Thanksgiving is almost upon us and I’m ready to carve the turkey. White meat or dark meat? I go for the white but I always remember my grandfather; he said the neck was the best part. I have yet to eat a neck, but one does wonder why turkeys have two kinds of meat. Observe a turkey and you will see a bird that walks around all day looking for food. The legs and thighs need muscles that do not fatigue. But in that rare instance when turkeys fly, they need quick powerful breast muscles. They need different muscles for different tasks.

Like most people in my profession, I started off studying anatomy. I believed that muscle was muscle, that muscles were the same for everyone. Eventually, exercise scientists were able to observe that not all human muscle fibers within a muscle were the same. Careful observation of muscle under a microscope revealed that muscle fibers were not the same color. Some were dark and some were light. Further research showed that some fibers were larger and stronger while other fibers tended to be smaller but with better blood supply. The smaller fibers (red) were labeled slow twitch (ST) and the larger fibers were labeled as fast twitch (FT). Want to eat slow twitch, chose the dark meat.

Like turkeys, we need both of these fibers. Slow twitch fibers are primarily used for aerobic activities, while fast twitch fibers are mostly anaerobic and used when exercise is intense. One might argue that they don’t really need FT, especially if their exercise program is primarily walking, a ST activity. But what if you trip or accidentally step off a curb, you need to catch yourself to prevent falling. Only your fast twitch fibers are quick and strong enough to avoid a fall. What if you want to lift your suitcase, carry your groceries? Even further, what if you want to play a sport, jump for a rebound? Everyone needs some fast twitch.

The percentage of FT and ST is established at birth and is about 50:50 in most humans. Some individuals have a prevalence of fast or slow. Top level sprinters have a majority of FT fibers, as much as 80%. Sprinters are capable of great speed but tend to fatigue rather quickly. Conversely, superior endurance athletes tend to have more ST than FT. While they are likely to have great endurance, they don’t have great speed.

FT fibers tend to atrophy as we age, one reason why muscles get smaller. This is probably the result of aging but also the result of disuse. As we age, we tend not to use our fast twitch as much. Aerobic activities like walking, jogging, cycling, and swimming are great for our cardiovascular systems but do not use FT muscles. How much FT you need depends somewhat on your own interests and aspirations. If you want to play sports, you will need FT. Are you slowing down, weaker, taking smaller steps? You need your FT to maintain power and strength. Fast twitch muscles are your anti-aging muscles.

Some atrophy in FT muscles is inevitable but we can train our fast twitch muscles to help preserve their size and strength. Maintaining FT is easier than regaining FT. Eating protein powders or turkey breast will not help; you need to train. How about yoga or Pilates? No. Strength training is probably the most common method of FT training, and strength training works if sufficient intensity is applied. If you’re lifting a weight you can lift 20 or 30 times, you’re not fully engaging your fast twitch. If you’re talking on your cell phone and drinking water while lifting, you’re not using your fast twitch. Greater intensity recruits more FT.

But you don’t need a weight room. Racket sports, basketball and volleyball help. I am a big proponent of simple activities like jumping, skipping and hopping. These are strenuous activities and require a good warm up and gradual progression. Hang a target, jump and reach as high as you can. Run and jump. Hop on two legs and then one. Sprint up a flight of 10-12 stairs, taking two or three at a time. Sprint up a small hill for five seconds. Throw a medicine ball, quickly lift a kettlebell overhead, jump onto a stable bench and off again. Fast twitch training is not endurance training; several intense seconds interspersed with rest intervals is the key. Do this to keep your power as you age.

Jim Johnson is a retired professor of exercise and sport science after teaching 52 years at Smith College and Washington University in St. Louis. He comments about sport, exercise, and sports medicine. He can be reached at jjohnson@smith.edu.