Are Single-Joint Exercises Overrated?
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TRAINING TAKEAWAY:
At first glance of the available research, the answer seems to be “yes.” However, there are enough clues in the research and practical considerations to recommend single-joint exercises to those looking to maximize hypertrophy.
Background
Exercises can generally be classified as either multi-joint (MJ) or single-joint (SJ). As their names suggest, MJ exercises require movement at more than one joint (e.g., bench press) while SJ exercises require movement at only one joint (e.g., tricep extension). MJ exercises are regarded as more efficient because the demands at multiple joints require more muscles to be involved.
However, when it comes to maximizing hypertrophy for secondary muscles (in particular, limb muscles such as the triceps), there are multiple perspectives. Some argue that SJ exercises provide a more targeted stimulus whereas others argue that adding SJ exercises to a program is redundant.
Luckily, a recent meta-analysis by Rosa and colleagues provides insight into the research in this area.
Study Overview
Rosa and colleagues meta-analyzed seven studies that compared hypertrophy of limb muscles between MJ and SJ exercises. Below are some key characteristics of these studies:
All studies included training to failure.
Six of the studies featured untrained participants while one of the studies featured trained participants.
Six of the studies measured upper body hypertrophy while one of the studies measured lower body hypertrophy.
Four studies equated set volume, two studies did not equate set volume, and one study had both equated and non-equated conditions.
Three studies compared MJ only training to SJ only training, three studies compared MJ only training to SJ plus MJ training, and one study had both of these comparisons.
The meta-analysis of all seven studies did not reveal a meaningful difference in muscle hypertrophy of limb muscles between MJ and SJ exercises (Standardized Mean Difference [SMD] = 0.07; 95% Confidence Interval = -0.09 - 0.12).
The authors also performed a subgroup analysis to compare results between studies with and without equated set volume, but the difference was trivial (SMD = 0.17). Similarly, the authors investigated whether results differed if MJ training was compared to SJ only training or compared to a combination of MJ and SJ training. Again, this difference was trivial (SMD = -0.01).
What Does This Mean for Training?
This is the first meta-analysis to compare the effects of SJ and MJ training on hypertrophy of limb muscles, and the overall data is not too promising for SJ exercises. However, especially in a relatively small body of literature, it’s worth diving deeper into the included studies for additional clues.
First, it’s worth noting the obvious limitations from the characteristics of the included studies listed above. Perhaps most importantly, we should be cautious extrapolating these data to trained individuals as all but one study featured untrained participants. Additionally, these data may not apply to all muscles – all except for one study measured the biceps and/or triceps.
In addition to considerations for different muscle groups, we should also consider hypertrophy at different regions within a muscle (i.e., regional hypertrophy). We’ve seen this point be vital for interpretation in other areas of research, but it’s worth repeating: the conclusions of a given study are limited to the site(s) measured. In many of the studies included in the present meta-analysis, a single hypertrophy measurement was taken. These measurements may be a whole muscle measurement (e.g., lean mass in the upper limbs via DXA) or measure one site along the length of a muscle (e.g., muscle thickness 50% of the way down the upper arm via ultrasound). Both of these approaches may fail to detect differences in hypertrophy at certain sites.
Luckily, one of the included studies by Brandão and colleagues allows us to look at this concept as it featured multiple measurements of triceps hypertrophy. This study featured four groups, but two are most relevant here: one group that performed only the bench press and one group that only performed lying barbell tricep extensions. The overall increase in triceps was nominally larger in the tricep extensions group (+9.5% vs. +4.8%), but this difference was not statistically significant. More interestingly, the authors also measured hypertrophy of the triceps lateral head, long head, and middle head. While the middle head hypertrophy was not significantly different, a clear pattern emerged here in which the bench press group experienced greater lateral head hypertrophy (+7.2% vs. +0.6%) while the tricep extension group experienced greater long head hypertrophy (+17.5% vs. +2.1%). We shouldn’t over-index on a single study, but these are arguably the most granular measurements of hypertrophy in this body of literature and also featured the gold standard for measuring muscle size (MRI).
With that said, it’s worth noting that these findings may be unique to biarticular portions of muscles; the triceps long head crosses the shoulder joint in addition to the elbow joint and thus is less involved with some simultaneous elbow and shoulder actions. We see a similar result in the rectus femoris (a biarticular quadriceps muscle) as they grow more from leg extensions (SJ exercise) compared to MJ exercises.
Unfortunately, it’s likely that there are unique considerations for every MJ exercise. For example, dumbbell rows considerably underperformed compared to bicep curls for biceps hypertrophy in one study whereas another study reported similar biceps hypertrophy between lat pulldowns and bicep curls. Further, the execution of each exercise (e.g., narrow vs. wide grip pulldowns) likely also plays a role. To add a final layer of complexity, individuals may differ considerably in which muscle(s) “give out” first in an exercise and thus which muscle(s) are likely to receive a meaningful hypertrophic stimulus.
On the other hand, SJ exercises simplify a lot of this calculus due to the precision they offer. For example, additional MJ volume for the quads would have to come in the form of squat pattern exercises. The most difficult part of the range of motion in these exercises will generally be when the muscle is at a relatively long length. If looking to also include an exercise with a shorter muscle length at the most difficult part of the range of motion, that’s much easier to do via a SJ leg extension compared to a squat pattern (which would likely require some sort of banded set-up).
A final practical benefit to keep in mind is the fatigue management that seems to come with SJ movements. While MJ exercises have the added benefit of additional stimulus to the other involved muscles, adding a ton of MJ volume (even if it did lead to the same hypertrophy for the limb muscle being targeted) may be quite difficult to tolerate for many individuals compared to simply adding SJ volume.
Practical Application
If you’re looking for a minimalist training approach with the greatest overall return on each set performed, MJ exercises should make up the majority of your program. If you’re looking to maximize hypertrophy of all muscles, some evidence and practical considerations lead us to recommend a healthy variety of exercises, including SJ exercises, in your program.