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.     

The effects of substrate utilization,manipulated by caffeine,on post-exercise oxygen consumption in untrained female subjects

Summary The effect of substrate utilization manipulated by caffeine on post-exercise oxygen consumption was investigated in five untrained females (age=21±1.5 years), following 90 min of treadmill walking at 55% maximal oxygen consumption. Each subject participated in the two trials (control and experimental) within 2 weeks of each other. Immediately following the measurement of resting oxygen consumption, subjects consumed one of the two test beverages 60 min prior to exercise: 5 mg of caffeine per kg of bodyweight in 200 ml of orange juice (CA) or 200 ml of orange juice (C). Assignment of CA and C was made in a random, double blind fashion. Immediately prior to the exercise phase (0 min) resting oxygen consumption was again measured. Following exercise, subjects returned to the same pre-exercise sitting position where respiratory data was collected over 1 h. No significant differences were found in resting oxygen consumption and respiratory exchange ratio (R) prior to caffeine ingestion (−60 min). One hour after caffeine ingestion (0 min) oxygen consumption and free fatty acid (FFA) levels increased significantly compared to C. During and 1 h following exercise, oxygen consumption and FFA levels were significantly greater, with R values being significantly lower in CA compared to C. These findings provide further evidence that metabolic substrate is somehow implicated in elevating oxygen consumption following exercise cessation.     

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     

Plasma sulpho-conjugated catecholamine dynamics up to 8 h after 60-min exercise at 50% and 70% maximal oxygen uptakes

The prolonged effects of steady-state exercise and meals on plasma sulpho-conjugated catecholamines (CA) after exercise were examined. Seven male subjects exercised on 2 separate days for 60 min at 50% and 70% of maximal oxygen uptake ( ) on a cycle ergometer and then rested, for 8 h sitting in an armchair. A control trial without any exercise was also performed. At 2 h after the end of exercise the subjects were given a meal. The plasma free and sulphated CA, oxygen uptake ( ) and heart rate (HR) were all measured before exercise, during exercise and hourly during the 8-h recovery period. The sulphated noradrenaline (NA-S) and adrenaline (A-S) concentrations increased after exercise, and, furthermore, only the NA-S concentrations remained elevated for 6 h after exercise at 50% and for 8 h at 70% trial, compared with the control trial. There were no changes in either the plasma NA-S or A-S concentrations after consuming a meal, whereas the dopamine sulphate concentration demonstrated a dynamic change. A significantly higher excess postexercise was observed at 2 h postexercise at 50% and at 6 h postexercise at 70% trials. The mean HR was still elevated at 6 and 8 h after exercise, which closely correlated with the duration of the elevated NA-S concentrations. These results suggest that sulphated CA, especially NA-S, could represent an additional index of sympathetic nerve activity after exercise, and that a meal containing small amounts of the amines would seem to have no effect on plasma NA-S and A-S concentrations.     

Resistance exercise increases postexercise oxygen consumption in nonexercising muscle

This study examined the effect of knee extension resistance exercise on muscle oxygen consumption in nonexercising forearm flexor muscles after exercise. Seven healthy male subjects were performed six sets of unilateral knee extension exercise until exhaustion at 40, 60, and 80% of 1 repetition maximum (RM) on separate days. The values at rest, at the end of exercise, and during recovery after exercise were measured by near-infrared spectroscopy. The at the end of exercise was significantly (P < 0.05) increased by 1.8 ± 0.2, 1.7 ± 0.2, and 1.4 ± 0.3 fold over resting value at 40, 60 and 80% 1RM, respectively. returned to the resting values after 1–5 min of recovery and then showed no further significant change for all exercise intensities. This study suggests that knee extension resistance exercise at 40, 60 and 80% 1RM induced an increase in and that the increase of after exercise returned to resting value in several minutes.     

Benefits of caffeine ingestion on sprint performance in trained and untrained swimmers

Summary The influence of specific training on benefits from caffeine (Caf) ingestion was examined during a sprint test in a group of highly trained swimmers (T) and compared with the response of a group of untrained occasional swimmers (UT). Seven T and seven UT subjects swam freestyle two randomly assigned 2 × 100 m distances, at maximal speed and separated by 20 min of passive recovery, once after Caf (250 mg) and once after placebo (Pla) ingestion. Anaerobic capacity was assessed by the mean velocity (meters per second) during each 100 m and blood was sampled from the fingertip just before and 1, 3, 5, 7, and 9 min after each 100 m for resting and maximal blood lactate concentration ([1a^–]_{b, max}) determination. The [[1a^–]_{b, max} was significantly enhanced by Caf in both T and UT subjects (P<0.01). However, only T subjects exhibited significant improvement in their swimming velocity (P<0.01) after Caf or any significant impairment during the second 100 m. In light of these results, it appears that specific training is necessary to benefit from the metabolic adaptations induced by Caf during supramaximal exercise requiring a high anaerobic capacity.     

The effect of exercise intensity and duration on the oxygen deficit and excess post-exercise oxygen consumption

Summary Nine males with mean maximal oxygen consumption ( ) =63.0 ml· kg^–1 · min^–1, SD 5.7 and mean body fat = 10.6%, SD 3.1 each completed nine counterbalanced treatments comprising 20, 50 and 80 min of treadmill exercise at 30, 50 and 70% . The OZ deficit, 8 h excess post-exercise oxygen consumption (EPOC) and EPOC:O₂ deficit ratio were calculated for all subjects relative to mean values obtained from 2 control days each lasting 9.3 h. The O₂ deficit, which was essentially independent of exercise duration, increased significantly (P<0.05) with intensity such that the overall mean values for the three 30%, 50% and 70% workloads were 0.83, 1.89 and 3.09 l, respectively. While there were no significant differences (P>0.05) between the three EPOCs after walking at 30% for 20 (1.01 l), 50 (1.43 l) and 80 min (1.041), respectively, the EPOC thereafter increased (P<0.05) with both intensity and duration such that the increments were much greater for the three 70% workloads (EPOC: 20 min=5.68 l; 50 min=10.04 l; 80 min= 14.59 l) than for the three 50% workload (EPOC: 20 min =3.14 l; 50 min=5.19 l; 80 min= 6.10 l). An analysis of variance indicated that exercise intensity was the major determinant of the EPOC since it explained five times more of the EPOC variance than either exercise duration or the intensity times duration interaction. The mean EPOC:O₂ deficit ratio ranged from 0.8 to 4.5 and generally increased with both exercise intensity and duration. These data imply that the EPOC is more than mere repayment of the O₂ deficit because metabolism is increasingly disturbed from resting levels as exercise intensity and duration increase due to other physiological factors occurring after the steady-state has been attained.     

The effects of protective clothing on energy consumption during different activities

Protective clothing (PPC) can have negative effects on worker performance. Currently little is known about the metabolic effects of PPC and previous work has been limited to a few garments and simple walking or stepping. This study investigated the effects of a wide range of PPC on energy consumption during different activities. It is hypothesized that wearing PPC would significantly increase metabolic rate, disproportionally to its weight, during walking, stepping and an obstacle course. Measuring a person’s oxygen consumption during work can give an indirect, but accurate estimate of energy expenditure (metabolic rate). Oxygen consumption was measured during the performance of continuous walking and stepping, and an obstacle course in 14 different PPC ensembles. Increases in perceived exertion and in metabolic rate (2.4–20.9%) when wearing a range of PPC garments compared to a control condition were seen, with increases above 10% being significant (P < 0.05). More than half of the increase could not be attributed to ensemble weight. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Statement: Energy expenditure is a crucial parameter in the assessment of heat and cold stress, calculation of requirements of food (expeditions, military) and air supplies (SCBA time limits). The observed effect of protective clothing (increases up to 21% in energy use) indicates that neglecting it may put workers at risk in extreme conditions.     

The effect of caffeine ingestion on physical performance after prolonged exercise

Summary The purpose of this study was to determine the effect of caffeine ingestion on physical performance after prolonged endurance exercise. Twenty three trained male volunteers participated in a 40-km march and were divided into two groups, matched for caffeine clearance rate and aerobic capacity. The experimental group ingested, prior to the march, a caffeinated drink at a dose of 5 mg·kg⁻¹ body mass and at the 3rd and 5th h of marching an additional drink at a dose of 2.5 mg·kg⁻¹ body mass. The control group ingested a drink of equal volume at the same times. Upon termination of the march each subject performed a cycle ergometer test at an intensity of 90% maximal oxygen consumption. Time to exhaustion and rate of perceived exertion (RPE) were recorded. Blood samples were drawn predrink, at the 3rd and 5th h of marching and immediately after the cycle ergometer test, and were analysed for caffeine, free fatty acids (FFA), lactate and glucose levels. Plasma FFA levels increased during the march (p<0.05), with no significant difference between groups. Lactate levels increased in the experimental group (p<0.05), with no significant change in the control group. Glucose levels did not change significantly in either group. After the cycle ergometer test, lactate levels were significantly higher in the experimental, as compared to the control group (3.77±0.33 vs 2.52±0.35 mmol·l⁻¹, respectively). There was no significant difference between treatments in the time to exhaustion on the cycle ergometer, but RPE was different (p<0.05). Under the conditions of this study, the results do not indicate caffeine ingestion as an ergogenic aid which will postpone exhaustion following prolonged endurance exercise. This work was presented, in part, at the Canadian Association of Sports Sciences Annual Meeting, October 1987, Lake Louise, Alberta, Canada     

Some aspects of metabolism following a 35 km road run

Summary The metabolism of eight men (mean: age, 26.0 years; maximal oxygen consumption, 65.0 ml·kg^–1 · min^–1; body fat, 10.3%) was measured on counterbalanced control (baseline values for 8h) and experimental (post 35 km run values for 8 h) days. The excess postexercise volume of oxygen consumed of 32.37 1 and increase in energy used of 594 kJ during the 8 h after completion of the run were equivalent to average increases of 23.7 and 21.1%, respectively, when compared with time-matched controls. Furthermore, the oxygen uptake and energy expenditure were still elevated by 12.7 (P<0.0005) and 9.7% (P=0.001), respectively, at the mod, of this period but the fact that they had returned seline 24 h after the 35 km road run contrasts with some reports in the literature that metabolism is still elevated at this time following less demanding exercise intensities. Rectal temperature was elevated by 2.3° C at the end of the run but the difference had decreased to 0.2°C by 7 h postexercise. The respiratory exchange ratio and changes in blood metabolites (nonesterified fatty acids, glycerol and ketone bodies) indicated a greater postexercise utilisation of fat notwithstanding a 6300 kJ meal ingested on both control and experimental days. The highest measured serum creatine kinase enzyme activity of 1151 U.l^–1 (P< 0.05) occurred 24 h postexercise, as compared with the control value of 145 U · 1^–1, and indicates the possibility of skeletal muscle damage.     

The effects of cigarette smoking on maximal oxygen consumption and selected physiological responses of elite team sportsmen

Summary The acute and chronic effects of cigarette smoking on selected physiological responses were determined in seven well-trained non-smokers and seven well-trained habitual smokers. Non-smokers and smokers did not differ significantly with respect to maximal oxygen consumption ( ). The acute effect of smoking two cigarettes immediately prior to a graded exercise stress test on a treadmill ergometer did not significantly alter the of either group. However, the time taken for non-smokers to reach exhaustion decreased significantly (F=5.381, P<0.05) by a mean of 0.64 min. Smokers recorded lower scores for forced vital capacity (FVC) and forced expiratory volume in the 1st s exhalation (FEV₁) than non-smokers. Only the mean FVC of smokers recorded 5 min post-exercise was significantly altered by pre-exercise smoking. No differences were found between the resting heart rates (HR) of non-smokers and smokers. Smoking two cigarettes significantly (F=44.720, P<0.01) increased the mean resting HR of smokers and non-smokers by 15.8 beats·min^–1 and 15.6 beats·min^–1 respectively. No alteration to the exercise HR of either group was found under smoking conditions of the tests.     

The effects of caffeine on memory for word lists

The present study investigated the effects of caffeine on memory for supraspan word lists. Twelve groups of male and female college students classified as high or low impulsive were administered (PO) 0 mg/kg, 2 mg/kg or 4 mg/kg of caffeine. Subjects listened to four word lists presented at a fast rate and four at a slow rate. Caffeine inhibited females' recall during the slow rate, but not the fast rate. Caffeine had no effect on the recall performance of males. The observed effects of caffeine were not influenced by subjects' typical amount of caffeine consumption, verbal ability, or level of impulsivity. The results suggest that caffeine may impair the efficiency with which females rehearse information in working memory.     

Theoretical predictions of maximal oxygen consumption in hypoxia: effects of transport limitations

A Krogh-type model for oxygen transport is used to predict maximal oxygen consumption (V(.-) O(2max)) of human skeletal muscle under hypoxic conditions. Assumed values of capillary density, blood flow, and hemoglobin concentration are based on measurements under normoxic and hypoxic exercise conditions. Arterial partial pressure of oxygen is assumed to decrease with reductions in inspired partial pressure of oxygen (P(I)O(2)), as observed experimentally. As a result of limitations of convective and diffusive oxygen delivery, predicted V(.-) O(2max) values decline gradually as P(I)O(2) is reduced from 150 mmHg to about 80 mmHg, and more rapidly as P(I)O(2) is further reduced. At very low levels of P(I)O(2), V(.-) O(2max) is limited primarily by convective oxygen supply. Experimentally observed values of V(.-) O(2max) in hypoxia show significant dispersion, with some values close to predicted levels and others substantially lower. These results suggest that maximal oxygen consumption rates in hypoxia are not necessarily determined by oxygen transport limitations and may instead reflect reduced muscle oxygen demand.     

Maximum oxygen consumption in dogs during muscular exercise and cold exposure

Maximum oxygen consumption for a short exhaustive work (Ex max) and for a severe cold stress (Ex max) were investigated in 8 dogs. Heart rate, plasma catecholamines and substrate concentrations were measured under both conditions. Mean C was lower than mean Ex max. Heart rate and plasma lactate were also lower during cold exposure than during exercise. Average plasma epinephrine concentrations were not significantly different and average plasma norepinephrine concentrations were similar under C and Ex max conditions. A positive correlation was found between plasma lactate and epinephrine concentrations measured under both conditions.It may be assumed that maximum oxygen consumption during muscular exercise is higher than during shivering thermogenesis. This difference does not seem to be due to differences in the involvement of the sympathico-adreno-medullary system.     

Effects of acute exercise on the soleus H-reflex and self-reported anxiety after caffeine ingestion

The effects of moderate intensity cycling exercise on the soleus H-reflex and state anxiety were examined among 16 individuals whose anxiety was experimentally manipulated by consumption of a large dose of caffeine. The soleus H-reflex and state anxiety were measured before and 1 h after consuming caffeine or placebo and then again 10 min after 30 min of either cycling at an intensity of 60% VO(2peak) or quiet rest. We found that (1) caffeine consumption did not influence the amplitude of the soleus H-reflex, but it did increase state anxiety; (2) acute exercise reduced the soleus H-reflex after consumption of either caffeine or placebo, but it reduced state anxiety only after consumption of caffeine; and (3) there was no evidence of a relationship between changes in the soleus H-reflex and state anxiety. Exercise-induced anxiolysis does not appear to underlie the postexercise reduction of the soleus H-reflex.     

Knee extensor muscle oxygen consumption in relation to muscle activation

Recently, fatigability and muscle oxygen consumption (mVO₂) during sustained isometric contractions were found to be less at shorter (30° knee angle; 0° = full extension) compared to longer knee extensor muscle lengths (90°) and, at low torques, less in the rectus femoris (RF) muscle than in the vastus lateralis and medialis. In the present study we hypothesized that these findings could be accounted for by a knee angle- and a muscle-dependent activation respectively. On two experimental days rectified surface EMG (rsEMG) was obtained as a measure of muscle activation in nine healthy young males. In addition, on day 1 maximal torque capacity (MTC) was carefully determined using superimposed nerve stimulation on brief high intensity contractions (> 70%MVC) at 30, 60 and 90° knee angles. On day 2, subjects performed longer lasting isometric contractions (10–70%MTC) while mVO₂ was measured using near-infrared spectroscopy (NIRS). At 30°, maximal mVO₂ was reached significantly later (11.0 s ± 6.5 s) and was 57.9 ± 8.3% less (average ± SD, across intensities and muscles) than mVO₂ at 60 and 90° (p < 0.05). However, rsEMG was on average only 18.0 ± 11.8% (p = 0.062) less at the start of the contraction at 30°. At 10%MTC at all knee angles, maximal mVO₂ of the RF occurred significantly later (28.8 ± 36.0 s) and showed a significantly smaller increase in rsEMG compared to both vasti. In conclusion, it is unlikely that the tendency for less intense muscle activation could fully account for the ∼60% lower oxygen consumption at 30°, but the later increase in RFmVO₂ seemed to be caused by a less strong activation of the RF.     

A metabolism chamber for measuring oxygen consumption in the laboratory rat and mouse

Details are given for the construction and use of an inexpensive metabolism chamber to measure oxygen consumption in a relatively large group of laboratory rodents in a brief time. Metabolic rates (MR) were measured regularly in male and female Sprague Dawley rats, 11–114 days old, and mice, 100 days old. Adult mice had higher MR than rats of approximately the same age. Female rats and mice had higher MR than males at all times. To demonstrate the versatility of the metabolism chambers adult rats were injected once or for 9 consecutive days with 6-n-propyl-2-thiouracil (PTU) to inhibit thyroid function and reduce MR, or with the carboxymethyl-cellulose (CMC) vehicle. PTU failed to lower MR in the animals most probably because CMC vehicle tended to increase MR, an effect more prominent in males than females.     

Resting oxygen consumption in rats during food restriction,starvation and refeeding

Oxygen consumption was measured in male rats during starvation and during different regimens of restricted feeding and refeeding after starvation. Changes in oxygen consumption and body mass were mostly parallel, but rats with a very reduced food intake displayed the same reduction in oxygen consumption as starved rats, despite the smaller reduction in body mass. Also, rats fed different amounts of food after starvation had different oxygen consumptions, but displayed the same changes in body mass. Two different refeeding regimens with restricted food amounts either induced a further depression of oxygen consumption (i.e. below starvation oxygen consumption), or a stabilizing of oxygen consumption on the level of starvation. The changes in oxygen consumption during restriction and feeding after starvation indicate that reductions in resting metabolic rate may not always be predicted from either body mass change or food intake.