The Perfect Fat Burning Zone

Endurance athletes tend to consume too little protein and too many refined foods.

Q: Hi Gale - I am soooo confused about fat burning and heart rate zones. I just attended a triathlon seminar for women only, and in one of the handouts they discuss finding your "fat burning zone" and talk about extended training in that zone.

Based on the calculation they provided, my fat burning zone would be at a heart rate of 139 or below. This seems impossible!

First of all, I am a very fit 46-year-old woman who can hit a heart rate of 145 just by walking quickly. Add any incline at all, or bring it to a slow jog, and I am immediately into the low 150s. If I run at race pace for any period of time, I am in the high 160s to mid 170s. On a cool down, my heart rate drops back to 132 beats per minute within two or three minutes.

I think my heart rate is just higher to begin with. I attended an excellent seminar several years ago and at that time determined my zones to be as follows: fat burning (aerobic) 139 to 156, 80 percent of maximum heart rate was 157 to 167, and the anerobic zone was 168 and above.

The highest heart rate I've ever hit was 183. I've trained according to those zones ever since and felt comfortable with it. One important thing I learned was to pay attention to my heart rate for signs of a cold coming on, etc. For example, if I can't get my heart rate above 140 on a normal workout, then I back off because my body is probably fighting something or is unusually stressed. Nine out of 10 times this theory has proven to be correct.

My question is, would I see more fat disappearing if I worked in the lower zones longer? But if I do that, then how do I meet my training goals for triathlons? I don't actually care to lose weight, but would like to see more muscle definition—something that seems harder to attain at this age.

Additionally, I am one of those people who thinks I haven't really worked out if I'm not in the 145 to 165 heart rate range for at least 30 minutes of a 50-minute workout.

Obviously, I'm confused about all this. Any advice would be greatly appreciated.

Regards - CG

A: CG, you have plenty of good questions. First, I'm not sure what kind of formula they used at the seminar for women to recommend "fat burning." Generally, age-based formulas are very inaccurate for active people as they age. I'm very close to you in age and working at a heart rate of 139 would put me in training Zone 1 for the run and training Zone 2 on the bike. These are indeed mostly aerobic zones.

Just a point of clarification: we are producing energy aerobically and anaerobically all the time—even as you sit here reading this column, you are producing some energy anaerobically. The percentage of energy coming from aerobic production changes as exercise intensity changes.

Examining Lactate Threshold

One of the indicators of the change from primarily aerobic energy production to greater anaerobic energy production is lactate threshold (LT). For healthy, unfit people LT is often around 50- to 60-percent of maximum heart rate. For fit people, LT can be some 80- to 90-percent of maximum heart rate. So, although maximum heart rate can be exactly the same for you and one of your unfit friends, your LT heart rates can be quite different.

For athletes, the good news is that LT is "trainable". This means you can utilize training principles and specific workouts to move your LT to a higher percentage of your maximum heart rate. In turn, you can go faster at LT and you can keep higher speeds for longer periods of time.

Deciding what heart rate is most appropriate for your workouts is related to your personal goals and is part of the periodization process. If you're trying to build your aerobic endurance, then longer workouts at a mostly aerobic pace is one strategy. If you're trying to improve your speed at LT, that goal requires a different type of workout, placed at a particular time of the year.

Working Out to Lose Weight

Workouts designed to improve muscle tone may or may not be workouts designed for a weight loss program. As a general rule, losing weight is a matter of burning more calories than you consume over the long haul. It is slightly more complicated than this because cutting major amounts of calories from your diet can actually slow metabolism and cause your body to conserve energy.

It looks like you don't need or want to lose weight anyway. Rather, you're interested in building more strength, speed and muscle definition, which involves a combination of proper diet and the appropriate workouts.

On the diet side, in my experience, I often find that endurance athletes (both male and female) tend to consume too little protein and too many refined foods. If your diet does not include a good mix of protein, fat and carbohydrates you will not meet your athletic goals—performance or appearance. (This column is too limited to go into too many diet details.) One step in the right direction is to keep a detailed food log for three to seven days to see the details of your diet.

Assuming you have your diet in order, good nutrition helps you build the muscle tissue in response to a workout stimulus. Many athletes find that a strength training routine that changes depending on the time of year not only builds beautiful muscles, but more racing speed, too.

If you want more information on all these subjects, check out the free download section on my training plan page. There you will find brief discussions on training intensity, strength training and more.

I hope this helps!


Gale Bernhardt was the 2003 USA Triathlon Pan American Games and 2004 USA Triathlon Olympic coach for both the men's and women's teams. Her first Olympic experience was as a personal cycling coach at the 2000 Sydney Olympic Games. Thousands of athletes have had successful training and racing experiences using Gale's pre-built, easy-to-follow training plans. For more information, click here. Let Gale and Active Trainer help you succeed.

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