If you follow any weightlifters or fitness influencers on Instagram, chances are you've seen someone tag their posts with #legday. There are more than 13 million #legday posts on the 'gram, including memes about how difficult it is to recover from a difficult leg day. These posts might lead you to think that leg day is one of those bogus social media holidays, but it's actually a thing outside of the Instagram fitness world.
When people talk about #legday, they're referencing split training, a resistance-training method that involves dividing weekly workouts based on the specific muscle groups worked, according to the American Council on Exercise. Instead of exercising your whole body, you work one or two muscle groups each day, for example: Monday you work your back and biceps, Tuesday you focus on chest and triceps, Wednesday you rest, Thursday is leg day, Friday you work your shoulders, and on the weekend your rest. As you can imagine, split training takes time to plan and execute. For people looking to build muscle, though, split training can be an effective and convenient method.
Split training is more than a scheduling hack, and there's some science to the phenomenon. From a physiological standpoint, studies suggest that muscles need at least 72 hours of rest between high-intensity strength-training workouts to repair — and that repair time is super important. If you exercise too frequently, or work the same muscle groups over and over again, then muscle tissue can't repair, and it's harder to build muscle. So, splitting your workouts throughout the week gives your muscles time to recover and rebuild before you work them again. And split training allows you to train more overall than a full-body workout permits.
While split training works for some people, the research suggests that it's not necessarily magical. For example, a 2015 study examined whether split training was more effective than a full-body workout at improving people's strength and hypertrophy (a.k.a. muscle size). At the end of an eight-week program, the group that did split training had increased their biceps and triceps size infinitesimally.
So, should you try split training? That depends on your workout goals. If your goal is to simply improve muscular strength and fitness, then you might benefit from breaking up your workouts so you work your upper body for two days, and your lower body for two days. Or if you know you want to improve your upper body strength specifically, then you might consider a split-model so you can perform more work on your arms and shoulders, while also giving yourself time to recover. Split training tends to be popular with bodybuilders who are aiming to develop certain levels of muscular definition over a short period of time. Often split training is recommended for individuals who already have a grasp on strength-training, rather than beginners who are still learning the right way to lift weights. (If you're not sure what exactly your goals are, this video helps explain who should try split training.)
The thing is, most of us do not need to do split training, because it's more important to prioritize functional, total-body strength. The American College of Sports Medicine recommends that people work major muscle groups (legs, chest, back, shoulders, arms, hips, abs) 2-3 days a week with at least 48 hours between each exercise session in order to maintain a healthy level of physical fitness. Specifically, they recommend that you do 8-10 exercises that target the major muscle groups for up to 15 repetitions — and that might be challenging enough for you. If you're curious what this type of strength-training circuit would look like, it's a good idea to ask a certified personal trainer to show you. Next time you hear someone bragging about their leg day, keep all this in mind. We all have different ideas of what #gains mean, and for some people, full-body workouts are better.