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Myth Monday: Skipping The Gym Won’t Set Me Back Too Far



Sticking to a consistent exercise routine can be hard. Work, family, weather, and a host of other factors often create a perfect storm dead set on keeping us out of the gym. As fitness professionals, one advantage we have over the rest of the population is a deeper understanding of what happens when we take one, two, or even three weeks off from exercise (this is referred to as “detraining”). This knowledge serves as great motivation for those times when we could use a little kick in the butt to fit in our workouts. The purpose of this blog is to share some of this knowledge with you, hopefully providing some of that same motivation.

Effects on Body Composition

Depending on a host of factors such as your age, weight, fitness level and more, an hour of intense exercise likely will result in a caloric expenditure between 350 and 650 calories. If we choose the mid-point of 500 calories and account for two weeks of skipped exercise, or eight missed exercise sessions, this results in a 4,000 calorie swing in energy balance. Since we know that one pound of fat equals a 3,500 calorie surplus, we can determine that this time off has accounted for over a one-pound swing in body weight. Since skipping workouts is rarely an isolated behavior, it is safe to say that over the course of a year or two, one easily could find themselves five to ten pounds heavier than they would have been had they tightened up their exercise routine. Do the math for five, ten, or twenty years, and it’s quite shocking just how much weight these small breaks from exercise can add up to.

Effects on Favorable Exercise Adaptations

Upon returning from a brief exercise-hiatus, we all are greeted with a rude awakening –the workout we thought we had mastered once again is kicking our butt. The reason for this is the deterioration of many of the beneficial adaptations that had increased our capacity for exercise. Some of these changes are detailed below.

Decreased aerobic fitness

  • Research has shown that aerobic fitness can decrease by up to 10% within a few weeks of taking time off.

Decreased cellular energy production

  • Research has shown that after as little as 3 weeks off from exercise, cellular enzyme activity decreases by 20% to 75%, depending on the specific enzyme. This decreased enzyme activity impairs energy production for exercise. Additionally, critical energy-producing structures in our cells (called mitochondria) reduce in number during this same period. Essentially, our bodies become less efficient producers of energy, resulting in a decreased capacity for exercise.

Decreased muscular strength and power

  • Research has shown that previous strength gains decrease by up to 10% within 4 weeks of time off, and power output (“speed strength”) decreases by up to 17% in the same period of time.

Decreased muscle size

  • Research has shown that muscle size decreases from 6% to 12% within 2 to 3 weeks of training cessation. Additionally, new weight lifters who completed an 8 week strength training program lost all of their gains in muscle size within 4 weeks of stopping exercise.

Take Home Message

It should now be clear that short breaks from exercise can have very significant detrimental effects on both body composition and a host of other desirable fitness adaptations. Hopefully the next time you are not feeling particularly motivated to exercise, some of this information will help you get started.

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