Halting a weightlifting program causes unfavorable detraining, or the loss of training adaptations such as enhanced strength or muscle size. Fitness benefits earned through years of weightlifting recede at a slower rate than those earned through two to six months of weight training. Factors of detraining, however, occur within a week of inactivity. Understanding detraining outcomes enables informed fitness decisions.
Your muscles become noticeably smaller after you stop weightlifting. In fact, individuals who have gained large amounts of muscle with training undergo greater muscle-mass loss with detraining. Each muscle contains thousands, if not millions, of microscopic muscle fibers. With detraining, your fibers decrease in diameter -- causing a visible size reduction over time.
Individual muscle fibers possess contractile proteins known as actin and myosin. During muscle movement, muscle fibers slide past each other as actin and myosin connect with surrounding fibers and pull against each other. Additionally, weightlifting builds extra actin and myosin along each muscle fiber. As your muscles become smaller with detraining, however, your amount of contractile proteins diminishes and strength decreases.
Muscular power combines speed and strength. For example, power determines your speed and force as you swing a baseball bat or bench press 100 pounds. Weightlifting augments power in many ways. For example, strength training improves communication between your brain and muscles -- enabling greater activation of your muscle fibers at an accelerated rate. In addition to lost muscle size, detraining removes some neurological, or brain-based, training benefits causing a reduction in muscular power.
As a muscle contracts during a weightlifting exercise, blood vessels within your working muscle become constricted. As a result, your heart must pump more forcefully for adequate blood flow through compressed vessels. Within months of weekly weight training, muscular thickness of one of the four heart chambers, known as the left ventricle, increases -- causing a stronger heart muscle. Detraining reverses muscles gains within your heart, however, and reverts cardiac strength to your pre-training level.
Effects on Body Composition
Body composition divides your total body weight into fat or fat-free mass. Generally, body composition reads as the percentage of your weight comprised of fat, also known as body-fat percentage. For example, a 200-pound person with 50 pounds of body fat holds a body-fat percentage of 25 percent. In the likely event that muscle loss occurs while fat deposits grow or remain the same during detraining, your body-fat percentage increases after a weightlifting program ends.