The Effect of Exercise Intensity on EPOCIt is well established that exercise increases oxygen consumption for several hours
after its completion (Gaesser and Brooks, 1984). As discussed, oxygen consumption
is used to assess caloric expenditure. Therefore elevated levels of 02 consumption
reflect a higher resting metabolic rate. Explanations for such a phenomenon are
connected to a number of historical events. It all began with Berzelius, who in 1808
found that lactate concentration was increased in ‘ the muscles of hunted stags(
Gladden, 2004)’ who relied on anaerobic pathways to attempt to escape their
predators. This was followed by Myeroff’s (1920) discovery that glycogen served as
a precursor for lactate (Gladden, 2004). Building on this work, Hill proposed the 02
debt theory, which suggested that 1/5 of the increase in 02 consumption was used in
the oxidation of lactate. This in turn provided the energy to convert lactate build up
during exercise back to glycogen, thus repaying the ‘debt’ incurred through
anaerobic processes. Scientists further noted that the 02 debt produced a curve that
was characterized by a rapid phase of 02 dissipation, followed by a slow phase of
decline. Margaria et al. (1933) called the fast phase alactacid, followed by the
slower lactacid phase. The alactacid phase was postulated to account for
replenishment of non lactic acid components of anaerobic energy utilization, such as
the phosphorylation of free creatine to form creatine phosphate. The lactacid phase
was said to replenish glycogen stores from lactate. However, Gaesser and Brooks
(1984) suggested that these explanations were to simplistic and that evidence
pointed to the majority of lactate being oxidized following exercise, with the
remainder serving as a carbon skeleton for a number of processes of which glycogen
replenishment is just one. Further, it was stated that the oxygen utilization could be
linked to a number of phenomenon, including the residual effects of hormones, and
increased temperature. In this historical review, Gaesser and Brooks (1984)
introduced the new terms - excess post exercise oxygen consumption (EPOC) and
recovery 02 to eliminate the ‘ implication of causality in describing the elevation in
metabolic rate above resting levels after exercise.’
Today another historical battle exists. Across countries exercise participants purport
the superiority of high intensity interval training (HIIT) which is short over low to
moderate intensity long duration training. One of the purposes of this article is to
analyze the evidence for this claim and allow the reader to conclude from there.
Shawn Phillips, one of the leading spokesman for HIIT stated that
‘You knew deep down, anyhow, that busting your butt burned off more fat than an
exercise that allowed you to read at the same time, didn't you? Well, research shows
our instincts were right…
HIIT speeds up your metabolism and keeps it revved up for some time after your
workout. The bottom line is HIIT training burns a greater number of total calories
than low-intensity training, and more calories burned equals more fat lost. What I'm
suggesting is you forget about the "calories burned" readout on the stairstepper or
Lifecycle; if you practice HIIT training, the majority of calories burned will come after
your workout!’
The above statement paints an appealing picture.
In reality however, the scientific
evidence suggests that it is unequivocally false (Laforgia et al., 1997, Gore and
Withers, 1990, Freedman-Akabas, 1985). First, HIIT training is normally purported
to take less time than lower intensity sessions. However, to control variables
Laforgia et al. (1997) examined the effect of intensity on EPOC, while matching total
work performed in each session. Participants consisted of eight male middle distance
runners, who performed 30 minutes of 70 % V02 max treadmill running in condition
one, and interval training in condition two. Interval training consisted of 20, one
minute sprints at 105 % of V02 max. The session lasted 60 minutes, as sprints were
interspersed with 2 minute intervals in which participants performed active
recovery. It was found that the 70 % V02 max condition metabolized 31 extra
calories over the entire nine hours following exercise, while the high intensity
condition metabolized 64 extra calories as extrapolated by EPOC. This equates to a
negligible 33 extra calories for the high intensity condition. Laforgia et al. (1997)
suggests that a comparison of the excess calories above moderate intensity exercise
‘for the interval treatment is of little physiological significance to the energy balance
of athletes because this amount of energy is equivalent to the kilojoules in only 75 ml
of orange juice (1/3rd cup).’ They further conclude that ‘the major contribution of
both treatments to weight loss was via the energy expended during the actual
exercise. The excess post exercise energy expenditure is therefore of negligible
physiological significance as far as weight loss is concerned.’
In another study, Gore et al. (1990) examined the effect of both intensity and
duration on EPOC. Participants consisted of nine males with an average of 21 years
of age. Participants exercised at 30 %, 50 %, and 70 % V02 max, each at 20, 50,
and 80 minute durations. The effect of duration on exercise found no significant
difference in the 30 % V02 max condition, whose 8 hour EPOC was a little over 1
liter of 02, amounting to approximately 5-6 extra calories metabolized. The effect
of duration on the 50 % V02 max condition found that EPOC went from
approximately 3 liters at 20 minutes, to 5 liters at 50 minutes, and finally to 6 liters
at 80 minutes of duration. The effect of duration on the 70% V02 max condition
found that EPOC went from 6, to 10, and finally 14.6 liters of 02 consumed for 20,
50, and 80 minute durations. As a reference the 14.6 liters of 02 consumed in
excess in the 70 % V02 max, 80 minute duration condition was approximately 70
extra calories of energy expended or approximately 40 extra calories than the 50
minute condition at 50 minutes duration. While the data from this study clearly
shows a positive relationship between intensity and duration on EPOC, the amount of
calories metabolized in excess is concluded by the authors to be ‘ of little
physiological significance for weight loss…’ Further, the average amount of calories
metabolized during EPOC was approximately 4 % of the total energy cost of
exercise, which addresses the statement that , ‘the majority of calories burned will
come after your workout( Phillips)!
Further, the 70 % V02 max condition is comparable to the 65 % condition discussed
in the Romijn et al. (1995) study which metabolized the highest amount of fat during
training. This is significant because the EPOC in the supramaximal high intensity
condition in the Laforgia et al. (1997) study, was nearly equivalent to the 70 % V02
max, long duration session. This suggests two outcomes. First, if exercise is
performed at 65 % V02 max for a longer duration such as 60 minutes, then the
EPOC generated may possibly approximate HIIT training intensities, secondly during
the training session overall calories expended will be greater, with a higher
proportion of those calories coming from lipids, as opposed to the overwhelming
majority of glycogen utilization found in the supramaximal protocol.
http://www.abcbodybuilding.com Exercise Intensity & Nutrients 6
The next inherent flaw made in the hi intensity vs. low to moderate intensity
argument is that it fails to take into account the fact that bodybuilders are primarily
high intensity athletes. As such they may already receive the benefit of optimized
EPOC.
Melby et al. (1993) tested the effect of resistance exercise on metabolic rate during
the 2 hours following exercise and on resting metabolic rate (RMR) the following day,
measured 15 hours after exercise. Seven males with previous experience in
resistance training performed 60 sets of both upper and lower body exercises, over a
90-minute time span. 2 hours after exercise, the average total EPOC was 7 Liters of
O2, which adds up to about 35 extra calories oxidized in comparison to the control
group. The total EPOC after 15 hours of exercise accounted for approximately 180
extra calories metabolized. In another experiment (Jamurtas et al., 2004) ten male
athletes lifted weights for 60 min at 70-75% of 1-RM. It was found that the weight
lifting group utilized had a 150 calorie increase in resting energy expenditure as
extrapolated from EPOC.
