Imagine not training for 2-3 weeks and then getting back into the gym by performing a heavy leg day. You probably already can feel your sore legs cramping up while walking up the stairs.
But now imagine that same leg day after 3 months of consistency in which you were training your legs hard 2 times per week. You probably won’t experience much muscle soreness the day(s) after. This is because of a concept that is known in exercise sciences as the Repeated Bout Effect.
In essence, the repeated bout effect describes how your body gets used to the muscle-damaging response produced by strength training. As a result of the repeated bout effect, you also experience less muscle soreness over time.
If this sounds vague now, no worries. We will dive deeper into the causes of muscle soreness in the next paragraph.
What Causes Muscle Soreness?
When you train with weights, your muscles are under stress. If your muscles are not accustomed to this training stress, they experience more micro-tears than usual. Micro-tears in muscle is often referred to as “muscle-damage.”
A by-product of muscle damage is muscle soreness (a.k.a. DOMS). You typically experience the most muscle soreness after 24-48 hours of “muscle-damaging” exercise.
As mentioned, mostly unaccustomed training tends to result in a high degree of muscle damage. So you’ll experience the most muscle soreness when you get back into exercising after a training break or if you start performing new exercises in your routine.
This especially holds true if some of the exercises you do train your muscles at long lengths or overload the eccentric (lowering) portion of a lift. This tends to result in greater degrees of muscle damage as well.
Repeated Bout Effect Reduces Soreness
Research repeatedly shows that as you train consistently, your muscles experience less muscle damage. This protective mechanism against muscle damage is the earlier mentioned “repeated bout effect.” Because you experience less muscle damage with consistent training, you also experience less muscle soreness.
This is a perfectly normal training adaptation if we consider that your body is basically a machine of efficiency. The more consistently you do something, the less it impacts you because your body adapts to the activity. This holds true in more aspects than just training. For example, the more consistently you wake up at 6am, the easier it will be to wake up at that time since it becomes your new “normal.”
The exact mechanisms through which the repeated bout effect occurs are not 100% clear yet. But it’s likely related to the connective tissue (tissue that attaches muscle to bone) and nervous system adaptations you achieve when you train consistently. These adaptations help you coordinate muscle contractions better to reduce individual muscle fiber strain and, therefore, reduce muscle damage.
Is The Repeated Bout Effect Bad?
The “no pain, no gain” mentality is pretty popular. Because of this, many people see becoming sore as some kind of “reward” from their training. If they are less sore all of a sudden, some people may think their training is less effective. But muscle soreness is actually a poor indicator of whether you are training effectively for muscle growth.
We should not chase constant soreness if muscle growth is the goal. Far from it, actually, since excessive muscle soreness can impair your performance and hold you back from what’s truly important for muscle growth: Progressive Overload.
Research consistently shows that being sore suppresses training performance. One 2017 study found that a high degree of muscle damage directly interferes with strength performance and reduces joint range of motion. Just think back to the last time you experienced muscle soreness, your muscles probably felt stiffer and you weren’t able to lift as much weight.
So the repeated bout effect is not something that will harm your results. In fact, it can help you get better results since you will be able to handle more intense training once you feel sore less frequently.
Conclusion: Focus on Progress, Not Soreness
If you no longer feel sore after every training session, usually, there is nothing to worry about. You likely no longer feel sore because of the repeated bout effect, which is a beneficial training adaptation.
As long as your training is challenging and you are making consistent strength progress, you are still on the right track.
Lastly, I want to finish off by mentioning my eBook that goes into how you can maximize your muscular potential. This book translates the currently available scientific research regarding muscle growth into “Simple English”, so everyone can start implementing an evidence-based approach to training and nutrition.
So if you are interested in learning more about how to maximize muscle growth, check out my eBook “The Art & Science of Muscle Growth.”