Skeletal muscle is remarkably plastic and can adapt to an array of circumstances in accordance with the demands imposed upon it. Consequently, consistent, progressive resistance exercise leads to increases in muscle size and strength. But life happens, and sometimes the performance of resistance exercise isn’t so consistent. In fact, it’s quite common for people to take off a few weeks from resistance exercise altogether, whether that be due to obligations outside of the gym, decreased motivation, illness or injury, etc. So, what exactly happens during these periods, and how long does it take for these changes to manifest?
While the principle of “use it or lose it” holds true, it ultimately comes down to the amount of time off from resistance exercise. In athletes (powerlifters and division I American football players), 14 days of detraining (i.e., no formal resistance exercise or structured physical activity) led to a nonsignificant reduction of about 2 kilograms in 1-repetition maximum (1RM) back squat and bench press strength.[1] There was also a nonsignificant 5.2% reduction in vastus lateralis type I muscle fiber area and a significant 6.4% reduction in type II muscle fiber area.
In a separate study, in which men with some resistance training experience performed a 4 weeks of a resistance exercise intervention for 4 weeks and then detrained for 2 weeks, there were no changes in rectus femoris cross-sectional area or in total lean mass. Furthermore, the gains in 1RM leg press strength accrued during the training period were maintained.[2]
In addition to these findings, which suggest that 1RM strength is relatively robust in men, 6 weeks of detraining in men with some resistance training experience did not significantly reduce 1RM bench press or squat strength.[3]
There have also been a couple of studies in untrained men that examined long-term changes in muscle size and strength between a group that continuously performed resistance exercise and a group that cycled through periods of 6 weeks of training and 3 weeks of detraining.[4][5] In these studies, increases in muscle size and strength were similar between groups.
Evidently, taking a week (or three) off from the gym doesn’t have much impact on muscle size and strength in men. However, more substantial decreases in muscle size and strength have been reported during detraining periods of 8–12 weeks.[6] This leads to the question: how much work is required to mitigate these adverse effects?
In one study that had untrained men perform resistance exercise 3 times per week for 8 weeks and then reduce their training frequency to either once or twice per week and reduce the amount of volume performed by 50%–60%, quadriceps cross-sectional area and half squat 1RM were both maintained.[2]
In a second study,[7] younger and older adults (20–35 and 60–75 years old, respectively) underwent 16 weeks of progressive resistance exercise, training the quadriceps 3 days per week. The participants then reduced their training frequency to once per week and reduced their training volume to one-ninth of what was performed during the initial 16-week training program.
In younger adults, it was found that the increase in thigh lean mass from the initial 16 weeks of training was maintained throughout the maintenance protocol. In contrast, the initial increase in thigh lean mass was not maintained in older adults (60–75 years old). Notably, a less severe reduction in training volume, one-third of what was performed during the initial 16-week training program, was also insufficient to maintain thigh lean mass in these participants.
For strength, knee extension 1RM was significantly higher at the end of the maintenance protocol (week 48) compared to the end of the initial 16-week training period in younger adults, whereas in older adults, the initial increase in knee extension 1RM was maintained throughout the maintenance protocol.
As evidenced by the above, younger adults can get away with doing very little resistance exercise for an extended period without experiencing reductions in muscle size or strength, but older adults don’t seem to have the same luxury, at least when it comes to retaining muscle size.
In younger adults, the evidence suggests that 1–3 weeks of detraining after several weeks of regular, progressive resistance exercise does not pose a significant risk of muscle and strength loss. Furthermore, reducing training frequency to 1–2 times per week and performing approximately one-ninth of previous training volume may be sufficient to maintain muscle size and strength.