After a hard session at the gym many of us typically head home, turn the TV on, and slump on the sofa for the evening. We feel justified in doing so. The hard work of the day is done.
Or at least, it may feel like that. But while we are slipping into a relaxed post-exercise daze, content to do nothing more than rest aching limbs, our bodies continue to work on our behalf. On the surface all may be calm, but in the microscopic heart of our biological systems the workout continues.
The effect, known as Excess Post-Exercise Oxygen Consumption (EPOC for short) or, more informally, the after-burn, has been known about in scientific circles for decades. But more recently scientists have been focusing on the potential of EPOC to maximise our weight loss and fat-burning efforts, and figuring out ways to tweak workouts to increase the EPOC effect.
It’s easy to understand why. The after-burn is your workout bonus, a free gift for having the strength of character to get out there and exercise in the first place. Here’s what EPOC is, what it does, and how you can make the most of it.
Three phases of burn
Quite simply, after exercise your body expends energy recovering from the effort.
“After cardiovascular exercise or weight training, the body continues to need oxygen at a higher rate than before the exercise began,” explains Dr Len Kravitz, associate professor of exercise science at the University of New Mexico in the US. “This sustained oxygen consumption is known as EPOC.”
If the body is consuming oxygen at a higher rate than would be normal at rest, it’s also using more energy. There’s good reason for that. After exercise, the body undergoes a subsequent workout at the chemical level to restore muscles to their previous state, and prepare them for further activity. Specifically, oxygen is used to remove lactic acid from muscles and replenish stores of myoglobin, an integral part of the muscles’ internal oxygen supply.
Scientist Dan Gordon, principle lecturer in exercise physiology at Anglia Ruskin University in the UK, identifies three EPOC phases. The first happens in the initial few minutes of recovery after exercise, the second for an hour or so after that and the third potentially for a number of further hours. “Each phase is associated with the restoration and recovery of specific physiological and metabolic parameters,” states Gordon.
The implications of that are significant. In effect, our bodies are continuing to burn calories many hours after finishing exercising. And while the number of calories burned declines steadily during that time, the cumulative effect of EPOC over months and years can make a big difference to your attempts to maintain a healthy weight.
Exercise for EPOC
Much of the science behind EPOC has been known for a while, but now experts are pinpointing what type of exercise is likely to optimise its calorie burning effects.
“Studies have found that the magnitude (amount of elevation in oxygen consumption) and duration (length of time the oxygen consumption is elevated) of EPOC is dependent on the intensity and duration of exercise,” writes Dr Kravitz in a paper on the subject.
“It generally takes anywhere from 15 minutes to 48 hours for the body to fully recover to a resting state.”
When it comes to aerobic exercise, studies suggest that the intensity of exercise has the biggest effect on EPOC. The more intense your workout, the longer and stronger your exercise after-burn.
One early study from 1991 showed this clearly. Subjects were asked to exercise at 29 per cent, 50 per cent, and 75 per cent of VO2 max for 80 minutes (VO2 max is a measure of the amount of oxygen you can effectively use during exercise). Whereas exercise at 29 per cent intensity produced a minor EPOC effect, the highest intensity workout burned up an extra 150.5 calories in EPOC alone. If that doesn’t sound like much, remember that it means 150 calories over and above the energy expended during the actual workout. Then multiply that figure by the number of intense workouts you might complete in an average year.
A more recent study, published in the Journal of the American College of Nutrition, confirmed the effect, and suggested that exercise intensity was more important than duration for EPOC benefit. Subjects were asked to exercise at either low or high intensity, until they’d burned 500 calories. The low intensity athletes exercised for longer to reach that goal, but their high intensity counterparts, who exercised for less time, benefitted from twice the EPOC effect, expending an extra 45 calories – against 24 – in the recovery period.
“These studies reveal that EPOC can contribute significantly to overall caloric expenditure,” adds Dr Kravitz, “but do appear to vary somewhat between subjects.”
Hard workouts versus long ones
The EPOC effect does increase gradually the longer you exercise, but the biggest gains are seen when the exercise is also intense. In other words, it’s probably better to do short, sharp bouts of exercise than longer, less intense ones, at least in terms of maximising the after-burn.
Further studies have borne this out. One piece of research, published in the Journal of Applied Physiology, compared a single run of 30 minutes at 70 per cent VO2 max to 20 one-minute bouts at 105 per cent VO2 max. It found that the interval training enjoyed more than double the EPOC advantage (75 calories compared to 34.5) of the continuous run.
There have been fewer studies examining the relationship between resistance training and EPOC benefits, but those there have been also suggest that a weight training session can result in increased calorie burn several hours after the workout has ended. Again, the more intense the workout, the stronger the after-burn.
What’s clear is that the EPOC effect is real, and can mean that you are burning calories and processing fat long after your workout is over.