Lactic Acid

If you're a fitness freak, then you should already know that muscle soreness is not caused by lactic acid, and neither is lactic acid buildup a bad thing. In fact, lactic acid is actually a fuel and muscles produce it directly from glucose, burning it to produce energy.

The understanding now is that muscle cells convert glucose or glycogen to lactic acid. The lactic acid is taken up and used as a fuel by mitochondria, the energy factories in muscle cells.

In fact, lactic acid actually disappears from our muscles in about an hour after exercise, so that is not what causes soreness. Coaches apparently have known this all along, despite so many running websites and magazines telling us to work out at our "lactic threshold" - that point where you feel your muscles being worked out to the fullest.

Yet, Dr. Brooks said, even though coaches often believed in the myth of the lactic acid threshold, they ended up training athletes in the best way possible to increase their mitochondria. "Coaches have understood things the scientists didn't," he said.

Through trial and error, coaches learned that athletic performance improved when athletes worked on endurance, running longer and longer distances, for example.

That, it turns out, increased the mass of their muscle mitochondria, letting them burn more lactic acid and allowing the muscles to work harder and longer.

So folks, this is yet another way in which distance running helps you - it makes you faster! Incidentally, if you're wondering what actually causes muscle soreness (now that we know it's not lactic acid) - it's, essentially, your muscles repairing themselves. Pushing yourself to your limit causes microdamage to muscle fibres and the soreness you feel hours after your workout is called DOMS (or delayed onset muscle soreness).

It takes at least eight hours to feel this type of soreness. You finish a workout and feel great; then you get up the next morning and your exercised muscles feel sore. We used to think that next-day muscle soreness is caused by a buildup of lactic acid in muscles, but now we know that lactic acid has nothing to do it. Next-day muscle soreness is caused by damage to the muscle fibers themselves. Muscle biopsies taken on the day after hard exercise show bleeding and disruption of the z-band filaments that hold muscle fibers together as they slide over each other during a contraction.

So the next time you feel that soreness, remember to take it easy until it goes away.

On one day, go out and exercise right up to the burn, back off when your muscles really start to burn, then pick up the pace again and exercise to the burn. Do this exercise-to-the-burn and recover until your muscles start to feel stiff, and then stop the workout. Depending on how sore your muscles feel, take the next day off or go at a very slow pace. Do not attempt to train for muscle burning again until the soreness has gone away completely. Most athletes take a very hard workout on one day, go easy for one to seven days afterward, and then take a hard workout again.

The stuff about lactic acid is from an NYT article, and can be read here. The stuff about muscle soreness is from DrMirkin.com and can be found here.