Heart Rate Zones… FAT BURNING or WASTING TIME April 8, 2010

Please read if you are one of the many people who use the FAT BURNING settting on cardio machines…

Written by: Ashley Kipp, CTS Expert Coach, USAC Cycling Expert Coach

For the past few years, in the world’s obsession with weight loss and fitness, we’ve all been bombarded with the message that low intensity, longer duration training sessions are the only way to go. The media touts that lower-intensity workouts are the best way to reach the “fat burning zone” and to achieve the weight loss goals for which many of us strive. Training too hard, they claim, will take you beyond fat burning…but where will it take you?

As health conscious individuals, it is important for us to realize that our goals in fitness should be much more dynamic than merely weight loss. We are training for overall health and to be the very best that we can be. Exercise is not just a way to burn calories, it is the path to becoming more fit, and one of the positive benefits of developing your aerobic engine is increasing your capacity for burning fat.

Increased aerobic fitness will help you achieve the lean body you’re striving for by increasing the work you can do while still burning a mixture of carbohydrate and fat. The aerobic engine is the only one of your energy systems that can burn fat, and using it at the upper end of it capacity burns both fat and a lot of total calories. Athletes training for performance goals, rather than merely for weight loss, generally work far above the touted “fat burning zone,” because that’s what’s necessary to actually cause significant physiological adaptations. One of the positive side effects is that their training intensity allows them to burn a heck of a lot more calories in relatively shorter periods of time than someone slogging away at the gym on the Stairmaster barely moving for 90 minutes. Consistent and intense training sessions, balanced with appropriate amounts of recovery of course, have brought them to where they are. Training above the “fat burning zone” provides the stimulus that trains the aerobic system to work longer at a higher level, using a mixture of carbohydrate and fat for fuel. Training hard enough, while still relying on the aerobic system for endurance allows for increased mitochondrial mass, increased enzyme activity, and increased capillary density around the muscle fibers, which also all lead to more efficient fat burning…another plus to being an active individual!

It is true that relatively more fat than carbohydrate is burned at lower intensities. In fact, sitting on the couch at home and watching TV is one of the best “fat burning” exercises out there! That’s all that you’re burning…granted it may be very little…due to the fact that your muscles are requiring little to no fuel. It is also certainly true that higher intensity workouts (those above 85% of VO2 Max) require primarily muscle glycogen (carbohydrate) for fuel. The fat burning process cannot be relied on for high intensity efforts, as the oxidation process of fat is too slow to provide the quick bursts of energy needed for intervals and sprints. Like Goldilocks found with the bears’ beds and porridge, somewhere in the middle is the best place to be. Exercising at very low intensities means having to run, ride or swim for hours in order to do enough work to make a difference. Training too hard burns a lot of energy, but most of it is carbohydrate and the accumulation of lactic acid stops you from maintaining the intensity level very long. Between these two extremes lies the moderately-high intensities you can sustain by using the full capacity of the aerobic system, with a little contribution from the anaerobic system thrown in to supply an extra kick.

The bottom line is that as athletes we need to train in order to develop our aerobic engines, not merely to burn calories. That will just be an added benefit. So next time you decide to go for a long jog, an afternoon bike ride, or even head to the gym for a session on the cardio machines, try stepping up the pace some. You’ll benefit in many more ways than one.