We often get asked these questions so I thought I’d attempt to make some sense of this often misunderstood component of training. For this discussion we’ll limit the topic to cardio as it relates to body fat and weight loss. Cardio for sports performance or heart health would lead us down a different path.
Most research suggests that you burn somewhere in the range of 70% fat while at “rest.”. Fat is a very efficient fuel source so if you go slow enough (what’s slower than rest?) then you can count on burning mostly fat. Even though the PERCENTAGE of fuel burned at rest is mostly fat, the TOTAL calories (energy) burned is low. Most people do cardio because it will take them too long to see the effects of fat burning from rest, especially if their diet is less than perfect (which unless you are a competitive bodybuilder, it most likely is. Let’s face it. You gotta live right?).
So you decide to do some cardio to speed up the fat burning process. But how much and what type is best? Walking burns mostly fat, where as running burns more carbohydrates (3 main sources: muscle glycogen, liver glycogen, blood sugar). The higher the intensity of exercise (from rest to walking to running) the higher the PERCENTAGE of carbohydrates burned. Intense weight training is at the top of this spectrum, deriving most of it’s energy from carbohydrates. This is why it is important to have ample carbohydrates prior to weight training or you may become light headed as a result of low blood sugar during an intense weight training session. You should also consume ample carbohydrates following the weight training workout to replenish lost muscle and liver glycogen due to the training session. When we design meal plans we design carbohydrate intake around a client’s training schedule to allow for fat loss while providing the right amount of carbohydrates at the right time in relation to their training.
If a client has been sedentary and is considerably overweight then the first goal is simply to set the calorie equation out of balance: eat less and move more. Where the calories come from is not as important to this person, at least in the beginning. We want them to start losing body weight and feeling good about the results they are seeing. Their training program is not designed to maximize muscle growth while getting to extremely low levels of body fat. Interval training would be great as would any of the fun programs on any of the cardio machines in the gym. A simple jog-walk program outside would elicit results and be fun for this type of client as well. As this person progresses, however, or if we are dealing with a more advanced client, then it’s important to be aware of how many carbohydrates the client is burning during cardio as it relates to recovering from their strenuous weight training schedule. If muscle tone or mass is the goal then the client should keep their cardio sessions in the “fat burning zone” that we hear about so much. All this means is that it’s going to take this client longer to burn the same amount of calories when compared to the previous client, but the calories they do burn will be more from fat and less from carbohydrates. This will allow them to replenish muscle and liver glycogen and thus spare muscle tissue more effectively while on a calorie deficient diet. For this type of client a slow walk on a slight incline would be advised, as would a moderate pace on a stationary bike. Slow and steady should be this client’s goal for cardio.
Now how much is too much? Well after years of anecdotal evidence suggesting that extremely long bouts of cardio (of any type) will decrease muscle mass and tone, there is now some good scientific evidence to support this claim. Basically, if a person does long bouts of cardio (45-60 minutes or more) their DNA expression actually changes to tell their muscles to get smaller! I continually see it in bodybuilding, especially at the local level. I’ll see a guy who looks incredibly thick and full in the off season show up to a contest scrawny and flat because he was doing 2 or more hours of cardio a day. This new research suggests that if your ultimate goal is at all muscle related then you should keep your cardio sessions short. How short? Well I’ve found that I see a very significant change in my physique when I go over 35 minutes of cardio per session. Cardio bouts over 35 minutes cause my upper body to deflate. This is not good for me, as my legs are my most developed body part to begin with and I’m working very hard to NOT be “bottom heavy”. These concepts are partially what HIT cardio training is based on. Short intense bursts of cardio that aren’t supposed to “burn” muscle, or in this case “signal” muscles to get smaller. The exact time which a person’s DNA expression changes are impossible to predict so play around with it and pay attention. It might be 30 minutes or it might be longer depending on how your body reacts.
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