The science behind exercise has come a long way since the aerobic and cardio craze that started in the 1970s, and many people that walk, jog, swim or bike continue to lose muscle mass, but don’t understand why. They might notice some visible signs of muscle loss and strength such as slower walking, reduced endurance and mobility, declining posture and poor balance, and check them off to aging. It’s called sarcopenia, the age-related (and lifestyle-related) loss of muscle mass and strength).

Sarcopenia is also associated with some chronic conditions like Type 2 diabetes, dementia, a few cancers, cardiovascular diseases and visceral fat. The latest research shows muscles are so vital to our health that many doctors are including muscle strength measurements in addition to blood pressure, breath, weight, pulse and temperature at annual checkups. Muscles are the foundation of our metabolic health, and we need to strengthen them. Muscle strength is also vital at every age.

Nothing is wrong with aerobics; movement is fundamental, and any way we do it benefits our health. However, these forms of exercise don't supply sufficient load to strengthen muscles, so it is vital to incorporate high-intensity resistance training because muscles, not aerobic fitness, will enhance our health and reverse conditions associated with sarcopenia.

Intensity is required to gain muscle strength because motor units and muscle fibers make up our muscles. They come in three categories: small, endurance ones, slow-twitch fibers; mid-size intermediate-twitch fibers; and the muscles used for explosive, high-peak movements, fast-twitch fibers. First, the small endurance fibers start working, and when they tire, the intermediate fibers kick in to help them recover. Then, if needed, the big, powerful ones are activated. The small endurance fibers are the most used, and are also the most resistant to fatigue and the quickest to recover; that’s why we can walk for hours.

We use the slow, endurance and intermediate fibers for most day-to-day activities. Because we don't usually go all-out and sprint 100 yards daily, we rarely use the fast-twitch fibers—they are the first to be weakened by sarcopenia and atrophy. Building them back requires intensity; they need to be overloaded to grow. We do that with high-intensity training using body weight and resistance bands, which is perfectly appropriate for people of all ages and in any condition. Using resistance bands takes muscles through their entire range of motion, plus movements are super-slow without explosive motion, so this is safe for everyone.