What is the best way to maximize your muscle growth? Should you follow bodybuilding tradition and use short rest intervals? This approach is thought to improve testosterone and growth hormone secretion, increase metabolic fatigue, and give you a great pump! Alternatively, you could take longer rest times. This approach would let you lift more weight (or get more reps with the same weight), thus increasing your overall volume load (i.e. total reps x weight). Which approach should you choose? Let’s see how the latest science (and some practical training wisdom) can help you build more muscle.
Note: if you don’t care about the highlights of this study, feel free to scroll down to the practical application section near the bottom. I won’t be offended.
Several studies have compared different rest times. However, the way these studies were done did not always control all the variables. For example, one study might have the longer rest interval group use more weight than the shorter rest interval group. Now you are comparing two variables (i.e. load and rest intervals). This prevents you from knowing how one variable (e.g. rest times) impacts your muscle growth. Another difference that has come up in previous studies is that longer rest interval groups got more reps and thus used a higher volume load (weight x reps) per set. Again, is it volume load or rest time that is important? This study looked to compare both long and short rest intervals with and without the same volume load.
- The subjects were 28 young (18–34 years old) individuals (18 men and 10 women) who were “recreationally active” (i.e. they were not training regularly with weights).
- Researchers tested 1RM for unilateral (one leg at a time) leg press. They measured quadriceps (front thigh) muscle mass with MRI (magnetic resonance imaging).
- Each subject did 2 different training protocols – one for their left leg and one for their right leg.
- With 28 subjects, you have 56 total legs and thus 14 legs doing each of the following four training protocols:
- Protocol 1: Long rest interval – 3 minutes
- Protocol 2: Short rest interval – 1 minute
- Protocol 3: Long rest interval (3 min), but the same volume load as the short rest interval (protocol 2)
- Protocol 4: Short rest interval (1 min), but the same volume load as the long rest interval (protocol 1)
- Subjects did protocol 1 or 2 with one leg and then the other leg with protocol 3 or 4.
- All subjects trained with 80% of their 1RM (one-repetition maximum).
- Subjects trained 2x per week for 10 weeks.
All the subjects got stronger and gained muscle mass. This is not surprising – especially considering that none of the subjects were training with weight regularly. The two protocols that resulted in the greatest gains in muscle mass were the long rest interval (protocol 1) and the short rest interval that used the same volume load as the long rest interval (protocol 4).
- Training studies are hard and expensive. As a result, the number of subjects, lifting experience of the subjects, and length of study are usually less than most coaches and lifters would prefer. However, this is still a lot better than the traditional approach researchers used to use (click HERE for details).
- It is great that they measured muscle growth with MRI as this is more accurate than using a tape measure.
- Unfortunately, the subjects did not train regularly with weights. Thus the relevance of the research findings may not apply to experienced lifters.
- It was nice to see both men and women included in this study. However, this means that you are working with fewer total men or women. This makes it harder to know if there would be a greater sex difference in optimal rest intervals.
- By using young subjects, you do not know how things would change with older lifters.
- Many training studies use a between-subjects design. For example, you do program A, and I do program B. The limitation with this design is knowing why one training protocol worked better than the other one. If you build more muscle than me, is that because program A is better, or that you have superior muscle-building genetics? This study uses more of a within-subject design which tests different training protocols on the same subjects. For example, you try training protocol A with your left leg and training protocol B with your right leg. This removes the influence of genetics. If protocol A makes your left leg grow more muscle, than your right leg which used protocol B, it is because of the training. However, this study is not a pure within-subject design because the 28 subjects were tested with only 2 of the 4 protocols.
- You always have to be careful when a study uses only one exercise. While this makes for a nice, controlled experiment, it limits the ability to claim that a certain protocol is best for overall training. Remember, that every set of every exercise dips into your recovery reserves. The amount of volume you can tolerate when just training only your legs (and with only one exercise) might be higher than when you are training your whole body.
- If you want to get strong, you need to rest long enough to lift heavy weight each set. Thus, the traditional recommendation of longer rest times for strength building is still a great idea. For building muscle, you must get a sufficient volume load. If you use shorter rest times, you will need more sets to get the same volume load as you could get with fewer sets and longer rest times.
- Use caution when increasing training density (i.e. more sets with less res times). While this can work for building muscle (as shown in this study) and can be useful for fat loss, it may also burn you out if you train your whole body that way. You may find that using less sets, with longer rest intervals, but getting more out of each set leads to better long-term results.
- Optimal rest times will also depend on your strength levels. The stronger you get, the more a hard set will take out of you and the longer you will need to rest between sets.
The one thing I have seen consistently in myself, my clients, and athletes, is that muscle growth comes when there is substantial improvement in performance on key exercises. Muscle growth plateaus occur during times of stagnated progress. Base all other training decisions (e.g. volume, frequency, rest intervals, etc.) on what is most effective for helping you add weight to exercises in a 5-10 rep range.
To learn how to build muscle without drugs, check out my book: Size for Skinny Guys: A Hardgainer's Guide to Building Drug-Free Muscle.
If you have questions or suggestions for future topics, drop them in the comment section below.
Thanks for reading!
Longo, A. R., Silva-Batista, C., Pedroso, K., de Salles Painelli, V., Lasevicius, T., Schoenfeld, B. J., Aihara, A. Y., de Almeida Peres, B., Tricoli, V., & Teixeira, E. L. (2022). Volume Load Rather Than Resting Interval Influences Muscle Hypertrophy During High-Intensity Resistance Training. Journal of strength and conditioning research, 36(6), 1554–1559. https://doi.org/10.1519/JSC.0000000000003668