Muscle fiber

Muscle fiber comes in two types: fast twitch and slow twitch

Fast twitch fiber performs short-duration, high-intensity efforts like sprints and weightlifting.

Slow twitch fiber carries out long-duration, lower-intensity efforts like cardio (jogging, walking)

Fast twitch muscle fiber is white, because it contains no oxygen-carrying blood. It performs the anaerobic (zero-oxygen) muscle contractions. Red fiber, on the other hand, carries out aerobic contractions. It’s red because it’s filled with blood, which carries the oxygen it needs.

Fast twitch fiber contains stored energy in the form of adenosine tri-phosphate (ATP). It has enough for a burst of effort lasting second or two. It then uses creatine to replenish its ATP supply. It has enough creatine allow another several seconds of effort, for a total of about 10 seconds.

After the creatine is gone, the body uses much less efficient energy pathways that are highly inefficient and highly polluting. It’s those pathways that are primarily responsible for muscle soreness. Using them increases a muscle’s size, because it stores more water to dilute the waste products. But it does virtually nothing to increase the muscle’s strength. In fact, it’s counter-productive.

The only other way you can sustain an activity for more than 10 seconds in duration is to use red fibers–the aerobic fibers. But exercising those fibers doesn’t build muscle. In fact, the opposite is true. Sustained aerobic exercise stimulates a catabolic reaction that burns muscle for energy. So unless you’re doing weightlifting to stimulate muscle growth, you wind up with the thin physique of a long distance runner (skinny fat), rather than the muscular body of a sprinter (lean)

That 10 second limit for maximum muscle exertion is the reason that the longest sprint is 100 meters, a distance which takes elite runners about 10 seconds to run. When you lift weights, you’re growing muscle for the first 10 seconds or so, until the creatine runs out. In that time, you can perform 5 or 6 repetitions of most weight lifting exercises. If you’re using less weight than you could be using in those 10 seconds, you’re making fewer gains than could, as well. Additional lifts after those 10 seconds serve to increase muscle soreness in ways that impede the recovery process, without materially increasing your strength.

Once the muscle’s energy supply is exhausted, it uses fat to recharge. That’s one reason that weight training is so good for burning fat–especially if you do multiple sets

A good personal trainer will know the different way to stimulate efficiently your muscle fiber in order to increase strengh, muscle growth or weight loss (fat loss).

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