Monday, September 24, 2012

Cardio Duration

I had a client ask me recently why I push for an hour of cardio 2-3x/week as opposed to more days of cardio that add up to the same total.  After all, an hour of the stuff can feel like an eternity thanks to boredom and/or fatigue.

The short answer is fat metabolism.  In most cases, the reason a client is doing cardiovascular exercise is to burn fat.  It is important to be training at an intensity (usually monitored via heart rate) that is conducive to the utilization of fat as an energy source BUT, even with that variable dialed in, DURATION is a critical detail.

From minute 0-20, guess how much fat your body is mobilizing to fuel your activity......The answer is none!  Until right around the 20-minute-mark, your muscles' activity is fueled exclusively by glucose (sugar) stored within the muscles themselves.  Right around that threshold (20 minutes) your body first starts utilizing its fat reserves as a source of fuel. 

So why not stop at 20 or 30 minutes?  Well, that threshold isn't a switch that just turns off one pathway in favor of another.  At 30 minutes in, you have only been in fat-burning mode for 10 minutes and the percentage of calories burned in the form of fat is still WAAAAY lower than the percentage of calories burned in the form of glucose.  BUT as you carry on past that point, the balance begins to shift; The percentage of fat calories burned continues to increase and the percentage of sugar calories burned begins to decrease. 

At about 45 minutes into your cardio routine, your activity is predominantly fueled by the body's fat reserves.  It is also at about this point that the body begins to release endorphins, the body's own natural feel-good hormones.  Once you hit that point, you've usually pushed past the wall and another 15 minutes is relatively easy.  If not, be persistent and you will start to notice this.  Anyway, back to endorphins: They help create an association between doing something healthy and feeling good.

60 minutes of cardio is, in my opinion, the best tradeoff between workload, calories (especially fat) burned, and the natural mechanisms that promote the forming of beneficial habits.

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