Lactic acid and lactate are both products of cellular metabolism, and they both affect the way your body responds to exercise and how well you perform over time. Understanding how your cells power exercise can help you structure your training so you are getting the maximum benefit without putting yourself at risk for injury.
Fuel
During normal daily activities, your muscles are always carrying around a small supply of fuel, enough to get you from the car to to your office or up a flight of stairs. When you exercise at a high level of intensity for several minutes -- for example, chasing a runaway dog for 10 city blocks -- your body has to make fuel through a process called "anaerobic glycolysis," which means breaking down sugars into energy without oxygen. This process produces energy for your muscles, but it also creates lactic acid, which enters the blood stream, changes the pH balance of your blood, slows down enzyme activity and makes you feel tired.
Lactate
The terms "lactate" and "lactic acid" are often used interchangeably, but there is a difference: lactic acid is an acid, which means it can release a hydrogen ion and bind with a positively charged sodium or potassium ion to form an acid salt. For your own practical purposes in exercise training, the important thing to remember is lactate production is part of the way your muscles get fuel to keep working, and exercising at too high an intensity for too long will lead to the buildup of lactic acid, which will make your working muscles burn.
Threshold
When you are exercising, there is a degree of intensity at which your body stops being able to efficiently handle the lactate it is producing and lactic acid builds up, followed by the burn, fatigue and an inability to continue. This is called the lactate threshold. Trainers use blood tests to find the threshold for elite athletes because training just below your threshold is one of the most effective ways of reaching your peak performance. Training above the threshold is likely to lead to injury, and you can't sustain that level of effort very long.
Recommendations
You can gauge your own lactate threshold using a tool called the "talk test." Whatever your activity, you should only be able to speak a few words at a time here and there during exercise, not carry on a long conversation or sing. If you can't breathe at all, then you are working too hard, and lactic acid buildup will cut short your workout session. If you have an excess of air available, you aren't challenging your cellular metabolism as much as you could be.
References
- "ACE Personal Trainer Manual, 4th Edition": American Council on Exercise: 2010
- University of New Mexico; Lactate: Not Guilty as Charged; Len Kravitz, Ph.D.
- Marathon Physical Therapy and Sports Medicine: Performance Enhancement
- Mayo Clinic: Mayo Clinic on the Summer Olympic Games
- American Council on Exercise; Kettlebells: Twice the Results in Half the Time?; Chad Schnettler
