It’s no secret that muscle size and strength decline rapidly after the age of 50. What does this mean and what can we do about it?
First we must look at the different muscle types. Slow-twitch muscle fibers are small, and fast-twitch fibers are large. The slow-twitch fibers are the endurance fibers, which predominate in marathon runners and other endurance athletes. Like the Energizer Bunny, they don’t give out; however, they don’t generate much force. Fast-twitch fibers are the strength fibers, which predominate in sprinters, weight lifters, and other strength athletes. They are strong, but fatigue rapidly. Most of us are born with roughly equal balance of slow/small and fast/large fibers.
As we age, the motor units that we lose are mainly the fast-twitch variety (called sarcopenia). The slow-twitch fibers show practically no change as we age.
In short, the decay of muscle size with age is virtually all due to loss of fast-twitch fibers. This means the untrained person becomes slower and weaker with age and results in loss of independence over time.
Reduced physical activity is the main culprit of fast twitch muscle fiber degeneration. Resistance training is the best antidote. We can keep our fast-twitch fibers alive and well with resistance training. Resistance training has been shown to positively affect neurological, hormonal, and mechanical factors associated with muscle maintenance and growth. You could fill up a small warehouse with research touting the benefits of resistance exercise in reducing sarcopenia and its impact on independence, falls, and mobility. The bottom line is that resistance training can have a positive effect on all aspects of the neuromuscular and biochemical decline that accompanies aging.
As in the case of resistance training, variation is the key to long term success. Change keeps you motivated and gives your body and your mind an opportunity to adapt and grow stronger and fitter.
Reference: Human aging, muscle mass, and fiber type composition. Lexell, J. J Gerontol A Biol Sci Med Sci. 1995 Nov;50 Spec No:11-6.