Whether due to illness, injury or sheer lack of time, when you miss several workout sessions, the muscle and strength you have worked so hard to build may seemingly weaken with each passing day. Also known as de-training, loss of muscle and cardiovascular capacity can vary based on the level of conditioning you had achieved. The better shape you were in prior to stopping exercise, the longer your muscle will last, according to the American Council on Exercise. Because maintaining muscle is vital to your good health, always speak to your physician if you are concerned that you may not be able to exercise.
The Science Behind Muscle Loss
When you lift weights or perform resistance-training exercises to build muscle, your body releases special enzymes that encourage muscular development, according to Go Ask Alice!, a health and wellness resource from Columbia University. These enzymes also are responsible for maintaining muscle mass between workouts. You start to lose muscle mass because the enzymes start to break down when you stop resistance training.
The time frame for muscle loss can occur fairly quickly, according to Go Ask Alice! You may start losing muscle mass as quickly as 1 1/2 weeks after ceasing exercise. At the two-week point, you can lose up to 80 percent of the muscle mass you have gained. While every person is different, missing out on your resistance-training exercises can have an effect in a matter of weeks.
The major influencing factor in how quickly you lose muscle mass is your condition before you ceased training, according to ACE. For example, previously sedentary individuals who have just started exercising will lose muscle faster than a person who has been regularly exercising several days per week. If you have achieved a high level of fitness, such as that of a trained athlete, you may be able to retain your fitness level for up to 12 weeks, according to ACE.
While de-training can be a negative effect of sedentary activity, one benefit of consistent exercise is building muscle memory. Once you have established the muscle mass, the muscle is easier to re-train when you resume resistance-training exercises, according to Go Ask Alice! Some athletes put this principle to good use to achieve a higher level of fitness by taking two to four weeks off from training, then working to hit the gym again and achieve an even higher level of fitness. If you use this approach or are returning to resistance training after injury or illness, starting slow is vital. Remember that you may not be as strong as you once were, so you will need to rebuild your muscle mass.