Dear Pepe,

You bring up an interesting concept; however, what happens in the body may be a bit more complicated.

For those of us who don't have a degree in biochemistry, this question refers to the process of glucose metabolism — or more simply put, how the body uses energy in exercise. During anaerobic exercise (exercise that does not require oxygen to produce the necessary energy, ATP, to carry out the activity, such as weight lifting), lactic acid (lactate) is formed when pyruvate (an intermediate substance in glucose metabolism) combines with hydrogen, in the presence of an enzyme, lactate dehydrogenase. Once lactic acid is formed, it quickly diffuses from the muscle into the blood, where it is buffered and carried away. If this didn't occur, you'd tire out very, very quickly. Eventually, though, as you continue to work out, the clearance of lactic acid can't keep up with its formation, and eventually builds up in the muscle and blood, causing fatigue. The acid build-up inactivates certain enzymes that are involved in energy transfer. It also decreases the muscles' ability to contract. These processes lead to fatigue.

The lactic acid that has remained in the muscle can be reversed back into an energy source (pyruvate) during recovery or when the pace of exercise is slowed. How quickly this recovery can occur will vary from individual to individual. This process doesn't create more energy than you began with. Some of the lactate has dissipated from the muscle. Although some of the dissipated lactate may be converted into glucose during the Cori Cycle (another metabolic process, occurring in the liver), it is unlikely to occur at the speed that you suggest.

Hope this helps you to understand how complicated our bodies really are!

Alice

Related Q&As

Muscle soreness and weightlifting

Losing fat and building muscle mass: Can this be done simultaneously?

Training for a marathon

Fat to muscle?

Is there a proper workout order routine?