Partial Vs. Full Reps… Or Both?

[01dragonslayer]

A potentially game changing study has just been published. It may change how you perform your exercises forever. Or it may not. Let’s have a look.

The study titled “the efficacy of incorporating partial squats in maximal strength training” is about combining partial and full reps in your training. The debate on whether training with a partial range of motion (ROM) has any benefits compared to training with a full ROM has been going on for decades.

One reason many people have trouble understanding the effects of ROM is because they think ROM is equal to the distance a weight or body part travels. It’s not. ROM is equal to the amount of degrees a joint flexes. Look at the illustration of elbow flexion ROM below.

Now that we’re clear on the definition of ROM, here’s the Cliff notes on the current state of the research on full vs. partial ROM training.

Muscle Growth Research​

• In a study comparing Scott curls with a full compared to a partial ROM, there was a trend for greater growth of the arms in the full ROM group [2].
• Research comparing full to partial squats, including unpublished work by exercise scientist Truls Raastad in Norway, shows that full squats lead to more muscle growth of the quadriceps than partials [6].
• A full leg training program including squats resulted in more thigh muscle growth when performed with full reps than with partial reps [7].
• Training the quadriceps at long muscle lengths results in higher muscle activation than training at shorter muscle lengths. This remains true when absolute or relative training intensity is held constant. In general, at long muscle lengths a muscle is under greater biomechanical stress (shorter moment arm, reduced cross-bridge formation and reduced force production per sarcomere). [9]
• Over the course of a partial rep leg training program, quadriceps muscle activation decreased in the part of the ROM that wasn’t exercised [9].

Strength Training Research​

• Full reps led to greater strength development than partials for leg extensions, Scott curls and squats [1-2, 5-7, 9].
• Full ROM bench pressing did not build more strength than partial reps in one study, but in this study ‘partial’ reps just meant avoiding the last 2-5 inches to lock-out [3]. Since the bench press has a steeply increasing strength curve, once you’ve passed the sticking point the last few inches are incredibly easy. So easy you may as well not do them?
• A replication of the bench press study showed that full ROM bench presses did in fact lead to greater strength development than avoiding lock-out and keeping ‘tension on the muscles’ [4].
• Partial reps build strength specifically in the part of the movement you train with limited transfer to the rest of the movement [1, 5-9].
• Whether partials are better than full reps at improving the exercised portion of a lift varies. In untrained subjects study deep squats outperformed partial squats in building partial squat strength [5]. In a study on leg extensions partial reps were no better than full reps at any part of the movement [1]. In a study on recreationally active subjects there was no difference [7]. In a study on resistance trained subjects partial squats were better at building the partial squat than full squats [6].
• In general, more advanced lifters and more complex exercises benefit more from partial reps due to the principle of training specificity. Beginners and simple exercises do not require ROM-specific training to induce maximum muscle growth and build strength across the entire movement.
• Core training may be an exception. Research on back extensions found that training with a greater ROM did not benefit strength development in the spinal erectors [8]. Stuart McGill’s well known research shows the functional anatomy of the core is best suited towards stabilization, not actual movement. A full review of optimal core training is beyond the scope of this article though. They call these things bullet points and I already have more bullets than there are chambers in most guns.

Power Training Research​

• Full squats are better at developing power and jumping performance than partial squats [5-6]. This is a strong finding in favor of full squats. Partial squats have visibly greater movement specificity to jumping and result in higher power output than full squats [10]. Still, full squats are better to increase power than partial squats.

Note that all the above research compared training exclusively with a full versus a partial ROM. Competitive bodybuilders, powerlifters and to some extent Olympic weightlifters still regularly train with partial reps, but they all perform partials in addition to full reps. This is where the new study comes in.

Combining Full And Partial Reps: Double The Strength And Power?​

Bazyler et al. [11] compared advanced trainees with an average squat of 324 pounds (147 kg) on a program of either 6 sets of full ROM squats (group F) or 3 sets of full squats and 3 sets of partial squats (group FP). At the end of the program, the group performing both partial and full squats developed more strength and more power than the group that always used full ROM.

“There was a trend for FP to improve over F in 1-RM squat (+3.1%) 1-RM partial-squat (+4.7%), isometric squat peak force allometrically scaled at 120° (+5.7%), and impulse scaled at 50 ms, 90 ms, 200 ms, and 250 ms at 90° (+6.3 to 13.2%,) and 120° (+3.4 to 16.8%).”

Case closed: using both provides the best of both worlds, right? Not so fast. A few caveats are in order.

• None of the measures of strength were statistically significantlydifferent between the 2 groups. Now this may have been due to lack of statistical power, but it’s certainly reason to take these findings with a grain of salt.
• Moreover, in the sticking point of the squat, the full squat group gained a significant amount of isometric strength, but the full+partial squat group did not.
• The full+partial squat group only gained more power on 1 measure (impulse scaled) and not the other (rate of force development) and it was only in the sticking point, not at the top of the squat. Even worse, the reliability of the results was low. Several results suffered from what statisticians call heterogeneity of variance, which basically means the 2 study groups were not strictly comparable.

Ok, recap: the results in favor of using both partial and full squats instead of just full squats to develop strength and power in the squat are questionable. Theoretically, however, it makes sense that incorporating partial squats increases power development. Partial squats allow for far greater power production than full squats [10]. If I ask you to jump, you will intuitively do a partial squat before jumping. No one sinks down into a full Olympic squat, ready for take-off.

When the results of a study are unclear, we need additional research. Fortunately, Bazyler et al. weren’t the first ones to study combined full and partial rep training. Massey et al. [3] compared groups bench pressing with an equal number of sets of either full reps or a combination of full and partial rep sets. Although the difference in strength gains were not statistically significant, the full rep group gained 25 pounds on their bench press compared to just 16.5 pounds for the full+partial group.

The authors replicated this study and found the almost exact same strength increases in both groups. This time, the strength difference was statistically significant: the full ROM group gained more strength than the full+partial ROM group [4].

These studies on the bench press provide strong evidence against the use of partial bench pressing. However, the subjects in Massey’s bench press studies were all only recreationally trained. As you read earlier in this article, advanced trainees may benefit more from the use of partials than beginners. In athletes, variable ROM training for the bench press improved power production even though it did not increase strength gains compared to regular full ROM training [12]. This corresponds with the findings by Bazyler et al. The subjects in the full+partial rep group gained less isometric strength in the sticking point of the squat, but their dynamic squat strength improved more because they became more explosive and could push through the sticking point better.

How can someone’s form be so bad yet so good at the same time?

What About Partials For Muscle Growth?​

Here’s where it gets really interesting. The diets of the subjects in this study were not controlled. As a result, the average body fat percentage in the full squat group fell by 10.3%. Body weight did not change in either group and body fat percentage did not change significantly (-5.3%) in the full+partial group. The only way body weight can remain stable while fat percentage decreases is by gaining lean mass. So the full squat group must have gained more lean body mass than the full+partial group. I emailed the corresponding authors about this, since they did not discuss this in their article, but I have not received a response.

Full reps have several advantages over partial reps to induce muscle growth. Full reps activate muscles along their entire length (with the right exercise selection at least) [9]. Stretching a muscle under load is a strong stimulus for muscle growth. It results in the addition of sarcomeres in series and in parallel, basically creating a thicker and longer muscle [9, 11]. The addition of sarcomeres in series is also why heavy weight training over a full ROM increases muscle length while stretching does not increase muscle length.

In in vitro muscle cells, animals and bio-artificial muscles, the combination of muscle activation and stretching has been shown to strongly increase protein balance, anabolic gene expression, anabolic hormone signaling – particularly insulin-like growth factor-1 and mechano growth factor – and muscle growth [9, 13-18]. Basically, stretching a muscle or activating it is a stimulus for the muscle to remodel itself and prevent damage in the future. Combining stretching and activation is therefore optimal to create a stronger and bigger muscle.

On the other hand, there are some theoretical benefits of using partial reps for muscle growth, such as increased metabolic stress. However, this is likely only relevant when training at a low intensity when there is otherwise not enough tension in the muscle for high muscle activation. (If you don’t understand how muscle grows in response to tension, read my article on structural balance in Alan Aragon’s Research Review where I explain this.) So far, partial reps have at best resulted in equal muscle growth as full reps in research.

And yes, that means most pro bodybuilders are training in a suboptimal way. If you can’t fathom the idea that a largely poorly educated and underground subculture’s intuitive way of manipulating the human physiology is not perfect, you have much to learn about this world.

As much as I love these guys, I do not consider them the foremost authority on exercise science.
So how does this all fit together? It depends on your goal.

Conclusion: Hypertrophy​

Partial reps do not seem to have any advantage over full reps to stimulate muscle growth. Full reps stimulate muscle activity over the entire muscle’s length. They also stretch the muscle under high tension. Exercise selection and accommodating the resistance curve to your strength curve are generally superior methods of adding variety to bodybuilding training than partial reps.

Conclusion: Strength​

Including partial reps can be beneficial in advanced trainees to strengthen parts of a movement as per the specificity principle. Geared powerlifters in particular can benefit from strengthening their lock-out due to the lack of passive assistance they get from knee wraps, squat & deadlift suits and bench shirts at the end of these exercises.

Novices are better off building a good strength base by sticking to full ROM training, because they are not developed enough to require ROM-specific training.

Conclusion: Power​

Partial reps for many exercises allow for greater power production, which can benefit power development. Just as for strength training, these benefits are greater for more advanced trainees.