Two important studies published this week show how interval training makes you stronger, improves endurance, and also can help to reduce the loss of muscle size and strength that inevitably occurs with aging. It may also reduce your risk for heart attacks and cancers.
The first study shows the mechanism through which high-intensity interval training strengthens muscles and helps slow down the expected loss of muscles with aging (PNAS, November 6, 2015). It shows that high-intensity interval exercise increases maximal oxygen use by changing how muscle cells manage calcium. It also explains why taking antioxidant pills can reduce the benefits of high-intensity exercise.
Male recreational exercisers cycled as hard as they could for 30 seconds, rested for four minutes, and repeated this sequence six times. Muscle samples from their thighs showed that this regimen broke down calcium channels in muscle cells.
How Interval Exercise Helps to Keep Calcium Channels Open
An electrical impulse travels down a nerve toward the muscle, opening sodium channels, small passageways in muscle cell membranes. The sodium channels allow large amounts of positively-charged sodium to pass into the cell. The cells try to neutralize this sudden positive electrical charge by releasing calcium from inside the cells to pass through calcium channels to go outside of the cell membranes. This generates the electrical impulse that makes the muscle contract.
The new discovery is that interval training breaks down calcium channels in muscle cells by producing large amounts of free radicals. This causes lasting changes in how the cells handle calcium, and helps muscles grow new and larger mitochondria. Mitochondria turn food into energy for your body, so growing new mitochondria markedly increases endurance and speed over distance to make you a better athlete. This study explains why so many other studies show that, compared to casual exercise, intense exercise enlarges existing mitochondria and forms new mitochondria which:
- gives you greater endurance and speed over distance and
- helps to reduce the loss of strength and muscle size that inevitably accompanies aging.
Why Antioxidant Pills Interfere with Training
The authors also showed that the same three minutes of high-intensity endurance exercise did not damage the calcium channels of elite endurance athletes, whose prodigious training had built up incredibly effective antioxidant systems for trapping and neutralizing free radicals.
These same researchers gave antioxidants to mice before and after they went through intense interval training. The antioxidant pills prevented the calcium channel changes that stimulate muscle cells to grow new mitochondria. This explains why several other studies have shown that taking antioxidants before exercising prevents the muscle-strengthening benefits of the exercise.
Preventing Loss of Muscle Size and Strength with Aging
The second study compared continuous exercise with high-intensity intermittent exercise in rats (Experimental Gerontology, published online November 3, 2015). The high-intensity interval exercise reduced inflammation in blood and skeletal muscles and helped to strengthen young rats and preserve strength in aging rats. In all mammals, muscles are made up of thousands of individual fibers just as a rope is made of many strands. With aging, we lose muscle fibers from markedly increasing signs of inflammation, oxidative stress and atrophy, which result in loss of muscle size and strength.
In this study, young and old rats were randomly assigned to two different six-week training regimens:
- continuous exercise 30 minutes/day, five days/week, or
- intermittent intense exercise (three times 10 minutes/day), five days/week.
The intermittent interval exercise was more effective in both young and old rats in reducing age-associated inflammation molecules that are signs of chronic diseases caused by aging (interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and malondialdehyde. These same tests are used in humans to measure inflammation. The high-intensity interval training:
- reduced blood and muscle inflammatory molecules in the old rats
- activated skeletal muscle growth factors in the old rats to increase the size and strength of their muscles
- reduced the inflammatory molecules that are responsible for loss of muscle size and strength with aging.
How Interval Training May Help to Prevent Heart Attacks
In the past 50 years, hundreds of studies have shown that exercise helps to prevent heart attacks by reducing inflammation. Inflammation causes plaques to form on the inner linings of arteries. Your immunity is supposed to protect you by dissolving the protective coatings of invading germs. When your immunity stays on all the time, it is called inflammation, and your own immunity dissolves parts of the inner linings of arteries to cause little holes that bleed and then clot. Only after the clot forms does a plaque start to form on the inner artery linings.
You do not have a heart attack just because your arteries are narrowed by plaques. An artery that is 98 percent blocked with plaques does not cause a heart attack. First a piece of the plaque breaks off from the inner lining of an artery leading to your heart. Then the area where the plaque broke off bleeds and then clots. The clots can extend until they completely block blood flow through that artery. The part of the heart muscle deprived of blood flow then suffers from lack of oxygen, hurts and starts to die. This is a heart attack.
Inflammation is triggered by chronic infections and the free radicals your body makes when it turns food into energy. Exercise helps your body to clear free radicals (Reactive Oxygen Species) that turn on your immunity to cause inflammation that causes plaques to form, and break off from arteries to cause heart attacks. Interval training is more effective than less-intense training in reducing inflammation.
How Interval Training May Help to Prevent Cancers
Normal cells live only a certain amount of doublings and then die. This is called apoptosis. For example, skin cells live 28 days and die. Red blood cells live 120 days and then die. Cancer cells try to live forever. So breast cancer does not kill you when the cancerous cells are in the breast, but the breast cancer cells can become so numerous that they spread to your brain, liver, bones, lungs, or other tissues and destroy them.
Apoptosis requires normal mitochondria that are inside cells and turn food into energy. Anything that increases the size and number of mitochondria may help to prevent and treat cancers. Compared to casual exercise, intense exercise is more effective in correcting the mitochondrial defect that causes normal cells to become cancerous and therefore, may be more effective in helping to prevent and treat cancers.
- A few minutes of high-intensity interval training is enough to produce exercise benefits at least equivalent to that achieved with traditional, much more time-consuming, endurance training.
- A few minutes of high-intensity interval training makes you a better athlete by increasing your maximal ability to take in and use oxygen (PLoS One, May 29, 2013;8(5):e65382; J Cardiopulm Rehabil Prev, Feb 13, 2014).
- A few minutes of high-intensity training breaks down calcium channels in the muscle cells and helps you grow mitochondria. Another benefit: Interval training takes far less time than conventional endurance training.
Caution: Intense exercise can cause heart attacks in people who have blocked arteries leading to their hearts. Check with your doctor before you start a new exercise program or make a sudden increase in the intensity of your current exercise program.
Gabe Mirkin, M.D., is a sports medicine doctor and fitness guru. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin has run more than 40 marathons and is now a serious tandem bike rider with his wife, Diana. His website is http://drmirkin.com/. Click to read Gabe’s full bio.