Why do I have pain in my muscles when I exercise?

Dr. Michael Roizen, MD
Internal Medicine
When you first start exercising, you may feel one kind of pain - a slow, burning ache in the muscles that is normal and not a cause for concern. This "normal" burning indicates you are reaching your anaerobic threshold, meaning you're at the limit of your endurance. The pain is believed to result from the buildup of lactic acid in your muscles, which occurs when your muscles are not getting enough oxygen (anaerobic means "in the absence of oxygen"). This burning is not an indication of an injury but that you're reaching your fitness limit. (Some world-class athletes and professional athletes believe that a massage - after stretching - removes the lactic acid from their muscles before their muscles have cooled down and lets them achieve peak performance again the next day.) The more you work out, the higher your anaerobic threshold (limit of endurance) will go, and soon you will be able to work out for longer periods and at a more vigorous rate.

Feeling sore after a workout does not mean that anything is necessarily wrong, especially if it occurs the next day. Unless you've actually sustained an injury, the pain will probably go away within a day or two, eventually producing lean muscle in place of flab. That's why you should space your workouts and rotate your activities, so that different muscle groups get worked on different days, getting a day off in between.

Pain is the muscles should not occur during exercise. Occasionally, when exercising at an intensity of which your body is not accustomed too, the muscles may begin to fatigue and cramp. When your body is working at higher intensities it may not be getting enough oxygen to meet the demands of the exercise. The lack of oxygen prevents the conversion of lactic acid to pyruvate within the cell.  When this happens, lactic build-up will cause muscle cramping.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.