How Bad Is It Really to Work the Same Muscle Two Days in a Row?

Is it OK to do a leg workout one day, then go for a run the next? That depends on a few factors.
Image Credit: LIVESTRONG.com Creative

How Bad Is It Really? sets the record straight on all the habits and behaviors you’ve heard might be unhealthy.

Gym jibber-jabber would have you believe that working the same muscle groups back-to-back is as bad as giving the finger to Hulk. Two leg days in a row? A crime against gains! As weight room wisdom has it, your muscles need at least 48 hours rest between being annihilated — no exceptions... ever.

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And for the most part, this is really sound advice for strength athletes. After all, your muscle groups ​do​ need time to repair themselves in order to reap the rewards of your training. However, this conventional wisdom actually ​isn't​ gospel for mixed-modality exercisers, cardio lovers or newbie lifters.

According to certified strength and conditioning coaches, for non-strength athletes, it's OK to work the same muscle groups two days in a row — and in many instances unavoidable. Below, two fitness experts break down where this original school of thought came from. Then, explain why it's better advice for some exercisers than others.

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Why Back-to-Back, Same-Muscle Workouts Can Be Bad

The idea that working the same muscle group two days in a row ​can​ be bad is based on solid exercise science about muscle hypertrophy.

"You aren't building muscle in the gym," says strength and conditioning coach Jake Harcoff, CSCS. "On the contrary, during your strength-training sessions you're essentially breaking your muscles down." They don't rebuild stronger until you leave the gym and adequately recover with nutrient-dense calories and sleep.

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"The harder you train your muscles, the greater damage you do to the muscle fibers and the longer you need to give them to rebuild and recover," Harcoff says. How fast these fibers are able to repair depends on a number of factors such as diet, hydration levels, age, overall health, stress levels, sleep and more.

According to a March 2017 study in the Journal of Applied Physiology, however, your muscles are most damaged (inflamed) 24 to 48 hours after a strength-training session. After that, science shows that the inflammation begins to taper off as the fibers repair themselves. Failure to let this amount of time pass between sessions puts your muscles in a constant state of damage.

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"If your muscles don't get enough time to recover, your muscles aren't able to repair," Harcoff says. That means you're not getting bigger or stronger. And the side effects of inadequate rest between training sessions are most likely to impact ​experienced​ lifters.

"More experienced lifters will need more and more training volume to make improvements, and therefore, an experienced lifter might need 3 to 4 days or more to fully recover before their next lift," he says.

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New lifters, on the contrary, can probably get away with doing the same lifts two days in a row. "A newer lifter will probably need less intensity and volume to make changes, thus, will likely be able to train the same muscles more frequently," Harcoff says.

"A new lifter may actually benefit from training subsequent days because doing so may allow them to practice and groove effective motor patterns," he says.

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When It's OK to Repeat Workouts

If you're an avid runner, boot camp lover or indoor cycling devotee, you might be wondering if this rule applies to you. And the answer is no, it doesn't.

"The rule applies to strength training, not cardio-focused workouts like running, cycling and most high-intensity group fitness classes," says says certified strength and conditioning coach Grayson Wickham, DPT, CSCS, founder of mobility platform Movement Vault. These workouts are less taxing on your muscle fibers compared to a rendezvous with the squat rack.

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"Running and cycling place less strain on the lower body compared to a heavy squat session," he says. Similarly, while boot camp classes often do incorporate dumbbells and kettlebells, often the load and overall volume is significantly less compared to that of a weight-lifting session, he says. As such, the overall damage to the muscle fibers takes less time to repair.

"You still need to make time to recover in workout programs that aren't strength-based," Wickham says. But so long as you're giving yourself two or three days of rest per week, you can still hit two of these cardio-focused sessions back-to-back.

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Regardless, Regular Rest Days Are a Must

"If you are working the same muscle groups two days in a row and not recovering well, that's a problem," Wickham says. "But if you're taking a day or two between working the same muscle groups and not recovering, that's also an issue."

In the short term, inadequate recovery can lead to symptoms such as prolonged (3 or more days) soreness, worsened sleep quality and an inability to show up to your next workout with sufficient energy, he says. Usually, these symptoms can be remedied by a few days of R&R.

Chronic inadequate recovery, however, can lead to generalized fatigue, sustained irritability, loss of libido, brain fog, nagging injury and constant bouts of sickness, Wickham says. All signs of a condition known as overtraining syndrome, these symptoms suggest that your workout program needs an overhaul.

"If you're experiencing these lasting symptoms, your workout program likely doesn't have enough built in time for rest, repair and recovery," he says. You'll also need to adjust the other 23 hours of your day to prioritize nutrient-dense food, stress reduction and quality zzzs.

How to Split Up Your Workouts if You’re an Experienced Lifter

If you're a more advanced lifter who wants to avoid the potential pitfalls of training the same muscle group two days in a row, you probably have questions about ​how​ to do that.

"The simplest way of knowing you aren't training the same muscles on back-to-back days is to train movements instead of specific muscles," Harcoff says. "An example of this would be spending a day on pushing exercises, followed by a day of pulling exercises, followed by a day of legs," he says.

If you work out four or more days a week, he actually suggests splitting leg day up into posterior (back of the body) movements and anterior (front of the body) movements. "You can work the posterior muscles of the legs (glutes and hamstrings) one day and the anterior muscles of the legs (quads and calves) another day."

Ultimately, however, because the best workout programs take your specific goals and exercise history in mind, Harcoff recommends hiring a trainer if you can swing it.

So, How Bad Is It Really to Work the Same Muscle Two Days in a Row?

Generally speaking, it's fine to work out the same muscles back-to-back — so long as you're not going all-out both days.

"It all comes down to the volume of the movements as well as the intensity that you're bringing to the movements on the consecutive days," Wickham says.

While it would be fine to go on a casual jog one day and do a circuit workout with air squats and lunges the next, it'd be less-than-ideal to PR your 10K run one day and then try to find a new one-rep max back squat the next, he says. "Similarly, you wouldn't want to do a heavy barbell back squat two days in a row," he says.

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