There is often quite a bit conflicting advice offered when evaluating the appropriate volumes and intensity at which someone should exercise.
Many "non-experts" propose a variety of different methodologies, in order to lose fat or lose weight. Often these methodologies have been born from personal experience or a misunderstanding of basic physiological principles.
It is important to understand the theory behind each of these approaches in order to accurately utilize the most effective methods available.
One important theory to understand is that of individuality.
In short, the concept of individuality explains that the same exercise may have different effects for different individuals. Essentially this says, "What works for one person, may not work for another."
Let's look at this more carefully...
In order to do this, let's compare two individuals, the first a highly trained aerobic athlete, the second a beginner who is not aerobically fit at all.
To simplify our comparison, let's say that the first athlete is capable of running on a treadmill at 18 km/h and at the second athlete is capable of running only up to 8 km/h.
(We could also compare their aerobic capacities, measured by their maximal oxygen uptake, or VO2 max)
Obviously, should we ask each athlete to run at 8 km/h, the highly trained aerobic athlete will find this a very easy task, whilst our unfit athlete will find this extremely challenging, as this speed is the maximum they are capable of doing at present.
So the same demand in terms of absolute speed or velocity has produced two very different aerobic challenges for two different people.
Looking at this example in a very simplistic manner, we could say that the second athlete is working at approximately 100% capacity in order to run 8 km/h, whilst our highly trained athlete is working at less than 50% capacity (8/18 = 44.4%)
When we consider the source of the energy used by each athlete, the least fit athlete would be utilizing a very high percentage of carbohydrates and a very small percentage of fat. The very fit athlete however, because of the low demand placed on their aerobic capacity, would be utilizing quite a high percentage of fat, as the exercise is making very little demand on their aerobic capability.
Hence, the better-conditioned athlete utilizes more fat in completing the same exercise intensity than the poorly conditioned athlete. This helps explain why a very fit person may also be quite lean, even though they appear to be exercising at a higher rate (or intensity) that a less conditioned person.
Many people without a strong theoretical background, and hence a reliance on their own personal experience only, propose methodologies that work for them. These people are usually well conditioned, enjoy challenging themselves having trained for a number of years, have high tolerances of pain and are both quite strong and very capable aerobically. As such, most aerobic exercise is relatively easy and will thus challenge their fat utilizing capabilities, even when exercising at relatively high rates. (Compare the physique of marathon runners, and long-distance runners, who are aerobically advanced to those of say, competitors in the field events, who do not have the same aerobic requirements and who therefore do not train to develop aerobic capacities to the same extent)
Whilst this appears to be in conflict with the concept of utilizing more fat at lower exercise intensities, it actually is not, as it is the individual's exercise intensity rather than an absolute value (such as the speed of their run) that is critical in determining the source of energy utilized in any particular exercise.
The use of a heart rate monitor is essential in order to accurately assess the appropriate level of intensity that any exercise has on an individual. Using "rules of thumb" such as Karvonin's principal in order to calculate appropriate heart rate ranges will allow the intensity of the exercise to be matched to the capability of the individual, and as such, will help to maximize results.
For the conditioned athlete, the exercise mentioned in the example above is very easy. As such, both the energy demand and subsequently the demand for oxygen are both low and the energy supply can easily be met by metabolizing fat.
For the beginner however, working close to or at the capacity, is incapable of supplying sufficient oxygen to meet the energy demands of the exercise, which in their case is high. As such, they need to utilize the most efficient source of energy available to them, carbohydrates! Therefore, the use of fat as an energy source in their case is relatively low.
In exercise, there is no “one size fits all” approach.
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Regards Kym
