Cardio

Surely you've noticed that you breathe heavier, and your heart beats faster when you excercise, do you have any idea why? To get more oxygen to the muscle. Oxygen is used in fat oxidization, a.k.a. fat burning. In fact, measuring the rate of oxygen consumption is one method used in determining amount of fat burned up (glycogen oxidization also occurs though).

So the cardinal rule of cardio is to reach and maintain a certain target heart rate. This target heart rate gets lower as you get older, maybe because the target heart rate is a % of basal metabolic rate which drops as you age as well(except maybe in very active folks). This is a speculation of mine, so I'm not 100% sure why this is.

Regardless, your heart has to beat faster! So why not beat as fast as possible, why only a range from say 120-150 beats per minute(bpm)? Too high an intensity causes glycogen stores to be mobilized, causing lactic acid buildup, muscle fatigue, and muscle cramps. Also leads to greater utilization of intra-muscular fat stores (not really bodyfat), and muscle protein for energy which means muscle breakdown.

When comparing 25% VO2 max. with 65% VO2 max. (light intensity(could do it for 10 hours) vs. medium intensity (could do it for 1-4 hours)), there are som interesting results. 25% intensity uses more % calories from body fat than 65% intensity, but total calories burn are say 70 vs. 110. So though the percentage is less for 65%, the net calories from body fat will be higher.

So medium intensity may be quite beneficial as well. So where to the rest of the calories come from during medium intensity exercise? Well, intra-muscular fat stores play an important role at this level. This fat isn't really considered body fat, as it is stored in the muscle cells themselves. So if we burn more of these during medium intensity exercise, would it not be safe to say that these stores must be replenished as well?

I would venture to say that medium intensity may be the way to go because it burns more net bodyfat calories than light, and excess fatty acids in the blood after exercise may get stored in the muscle to replace used up intra-musclular fat instead of body fat again.

Maybe this is one of the reasone interval training has become quite popular lately. This is probably the best overall way to do cardio. It mobilizes body fat and intra-muscular fat, and can be sustained for longer than medium intensity alone could (an is probably more comfortable as well).

I would also like to say that no cardio session should exceed about 40 minutes. Anything past this tends to promotes muscle protein breakdown in a big way. If you really want to do more cardio, split it up into several smaller sessions per day.

When to do Cardio

Lately, I have been reading a lot of articles claiming the early morning, before breakfast to be the best time for cardio. The main arguement being that working out on an empty stomach causes greater fat mobilization for energy, because glucose levels are low.

Since Muscle Media, a very reputable magazine that backs most of their information with research, also claims this, I hesitate to dispute this theory. But, being an academic, I can't help but wonder.

Low intensity exercise, and in fact, basal metabolism burn primarily fat for energy. Glucose is spared for use by nervous system since it can't use fat at all. So regardless of glucose availability, fat will be burned first if it can supply energy fast enough (hence low intensity is necessary).

However, eating a meal causes inulin release which definitely interferes with fat mobilization, so doing cardio, or even working out shortly (less than 1 hour) after a meal will be inefficient at best. So the real question is how long it takes for insulin to be cleared out of the system, which also depends on the meal. Chances are, insulin levels wouldn't drop to pre-breakfast levels for about 4 hours. And not eating for 4 hours can be quite unpleasant.

I can't really dispute this accepted fact of cardio timing, but what bothers me is that upon waking up, nitrogen level is very low, and cortisol (stress hormone) is way up. An ideal environment for muscle catabolism, and yes, fat catabolism as well(this presence of cortisol is probably what makes early morning cardio so effective). But I don't want my muscle wasting away in the morning.

A compromise: What I like to do now to get the best of both worlds, is upon waking up, have a small protein shake (no carbs for minimal insulin response) or supplemental glutamine (primary amino acid muscle is broken down for) or HMB (also involved in preventing muscle catabolism), and do my cardio about a half hour later. I may also supplement with caffeine/aspirin/ephedrine to maximize fat mobilization/burning.

But what about doing cardio after eating? Like I said, fat is mobilized in favour of glycogen even if the latter is readily available, so as long as you wait until insulin has been cleared out of your system (1-4 hours, depending on meal), cardio should burn as much fat as in the morning.

One last thing, cardio in the morning will definitely burn more fat because metabolism and stress hormones are already elevated. Say, without cardio you burn 10 grams of fat per hour, with cardio you burn 50 grams per hour, total of 60 grams. If you do your cardio in the afternoon, you may only burn 5 grams per hour without, but you'd still burn 50 during cardio, total of 55 grams. Sure it's less, but you burnt the 10 grams/hour in the morning already.

Was that confusing? Let me summarize: you burn more basal metabolic calories in the morning than in the afternoon, so when you add cardio, it'll look like the total calories are higher, but for the entire day, it would be no different!

This arguement of mine is just to give peace of mind to people who can't, or don't want to do cardio in the morning. I prefer cardio in the morning cause it wakes me up, gets it out of the way, and its easier to stick with (harder to find excuses to skip it)!

It may be that cortisol only causes more fatty acid mobilization, but not necessarily oxidization. So doing cardio in the morning is better because you actually burn all the fatty acids that have already been mobilized by stress hormones.

So when to do it?

Cardio sessions should be 20-40 minutes, 3-4 times a week.
Do cardio first thing in the morning.
Take caffeine/ephedrine/aspirine and 20-30 minutes before cardio.
Wait 30-60 minutes after cardio to burn up remaining fatty acids in blood.
Drink lots of water before, during, and after cardio for waste removal.
Use interval training, i.e. vary the intensity.

What Cardio to do and how long

Any exercise you do that gets your heart rate up to your target range will suffice. You may find exercises that use more muscle will do this easier, and may in fact burn more fat. The most important aspect of your cardio activity of choice: you should enjoy it!

Easier said than done!! If you can play some sports with friends, or go for a scenic rollerblade with a friend, it's far better than sitting on an excercycle! If you are stuck on an excercycle, stair climber or whatever indoor equipment, reading a magazine usually really helps pass the time more quickly.

I remember always hearing 'you have to do cardio for at least 20 minutes before you even begin to burn fat'. Again, I beg to differ. You burn fat before you even begin your cardio session! But if you ate a lot of fat recently, you may have high lipid concentrations in your blood which could delay body fat mobilization.

If you can do multiple shorter sessions per day, it may be as good, if not better than one 30-40 minute session. This is because your metabolism stays elevated for a short period even after you finish your cardio. So elevating your metabolism 3 times a day may result in more overall fat utilization than one 40 minute session.

But that's not very practical, so most of us have to live with one session (fine by me!). The accepted amount is 30-40 minute 3-5 times a week, depending on your goals, and your schedule. I'll list a few different exercises, and how many calories each one burns per hour to help you choose an exercise and session duration.

Stay tuned!