The benefits of weight training include greater muscular strength, improved muscle tone and appearance, increased endurance and enhanced bone density.
Many people take up weight training to improve their physical attractiveness. Most men can develop substantial muscles; most women lack the testosterone to do it, but they can develop a firm, "toned" (see below) physique, and they can increase their strength by the same proportion as that achieved by men (but usually from a significantly lower starting point). An individual's genetic make-up dictates the response to weight training stimuli to some extent.
The body's basal metabolic rate increases with increases in muscle mass, which promotes long-term fat loss and helps dieters avoid yo-yo dieting. Moreover, intense workouts elevate metabolism for several hours following the workout, which also promotes fat loss.
Weight training also provides functional benefits. Stronger muscles improve posture, provide better support for joints, and reduce the risk of injury from everyday activities. Older people who take up weight training can prevent some of the loss of muscle tissue that normally accompanies aging—and even regain some functional strength—and by doing so become less frail. They may be able to avoid some types of physical disability. Weight-bearing exercise also helps to prevent osteoporosis. The benefits of weight training for older people have been confirmed by studies of people who began engaging in it even in their 80s and 90s.
Strength training helps to maintain good flexibility. The ability of the body to resist the stresses that can result from an injury can be increased by obtaining a greater amount of strength. That is true in the athletic world and it has its advantages in performing everyday activities, such as lifting or carrying objects. Strength contributes to the overall efficiency of the human body. Starting a strength training program means you have started a new lifestyle because strength is reversible. It will decline if you do not continue to obtain a strength stimulus throughout your entire life.
For many people in rehabilitation or with an acquired disability, such as following stroke or orthopaedic surgery, strength training for weak muscles is a key factor to optimise recovery. For people with such a health condition, their strength training is likely to need to be designed by an appropriate health professional, such as a physiotherapist.
Stronger muscles improve performance in a variety of sports. Sport-specific training routines are used by many competitors. These often specify that the speed of muscle contraction during weight training should be the same as that of the particular sport.
Though weight training can stimulate the cardiovascular system, many exercise physiologists, based on their observation of maximal oxygen uptake, argue that aerobics training is a better cardiovascular stimulus. Central catheter monitoring during resistance training reveals increased cardiac output, suggesting that strength training shows potential for cardiovascular exercise. However, a 2007 meta-analysis found that, though aerobic training is an effective therapy for heart failure patients, combined aerobic and strength training is ineffective.
One side-effect of any intense exercise is increased levels of dopamine, serotonin and norepinephrine, which can help to improve mood and counter feelings of depression.