By Dr. Mercola
Peak muscle mass occurs, on average, sometime during your early 40s. After this, your muscle mass will begin to gradually decline, eventually leading to changes in your mobility, strength and ability to live independently.
Losing muscle mass even has implications beyond physical function, as loss of muscle mass can also lead to an overall decline in metabolic function. Many are not aware that maintaining muscle mass plays a role in metabolic and hormone function, playing a role in your risk of obesity, diabetes and heart disease.
If you ignore age-related muscle loss, it can easily progress into a health crisis characterized not only by reduced strength but also by accelerated aging and increased risk of chronic diseases.
Without intervention, you can lose an average of nearly 7 pounds (3.175 kilos) of muscle per decade.1 Other research has found that, after age 50, strength losses of 1.5 percent to 5 percent a year occur.2 What research is revealing, however, is that such losses are not inevitable.
"Without question, exercise is the most powerful intervention to address muscle loss, whether it occurs in the context of advancing age or debilitating chronic or acute diseases," said Nathan K. LeBrasseur, Ph.D., a researcher in molecular aspects of endurance and exercise at Mayo Clinic in Rochester, Minnesota.3
High-Intensity Interval Training Works Best for Aging Muscles
In a study by Mayo Clinic researchers, three types of exercise were pitted against each other, and a non-exercising control group, to determine if different types of exercise work better than others to protect aging muscles.4 A clear winner was revealed.
The study involved 72 sedentary people aged either 30 or younger or 64 and over. They engaged in 12 weeks of high-intensity interval training (HIIT) on stationary bikes, vigorous resistance training or a combination of exercises (moderate pace stationary bike combined with light weight lifting).
All of the exercisers experienced improvements in lean body mass and insulin sensitivity, and those who engaged in resistance training had boosts in muscle mass and strength. Among the HIIT group, improvements in endurance were particularly noted. However, additional notable differences were revealed when the participants' muscle cells were biopsied, revealing changes in genes.
Among the younger exercisers, the HIIT group had changes in 274 genes, compared to 170 genes for the moderate combination exercisers and 74 among the resistance group. The changes among the older exercisers were even more striking. As The New York Times reported:5
"Among the older cohort, almost 400 genes were working differently now, compared with 33 for the weight lifters and only 19 for the moderate exercisers.
Many of these affected genes, especially in the cells of the interval trainers, are believed to influence the ability of mitochondria to produce energy for muscle cells; the subjects who did the interval workouts showed increases in the number and health of their mitochondria — an impact that was particularly pronounced among the older cyclists."
HIIT Improved Age-Related Decline in Muscle Mitochondria
I now believe one of the best high-intensity exercises is the Nitric Oxide dump that I demonstrate in the video above. I typically do a modified version of one developed by Dr. Zach Bush. I use 8 pound weights in the video but it is best to use no weights initially. It takes about three to four minutes and is typically done three times a day every day, but must be at least two hours between sessions.
Your skeletal muscle derives its energy from your mitochondria — the energy storehouse of your cells, responsible for the utilization of energy for all metabolic functions. Mitochondria make up, on average, about 1 percent to 2 percent of your skeletal muscle by volume, but this is generally enough to provide the needed energy for your daily movements.
Your mitochondria have a series of electron transport chains in which they pass electrons from the reduced form of the food you eat to combine it with oxygen from the air you breathe and ultimately to form water. This process drives protons across the mitochondrial membrane, which recharges ATP (adenosine triphosphate) from ADP (adenosine diphosphate). ATP is the carrier of energy throughout your body.
However, as the researchers noted, mitochondrial decline with age is closely linked to reduced cardiorespiratory fitness, and decreased resting mitochondrial ATP production may be involved in the development of insulin resistance with aging.6
Exercise promotes mitochondrial health, as it forces your mitochondria to work harder. One of the side effects of mitochondria working harder is that they're making reactive oxygen species, or free radicals, which act as signaling molecules. One of the functions they signal is to make more mitochondria.
So, when you exercise, your body will respond by creating more mitochondria to keep up with the heightened energy requirement. Aging is inevitable. But your biological age can be quite different from your chronological age, and your mitochondria have a lot to do with your biological aging.
"Supervised HIIT appears to be an effective recommendation to improve cardio-metabolic health parameters in aging adults," the researchers concluded.7 As The New York Times noted:8
"It seems as if the decline in the cellular health of muscles associated with aging was 'corrected' with exercise, especially if it was intense, says Dr. Sreekumaran Nair, a professor of medicine and an endocrinologist at the Mayo Clinic and the study's senior author."
Exercise Triggers Mitochondrial Biogenesis With Whole-Body Benefits
Past research revealed that, aside from impacting your skeletal muscle and fat tissue, exercise induces mitochondrial changes that may also benefit your liver, brain and kidneys.
"Perturbations in mitochondrial content and (or) function have been linked to a wide variety of diseases, in multiple tissues, and exercise may serve as a potent approach by which to prevent and (or) treat these pathologies," researchers wrote in Applied Physiology, Nutrition and Metabolism.9
Another study touted exercise as a "possible cure" for the declines in mitochondrial biogenesis and mitochondrial protein quality commonly seen with aging. Not only did exercise training reverse or lessen age-associated declines in mitochondrial mass, but it also "decreased the gap between young and old animals in other measured parameters."10
"We conclude that exercise training can help minimize detrimental skeletal muscle aging deficits by improving mitochondrial protein quality control and biogenesis," the researchers wrote.11
At least two additional studies, one in the Journal of Applied Physiology12 and the other in Neuroscience,13 also showed that exercise induces mitochondrial biogenesis in the brain, with potential benefits such as reduction or reversal of age-associated declines in cognitive function and helping to repair brain damage following a stroke, respectively.
Mitochondrial damage can also trigger genetic mutations that can contribute to cancer, so optimizing the health of your mitochondria is a key component of cancer prevention. In fact, mitochondrial dysfunction is at the core of virtually all diseases. Exercise stimulates AMPK and SIRT1, which secondarily inhibit mTOR that is involved in aging and cancer. This in turn stimulates mitochondrial biogenesis and mitophagy, both of which are deadly to cancer.
In essence, cancer can be viewed as a metabolic disorder, and the key to prevention and recovery lies in restoring mitochondrial function and increasing mitochondrial numbers. Exercise helps you do both.
What Else is HIIT Good For?
HIIT and the similar high-intensity circuit training (HICT) can yield greater fitness benefits in less time compared to longer, low- or moderate-intensity workouts. In addition to promoting mitochondrial health, benefits include:14
Fat Loss and Weight Loss
HICT involves using multiple large muscles with very little rest between sets, yielding aerobic and metabolic benefits, the latter of which may continue for up to 72 hours after the workout has been completed. HICT may lead to greater fat loss than typical aerobics or resistance training because it increases levels of catecholamines (which increase resting energy expenditure) and human growth hormone (HGH) in your blood.
Improved VO2 Max
VO2 max is the maximum amount of oxygen you can take in while exercising. Your VO2 max can be used as a measure of cardiovascular endurance.
"When HICT protocols have been compared with traditional steady state protocols in the laboratory, HICT elicits similar and sometimes greater gains in VO2 max despite significantly lower exercise volume," according to Brett Klika, a performance coach for the Human Performance Institute in Orlando, Florida, and Chris Jordan, director of exercise physiology at the Human Performance Institute.15
Decreased Insulin Resistance
Research supports the use of HICT (and HIIT) for reducing insulin resistance, which is a contributing factor in the development of type 2 diabetes. Unfit but otherwise healthy middle-aged adults were able to improve their insulin sensitivity and blood sugar regulation after just two weeks of such training (three sessions per week).16
A follow-up study also found that HIIT positively impacted insulin sensitivity. The study involved people with type 2 diabetes, and just one session was able to improve blood sugar regulation for the next 24 hours.17 Kilka and Jordan added:
"Positive changes have been observed in insulin resistance in as little as [eight] minutes per week when executed at an intensity more than 100 [percent] VO2 max."18
Is HIIT Safe for Seniors?
HIIT may seem too intense for the elderly, but rest assured you can perform HIIT at any age and still reap major benefits. The only difference is that the older you are the lower your maximum heart rate will be, and the more gradually you will want to increase your repetitions.
That's one of the great things about HIIT — you can tweak it to your needs. You can still get benefits from working out at a slightly lower intensity; you simply increase the time you work out to make up for it. You'll still be working out very intensely, remember, so your total workout will still be short, relatively speaking. I typically recommend an HIIT session of 20 minutes, as follows:
- Warm up for three minutes
- Exercise as hard and fast as you can for 30 seconds. You should feel like you couldn't possibly go on another few seconds
- Recover for 90 seconds
- Repeat the high-intensity exercise and recovery seven more times (eventually, but start with just two or three repetitions)