Partial Vs. Full Range Of Motion
When it comes to stimulating muscle growth, there is quite a lot of debate about whether full range (FOM) or partial range (PRM) of motion is more effective. Well, it’s one of those topics in which you will come across lots of different opinions and no definitive answer. The good news is, lots of people use both FOM and PRM in their training and with success! So what is my opinion on FOM vs. PRM training for muscular hypertrophy? I guess we first have to look at the research!
What Is Full Vs. Partial Range Of Motion?
Before getting into some of the research on this topic, I think it’s good to first have a brief overview of what I mean by FOM and PRM. Let’s start off with FOM. Essentially with FOM, you are moving weight throughout the entire portion of a lift. Take a back squat: if you go all the way down to parallel (or even below if you can manage it!) from an extended (standing) body position, we say you have taken the weight through its complete range of movement (FOM). This is the same principle with the bench press. By pressing the barbell up from your chest until your arms are fully extended, you are taking the weight through the FOM of the exercise.
Now, say you perform the squat but this time, you carry it out with a PRM. This would mean that starting from an extended (standing) body position, you would descend to the ground and stop before you reach parallel. With a PRM bench press, you would push the barbell into the air from your chest but stop before your arms are fully extended with the barbell in the air. In both these cases, we say you have only taken the weight through a portion of the complete range that it can possibly move.
⇒The important thing to know between FOM and PRM is that it’s simply the difference in the range in which you move weights during a particular exercise.
A big debate at the moment is whether FOM or PRM is superior for building muscle. Well, there is no simple answer and research has shown the potential benefits for muscle growth using both techniques. However, what is not really clear, but has been popping up lately in research, is the potential mechanism for which PRM might influence muscle development. Pretty interesting stuff!
Partial Range Of Motion And Muscle Growth: The Non-Sciencey Version
So lately researchers have found that PRM can in some cases cause more muscle growth than FOM. At least in the case of the triceps (through a tricep push down exercise). In other words, if you perform a lying tricep extension exercise with PRM you develop more growth in your triceps than if you perform the same exercise with FOM (with the same weight being used in both cases). Why does this happen? By performing a PRM lying tricep extension, the tricep muscle is held under higher levels of tension. This causes restriction in blood flow to the muscle causing a reduction in oxygen and nutrient supply and a reduced disposal of waste products away from the muscle (e.g. lactic acid). All together, the muscle is placed under huge amounts of stress which ultimately leads to a muscle building processes being activated. Over time, this leads to bigger triceps! Cool, right? So, what we are saying is that PRM is likely to stress the muscle more than FOM, which lead to greater levels of muscle growth.
Figure shows the difference between a PRM and FOM squat. In the PRM squat, you squat down and stop before you hit parallel. Targeting primarily the quads. In the FOM squat, you squat to or below parallel. Activating more muscle groups (quads, glutes and hamstrings). ‘H’ represents the hips and ‘K’ represents the knees. In the FOM there is more activity at the knee and hip joints leading to more muscle activation.
What is interesting is that the weight used in the FOM and PRM tricep exercise was the same. The main argument at the moment for using PRM is that people can use more weight in comparison to FOM and thus it’s easier to overload the target muscle to a greater extent. Thus, leading to potentially greater levels of hypertrophy. Although this is true, it seems like that is not the only way through which PRM can lead to muscle growth.
Goto et al. 2017: A Potential Mechanism for PRM-Induced Muscle Growth
In 2017, Goto et al looked to investigate the potential mechanism by which PRM might cause muscle hypertrophy in trained men. In this study, they used 44 young trained men who underwent a resistance training protocol for 8 weeks. They were split into two groups. One group carried out a FOM lying tricep extension (from 0 to 120 degrees) while the other carried out a PRM lying tricep extension (from 45 to 90 degrees). Both were conducted with 3 sets and 8 repetitions (with the same weight). Before and after 8 weeks of training, the intramuscular oxygenated haemoglobin (Oxy-Hb) content, blood lactate levels, EMG signals (measure of muscle activity), as well as the cross sectional area (CSA) of the triceps brachii were measured.
⇒After 8 weeks of training, both PRM and FOM produced significant increases in the CSA of the triceps brachii muscle. However, PRM training produced a significantly greater increase in the CSA of the triceps brachii after 8 weeks in comparison to FOM training.
⇒After 8 weeks of PRM training the blood lactate concentrations were higher.
⇒EMG recordings of the activity of the triceps brachii after 8 weeks of PRM training were significantly higher than after 8 weeks of FOM training.
⇒After 8 weeks of PRM training there were significantly greater increases in the areas under the Oxy-Hb content curves than in comparison to FOM training.
⇒During the PRM program, there was a positive correlation between the percentage increase in CSA of the triceps brachii and the areas of the Oxy-Hb curves before and after 8-weeks of training.
⇒PRM training might be more effective than FOM in inducing muscular hypertrophy due to greater levels of intramuscular hypoxia (lack of oxygen) and thus metabolic stress generated within the triceps brachii.
Goto et al (2017). Figure shows the areas under the Oxy-Hb curves for PRM (A) and FOM (B) lying triceps exercise. The areas under the Oxy-Hb curves are greater for A indicating a greater reduction in oxygen in the triceps in response to PRM training.
Goto et al (2017). Figure shows the level of activation (EMG) in the triceps brachii in response to PRM (partial) and FRE (full) training. The level of activation is greater in response to PRM training. Indicating higher levels of tension.
Goto et al (2017). Figure shows higher levels of blood lactate following PRE (partial) training in comparison to FRE (full) training.
Goto et al (2017). Figure shows that CSA (cross sectional area) of the triceps brachii muscle is significantly greater following 8 weeks of PRE (partial) training.
Goto et al. (2017). Higher levels of correlation between Oxy-Hb content during PRE (partial) training and the increase in CSA of the triceps brachii. Indicating that the lack of oxygen in the triceps brachii following PRE training could account for the increase in muscular hypertrophy.
Do We Have A Potential Mechanism For PRM-Induced Muscle Growth?
Looking at the results of the Goto et al (2017) study, it’s possible that PRM training exerts a hypertrophic effect through a hypoxia-mediated mechanism. Given that PRM training was shown to lead to greater levels of muscle activity (higher EMG recordings) in comparison to FOM training, it’s likely that this sustained mechanical tension would lead to compression of the blood vessels of triceps brachii. This vascular compression in turn would lead to a reduction in the delivery of oxygen to the triceps. This was indicated by greater increases in the areas under the Oxy-Hb curves for the 8-week PRM training group.
The result of a lower supply of oxygen to the triceps brachii and a subsequent increase in lactic acid could lead to an up-regulation of multiple processes involved in hypertrophic signalling: increase in reactive oxygen species, increased growth hormone secretion and testosterone supply, and additional recruitment of type 2 muscle fibres (Nishimura et al. 2010). Given that the increase in CSA of the triceps brachii was highly correlated with an increase in area under the Oxy-Hb curves, it’s highly likely that the mechanism mediating the increase in muscle hypertrophy in response to PRM training is through a hypoxic-mediated mechanism.
Potential mechanism following the findings made by Goto et al. (2017).
Although this study showed greater levels of hypertrophy through PRM over FOM activity, it still doesn’t mean you should now replace everything with PRM training. However, it might actually be an important addition to your training, especially if you are a more advanced lifter looking to squeeze out extra muscle growth.
The decision to use PRM training in your program depends on what your goals are. For instance, if your goal is to develop your legs, then a FOM squat is certainly your best choice over a PRM squat. Simply because in a FOM squat you recruit more muscle groups. In a PRM squat you are only targeting primarily your quads. However, if you are looking to squeeze out a bit more growth on your quads (possibly because they lag in development), then a PRM squat might actually be a nice addition, given the current research.
It seems like PRM training can have a place in your program, especially if you are more advanced. If you are looking to target a particular muscle group and get more growth, than it seems that PRM training can provide another growth-inducing stimulus, likely through hypoxia. However, more research does need to be done to substantiate this link between PRM and hypoxia as the precise mechanisms are yet to be fully investigated.