The Doctor Weighs In

I received a query from a reader in response to the latest posting on emphysema. Here is the question:

"So if operating in anaerobic conditions is bad does that mean too much exercise at anaerobic conditions could be more detrimental than good?  In other words, is walking better for you than speed training?"

Here is my reply:

No, in training there is room for both. The physiological limit to anaerobic training is the quick buildup of lactic acid in the muscle. Above a certain level your muscles will simply ‘refuse’ to work.  The level of lactic acid in the muscle is determined by the balance between its formation and its clearance by the circulation.

In every intense exercise there is an initial aerobic phase that becomes anaerobic when the demand for oxygen outstrips the supply.  In the untrained athlete, high intensity speed training quickly results anaerobic conditions and buildup of lactic acid in the muscles.  In the trained athlete, the aerobic phase lasts longer.

There are 2 ways an athlete can increase his/her speed training tolerance:

• Increase delivery of oxygen to the working muscles through increased lung capacity (this is almost impossible because, unlike muscle tissue, lungs cannot expand much more due to exercise)  or by training at high altitude(not very practical, unless you are a competitive athlete); the same effect can be obtained with blood doping (illegal).
• Increase circulation to the muscles

 Speed training creates anaerobic conditions in the muscles because the circulation cannot keep up with the demand. Also, it has been demonstrated in animals as well as humans, that intense and repeated anaerobic exercise causes micro-injuries to the exercising muscle. The healing of these micro-injuries has several salutary effects: it results in neo-angiogenesis (formation of new blood vessels) due to the anaerobic conditions -just like any other healing wound. It also results in synthesis of new muscle tissue, increasing the muscle mass (hypertrophy).

The increased blood supply delivers oxygen and clears lactic acid buildup more efficiently, thus allowing a longer aerobic phase fueled by glucose stored in the muscle. The physiologic result is increased performance in high intensity speed exercises, like sprints.

Dov Michaeli, MD, PhD