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It doesn’t matter how dedicated the athlete, interruptions from training are inevitable. Periods of inactivity are frequently due to life’s unplanned events. Occasionally these phases are scheduled to avoid overreaching or allow recovery from an onset of overtraining syndrome. Unfortunately, a prolonged reduction in training efforts, or discontinuing all together, can result in a partial or complete reversal of training-induced adaptations. Muscular detraining is the result of marked decreases or cessation of physical activities.

Muscle does not turn to fat, no more than gold can mystically transform into wood. Skeletal muscle has the amazing ability to adapt and reform itself to meet physical demands. It also retains its ability to readjust to reduced physiological stressors during periods of reduced training stimuli or complete training cessation. Increases in fat mass are easily obtained if caloric intake remains elevated; loss of muscle leads to a decrease in basal metabolic rate. Caloric intake must always adjust to current activity levels.

The question progressively-focused bodybuilders frequently try to resolve is: how long is too long for periods of training cessation?

Anaerobic fitness

A review of over 50 studies and over 30 years of research was compiled for the Medicine and Science in Sports and Exercise journal, published by the American College of Sports Medicine. The purpose was to collect the data reported in exercise literature concerning the muscular characteristics of detraining, in both highly trained athletes and moderately or recently trained individuals.

Bodybuilders begin many physiological changes once training is stopped. Rapid and progressive reductions in oxidative enzyme activities result in reduced mitochondrial Adenosine tri-phosphate (ATP) production; these high energy phosphate molecules are used by the muscles for short bursts of power. Detraining affects are often characterized by a decreased muscle capillary density. This routinely takes place within the initial two to three weeks of training cessation. Arterial-venous oxygen difference also declines if inactivity remains continuous. Oxygen-carrying myoglobin concentration does not seem to be readily affected by training cessation.

According to data reported in exercise science articles, athletes can maintain, or suffer limited loss, in limit strength during short periods of no training. Strength performance in general is readily retained for up to four weeks of inactivity, but highly trained athletes’ eccentric force and sport-specific power may suffer significant declines after two weeks. During eight weeks of training discontinuation, there are decreased proportions of slow-twitch fibers with increased oxidative fibers in strength-trained athletes.

In a study of 12 weight lifters, a 14-day training cessation did not significantly change their one-repetition maximum bench press (-1.7 percent) and squat (-0.9 percent) performance. The authors of the study concluded that briefly inactive strength athletes could maintain many aspects of neuromuscular performance with only slight decreases in eccentric strength.

In another study, 12 weight lifters experienced a 6.4 percent decrease in fast-twitch muscle fiber cross-sectional area in 14 days. Interestingly, increases were observed in plasma concentrations of growth hormone (58.3 percent), testosterone (19.2 percent) and the testosterone-to-cortisol ratio (67.6 percent); cortisol levels decreased by 21.5 percent. The hormone changes would benefit any athlete trying to reverse the negative effects of overtraining syndrome.

Longer periods of training cessation are accompanied by more pronounced declines in limit strength for strength-trained athletes. The loss is limited to around seven to 12 percent for inactive periods lasting eight to 12 weeks. Results show that both muscle atrophy and diminished neural activation are responsible for the decline in maximal force during 12 weeks of inactivity.

Recently acquired strength gains appear to be lost at different rates, depending on the type of strength performance measured. Interestingly, there seems to be a direct relationship with the type of training used prior to the inactive period. One group of researchers reported that functional strength was better preserved during 12 weeks of inactivity after 12 weeks of concentric (muscle contracts while pushing or pulling a load) and eccentric (muscle stretches while resisting a load) resistance training. Performance of eccentric muscle contractions is essential to promote greater and more long-lived neural adaptations to training. Progress from speed-strength training is better maintained during training cessation if the previous training method also focused on developing explosive strength.

Aerobic fitness

What about those who sustain considerable strength levels in conjunction with remarkable aerobic endurance? Pete Pfitzinger is a former distance runner who later became a popular author and exercise physiologist. He is best known for his marathon accomplishments; he represented the United States in two Summer Olympic Games. According to Pfitzinger, the rate at which aerobic fitness declines is slower than most think. In fact, most elements go down at about the same rate at which they go up.

Pfitzinger insists that endurance performance tends to remain the same - or actually improve - after a few days without training. Allowing a rest from perpetual fatigue permits complete recovery and adaptation from previous training. But after two weeks, the benefits become outweighed by a loss in fitness. After three to four weeks, performance is likely to decrease by around three to five percent. Pfitzinger suggests that a 40-minute 10-kilometer runner could expect to slow down by about one or two minutes after a three-week break.

Two to four weeks of detraining leads to a decrease in the maximum amount of oxygen an athlete can carry by up to 10 percent, primarily due to a reduction in blood volume. Endurance training increases blood volume and when training is stopped, it rapidly declines. As it declines, less blood returns to the heart to be pumped with each beat. Since stroke volume decreases, the heart rate must then increase in order to run at the same pace.

Other effects on endurance output include a loss of flexibility, a decrease in lactate threshold pace and large reductions in muscle glycogen concentration and aerobic enzyme activity. “The fitter you are, the greater these losses tend to be,” Pfitzinger affirms.

Take-away message

The goal for successful bodybuilding is to always remain progressive. If the current routine has not led to any results - fix it. It is important to realize symptoms of overreaching, brought about by training too often; however bodybuilders usually become impatient and train too frequently. On the other hand, prolonged absences from training will impede results. Training consistently and sensibly is mandatory for bodybuilding success.

Personal physiological characteristics can impact the amount of muscle lost during detraining periods; as well as current fitness levels, training experience and duration of the cessation. If possible, limit the period of inactivity to less than two to four weeks. Longer periods should include some occasional physical activity; resulting in moments of peak muscular contractions and sufficient intensity. If not, muscle loss is inevitable and cardiovascular fitness will decline.

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MUJIKA, I., and S. PADILLA. Muscular characteristics of detraining in humans. Med. Sci. Sports Exerc., Vol. 33, No. 8, 2001, pp. 1297-1303.

PFITZINGER, PETE. What happens if you stop training? Online. Internet. June 2007. http://www.pfitzinger.com