The Type of Exercise That Will Keep You Young
Have you ever seen someone’s leg after they’ve gotten their cast taken off? The now-healed leg is noticeably smaller and weaker than the unbroken leg. Thankfully, six weeks in a cast isn’t long enough to cause permanent weakness. However, sarcopenia, which is a similar process that involves a loss of muscle mass throughout the whole body, begins in the late 20’s among most adults. Sarcopenia involves a decline in muscular power, strength, metabolism, bone density, physical functioning, and an increase in body fat. The good news is that we can maintain our musculature, physical functioning, and ability to play, as sarcopenia can be prevented…
The Science of Skeletal Muscle
Skeletal muscles are made up of two types of muscle fibers: slow twitch (Type I) and fast twitch (Type II a & b). The following image is a cross section of a muscle belly that shows both slow twitch (dark reddish color) and fast twitch (light white/pinkish color) muscle fibers.
Slow twitch fibers are recruited first to contract when we move. Next, fast twitch IIa are recruited and finally, fast twitch IIb. Not surprisingly, we only recruit fast twitch fibers when we use our muscles in a way that requires speed or strength. Specifically, we use our fast twitch fibers when we sprint or lift heavy things.
If we go long stretches of time without doing fast and strong movements, our fast twitch fibers atrophy, much like muscles that are not used when healing in a cast. To be clear, when adults stop doing fast twitch activities like jumping, running, and playing, their fast twitch fibers atrophy and die. Then, those fibers are replaced with intramuscular fat and connective tissue.
When we stop using our fast twitch fibers, they die and turn into fat and connective tissue.
What to Do
One way to preserve fast twitch fibers is to maintain a regular program of resistance training. The current resistance training guidelines for beginners includes completing 8-10 exercises that target major muscle groups for 1-2 sets of 8-12 repetitions to fatigue, on at least two non-consecutive days of the week.
Starting a resistance training program with machine weights is a good option for beginners who aim to learn the safe and effective range of motion of new exercises. Ultimately, it is ideal to work towards using free weights, because they require the use of stabilizing muscles and better improve functional strength that transfers to activities of daily living.
Exercise for Health verses Exercise to Preserve Fast Twitch Fibers
Is walking or jogging good enough to maintain fast twitch fibers? No. Ultimately, walking and jogging are much better than sitting, from a health and disease prevention perspective. Low and moderate intensity physical activities will improve heart health and prevent a range of different chronic diseases, but such activities do not maintain fast twitch fibers. The only way to maintain fast twitch fibers is to recruit them, which is done during high intensity (e.g. sprinting) and resistance training exercise. Thus, whoever coined the saying, “use it or lose it!” was spot on.
The only way to maintain fast twitch fibers is to recruit them, which is done during high intensity and resistance training exercise.
Disclaimer
If you are a beginning exerciser, it is important to increase the intensity and volume of exercise gradually. If your muscles are feeling sore from new exercise, it is important to do lower intensity exercise for a couple of days until the soreness decreases. High intensity exercise done while feeling overly sore puts a person at risk for injury.
Furthermore, while high intensity and resistance training exercise is important for maintenance of fast twitch fibers, it is recommended to do your high intensity exercise on nonconsecutive days of the week. In between high intensity days, low to moderate intensity exercise is beneficial.
Your Right to Know
As an exercise psychologist, it is heresy for me to recommend to the public that high intensity exercise, like running and weightlifting, is truly the ideal. Most of my colleagues highly discourage recommending to the public anything but walking and moderate intensity physical activity, because they believe people won’t do it. “If we set the bar too high, people will not exercise at all,” they say, “because high intensity exercise doesn’t feel good.”
Instead of patronizing people, I believe scientists should disseminate the science and let people decide for themselves whether or not to exercise at a low, moderate, or high intensity, or not to exercise at all. Furthermore, most research is funded with federal dollars. This is yet another reason why tax paying citizens should have access to the raw results of the research, without a sugar coating.
In sum, some exercise is better than nothing! If resistance training and high intensity exercise is not for you, a regular program of walking or jogging will provide life changing benefits for you. Thus, if your goals are to maintain heart health and prevent chronic disease, moderate physical activity will achieve those goals.
However, if in addition to improvement of health you aim to maintain your fast twitch fibers and the associated physical strength, power, lean muscle mass, resting metabolism, and optimal physical functioning– then high intensity exercise that involves a regular resistance training program is necessary. The research is clear that the way to maintain youthful living is to continue running, lifting, and playing.
Thanks for reading! 🙂
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References:
Haff, G., & Triplett, T. (2016) Essentials of Strength and Conditioning. Human Kinetics.
McLeod, M., Breen, L., Hamilton, D.L. et al. (2016). Live strong and prosper; the importance of skeletal muscle strength for healthy ageing. Biogerontology, 17: 497.
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