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May 6, 2022

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Do You Need to Perform Single-Joint Exercises for Optimal Muscle-Building?

Multi-joint (a.k.a., compound) movements such as squats, presses and rows are widely considered staple bodybuilding exercises. Some people in the field claim that multi-joint exercises are all you need to optimize muscle growth and that performing single-joint (e.g., biceps curls, leg extensions, etc.) exercises are thus superfluous. Alternatively, others champion the importance of performing single-movements  in a hypertrophy-oriented routine, citing the ability to better target a given muscle for development.

Who’s right?

Our recent meta-analysis helps to lend perspective on the topic, providing some practical insights as well as highlighting gaps in the literature that preclude our ability to draw strong conclusions. In this post I’ll delve into our meta-analytic findings and offer some key takeaways for program design.

What We Did
We searched the current literature to locate all randomized control studies that directly compared single- vs multi-joint training on site-specific measures of muscle hypertrophy (DXA, MRI, CT scan, ultrasound, or limb circumference measurement) in healthy adults. There were several studies conducted by Barbalho et al that we excluded from analysis due to evidence of research improprieties.

We then carried out a robust variance meta-analysis model to determine potential hypertrophic differences between single- and multi-joint exercises. We also subanalyzed studies based on whether they equated the number of sets per exercise per muscle group to assess if training volume had confounding effects on muscle growth.

What We Found
We identified 7 studies that met inclusion criteria. Our basic meta-analysis found similar gains in hypertrophy for both single- and multi-joint exercises. The relatively trivial confidence intervals of the effect size (-0.07 to 0.25) indicate that any differences would be of little practical relevance. Subanalysis failed to reveal that training volume had any effects on outcomes.

What are the Practical Implications of Findings
Looking purely at the meta-analytic findings, it would seem there’s no difference between performing single- vs. multi-joint exercises from a hypertrophy standpoint. If true, this would mean that you could simply rely on compound movements to get huge and hence save a good amount of time in the gym since multi-joint exercises are more time-efficient choices.

But hold on…

As often is the case in research, there are important gaps in the literature that must be taken into account from a practical standpoint. First and foremost, 6 of the 7 studies looked at biceps or triceps hypertrophy; the other study looked at the quads. Thus, no research has been done into the effects of multi-joint exercise on muscles such as the delts, glutes, hamstrings, and calves, among others.

Why is this an issue?

Well, evidence indicates preferential hypertrophy of the rectus femoris in the leg extension (a single-joint exercise) compared to the squat. This suggests that combining single- and multi-joint lower body exercises may have a synergistic effect on quad development. Moreover, research shows negligible growth of the hamstrings during the squat, suggesting that direct hamstrings exercises (e.g., leg curls, stiff-leg deadlifts, etc) are necessary for complete development of this muscle; logic would dictate this would also be the case for the calf muscles, which receive relatively little stimulation during compound lower body movements. Although studies on deltoid hypertrophy are lacking, both applied anatomy and EMG research indicate that shoulder presses focus primarily on the anterior head of the muscle; to work the middle and posterior delts would thus require targeted single-joint work (i.e., lateral raises and rear delt flys).

In addition, rarely do studies investigate the different heads of the upper arm muscles. One study did in fact show that the bench press (a multi-joint exercise) promoted greater hypertrophy in the lateral triceps head than the overhead triceps extension (a single joint exercise) whereas the overhead extension elicited greater hypertrophy in the long head of the tri’s compared to the bench press. It’s not clear whether the short and long heads of the biceps brachii would see similarly differential responses with the performance of single- versus multi-joint exercise (i.e., curls vs rows), but the possibility can’t be ruled out.  

Finally and importantly, no research on the topic to date has assessed growth at multiple sites across a given muscle. Numerous studies have shown that muscles can hypertrophy in a non-uniform fashion, with varying degrees of proximal, mid, and distal growth observed depending on a given training protocol. Although speculative, this raises the possibility that variations in length-tension changes between single- and multi-joint could promote hypertrophy at different aspects along the length of a muscle; we simply don’t know at this point because the topic has yet to be objectively studied.

Take-Home Conclusions:

From a practical standpoint, it’s relatively clear that multi-joint movements promote substantial hypertrophic benefits even in muscles that many people customarily believe require “direct” training (e.g., biceps and triceps). Accordingly, for those who are time-pressed and do not aspire to bodybuilding-type goals, this implies you can construct a routine based solely on multi-joint exercises and derive substantial benefits from a hypertrophy standpoint.

On the other hand, if the goal is to optimize your muscular potential, it appears necessary to include single-joint exercises as part of a comprehensive training program. This will help to ensure that all the body’s major muscles, as well specific subdivisions of a given muscle, are maximally stimulated for development. Program design should focus on integrating applied anatomical theory that takes into account each muscle’s unique composition and function.