Not long ago in this column we discussed the Target Heart Rate Zone. Following that train of thought, some of you may wonder if there is an optimal range for maximizing body fat loss – a fat burning zone. This is an especially valid question if you look closely at the monitors on cardiovascular exercise machines. Some machines have a label referencing "fat burn" (or something to that effect) corresponding with levels on the heart rate indicator. Does this mean that you are only burning body fat when your heart rate is within this range?

Not long ago in this column we discussed the Target Heart Rate Zone. Following that train of thought, some of you may wonder if there is an optimal range for maximizing body fat loss – a fat burning zone. This is an especially valid question if you look closely at the monitors on cardiovascular exercise machines. Some machines have a label referencing "fat burn" (or something to that effect) corresponding with levels on the heart rate indicator. Does this mean that you are only burning body fat when your heart rate is within this range?


Well, no … with an asterisk. The human body receives calories from three sources: carbohydrates, proteins and fats, and breaks down those same three tissues for energy. Last week we discussed how to keep the body from breaking down the protein in muscle tissue for energy. This leaves carbohydrates and fats. Carbohydrates are broken down the easiest and most quickly for energy. They are always circulating in the bloodstream as glucose and stored in muscle and liver as glycogen. But, in seeming contradiction, our bodies prefer to break down fatty acids as an energy source. It takes our bodies time to convert these fatty acids into usable energy, so during times of activity, if the conversion rate cannot keep up with the pace of energy need, we rely on stores of glucose and glycogen. Think of our fat stores as the body’s pantry and our limited carb stores as the fast food joint on the corner.


That brings us back to the question of whether or not there is a "fat burning zone." If we burn more calories from fat during periods of light activity, that means we burn even more fat when we’re sitting around being lazy, right? Well, this is when it becomes a game of percentages. It is generally accepted that at rest the average human body gets about 70 percent of its energy from fat conversion and 30 percent from carbohydrates. So, rather than saying that our bodies burn MORE fat at lower intensity levels, it would be more accurate to say that a higher PERCENTAGE of the calories we burn during those activity levels come from fat.


During a run the percentages may be 40 percent fat and 60 percent carbohydrates. This seems to further enhance the position that we should do lower intensity exercises, doesn’t it? Not when we do the math. I’ll use myself as an example. My resting metabolism is somewhere around 2,400 calories per day. That’s 100 calories every hour. If 70 percent of those calories come from fat, that’s 70 calories an hour. A big, heavy individual like myself can easily burn 600 calories (or more) an hour at a brisk jog. Even if only 40 percent of those were from fat, that’s still 240 calories. More than three times as many! Or, from a different perspective, less than 20 minutes into the run more fat calories were burned than during an hour of sitting around.


The take home message is really this: higher intensity work is more beneficial than lower intensity work. We may often hear that "something is better than nothing." While I do believe that to be the case, I also (and more importantly) believe that anything worth doing is worth doing right. If you have set aside the time, gotten dressed appropriately and driven somewhere to exercise, don’t you owe it to yourself to put in the right effort to receive the greatest possible benefit? I think so!


The JRMC Wellness Centers, located in Pine Bluff and White Hall, offer a variety of fitness options for all ages and interests. Free weights, machines, cardio equipment, personal trainers and a full schedule of Les Mills classes are available at both facilities. For more information call the Pine Bluff (541-7890) or White Hall (850-8000) facility.