First, lets define EPOC: Excessive PostExercise Oxygen Consumption, or simply, recovery oxygen consumption. Following exercise, the body does not immediately return to resting levels. Light, short duration activity, which causes little disruption in body temperature and hormonal balance, is followed by rapid recovery, almost unnoticed. Of course what's classed as'light' exercise depends on the physical condition of the individual, for instance, an overweight person whom is unused to any considerable amount of exercise or even movement, will not recover as quickly doing the same activity as someone who is generally better prepared for physical exertion. One half of the total oxygen recovery consumption will occur within 30 seconds and total recovery within 4-7 minutes, this is known as the fast component in recovery oxygen consumption.
On the other hand, stressful exercise such as completing 20 back squats nearing muscular failure, or running 400m as quickly as possible will require considerable time for resting metabolism to occur (slow component). The length and the intensity of exercise will determine how long this takes; research has shown this can take as long as 24 hours for the body to return back to baseline oxygen consumption levels (McArdle, Katch and Katch, 2007). To reiterate, a considerably greater oxygen debt will be placed upon the body following strenuous exercise. This means that the body will utilise more oxygen (Litres) in an attempt to return to pre-exercise oxygen consumption.
Why does the body need so much oxygen following exhaustive exercise (where the activity requires a significant anaerobic component as well as aerobic)? There are a few factors that contribute to EPOC; a small part of it is used to aid re-synthesis of lactate to glycogen (although this is mostly the job of dietary carbohydrates - which is a good thing for fat loss). Elevated body temperature also contributes to EPOC. Temperature can rise by up to 3c during exhaustive exercise and can remain elevated for hours after the exercise. This stimulates metabolism to increase oxygen consumption during recovery. Natural Fat burners guys...
Up to 10% of of recovery oxygen will be used to take the blood from the trained muscles back to the lungs, as well as the restoration of oxygen lost via bodily fluids and that which is bound to myoglobin in the active muscles. Ventilation volumes remain elevated, the heart works harder and requires greater oxygen supply during prolonged recovery, tissue repair and redistribution of key minerals and ions and the residual thermogenic hormones relaesed during exercise all go towards keeping metabolism elevated during EPOC.
In summary, after prolonged strenuous aerobic or exhaustive anaerobic activity the body requires more oxygen for considerable lengths of time to recover. This means a potential greater kcal expenditure during EPOC, rather than just kcal expended during exercise, something which can make weight management easier for everyone.
However, attempting to train at the intensity and duration required to induce said EPOC is difficult. Extreme intensity is necessary, something which trainees need time to work up to. Imagine performing 20 back squats with a weight you would usually do 10, or a cross country race for for a 5 second pb, or perhaps 2 minutes worth of clean and press with a 70%1rm followed by 50 burpees. Extreme pain comes to mind. This is where intervals can become very useful. Shorter (supermaximal) bouts of exercise, intermittently spaced between rest periods, can produce substantial recovery oxygen consumption for well over an hour (McArdle, Katch and Katch, 2007).
An exercise that when performed continuously would normally cause exhaustion within several minutes can be split up into intermittent segments of work and rest periods. By structuring the workout in such a way a much greater volume of workload can be achieved thus overloading the energy transfer system. Exercise up to 8 seconds (all-out intensity) relies on intramuscular phosphates to provide the majority of the energy. Due to quicker recovery and lower blood lactate levels, intense exercise can follow after a brief recovery period. Total work volume over a session can increase using interval training. Christenson EH, et al. found that by adding a 5 second rest period to every 10 second of running the athlete improved the total distance ran by nearly 5 times that of the distance ran at a continuous speed before exhaustion.
Total Distance run (yards) for 4 min of continuous (until exhaustion) - 1422
Total Distance run (yards) for 10s exercise/5s rest - 7294
{Same speed for both days)
Intervals are a fantastic tool for increasing workload, past the point one would usually fail at if exercising continuously. This means greater kcal expenditure and potentially better weight management. Think twice before you jump on that treadmill and half ass that 5km. Utilize full body weight lifting movements within your intervals (squat thrusters/clean and press etc.) to produce the physiological adaptations associated with weight bearing movements (increased muscle mass/strength etc.) AND burn substantial kcal during and after exercise!
Ross - Natural Aesthetics
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