Want to save muscle strain? The answer is to cross-train


Injuries are the bane of many people who exercise. Cross-training is one of the best ways to prevent injuries from slowing you down.

Cross-training means participating in several different sports rather than just one. Every sport stresses specific muscle groups. Repeated activity in the same sport causes repeated stress on the same muscle group. But if you practice different sports during the week, you will change the stress as you change sports.

Running primarily stresses the lower leg, while biking stresses the upper leg. Mixing the two alternates the stress between lower and upper leg muscles.

How much of each exercise should you do? One way is to exercise for the same length of time each day. A better way is to compare theamount of energy required for each sport.

Walking at 3 mph uses only two-thirds as much energy as running 1 mile. Walking 5 mph will use 1-1/5 times as much energy for the same distance. And walking at a moderate pace uses the same energy as running the same distance.

Running a mile is comparable to cycling 3 miles, swimming 1/4 -mile, rowing 1/2 -mile and participating in aerobic dancing for 10 minutes.


Q: After I work out, my muscles feel stiff and sore the next day. Will I recover faster by exercising at a slow pace the day after, or should I skip exercising that day?

A: It is common for your muscles to feel weak, tired and sore the day after a vigorous workout. You will recover faster by taking the day off.

There are two reasons muscles feel sore eight to 24 hours after exercise. First, vigorous exercise damages the muscle fibers. Biopsies done the day after vigorous exercise show damage to the fibers and bleeding into the fibers. Exercising damaged muscle fibers will delay your recovery, just as exercising torn muscles will delay healing.

Second, vigorous exercise depletes the muscle sugar stored in each fiber. Low muscle sugar causes heaviness, weakness and tiredness. Those symptoms disappear after you eat and your body has time to process the food and replenish the supply of stored muscle sugar.

Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.

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