Eur J Appl Physiol (1993) 67:420M25 European Applied Physiology

and Occupational PhysmLogy © Springer-Verlag 1993

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

Jo Smith and Lars Mc Naughton

University of Tasmania at Launceston, Centre for Human Movement Studies, P.O. Box 1214, Launceston, Tasmania 7250, Australia

Accepted July 2, 1993

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 (1202max). All ventilation mea- sured was undertaken with a standard, calibrated, open circuit spirometry, system. No differences in the 40%, 50% and 70% VO2max trials were observed among resting levels of oxygen consumption (1202) for either the men or the women. The men had significantly high- er resting 1202 values being 0.31 (SEM 0.01) l 'min -~ than did the women, 0.26 (SEM 0.01) l '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 rain; and 70% - 39.1 min. The highest EPOC, in terms of both time and energy utilised was at 70% 1202 . . . . The regres- sion equation for the men, where y- -02 in litres, and x = exercise intensity as a percentage of maximum was y=0.380x+l .9 (rZ=0.968) and for the women is y = 0.374x - 0.857 (r 2 = 0.825). These findings would in- dicate that the men and the women had to exercise at the same percentage of their 1202max 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.

Key words: Metabolism - Respiratory exchange ratio - Excess postexercise oxygen consumption

Correspondence to: L. Mc Naughton

Introduction

Gaesser and Brooks (1984) have claimed that numer- ous studies since 1910 have reported an increase in oxygen consumption (1202) above resting levels in the period after exercise. Traditionally, this has been termed "oxygen debt" (Hill and Lupton 1923) but more recently it has been called the "recovery energy expenditure" (Elliot et al. 1992: Mole 1990; Poehlman 1989; Sedlock et al. 1989) or excess postexercise oxy- gen consumption (EPOC; Gaesser and Brooks 1984). However, the nature and extent of the EPOC has been controversial and much work has been undertaken to determine cause and effect relationships (Bahr et al. 1990; Chad and Wenger 1986; Gore and Withers 1990a; Sedlock et al. 1989). An interesting and compre- hensive review has recently become available (Bahr 1992).

It has been suggested that EPOC can have impor- tant significant implications for the control of body mass (Bahr and Maehlum 1986: Brehm and Gutin 1986; Chad and Wenger 1986; Franklin and Rubenfire 1980; Sedlock et al. 1989) but it is a controversial topic. In those studies that have found a significant EPOC, its length has been recorded as being between 1 and 48 h (Bahr et al. 1991, 1992; deVries and Gray 1983; Ed- wards et al. 1935; Margaria et al. 1973; Sedlock et al. 1989; Withers et al. 1991). However, it should be noted that several studies have failed to find a significant EPOC even with prolonged and intense [70% maximal oxygen consumption (VOzmax)] exercise (Freedman- Akabas et al. 1985; Kaminsky et al. 1987).

Recent work has suggested that EPOC can also be augmented by resistance training of either the set weight training (Murphy and Schwarzkopf 1992) or the circuit training type (Elliot et al. 1992). They have sug- gested that aerobic exercise per se is not necessary to have a significant EPOC effect (Elliot et al. 1992) and that the magnitude and duration of EPOC is greater for circuit training than for set weight training but that weight training produces an EPOC somewhat less than

421

tha t s een for a e r o b i c exe rc i se ( M u r p h y and Schwarz - k o p f 1992).

I f E P O C is i n d e e d i m p o r t a n t for con t ro l of b o d y mass , and it has b e e n sugges t ed b y B a h r e t al. (1991) tha t f a t ty ac id u t i l i za t ion is g r e a t e r in the r e c o v e r y pe- r i od a f t e r exerc i se , t hen it is a lso i m p o r t a n t to quan t i fy w h e r e pos s ib l e t he e x t e n t o f such E P O C and the e n e r - gy e x p e n d i t u r e i nvo lved d u r i n g tha t pe r iod . B r e h m and G u t i n (1986) have shown tha t the E P O C e n e r g y e x p e n d i t u r e r a n g e d b e t w e e n 1 2 . 6 k J and 71 .4kJ , w h e r e a s S e d l o c k et al. (1989) have f o u n d E P O C ene r - gy e x p e n d i t u r e b e t w e e n 50.4 kJ and 121.8 kJ in men . S e d l o c k (1991) l a t e r w e n t on to d e t e r m i n e the e n e r g y cos t of E P O C , a f te r exe rc i se of 850 kJ e n e r g y cost , to b e 30 kJ and 36 kJ a f te r exe rc i se at 40% 1902max a n d 60% T~O2rnax, r e spec t ive ly .

W i t h r e s p e c t to in t ens i ty of exe rc i se the resul t s a re con t r ad i c to ry . K n u t t g e n (1970) has shown tha t E P O C v a r i e d wi th the i n t ens i ty o f exe rc i se as wel l as the du ra - t ion. A t l o w e r levels of i n t ens i ty t h e r e we re on ly smal l changes in E P O C bu t a t h ighe r in tens i t i e s the changes we re g r e a t e r and in fact we re a lmos t e x p o n e n t i a l a t 98% VO2. C h a d and W e n g e r (1985, 1986) and C h a n d and Q u i g l e y (1991) have shown tha t i n t ens i ty of exe r - cise is i m p o r t a n t in ra i s ing E P O C . H o w e v e r , in b o t h ins tances t hey have shown tha t exe rc i se at 50% 19Oamax has a m o r e subs t an t i a l E P O C than exe rc i se at 70% VO2max. C h a d and. W e n g e r (1986) have f o u n d tha t the E P O C at 50% VO2ma× was 1.5 t imes g r e a t e r t han tha t a t 70% 1902m~x, sugges t ing also a h ighe r en- e rgy m e t a b o l i s m at this level . B a h r (1992), in a r e c e n t set o f e l e g a n t e x p e r i m e n t s , has f o u n d an e x p o n e n t i a l i nc rea se in E P O C wi th i nc rea s ing exe rc i se in tens i ty . In the mos t e x t r e m e case, t he d u r a t i o n of E P O C was 10.5 h at an in t ens i ty of 75% 1902 . . . .

T h e a im of this e x p e r i m e n t was to inves t iga t e and c o m p a r e t he e x t e n t o f E P O C (if any) in m e n and wo- m e n of s imi la r f i tness levels a f te r 30 min of exe rc i se at 4 0 % , 50% and 70% 1902~ax and to d e t e r m i n e the en- e rgy c o n t r i b u t i o n r e l a t i ve to t he to ta l e n e r g y e x p e n d i - ture .

Methods

Subjects. Eight male and eight female physical education students from the University of Tasmania at Launceston participated in the study voluntarily. The subjects were not cyclists, however all regularly engaged in physical activity and exercise which may have involved cycling. Prior to participation, all the subjects com- pleted an informed voluntary consent form and a medical history questionnaire. Their physical characteristics were: mean age, men 21.1 (SD 3.6) years, women 20.4 (SD 3.1) years; mean body mass, men 71.6 (SD 6.2) kg, women 64.0 (SD 5.7) kg; height, men 179.8 (SD 7.2) cm, women 167.6 (SD 5.1) cm; mean body fat, men 10.6 (SD 4.9) %, women 16.3 (SD 6.8) %.

Protocol. Anthropometric measurements of the subjects were taken 1 week prior to the first test day. These included height, mass, and skinfold measurements at six sites (triceps, subscapu- Iar. suprailiac, biceps, thigh and medial midcalf), measured to the nearest 1.0 mm with Harpenden skinfold calipers (Harrison et al. 1988). The subjects were also famiharised with the Repco Exer- tech cycle ergometer (model no. EX10). exercising at a constant

pedalling rate, while breathing through a mouthpiece and Hans Rudolph breathing valve (model no. 2700), which was linked to an open circuit gas analysis system via 3-cm internal diameter tubing.

Prior to the beginning of the VO2max test the 02 and CO2 analysers (paramagnetic - Applied Electrochemistry model S3A and an infrared Heraus Binos 1, respectively) were calibrated with three known standards of O2:CO2 mix (15.6:2.9; 17.8:3.8 and 19.4:4.8, respectively) as well as nitrogen and room air. A Rayfield air meter (Rayfield Equipment, Vermont) was used to measure ventilation parameters and this was calibrated with a 1-1 syringe prior to all tests. The syringe was operated manually in time with a metronome to input various ventilations (1. rain -J) to resemble actual breathing patterns.

All subjects performed a stepwise incremental test on the cy- cle ergometer to measure VO2max. The 1)O2max test consisted of a 5-rain warm-up, pedalling at an intensity of 75 W, after which time the intensity was increased by 25 W every 2 min (Chad and Quigley 1989). To attain maximal values, verbal encouragement was.given to all subjects. The criteria upon which the attainment of VO2 .... was based included the following: 1. The attainment of estimated maximal heart rate (based upon 220-age) 2. A change of less than 150 ml .min- I in 1)O, subsequent to an increase in exercise intensity 3. Voluntary cessation of exercise by the subject upon reaching a state of exhaustion (Chad and Quigley 1989, 1991). Pulmonary ventilation, VO2 and carbon dioxide production were measured and recorded at 30-s intervals during the test. The 1)O2 was then plotted against power output to determine each sub- j.ect's work rates for the different intensities (40%, 50%, and 70% VO2max). This estimation was later confirmed in a 10-rain pretest, by measuring the 1)O2 at that particular work rate.

Beginning 1 week after the VO2m~× test and confirmation of work rates, each subject was tested at approximately the same time of day at weekly intervals, for the three intensity trials. The order in which the three differing intensitms were performed was randomized to counteract any possible training effect. Protocols for the 40%, 50%, and 70% VO2ma,~ test sessions were identical, with the exercise duration held constant at 30 min.

Procedure. The subjects reported to the Human Performance La- boratory at the University of Tasmania at Launccston, following an overnight fast, and consumed no food or beverage, with the exception of water, until the completion of the experimental. Resting metabolic rate (RMR) was determined by measuring VO2 by open mrcuit spirometry over period of 60 rain, at l-rain intervals. The subject covered with a blanket rested quietly dur- ing this period in a darkened room at 22-23 ° C.

During the 30-mln exercise period the subjects pedalled at their known power output to elicit the given percentage of their 1)O2max. Feedback was obtained during the test from the on-line computer system so that the subjects could maintain more exactly their given work output at the given percentage of 1)O2 . . . .

At the completion of exercise the first postexercise measure- ment was taken and then at 2-min intervals for the next 3 h. Throughout this period the subjects rested as before in a dark- ened room, covered with a blanked. The measurement of EPOC was taken from the immediate postexercise period until + 12 ml 02" min-1 of the RMR was reached for five consecutive 2-rain measurement periods and when there was no statistically signifi- cant difference between the mean value of RMR and that ob- tained during the test. Energy expenditure during this time was calculated for each subject by summing the net energy expenda- ture for each 2-min period during EPOC (Sedlock et al. 1989). Energy in kilojoules was calculated from the nonprotein respira- tory exchange ratio (R) for each litre of oxygen for each 2-min period.

Statistical analysis. The comparisons made with the data included comparisons between the men and women as well as comparisons

422

Table 1. Oxygen consumption and the energy used above resting level in the men and women studied, during 30 min at three exercise intensities

Exercise intensity (% "VO2max)

40% 50% 70%

mean SEM mean SEM mean SEM Men

oxygen consumption (1 O2) 45.9 0.04 55.2 a 0.04 78.2 ab 0.05 energy (kJ ) 936.2 24.2 1118.9 ~ 32.4 1589.3 ab 37,4

Women oxygen consumption (1 02) 37.6 0.03 46.9 a 0.03 65.1 ab 0.05 energy (kJ) 763.9 24.4 956.4 a 29.8 1326.4 ab 41.2

12Oa ... . Maximal oxygen consumption a Significantly higher than the preceding test value (P < 0.05) b Significantly higher than the 40% test value (P < 0.01)

Table 2. Excess post-exercise oxygen consumption (EPOC), the energy used and the EPOC duration for the three exercise intensities in the men and women studied

Exercise intensity (% VO2max)

40% 50% 70%

mean SEM mean SEM mean SEM Men

oxygen consumption (1 02) 16.3 0.03 22.1 a 0.03 28.1 ab 0.06 energy (kJ) 333.5 15.5 451.1 a 28.9 585.1 ab 34.1 duration (rain) 31.2 1.9 42.1 a 2.6 47.& u 2.9

Women oxygen consumption (1 02) 12.1 0.06 20.8 a 0.04 24.3 ab 0.09 energy (kJ) 247.4 20.6 420.8 a 23.5 495.2 ab 35.3 duration (min) 26.9 1.5 35.6 a 2.1 39.1 ab 2.6

VO2max. Maximal oxygen consumption a Significantly higher than the preceding test value (P < 0.05) u Significantly higher than the 40% test value (P<0.01)

among the different exercise intensities. A multiple analysis of variance (MANOVA) was used for this purpose (Keppel 1982). A significance level of P < 0.05 was chosen prior to the start of the test as acceptable.

Results

The mean, 1202max for the men was 3.6 (SEM 0.4) and for the women was 3.1 (SEM 0.3) 1-min -1 and when adjusted for body mass these were 50.3 (SEM 4.7) m l . k g - l . m i n -1 and 48.4 (SEM 7.6) m l . k g - l ' m i n -1, respectively. These were not significantly different.

During the three trials no differences were seen in resting VOa levels for either the men or the women, in absolute terms or relative to body mass, indicating that they were in similar states of rest. The values were 4 . 3 m l . k g - l . m i n -~ for the men and 4 . 1 m l ' k g -1. m i n - t for the women yielding energy expenditures of 2.5 kJ. kg - ~ and 2.6 k J- kg - 1, respectively.

The amount of oxygen consumed and the kilojoules utilised, by the subjects during exercise is shown in Ta- ble 1. In all three sessions the men consumed signifi- cantly more oxygen that the women (P<0.05) , but these differences disappeared when the subjects were compared on the basis of equal body mass.

The E P O C data is shown in Table 2. Each mean value was significantly greater than that at the intensi-

ties below it. In absolute terms in all of the three con- ditions, the men had a significantly greater E P O C than the women but not when adjusted for differences in body mass, i.e. at 40% 0.23:0.19 1 0 2 ' k g -~, 50% 0.31:0.32 102"kg -1 and at 70% 0.39:0.38 102"kg -1.

As a percentage of the total energy expended, E P O C for the men accounted for 26%, 28% and 27% for the 40%, 50% and 70% l)O2max levels, respective- ly, while the women utilised 24%, 30% and 27% for the same levels. There were no differences between these percentages.

Figures 1 and 2 show the simple regression equa- tions for the E P O C curves for the men and women, in terms of both intensity of exercise and duration of ac- tivity (min).

Discussion

The aim of this study was to investigate the effects of 30-min of exercise at intensities of 40%, 50% and 70% VO2max on the E P O C and energy utilisation of men and women with identical levels of aerobic training.

Unlike the work of others (Brehm and Gutin 1986; Kaminsky et al. 1987; Passmore and Johnson 1960) the results of this study would suggest that there is an ele- vated 12Oa which relates to intensity of exercise when

423

30-

y=--1.

25

eJ 20 0

15-

10 25 3'0 3; 20 4; 5'0

Minutes of Exercise

Fig. 1. Simple regression equauons for the E P O C periods in men and women: (y = a + b x) where y = 02 (1) and x = exercise intensi- ty as a percentage of maximal oxygen consumption (1/O2 .... ). --m-- Men 02: • " "®- " " women 02

¢,1 0

30,

25-

20-

15-

10 3o 4b

~ y~-O.374x-0.857 r 2=0.825

5b 6b 7}) 8b Intens,ty of Exercise

(% ~)2max)

Fig. 2, Simple regression equanons for the EPOC periods in men and women: (y=a+bx) where y=O~_ (1) and x=min. ' . .@ ' - . men 02; - -*- - women 02

duration is kept constant. The absolute effect is greater in men than in women when fitness levels are similar but is due to differences in body mass.

In this study EPOC lasted for between 27 rain and 47 min but previous studies have demonstrated that EPOC may last anywhere up to 48 h (deVries and Gray 1983; Edwards et el. 1935; Margaria et el. 1973: Passmore and Johnson 1960). Withers et al. (1991) have found an elevated EPOC after a 35-km road run for a period of 8 h but this returned to normal within the 24-h period postexercise. In a recent study Sedlock (1992) has shown that EPOC lasted for 34 min which is similar to that shown in this study. However, Murphy and Schwarzkopf (1992) have found EPOC lasted only 15 rain and 20 min for set (SWT) and circuit weight training (CWT), respectively. This might suggest that if energy expenditure was an important factor, for exam- ple for control of body mass, then it is more important

to undertake aerobic rather that weight training exer- cise. Murphy and Schwarzkopf (1992) have suggested that CWT provides an extra 83% energy expenditure above SWT but that the duration of EPOC from weight training will generally be less than that from aerobic exercise.

An interesting study by Bahr et el. (1992) has shown that a significant EPOC occurs after short periods of supramaximal exercise (108% gO2max ). They have found EPOC lasted for 4 h and for shorter periods when the exercise duration was shortened and that in the 1-h period immediately following exercise, EPOC was linearly related to changes in blood lactate and plasma noradrenaline levels.

Sedlock et el. (1989) have suggested that the differ- ence between some of these studies finding such a large EPOC and those where no significant EPOC was found could be accounted for by dietary induced ther- mogenesis (DIT). This is not the case in this study where the subjects were in a fasted state prior to the test, so this in itself could not be a factor. However Sedlock et el. (1989) are right in suggesting that the interaction of DIT and EPOC needs further investiga- tion because this could have some significant conse- quences for individuals wishing to undertake exercise for loss of body mass. Bahr et el. (1991) have found that a prolonged EPOC was present in the fasted state but that there was no major interaction between food intake and previous exercise on EPOC. The research surrounding this particular area is wide and varied and many of the confounding results have been due to dif- ferences in experimental design (Bahr et el. 1991; Bray et el. 1974; Dallosso and James 1984; Segal and Gutin 1983; Tremblay et el. 1983).

The effects of increasing the intensity of exercise on EPOC was to prolong this period for both the men and the women and this is in agreement with the work of Sedlock et el. (1989) and Brehm and Gutin (1986). These latter authors have suggested that the magni- tude of the homeostatic disturbance is a major factor in determining the extent of EPOC. Gore and Withers (1990b) have found that exercise intensity was the most important factor in elevating EPOC since it ex- plained five times more of the variance associated with EPOC. Chad and Wenger (1986) have suggested that the duration of activity is more important for EPOC than the intensity of exercise but the present study would suggest that intensity can have a significant ef- fect even when duration is held constant, which is in agreement with some later work by Chad and Quigley (1989, 1991). In a protocol similar to the one used here they have found that EPOC was substantial for exer- cise above 50% gO2max.. However, they found an exer- cise intensity of 50% VOimax had a 1.7 (trained) and 1.8 (untrained) times greater EPOC value than an ex- ercise intensity of 70% VO2m,x for the same subjects. Our current study, however, is in direct disagreement with this work, finding a linear relationship between intensity and excess postexercise VO2, with EPOC in- creasing steadily as exercise intensity increased. The present study does lend support to the theory that

424

there is a minimal intensity of exercise needed to affect the long lasting energy expend!ture effect of exercise. Whether this occurs at 70% VO2max or at a slightly greater percentage of I202ma~, which needs to be indi- vidually assessed, cannot at this time be decided. Brehm and Gutin (1986) have suggested that recovery energy expenditure is only minimally affected by inten- sities in the 30%-50% range and at higher intensities of exercise the slope of the curve may rise more steep- ly. It does seem likely though, given the current litera- ture that suggests little or no observable effect of exer- cise on E P O C following high intensity exercise, that the most effective exercise intensity for loss of body mass, is a point somewhere between 70% 1202max and the anaerobic threshold (Th~n). as long as this point is above 70% 1202max. If this were not to be the case the subjects should exercise at that point just below the Than.

In a recent study, Elliot et al. (1992) have suggested that muscle mass is an important factor in the relation- ship between exertion and EPOC. They found that heavy lifting type activity (weight training) had a sig- nificantly higher E P O C effect than either cycling or circuit training, when both duration and intensity were kept constant. On the other hand, Sedlock (1992) has found no significant difference in E P O C between treadmill running and cycling when both intensity of effort and duration were kept constant. Again this adds to the controversy surrounding EPOC, as running usually involves a significantly higher fat free mass (mff) than cycling.

The percentage of energy utilised during E P O C was similar to that shown in the study by Elliot et al. (1992). In the present study the values were between 24% and 30%, whereas in the study by Elliot et al. (1992) the values ranged from 7% to 21% for cycling, circuit training and weight lifting. The values obtained for cycling approximate to those shown by Sedlock (1992). It would appear therefore that rnff may in fact be a significant factor in energy utilisation. In our study the men had a higher rnff than the women and also had a higher EPOC. However, the point made by Elliot et al. (1992) is relevant, in that "Fur ther investigations are needed to define whether exercising mass corre- lates with E P O C when total work remains con- s tant . . . " . Again, the variation in types of studies con- ducted makes this type of comparison difficult.

In terms of the energy expenditure effect of the var- ious exercise intensities used in this study the most ef- fective exercise in.tensity for energy expenditure utilis- ation was 70% VO2max. The difference between the lowest and highest exercise intensity energy values was a 70% increase for the men and 100% increase for the women. This would suggest that women wishing to em- ploy exercise to achieve a loss of body mass should use a higher exercise intensity rather than a lower one. However, a significant effect can be seen at lower exer- cise intensities; this study would suggest that even ex- ercise at 40% 1202max would be intense enough to give an energy expenditure effect. This supports the pre- vious work of Brehm (1988).

In conclusion, the results of this study add further to the controversy surrounding the origin of EPOC. In the current study, as exercise intensity increased, so did E P O C and also the number of kilojoules utilised by both the male and female subjects. Men and women utilise the same amount of oxygen and hence expend the same amount of energy when these figures are ad- justed for body mass. Those individuals wanting to em- ploy exercise to its best advantage for loss of body m. ass, should use an exercise intensity of at least 70% V02 . . . .

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