Excess post-exercise oxygen consumption

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Excess post-exercise oxygen consumption (EPOC) is a measurably increased rate of oxygen intake following strenuous activity intended to erase the body's "oxygen debt." The term oxygen debt is however a misnomer in that accounting terminology (e.g., credits and debts) should not be utilized in the explanation of a physiological phenomenon. [1] [2] In historical context the term oxygen debt was popularized to explain or perhaps attempt to quantify anaerobic energy expenditure, particularly in regards to lactic acid/lactate metabolism; in fact, the term oxygen debt is still widely used to this day. Direct and indirect calorimeter experiments have however, definitively disproved any association of lactate metabolism as causal to an elevated oxygen uptake.[3]

In recovery oxygen (EPOC) is used in the processes that restore the body to a resting state and adapt it to the exercise just performed. These include: hormone balancing, replenishment of fuel stores, cellular repair, innervation, and anabolism.

EPOC is accompanied by an elevated consumption of fuel. In response to exercise, fat stores are broken down and free fatty acids (FFA) are released into the blood. In recovery, the direct oxidation of free fatty acids as fuel and, the energy consuming re-conversion of FFA's back into fat stores (a futile cycle) both take place. [4] [5] [6]

[edit] Duration of the effect

The EPOC effect is greatest soon after the exercise is completed and decays to a lesser level over time. One experiment found EPOC increasing metabolic rate to an excess level that decays to 13% 3 hours after exercise, and 4% after 16 hours. Another study, specifically designed to test if the effect existed for more than 16 hours, conducted tests for 48 hours after the conclusion of the exercise and found measurable effect existed up to the 38 hour post-exercise measurement. (Schuenke 2002)[7]

[edit] Size of the EPOC effect

Studies show that the EPOC effect exists after both anaerobic exercise and aerobic exercise, but all studies comparing the two show that anaerobic exercise increases EPOC more than aerobic exercise does. Such comparisons are problematic however, in that it is difficult to equalize and subsequently compare workloads between the two types of exercise. For exercise regimens of comparable duration and intensity, aerobic exercise burns more calories during the exercise itself [1], but the difference is partly offset by the higher increase in caloric expenditure that occurs during the EPOC phase after anaerobic exercise. Anaerobic exercise in the form of high-intensity interval training was also found in one study to result in greater loss of subcutaneous fat, even though the subjects expended fewer than half as many calories during exercise.[2] Whether this result was caused by the EPOC effect has not been established, and the caloric content of the participants' diet was not controlled during this particular study period.

Some researchers use a measure of EPOC as a natural part of the quantification or measurement of exercise and recovery energy expenditure; to others this is not deemed necessary. After a single bout or set of weight lifting, Scott et al have found considerable contributions of EPOC to total energy expenditure.[8] In their 2004 survey of the relevant literature, Meirelles and Gomes found: "In summary, EPOC resulting from a single resistance exercise session (i.e., many lifts) does not represent a great impact on energy balance; however, its cumulative effect may be relevant.".[9] This is echoed by Reynolds and Kravitz in their survey of the literature where they remarked: "However, it should be emphasized that the overall weight-control benefits of EPOC, for men and women, from participation in resistance exercise occur over a significant time period, since kilocalories are expended at a low rate in the individual postexercise sessions."[10]

What is clear is that the EPOC effect increases as the intensity of the exercise and the length of time spent during the exercise phase increases. Most studies found a linear relationship with time of exercise and the effect.[11] One found a curvilinear relationship between the intensity and the EPOC effect, though others found a linear relationship.[12]

[edit] References

  1. ^ Harris, P. Lactic acid and the phlogiston debt, Cardiovasc. Res., 3:381-390, 1969.
  2. ^ http://www.springer.com/humana+press/nutrition/book/978-1-60327-382-4
  3. ^ http://www.ncbi.nlm.nih.gov/pubmed/15841591?dopt=Abstract
  4. ^ Bahr, R. Excess post-exercise oxygen consumption -magnitude, mechanisms and practical implications. Acta Phys Scand. Vol. 144, Suppl. 605, 1992.
  5. ^ Bahr, R. et al. Effect of exercise on recovery changes in plasma levels of FFA, glycerol and catecholamines. Acta Phys Scand. 143:105-115, 1991.
  6. ^ Bielinski, R. et al. Energy metabolism during the postexercise recovery in man. Am J Clin Nutr. 42:69-82, 1985.
  7. ^ Effect of an acute period of resistance exercise o...[Eur J Appl Physiol. 2002] - PubMed Result
  8. ^ http://www.ncbi.nlm.nih.gov/pubmed/19197214
  9. ^ Meirelles, Cláudia de Mello and Gomes, Paulo Sergio Chagas. (2004). Acute effects of resistance exercise on energy expenditure: revisiting the impact of the training variables. Rev Bras Med Esporte Vol 10, No 2 Mar/Apr 2004.
  10. ^ Reynolds, Jeff M, and Kravitz, Len. Resistance Training and EPOC Retrieved April 21, 2005.
  11. ^ Borsheim, E., and R. Bahr. 2003. Effect of Exercise Intensity, Duration and Mode on Post-Exercise Oxygen Consumption. Sports Medicine 33(14):1037-1060.
  12. ^ Borsheim, E., and R. Bahr. 2003. Effect of Exercise Intensity, Duration and Mode on Post-Exercise Oxygen Consumption. Sports Medicine 33(14):1037-1060.
  • Hill, A. V., Long, C. N. H. and Lupton, H. (1924). Muscular exercise, lactic acid, and the supply and utilization of oxygen. I–III. Proc. R. Soc. Lond. B 96,438-475.
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