The expressions "muscle mass" and "muscle strength" are often used concurrently, but each has a separate sports science meaning. Muscle mass is the physical size of the muscle; muscles are often large due to exercise and concentrated physical training, but not exclusively. Muscle strength is one of the accepted components of total fitness, which includes endurance, flexibility, power, and speed. For almost every conceivable athletic purpose, muscle strength is a more valuable commodity than mass. However, in many contact sports, particularly those with specific roles for players in specific positions, muscle mass is important to the ability of the athlete to obtain and establish position against an opponent; the strength and sport-specific techniques employed by the athlete once that positioned is established will be the more important attributes.
The concepts of muscle mass and muscle strength are also separated from muscular power, a concept that implies explosiveness, and muscular endurance, which is the ability of the muscle to work at a steady performance rate over time.
This athletic distinction between muscle mass and strength is apparent in players such as an interior lineman in American football; a rugby forward, particularly those who play in the front row of the scrum; and a center in National Basketball Association (NBA) competition. In elite-level international rugby, the pack of eight forwards will weigh an average of 250 lb (113.3 kg); the laws of physics are immutable, for if the respective techniques of each group are equal, the pack of 250-lb players, working together, will dominate a team with 220-lb (99.8-kg) players, even when the lighter athletes have greater individual muscle strength.
In American football, where the average lineman weighs over 300 lb (136 kg), most tactics involved in line play are founded on the principle that once the player has position, he will be difficult to root out. Basketball, while nominally a non-contact sport, places a significant premium on the large center who can establish an anchored offensive position adjacent to the basket, through which his or her team will operate their sets.
In individual sports, such as wrestling or boxing, muscle mass is also an important aspect of how the competitor develops the tactics to combat the opponent. The amount of mass behind a blow delivered will be a significant factor in the ultimate force applied to the opponent.
Muscles cannot become either larger or stronger through any device other than the proper application of diet and training principles. Anabolic steroids—much publicized as a means for athletes to become bigger and stronger—are only a training aid, not a magic elixir. Steroids assist in muscular development only when the athlete is carrying out the physical training necessary to develop the muscles.
The essential components to a program that will enhance the muscle mass of an athlete will include:
Muscle mass and strength are not mutually exclusive training goals, notwithstanding the different methods by which one may seek size and strength. Muscle strength may be attained through the simplest of means—gradual increase in workload imposed on the muscles that are desired as strength increase targets. Muscles tend to get larger as they become stronger; when a strength program is accompanied by endurance training or other significant energy production and corresponding caloric output, the athlete will often possess highly defined muscles, with reduced mass but increased muscular strength.