Myth: Your muscles start to atrophy after a few days if you don’t work out, so you should train each muscle group at least twice a week if you want to increase muscular strength and size. Training once weekly or less frequently is only good for maintenance.
Truth: It would make little evolutionary sense for your body to produce a costly adaptation like muscle hypertrophy only to allow it to be quickly lost. Unless you are immobilized, bedridden, starving yourself, or suffering from a disease that causes muscle wasting your muscles will not start atrophying only a few days after working out. It takes much longer – about three to four weeks – and even then the loss is very slow.
When I started training people long ago, if one of my clients did not work out for more than a few weeks while away for business or a vacation I would reduce their weights slightly when they returned. I quickly learned this was unnecessary and stopped doing it. Nobody was losing strength, and many clients even came back slightly stronger.
I don’t recommend people stop working out entirely when they’re away for a few weeks because even though you may not lose any progress you won’t be making any, either. Even if you don’t have access to a gym you can do bodyweight and isometric workouts anywhere with little or no equipment. However, you shouldn’t stress over it if you can only fit in a few workouts while you’re gone because you are not going to lose muscle. You can still gain muscle even if you are only able to fit in one brief, hard workout a week.
Which brings me to the next part; while once weekly training may not be optimal for people who recover and adapt more quickly it is not just for maintenance, either. Even if your exercise tolerance and recovery ability allow you to progress on two or three intense workouts per week you can still increase muscular strength and size training only once weekly, just not as much.
I don’t recommend it as a starting point for most people, but there are many successful high intensity training studios who have been successful promoting just one intense workout each week to busy people and are producing good results with them. In fact, one of the most dramatic drug-free physical transformations I’ve seen was in a person who worked out only once a week.
When I was in college I worked at the Gold’s Gym in Green Bay, WI (now Titletown Fitness). Every Saturday my brothers would drive up to the gym with a few of their friends. They would train their friends while waiting for me to train them during my breaks between clients. One of their friends was very tall and skinny when he started out. He was about six feet and three inches tall and weighed 145 pounds (about 1.9 meters and 66 kg), which earned him the nickname “Ethiopia”.
Once a week he would work out with my brothers. They did very basic HIT workouts usually consisting of stiff-legged deadlifts, leg presses, close underhand-grip pulldowns, chest presses, compound rows, and shoulder presses. Because they rushed between exercises these workouts often took less than twenty minutes to complete (not counting the occasional delays when someone had to stumble to the locker room to vomit from exertion). In less than one year “Ethiopia” gained about fifty pounds while staying lean, meaning most of the weight he gained was muscle.
Not only are your muscles not going to atrophy if you don’t train them every couple of days, you can even build them with very brief, infrequent workouts as long as you are willing to work hard enough.
Ogasawara, Riki et al. “Comparison Of Muscle Hypertrophy Following 6-Month Of Continuous And Periodic Strength Training.” European Journal of Applied Physiology 113.4 (2012): 975-985.