Guys, we may have been getting things wrong this whole time.
“Use full range of motion” has been a crucial part of perfecting exercise form forever. The thought process is that in order to get the full benefits of an exercise, this full range of motion would maximize the stress placed in the muscle which would equate to greater strength gains.
In fact, this is so ingrained in our heads that if someone doesn’t, you can be sure they’ll be met with “half repper” or “I count 0 reps!” Well, this may not be true. In fact, there’s evidence that suggests “half reps” could actually be getting a better workout than those using full reps!
The Three Muscle Contractions
To understand why partial reps can be awesome for muscle growth, we need to understand the three different types of muscle contractions.
Your muscle is actually composed of numerous different muscle fibers that are packed together to generate force together. Each one of these fibers is composed of long strands of contractile units known as the sarcomere. Within each sarcomere, there exist myofilaments that include thick filaments called myosin and thin filaments called actin.
These filaments lay on opposite sides of each sarcomere so that they overlap each other. Now, imagine you have this setup multiplied by thousands, which is how muscle fiber looks.
When activated, these filaments can pull on each other, bringing the ends of the sarcomere closer and closer together. Ultimately, this shortens the muscle and is known as concentric contraction (our first type of contraction). On the bicep, this occurs when the elbow flexes, while on the quadricep, it occurs during knee extension.
Another possibility is the filaments could exert force but not shorten or lengthen. This will allow a muscle to hold a force yet not move; think about the wall sit or a pause bench press (contraction #2).
Finally, the third muscle contraction! This occurs when the filaments let go of each other and slide back to the lengthened position; this is called the eccentric contraction. During the bicep curl, the arm is lower, and the elbow extends; during a leg extension, the leg comes down, and the knee flexes.
As it turns out, studies show that the eccentric contraction is able to exert more force and is most responsible for muscle growth and increases in strength due to the greater amount of tension.¹
Stretch Mediated Hypertrophy
At the same time, we need to understand another phenomenon known as stretch-mediated hypertrophy.
Stretch-mediated hypertrophy refers to recent observations in which a muscle experiences greater muscle growth when it’s performed in a stretched position. For example, deep chest flys which stretch out your pectorals, or chest muscles.
When a muscle is stretched, it creates greater tension, which triggers growth signals inside the muscle cells. Stretching also activates satellite cells, which are basically muscle stem cells. These cells multiply and fuse with existing muscle fibers, helping repair and grow muscles.
The most important thing to keep in mind is that when the muscle is in its lengthened state, it provides more stimuli for muscle growth. In theory, training a muscle in this lengthened state should produce more muscle growth.
The Research
Knowing the above, testing the theory would be pretty obvious. Have different groups of people perform an exercise yet only use different parts of the repetition. And this is exactly what researchers started to do.
So in a study from 2021, researchers had two groups of trainees. One group performed the bottom portion of bicep curls (fully extended to 90-degrees) while the other only performed the top portion (90-degrees to fully flexed).
At the end of the 5-week training program, the bottom-only portion group saw muscle growth of 8.9%, while the bottom group only saw an increase of 3.4%. That’s 2.6x more growth!²
You may be thinking, “Sure, but what about using the full range of motion?”
Well, a similar finding was found in a study from 2022 using leg extensions! However, in this study, the researchers also included a group using full range of motion. Still, the lower portion group saw more growth!
To be clear, those only performing the lower portion group saw more growth than those performing the whole range of motion! In addition, all groups saw similar increases in strength.³
Applying To Your Program
Before you start doing half-reps for your entire workout, we should consider some other variables.
The first is that muscle growth isn’t the only variable we need to be concerned about. You also need to consider things like muscle strength, the basic function of a muscle, and the health of your tendons and ligaments.
While the study above did show similar strength increases, we need to consider those were done with isolations, and findings may be different using compound lifts.
Secondly, there are other options to use. One thing we like is to perform an exercise with full range of motion until just about failure. You could then perform the last reps only using the lower portion. Or, perform with a full range of motion and then a drop set with the lower portion. You get the idea.
The other option is to use this information for your exercise selections. If we know that the lengthened position results in greater muscle growth, you could use exercises that stretch the muscle before hitting your compound lifts.
Research has shown that using lying leg curls instead of seated leg curls is better for hamstring development as the lying position stretches the muscle more.⁴ In addition, overhead triceps extensions have been found to be superior to triceps pushdown for tricep growth.⁵
Being more specific with your exercise selection could also get you the increase in growth while still using full range of motion.
References
Schoenfeld, Brad J., et al. “Hypertrophic Effects of Concentric vs. Eccentric Muscle Actions.” Journal of Strength and Conditioning Research, vol. 31, no. 9, Sept. 2017, pp. 2599–2608, https://doi.org/10.1519/jsc.0000000000001983.
Sato, Shigeru, et al. “Elbow Joint Angles in Elbow Flexor Unilateral Resistance Exercise Training Determine Its Effects on Muscle Strength and Thickness of Trained and Non-Trained Arms.” Frontiers in Physiology, vol. 12, 16 Sept. 2021, https://doi.org/10.3389/fphys.2021.734509.
Pedrosa, Gustavo F., et al. “Partial Range of Motion Training Elicits Favorable Improvements in Muscular Adaptations When Carried out at Long Muscle Lengths.” European Journal of Sport Science, vol. 22, no. 8, 23 May 2021, pp. 1250–1260, pubmed.ncbi.nlm.nih.gov/33977835/, https://doi.org/10.1080/17461391.2021.1927199.
Maeo, Sumiaki, et al. “Greater Hamstrings Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths.” Medicine & Science in Sports & Exercise, vol. 53, no. 4, 2 Oct. 2020, pp. 825–837, https://doi.org/10.1249/mss.0000000000002523.
Maeo, Sumiaki, et al. “Triceps Brachii Hypertrophy Is Substantially Greater after Elbow Extension Training Performed in the Overhead versus Neutral Arm Position.” European Journal of Sport Science, 12 July 2022, pp. 1–26, https://doi.org/10.1080/17461391.2022.2100279.
