MaxFat: Part Two

As we discussed a while ago the Fat Burn zone can be a confusing concept since exercising at your MaxFat level does not necessarily lead to an optimized ability to burn off excess body fat or even push up your fitness level. However, the truth is there are real benefits to understanding this concept and with being able to identify your own maxfat zone which can lead to a better training effect; whether that effect is increasing your ability to sustain long workouts (stamina), recover quicker from extensive training, increase your sustainable power and yes, even optimize your body composition (i.e., body fat %). The following information provides actual fat bump charts of athletes and exercisers who completed a Cardio-Metabolic Exercise Profile in our lab. Each chart suggests a different training history and their story may help illucidate more fully the fat utilization theories and how you could benefit from similar information.

Sample 1: The endurance runner

Typically an endurance trained exerciser who has trained a large percentage of the time in the sub-threshold levels will provide a fairly high fat utilization (6-9+ kcals/min) at their fat bump and their fat contribution will continue to decrease as intensity approaches the lactate or ventilatory thresholds (LT). Quite often at LT there will be little or no fat utilization and energy systems will be relying primarily on carbohydrate fuel (i.e., from stored glycogen in liver and muscle). This athlete showed a fairly high utilization even at the LT suggesting a good ability to spair the limited glycogen even at a fairly high sustainable pace.

Sample 2: The endurance cyclist

Notice the fat burn rate does not go up quite as high for this similar sized and fit athlete, though fat utilization is still present even at his LT. This is a very well trained endurance athlete like the runner example but because the test is on a bike the fat contribution will typically be lower. One theory for this is that since muscle recruitment and fatigue is more concentrated in the legs when cycling the fat utilization is limited by comparison.

Sample 3: Endurance Cyclist

A fit Cyclist during a 30 minute sustained effort just below his threshold wattage. Note the low contribution of fat for energy. This is actually not bad for an effort level of 80% of max VO2. Remember - fat contribution will decrease as you approach your threshold intensity.

Sample 4: Overtrained/ Unrecovered Fit Cyclist

This cyclist is a world class masters cyclist who came in for testing following a long hard ride. Note the random spikes of fat utilization. High intensity training can have residual effects on fat utilization compromizing the sparing or replenishment of glycogen for days. Other factors that might have contributed to this response may include unusually high stress response to testing discomfort (i.e., mask, etc.) or even eating behavior leading up to the test. Take away - be sure to evaluate your metabolic responses when you are fully recovered.

Sample 5: Very unfit new exerciser

Note the extremely low lactate threshold and low level of fat contribution throughout the test.
This individual had just started training on the elliptical machine 3 days per week and was hoping to start a running program. The test on a treadmill suggested that she would not be able to run even at a slow pace without exceeding her threshold. We encouraged her to spend most of her training in the next 6-8 weeks working below the threshold to avoid overreaching and to begin maximizing her ability to sustain work and use more fat as a fuel. Later we suggested she add some more intensity by including 1-2 interval workouts a week at or slightly above the LT (i.e., zone 3&4) to encourage greater fitness development.