While I believe it is not a great idea to work the same muscles or body parts two days in a row, my reasoning may surprise you because it doesn't have much to do with muscle fibres or overtraining and has a lot more to do with being a well rounded human mover.
A reader named Megan wrote to me on Facebook and asked: "Is the rule of not working out the same muscle groups on consecutive days set in stone? Or does it all depend on intensity?" The answer is both yes and no. Confused? I bet. So, let's take a closer look.
First, let's look at where this advice came from.
Body Building and Muscle Rest
Bodybuilders who work out for one to two hours while focusing on only one or two body parts are the ones who invented this rule of thumb. And like much fitness and exercise lore, that advice trickled down through magazines, blogs, and word of mouth until it became the type of conventional wisdom you might hear by the water fountain at the gym.
For lifters who are putting in the time and effort to truly break down and then rebuild their muscles with extraordinary dedication, it is definitely a good idea to take 48 to 72 hours between working out the same muscle group.
The reason is that when you strength train, you are actually making tiny tears in the fibers of the muscles that you are exercising. Then, after you finish the workout, your body automatically deploys satellite cells to zip around the body and repair those tiny muscle tears. This makes the torn muscle fibers both thicker and stronger than they were before, which is how you gain strength and muscle size.
If you are constantly tearing the same muscle fibers without giving them adequate rest, then you are simply re-tearing those muscle fibers before they have had time to repair themselves. Without the crucial rest and recovery period, your muscles cannot and will not fully grow, and—even if you don't end up injured— you will have less than stellar results from all your hard work.
OK, so most of us aren't spending 90 minutes blasting our glutes. Sure, some of you might be dedicated to having the largest calf muscles in your book club but most of us are exercising more practically or functionally. And when it comes to that, this rule isn't exactly set in stone.
If you really want to train the same muscles every day, you can do it with exercises that use your bodyweight and light to moderate body movement only. Exercises like:
- Pushups and pull-ups.
- Core strength exercises.
- Bodyweight squats and lunges.
- Plyometrics (light to moderate).
- Cardio type exercise (light to moderate) like walking, running, cycling, and swimming.
- Stretching or Yoga.
If you think about it, even if you aren't doing the exact same exercises each day, it's pretty hard to not use some of the same muscle groups. Overlap, to some extent, is inevitable and that is totally acceptable. If you attempted to fully isolate each muscle group by day of the week you could easily lose your mind. Even doing a back squat involves some input from your pecs.
Although the movements I listed above can, in fact, induce those tiny tears in the muscles, they aren't doing it at a level that you need to worry about (as long as you keep the workouts light to moderate). Your body will be able to recover quickly enough and the accumulated fatigue of a few back-to-back sessions will actually result in an increase in fitness, once you do take some time to recover. Check out the article called Why a Break in Training is Necessary for more info on how supercompensation works.