The magnitude of physical strength, often referred to as just strength, determines the ability of a person or animal to exert force on physical objects using muscles.

Strength can be divided into two categories. Short-term endurance and long-term endurance. In all muscle-based creatures, there are three muscle fiber types: Slow Twitch (Type I or ST), Fast Twitch A (also known as Type IIa or FT-A), and Fast Twitch B (Type IIb or FT-B).

Comparison chart

Notes

While most people have more or less equal amounts of the fibers, some people are genetically-gifted with a disproportionate composition of them, resulting in excellent performance in a relevant sport. For example, a person with high concentrations of fast twitch B fibers would make an excellent sprinter. Conversely, this means that the same person would perform terribly in a long-distance run.

Hypertrophy of the muscles usually results from any sort of sufficient physical activity, though to varying degrees of size, dependant upon the physical activity itself. Hyperplasia, the introduction of additional muscle fiber, has conflicting reports on whether is it possible in humans and whether the amount of fibers added would make any useful difference.

Miscellaneous

Many studies show that training one rigorously harms the other - eg. large muscles are good for maximal power during short time periods, but they consume lots of oxygen which muscles need a lot of during long periods of exercise.

Many athletes depend mostly on physical strength, even though coordination and dexterity also play an important role.

Identification

One can determine the type of muscle merely by looking at it. White meat is fast-twitch fiber, while red meat is slow-twitch fiber. The difference is due to the greater presence of myoglobin in slow twitch muscle, which gives it its red hue. Red meat from an animal would indicate that it came from body component that is expected to operate for extended periods of time, such as the legs. While white meat conversely comes from body parts that operate for extremely short periods, such as the muscles involved in chicken flight, an activity doesn't last long.

Human muscle composition testing requires a biopsy.