were not significantly different from rest. CEx performed at 70% O_2peak resulted in significant decreases (P<0.05) in pH and PCO₂. There was a significant decrease (P<0.05) in pH only during the 60sE:60sR IEx at 70% O_2peak. Changes in arterialised PCO₂ during the 60sE:60sR, 30sE:30sR and 15sE:15sR at both 50% and 70% O_2peak exercise tests were not significant. When exercising at the same percentage of O_2peak and with the total amount of work fixed, IEx results in significantly lower physiological responses than CEx in older men. All results are given as mean (SE).     

The effect of exercise intensity on the post-exercise esophageal temperature response

On 2 separate days, nine volunteers aged 23.8 (2.0) years performed 15-min bouts of treadmill running in a temperature-controlled chamber at 29°C at a power output that elicited either 70% (moderate) or 93% (intense) of maximum oxygen consumption. Exercise was followed by a 45-min recovery period. End-exercise esophageal temperature (T _es) was elevated by 0.97°C and 2.17°C above baseline for the moderate and intense exercise trials, respectively. Post-exercise T _es achieved a sustained elevated value of 0.38°C and 0.79°C within 15 min of exercise cessation. Systolic blood pressure (SBP) for both exercise trials became hypotensive for the full recovery period, with the magnitude of the reduction being greater for the intense exercise (P<0.05). Diastolic blood pressure (DBP) was unaffected by exercise intensity and values were lower than baseline between 15 min and 30 min post-exercise (P<0.05). Mean arterial pressure (MAP) was reduced from baseline for both exercise trials, with intense exercise showing a greater decrement (P<0.05). It was shown that the increase in the post-exercise hypotensive response, induced by exercise of increasing intensity, was paralleled by an increase in the magnitude of the post-exercise elevation in T _es (i.e., a difference of 0.41°C between conditions). Electronic Publication