Short answer: Professional bodybuilders and the amateurs imitating them in the gym often perform partial reps, especially when working the shoulders and the chest. Why?
The official explanation behind this strategy is that partial repetitions ensure constant tension on the targeted muscle group and therefore hit the area harder. However, a good argument could be made that the gains from this maneuver are marginal at best.
The Benefits of Partial Reps According to Bodybuilders
The advocates of half-reps provide the following points to justify partial range of motion (ROM) training:
1. Constant muscular tension
The demand on the muscles drops when the joints are locked due to the increased skeletal support. By eliminating the lockout position, bodybuilders prevent the muscles from entering “rest mode”.
For instance, if you do squats without fully extending your knees at the top of the movement, your quads will get smoked quicker because the musculature is under constant strain.
Partial reps pump the muscles with blood and lactic acid faster than complete reps and allow the lifter to reach muscular fatigue, and potentially failure, with a lighter load.
The hypertrophy scholars believe that this technique generates greater stress on the musculature resulting in prominent myofibrillar and sarcoplasmic hypertrophy.
2. Reduced stress on the joints
Bodybuilders keep their elbows and knees “unlocked” to increase the tension on the muscle and to “unload” the joint. Some believe that locking out the joints is inherently bad and causes problems in the long-term; others do it because the final part of the exercise triggers pain from previous injuries.
3. To keep the muscle fresh for “important exercises”
In a bodybuilding video that I watched a long time ago, a bro-scientist said: “Don’t lock out your joints during shoulder presses. That’s all triceps. It’s better to hit the triceps with other exercises. Keep them fresh.”
His idea was that the shoulder press was going to rob his pupil’s triceps of juice that’s better spent on direct triceps work. E.g., Skull-crushers, kickbacks, push-downs…etc.
4. Muscle Targeting/Activation
The aim of bodybuilding is to develop a muscle group rather than to move iron from point A to point B. Partial reps are a reminder of that goal. A bodybuilder who is doing half-reps on the bench is thinking about pumping his chest whereas a powerlifter benching with full ROM is focused on completing the lift and is not necessarily concerned with the degree of pectoral activation and pump that he is getting from the movement.
The use of lighter loads during pumping sets facilitates that mission too. When the weight gets heavy, one is more likely to enter “survival mode” and complete the lift by any means necessary without focusing on the targeted muscle group.
5. To get a quick pump
Partial training rises the pumping effect of each repetition and floods the muscle with blood and lactic acid resulting in a burning sensation.
6. To extend a set and reach full exhaustion
You’ve probably seen the following situation: A bodybuilder is doing triceps pushdowns. He starts the exercise with full ROM repetitions, but eventually, the muscle fatigues and the triceps become too weak to lock out the elbow. The bodybuilder continues to do partials until even the strongest part of the exercise (the beginning) becomes impossible. The purpose of this technique is to reach complete muscular failure from top to bottom.
The text above would make for a great write-up in a mainstream bodybuilding magazine or website, but the reality of the situation is different.
The effectivity and the benefits of the points above aren’t as unequivocal as the believers in bodybuilding dreams and their teachers would like you to believe. Here’s the true story.
1. Locking the joints at the end of a rep is fine.
Many gullible souls still think that locking out your joints is bad. Hence why bodybuilders often claim that they are saving their precious elbows by doing partial bench presses and overhead lifts. Yet there’s nothing fundamentally unhealthy about locking your joints when lifting. They are designed for that.
Moreover, the lockout position represents the most stable biomechanical structure for supporting heavy weights. If the final range of motion is not trained, the tendons and the muscles will be weaker when forced to exert force over that amplitude. This increases the risk of injury in sports and outside of the gym.
Locking out is dangerous only if you land on a fully locked joint e.g., ending a jump with locked knees. This is why it feels natural to bend your knees after a jump as the movement of the legs acts as suspension absorbing the impact. If you look at skaters jumping off stairs, you’ll see that they squat when landing.
But this isn’t happening during strength training. The joints enter the lockout position gradually and under the support of muscular force.
2. Time under tension is just another hypertrophy concept that doesn’t have a high practical value.
If you listen to the mainstream bodybuilding doctrines, you will quickly fill your head with various training principles which sound sweet in theory, but don’t offer the promised benefits in practice. Time under tension is one of them.
Consider the following:
Person A performs all exercises over their full range of motion. This allows him/her to do more repetitions thanks to the “mini-rests” at the top.
Person B does partials to “keep the tension on the muscle” and gets a great pump.
Exactly. There are too many factors involved to predict the end result.
In the first case, person A is spending less time under tension, but he/she is also moving the weight over a greater length. In the second scenario, person B enjoys more time under tension, but the range of motion/positive work is reduced.
Thinking that similar training calibrations can elicit hypertrophy hiding somewhere in your natural reserves is fairly naive.
3. Bodybuilders are on steroids allowing them to produce all sorts of theories.
Steroids work, brother. Studies show that non-lifters on roids gain more muscle than men who lift. (read more). The chemical substances subsidizing the growth of bodybuilders allow those “hypertrophy professors” to synthesize all kinds of muscle-building philosophies to explain their growth.
If you let them, they will flood your craniums with the most absurd statements on the planet. The base of the pro’s power will always be chemical. Without the drugs, they will all lose a monumental percentage of their size.
Similar methods have inconsequential value. Do you really think that bodybuilding would be any different if you remove partial rep training entirely? I doubt the size of the guys will change by one gram.
4. Many people use partials as an excuse to cheat.
What do unenlightened individuals do to increase their pull-up reps? They switch to “biceps hangs” instead of lowering themselves all the way down.
A while back, I met a dude at the local pull-up bars who furiously criticized me for doing dead hang pull-ups with a pause at the bottom. He called me a “cheater” and told me that I’m destroying my shoulders.
Ironically, he was doing half-rep pull-ups with his scapulae depressed the entire time – a move that is more likely to cause shoulder impingement than full ROM pull-ups because the humeral head could get “trapped” by the structures surrounding it.
Another demonstration of half-rep cheating would be many 2-plate bench competitions. Most competitors don’t lock their elbows to get more reps.
If training with a full range of motion was easier, they wouldn’t be doing that.
5. Intelligent bodybuilders who use partials rarely make it their bread and butter system.
Smart bodybuilders realize that half-rep training could be beneficial in a thin number of situations (e.g., limited equipment), but they know that full ROM training is still the most stable way to train in the long run.
How to Get the Best of Both Worlds
If you want to implement partials into your training, one of the most logical ways to do it would be a back-off set done with a lighter load after the main working sets. This way you’re getting the benefits of full ROM training combined with the pump offered by partials.