Get Moving! Why Inactivity Causes Muscle Loss
Dr. Gabe Mirkin provides a scientific perspective on the effects of inactivity.
An athlete’s worst nightmare is being told that they need to refrain from exercising or training for an extended period of time. Their first thoughts tend to focus on how far the resting period will set them back, how much strength they’ll lose, and how long it will take to get back to their current shape. How true is the saying, “use it or lose it”? Read on to see what the research has found.
Use it or Lose it?
The first question an injured athlete often asks is,“How long until I’m back?”. Unfortunately, even short periods of inactivity cause dramatic loss of muscle size and strength. In fact, one study found that after just two weeks of having one leg put in a cast, all 32 men in the study lost a tremendous amount in all measures of physical fitness, strength, and muscle size in the immobilized leg (Journal of Rehabilitation Medicine, 2015). Another study showed that a person loses significant strength after stopping exercise for just four days (Experimental Gerontology, 2013). While taking time off to allow your body to fully recover is advised, you should be prepared to feel a little weaker when you return to training. By being mentally ready for this change, you can avoid feeling frustrated and negative about the change.
The Impact of age
It’s well-known that a lot of physical changes take place as we age. The younger we are, the easier it is to get into shape and stick to a training program. But what about losing our conditioning? Does age make a difference here too? A study compared 17 young men (average age 23) and 15 older men (average age 68) to investigate the impact of age. Surprisingly, the younger men lost 30 percent of muscle strength and the older men lost 25 percent. Another factor in this comparison is that people who started with larger muscles are the ones who lost the most strength when an injury, illness, or vacation stopped them from exercising. That explains why younger people lost strength at a faster rate than older people – generally, they carry more muscle mass. The young men in the study had about two pounds more muscle weight in each leg than the older men did, but after two weeks of inactivity, the young men lost 17 ounces of muscle, compared to a nine ounce loss in the older men.
Muscles are made up of thousands of individual fibers, like a rope is made of many strands. Regular exercise enlarges the size of thesefibers. On the other end of the spectrum, inactivity causes muscle fibers to become smaller. Therefore, those with the largest fibers lose the most muscle size and strength when they stop exercising.
Now that you’ve been cleared to get back to training, you’re anxious to get back to where you left off. You want to realistic with yourself in terms of how long it could take to get back to your previous condition. Looking at the study where participants had one of their legs in a cast, after two weeks of immobilization, the participants trained on a bicycle 3-4 times a week for six weeks. They regained some, but not all, of the muscle size and strength they had lost. If your goal is to regain strength and muscle size, aerobic training (such as running and cycling) should not be the only forms of rehabilitation training used. Strength training should be used along with aerobic activity to regain lost muscle strength and size – you need to lift weights or do some other form of strength training for recovery and to rebuild your muscles. Other studies show that it usually takes at least three times as long as the period of inactivity to recover full strength (Journal of the American Medical Association, 2007).
Why Aerobic Exercise is not Enough
To make a muscle larger and stronger, you must exercise intensely enough to damage muscle fibers. When you use your muscles, you contract the muscle and shorten its fibers. Muscle fibers are made up of blocks touching end to end to form the long stringy muscle fiber.Where a block touches the next block is a point called the Z-line. You have to damage the Z-line to make a muscle grow larger and stronger. If you’re relying on aerobic exercise, specifically cycling, you need to pedal with great pressure, in order to damage the muscle fibers at the Z-lines enough to make them stronger. However, most people don’t pedal hard or long enough to cause enough damage to make the muscle larger and stronger when it heals. Adding weight training to the recovery program will help to regain the lost strength and muscle size.
What Does This all Mean for you?
If you have to stop exercising for even just a few days because of an injury, vacation, or illness, expect to lose strength and endurance. When you resume exercising, be sure to include some form of strength training in order to regain your lost strength. Caution: Pain at the site of an injury means that you are tearing the previously injured muscle fibers and should stop exercising immediately. If you are advised to stop exercising due to a medical condition or injury, take the necessary time off and follow-up with your health care provider before jumping back into your activity patterns. The possibility of re-injuring yourself is high, which will only set you further back and cause more strength and muscle loss.
Dr. Gabe Mirkin, M.D
Article adapted from Dr. Gabe Mirkin’s “Inactivity Causes Muscle Loss” published at www.drmirkin.com, July 26 2015.
Dr. Gabe Mirkin is a physician with over 40 years of experience, a radio talk show host, author, professor, and former marathon runner. Having graduated from Harvard University and the Baylor University College of Medicine, he is one of a very few doctors board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology.