Cardio, MHR, and fat vs. muscle loss

[Flyersfan]

I've read a lot and am having a hard time finding answers to a couple of questions.

Right now I'm doing 2-3 days of cardio and 2 days with the weights over a 7 day period. My goal is to cut - I have a little gut that has to go. :) My diet has been modified appropriately.

Low intensity cardio is boring, so I hop on the bike and run the hills program for 50 minutes. I really work up a sweat and feel great afterwards, albeit tired.

First question: during the most intense portions, my heart rate is approx. 90-92% of my MHR (maximum heart rate). Is this dangerous over short periods (90 seconds or less)? I don't want my heart to explode so I wouldn't try to stay there for the long haul.

Second: since I'm above the fabled (mythical?) fat burning range, will my body break down a lot of muscle? I'm made nominal gains every week, so I haven't lost any strength yet. But, I've only been at this for a month and don't have any long term results.

I seem to be on the right track because I've already lost about an inch from my waist. I only have 2-3 inches to go, and I don't think my bf% is high.

Comments from those who went through a cutting cycle and were happy with the results would be most appreciated.

[aka23]

Originally posted by Flyersfan
First question: during the most intense portions, my heart rate is approx. 90-92% of my MHR (maximum heart rate). Is this dangerous over short periods (90 seconds or less)? I don't want my heart to explode so I wouldn't try to stay there for the long haul.

Short intervals of high intensity training are an excellent way to improve fitness and reduce body fat. There is little medical risk unless you have known health/heart problems.


Second: since I'm above the fabled (mythical?) fat burning range, will my body break down a lot of muscle? I'm made nominal gains every week, so I haven't lost any strength yet.

Your body is burning fat whether you are in the "fat burning range" or not. As you move to a higher intensity, a larger percentage of the calories comes from muscle gylcogen and a smaller portion come from fat. However, you are burning more total calories at higher intensities, and may even be burning more total fat.

Using protein muscle for energy is highest when there is inadequate muscle gylcogen. This might increase if you exercise on an empty stomache, exercise immediately following doing weights, excerise for a long duration (especially high intensity for long duration), exercise while on a low carb diet (lower starting muscle glycogen), or do not eat soon after the finishing the cardio. 90-95 seconds at high intensity is nothing to worry about.

Serious bodybuilders sometimes recommend less than 50 minutes total to minimmize muscle loss. Some recommend as low as 20 minutes. The downside is that your body burns the most fat during the longer durations in which muscle glycogen is lowest. The optimal duration depends on your personal goals. If your focus is cutting, I would suggest 30-60 minutes on most days of the week.

A few refernces are below:
http://www.fitstep.com/Advanced/Questions/Questions/Cardio/maxcardio.htm
http://www.ast-ss.com/dev/qa_search/full_text.asp?ID=1599
http://www.brandyblackledge.com/fitness.htm