75 day challenge into single digit bodyfat %

[skunkworks]

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Interval sprints wont burn fat. It will mostly burn his carbohydrate intake. Long distance running is best for his goal of lowering his BF% but what he could add for a more effective muslce strength building, and fat burning is hill running. Adding multiple hills in will give his body the shock it needs to burn fat and it also builds strength in the quads.

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sanmarcosrun1, your advice is a bit out-of-date.

Low-intensity cardio work (like long-distance running) uses more fat stores for energy, but high-intensity exercise causes greater postexercise fat oxidation and energy expenditure. This effect is significant enough that there is a similar amount of fat burned after 24 hours when comparing low vs. high intensity exercise. (See: Saris WH, Schrauwen P. Substrate oxidation differences between high- and low-intensity exercise are compensated over 24 hours in obese men.)

High-intensity exercise is better for increasing cardiovascular fitness (read up on the research behind the Tabata protocol) as well as preserving/increasing lean mass (many sources, I can provide some if you'd like). In addition, there is a lot of research that supports high-intensity exercise being as good if not superior for reducing body fat. Intuitively, we can hazard a big fat assumption that, at the very least, maintaining more of your lean mass after exercise means increased base metabolic rate, which in turn means more fat burned.

The bottom line is that there is a lot more to reducing body fat than the direct energy expenditure that exercise causes. The intensity level of the exercise makes a difference. You seem to understand that partially since you do advocate hill running -- one way of increasing intensity.

[sanmarcosrun1]

I understand what you are saying. I guess we are just misinterpreting intensity levels. I know when most people think of long distance running for fat burn use it is about 40-50% VO2max intensity. To me the best range is 65-80% VO2max as this produces the effects you are talking about post exercise as well as burning fat during the exercise.