Sacred Cow: To burn fat, you need to ride at an easy intensity for a long time.
My Take: To burn fat, you have to burn lots of calories on the bike, and riding hard burns more calories than riding easy.
As exercise intensity changes, so does the fuel that you use. Sitting here typing this on my keyboard, I am burning mostly fat, but if I go out and do a 20 K TT, I am burning pretty much all carbohydrate. Why is this? Fat is a great fuel, it supplies practically endless amounts of energy. Even the leanest cyclist has enough body fat to fuel several hundred miles of riding. The problem is that as exercise intensity goes up, fat simply can’t release its energy quickly enough to fuel those muscles and pound those pedals. This means that as eintensity goes up, the percentage of fuel that is carbohydrate goes up and the percentage that is fat goes down. When you are at 20% of your aerobic capacity ( ~ 25% of your threshold power) you are using about 60% fat and 40% carbs,, with a little bit of protein. By the time you are at 50% of your maximal aerobic capacity (~ 60% of your threshold power) those number are flipped and you are using more carbohydrates than fat . So that by the time you are going along at any decent clip ,you are using mostly carbs. So at easy intensities, you are burning more fat as a percentage of the total. This is where the “fat burning zone” myth came from.
Now, let me ask you a question. Would you rather have 60% of $500 or 40% of $1000? You don’t have to think too hard about that one do you? Think of your fat burning the same way. If you burn a total of 500 calories and 300 of those are from fat, you aren’t nearly as far along towards looking like Chri Froome compared to if you burned 1000 calories and 400 of those were fat. Not only did the more intense 1000 calorie ride burn 100 more fat calories during the ride, it burned 500 more calories TOTAL. This means that when you eat a meal later on, the calories that you consume will go to replenishing all of the carbohydrates you used, rather than being stored as fat! I want to re state that last point as it confuses many. During the harder rider ride, you burn more TOTAL calories. This means that the food you eat later is less likely to be turned into fat.
The whole equation is pretty simple really. Negative energy intake equals fat loss. You burn more calories when you ride harder. This along with my bonus sacred cow from a few weeks ago should convince you that you don’t have to spend the whole winter riding easy. Have fun, get out there and hammer a little!
Sean Burke is the Head Coach for Crank Cycling in San Diego CA.