Muscular Adaptations

When muscles are challenged by the lifting of weights, many physiological changes occur. A muscle can grow bigger, become more efficient, change its composition, and increase its strength and speed. The change depends on what kind of a weight-training program you embark on. Different training methods, even if they all involve weights, have their own unique effects on muscle. You'll read about this in more detail in chapter 5.

One of the primary adaptations that the body makes to weight training is muscular hypertrophy, an enlargement of the muscle fiber. When the muscle is stressed, the protective outside covering of the individual muscle fibers gets stretched. This stretching creates spaces where various materials, such as nutrients, can flow in and out. Weight training increases protein synthesis (the making of protein), and protein is food for muscle. The increase in protein synthesis creates larger muscle fibers. Other studies have shown that hyperplasia, the splitting of muscle fibers to make more muscle fibers, can take place as well. For our purposes, I refer to muscular enlargement as hypertrophy.

Unfortunately, hypertrophy doesn't take place immediately. In fact, as we've seen in chapter 1, the swelling that you get in the beginning of a weight-training program is not a muscle fiber adaptation, but increased water. Actual muscular hypertrophy takes more than 10 weeks to occur. The length of time required is all the more reason for having a written training schedule and sticking with it (which I discuss in chapter 7).

Muscle fibers adapt in other ways to weight training. Muscle is generally divided into Type I (slow-twitch) and Type II (fast-twitch) fibers. Type I fibers are fatigue resistant; they are used for cardiovascular and muscular endurance work. Type II fibers fatigue quickly, but are big, strong, and quick. They are used for strength and power work. Consequently, Type II fibers hypertrophy more than Type I fibers. Although fiber types will always be mixed throughout the body, aerobically trained muscles have a predominance of Type I fibers, whereas weight-trained muscles have a predominance of Type II fibers. One theory says that we are born with a set ratio of Type I to Type II fibers and that although you can change a certain portion of them through exercise, for the most part you are stuck with what you have. This conjecture may be another explanation for why some women get large hypertrophy gains and others get less.

Another muscular adaptation to strength training is increased strength. Strength is the maximal amount of force a muscle or muscle group can generate at a specified velocity. Typically strength movements are slow compared to other movements because it takes time to generate maximal force. A neophyte embarking on a weight-training program typically sees huge strength gains in the first few weeks, because of an increased cooperation of the nervous and muscular systems. Such gains also occur when an advanced trainer changes up her exercise program. As we train with weights and progress in our programs by adding more weight, we will get stronger. Certain training methods can assist with our maximum strength gains.

Muscle can also become more powerful through weight training. Power is the ability to exert force at a high speed of movement. It requires a lighter resistance and higher velocities than does pure strength training. Someone who is powerful is both strong and quick. Strength and power are closely intertwined, especially in sports. In fact, few sports exist without power except, ironically enough, powerlifting.

Delayed onset muscle soreness