How important is the ‘after-burn’ transition from exercise to rest?

The human body is a series of systems craving homeostasis, a term referring to a general sense of equilibrium, or baseline level of operating. In a resting state, the physiological energy demands are relatively low, as energy is required for only basic processes such as breathing, blood circulation, brain/neural function, cell growth, and temperature regulation. These vital functions account for approximately 60 percent of the calories expended throughout the day. The remainder is largely dictated by exercise/physical activity, digestion, and variable factors.

Oxygen is the paramount fuel of the body. An individual at rest typically requires about 3.5 milliliters of oxygen per kilogram of body weight per minute. Exercise greatly enhances the cellular demand for oxygen, hence we are “burning” more calories, while we are exercising. But what about when we are driving home from the gym — do the cellular demands return to homeostasis immediately? The answer is no. This phenomenon is termed Excess Post-Exercise Oxygen Consumption (EPOC).

EPOC does allow for more calories to be burned at rest following exercise, but this has been sensationalized in popular media. The “after-burn” or “rollover calories” expended can be a helpful tool for fat loss, but science suggests this is only a small piece of the puzzle. Let’s look at EPOC and how you can leverage this phenomenon for fat loss.

If you are on a jog and abruptly stop to sit down — is your heart rate still elevated and are you still breathing heavily? Of course. Exercise is a stressor that disrupts homeostasis, enhancing the demand for oxygen within cells. When we stop exercising, we are not instantaneously back to homeostasis. This increased demand is a long, down-sloping curve that can last anywhere from a few minutes to three days, since there are numerous factors which influence this metabolic recovery process. Considering all the different ways in which we can exercise, how can we influence these factors to elicit a greater EPOC and ultimately stimulate for fat loss?

Studies have shown that when the intensity is equal, a longer duration of exercise may not be worth your time. Instead, prioritize more frequent exercise sessions per week rather than fewer, longer sessions, if possible. Research indicates that stimulating EPOC is about disrupting homeostasis and revving your engine more frequently, as opposed to for a longer duration of time.

If you work harder, you will expend more calories. If you expend more calories during your workout, your magnitude and duration of EPOC will be greater. Intensities greater than 80 percent to be most effective for expending calories at rest after exercise, research has shown. Exercising at a high intensity is key to stimulating caloric expenditure and therefore allowing for greater EPOC

High intensity interval training has gained much popularity over the years, and for good reason. The number-one reported barrier to regular exercise each year is time -- everyone could use couple extra hours in the day. High intensity interval training allows exercise to be driven in a time-sensitive way, by training at higher intensities for brief periods followed by relatively small rest periods. This is shown to be very effective, especially with whole-body resistance training.

Practically, this means EPOC can be stimulated in a short period of time if higher intensities and short rest periods are utilized.

Managing individual body mass is most basically a function of the calories being consumed relative to the calories being expended each day/week/year. This is known as caloric energy balance. The rolling ratio will ultimately dictate weight gain and weight loss for most. If an individual is consuming more calories than they are expending throughout the day (caloric surplus), weight gain is inevitable. Conversely, if there is a caloric deficit, fat loss is more likely.

The calories burned during EPOC are directly correlated to the calories burned during exercise itself. Exercising more frequently at higher intensities with shorter rest periods is very strenuous. It is paramount to understand that the primary driver of fat loss is sound nutritional habits and regular daily exercise.

AJ Lamb is the supervisor and senior exercise physiologist at Zarett Rehab and Fitness, and an adjunct lecturer in kinesiology at Penn State Abington. Contact him at ajl5419@gmail.com.