About Fat Metabolism
During aerobic exercise, stored fat is broken down into fatty acid chains and glycerol, its basic components. They are released into the bloodstream and muscle cells, where the fatty acids are transported into the cells' mitochondria and broken down by complex series of chemical actions to produce energy, carbon dioxide and water. Glycerol is sent to your liver for storage and to make other compounds. Fat metabolism continues as long as oxygen and glucose are present in your cells.
The Time Factor
Your body needs to be at a steady state of aerobic exercise for at least 10 minutes to increase the amount fat used for energy, according to exercise physiologist William McArdle. In the first three to five minutes of aerobic exercise, such as jogging and cycling, your body uses glucose as the main fuel source. After five to 10 minutes of exercise -- depending on your fitness level -- your body begins to increase the amount of fat used for energy.
Abdominal Exercises
Because you cannot do crunches or other ab exercises for a long period of time, as you can jogging or cycling, your body uses glucose for energy and never uses fat as the main source of fuel. Even if you can sustain abdominal contraction for five minutes, you can hurt your spine and develop abdominal pain from excessive flexion. Dietitian Ellen Coleman says the fat-burning process occurs throughout your body, never in any specific part. The only way for you to reduce overall body fat composition is by expending more calories than you consume.
Things to Consider
Rodney Corn, co-founder of PTA Global, recommends full-body exercises to burn the most calories and increase muscle mass, which is the site of fat metabolism. Although you can incorporate crunches into your workout, add other full-body exercises, such as push-ups on a stability ball, squats and shoulder press combo, sprinting, rope jumping and medicine ball throws.
Expert Insight
Coach Robert dos Remedios, author of "Cardio Strength Training," recommends interval training -- high-intensity exercise followed by a short period of rest, repeated several times -- to use more fat calories in less time. Not only will you burn more fat than steady-state exercises, you will not be as bored while working out. You can use any exercises for interval training, such as sprinting, push-ups, pull-ups, squats, kettlebell swings and Olympic lifts.
