Multi-joint exercises vs single-joint exercises for muscle hypertrophy: an overview

A widespread idea in the world of resistance training is that multi-joint exercises are inherently more effective for developing hypertrophy than single-joint exercises.

However, the technical reasons behind this hypothesis are quite questionable to say the least, and there is a strong suspect that are based on appeal to tradition or appeal to belief, an emotional or moral attachment, or the spontaneous association between high (external) loads, strength and hypertrophy.

The article explores the issue by comparing the conflicting theories and finally examining the published scientific research to date. It should be noted that the topic here is only the inherent efficiency of the two exercise types in developing local muscle hypertrophy, and not other purposes for which multi-joint exercises may be unquestionably more efficient.

Multi-joint exercises are superior to single-joint exercises: the most common arguments

The fact that multi-joint exercises are more efficient to promote muscle hypertrophy is certainly a theory also supported by many academics. Here are exposed the most common arguments:

• Higher central nervous system activation;
• More muscles involved;
• Greater anabolic hormones response;
• Greater strength development;
• Greater load and mechanical tension;
• Greater time-efficiency;

1. Higher central nervous system activation

Sometimes mentioned as an advantage of multi-joint exercises for hypertrophy is the greater involvement of the central nervous system (CNS), for example to support the greater demands for balance, coordination, stability and general motor control.

The first doubt about this vague concept is that these mechanisms are questionably useful for the hypertrophy development of a prime mover muscle, but often they can compromise the mechanical tension needed to develop it. So, the fact that the CNS is more involved because of these greater demands has nothing to do with the muscle hypertrophy adaptation for a specific muscle.

If it is true that the CNS is generally more involved in response to skills of greater complexity, this should not be confused for the increased recruitment of an agonist muscle, nor as a greater hypertrophic stimulus. On the contrary, the greater the complexity of a movement and the less localized may be the work and mechanical tension (even if it is not always the case).

Finally, it is also wrong to judge a multi-joint movement as synonymous with greater demand for balance, coordination and stability. A multi-joint movement can be performed in conditions of greater stability than a single-joint movement. If anything, this distinction should be made for the comparison between free weights and fixed-plane machines regardless of whether they are single- or multi-joint, or in any case it should be assessed on a case-by-case basis. For example, a unilateral body-weight calf raise is far more unstable than a chest press.

2. More muscles involved (indirect work)

Another presumed advantage often recognized to multi-joint exercises for hypertrophy is the involvement of more muscles at the same time, making the additional use of single-joint exercises unnecessary (1,2,3). It should be noted that this argument does not strictly concern the inherent hypertrophic potential of the two categories (i.e. the topic of the article) but is, however, still questionable.

Often the additional muscles involved in a multi-joint exercise act through a so-called indirect work, that is they are not prime movers (or agonists muscles), but have synergistic or stabilizing role. The problem with indirect work is that it is generally not as optimal as direct work for the same muscle (2,4,5), to the point that many authors propose to count it as a partial set or as a partial set-volume (5,6).

However, this principle cannot be generalized. While for many muscles indirect work is suboptimal, for others it may be effective (1,5,7). To figure out when that happens, the relationship between the functional anatomy of the target muscle and the biomechanics of the exercise need to be assessed on a case-by-case basis. Nevertheless, the additional muscles involved in a multi-joint exercise often do a suboptimal work.

Another notion is that single-joint exercises would typically involve few muscles, which is questionable. For example, in horizontal push exercises the additional synergistic muscles involved compared to chest flyes are only the triceps, but in the latter the biceps are much more recruited, leading to a similar global muscles involvement (8); similar considerations can be made for many other exercises (9). Some single-joint exercises are however “multi-muscular”, since they involve a very large musculature: among them, pullover, hip extension, straight-legged deadlifts or nordic hamstring curl. So it is not always true that single-joint exercises involve few muscles (3).

3. Greater anabolic hormones response: the hormone hypothesis

A well-known notion is that the more muscles are involved, the greater the acute increase of anabolic hormones such as testosterone and GH (10). This is often cited as one of the basic theoretical notions to support the alleged superiority of multi-joint exercises for hypertrophy (3). In the past, it was believed that these short-term hormonal increases would determine the magnitude of hypertrophic response, even affecting the muscles not involved in training, a theory called hormone hypothesis (11).

In recent research, however, the hormone hypothesis has been challenged, and many current scientists’ positions suggest that the acute increase in anabolic hormones does not have a significant impact on muscle growth (11,12,13). So, although it may be true that a multi-joint exercise produces a higher hormonal response, this would not be the mechanism that makes it more effective for muscle growth.

Furthermore, in many cases the differences in the hormonal response may not be significant, because both the multi-joint and single-joint exercise often involve pretty much the same amount of muscles; just look at the examples mentioned above (9). What would determine the greater hormonal response would not be the multiple joints rotated per se, but at most “multi-muscularity”, also a feature of several single-joint exercises.

Finally, in practice this idea would have even less applicability, since a typical hypertrophy workout includes various exercises involving more or less muscles: it will not be replace some multi-joint with single-joint exercise that reduce the hormonal response in a workout based on many exercises and many sets. Furthermore, even if these responses were relevant, there are still other more important local mechanisms (11), often optimized with single-joint exercises.

4. Greater strength development

A classic argument supporting the advantage of multi-joint exercises is their superiority in developing strength. In the context of muscle building, the development of strength is a means to applying progressive overload, and therefore increasing various stressors over time such as loads, for the benefit of local hypertrophy.

But progressive overload is also applicable to single-joint exercises, since the same principles are still valid for this category. There is no reason to believe that the increase in loads and strength are not consistent with single-joint exercises. Since strength is specific to the movements, it follows that with training it will also improve with single-joint exercises.

But the further objection is that single-joint exercises are inconsistent with high intensities of load (<8 RM), and therefore with the development of maximum strength. While it is true, it is not intended to mean that multi-joint exercises cannot be used when it is required to develop this quality. Rather, the argument is that the progressive increase in strength also develops with single-joint exercises using only loads in the moderate range (8-12 RM), which is certainly not less effective than the high range (<8 RM) to optimize hypertrophy (14).

Another aspect is that the inconsistency between high intensities of load (<8 RM) and single-joint exercises is true in principle; but some single-joint exercises, especially if performed by advanced athletes, can also be performed at high intensity of load (15), and thus develop strength. But to prevent possible misunderstandings, it is not even intended that single-joint exercises can be used as an alternative to develop maximum strength in a general sense.

5. Greater load and mechanical tension

A topic closely related to the previous one is the difference in load capacity between single-joint and multi-joint exercises. As is known, the former require the use of often even much lower external loads than the latter. This happens for a number of reasons, including mainly the changes in the levers and/or the involvement of more or less muscles.

Given these features, a spontaneous association is always made between higher loads and a presumed greater mechanical tension, and therefore more hypertrophy (2). This reasoning, however, does not take into account that the external load is not at all an indicator of the internal load on the muscle (in this case represented by local mechanical tension). That is, using a higher external load thanks to multiple joints involved, requires that the greater force expressed is favored by a distribution of the tension on more muscles involved and/or by a reduction of the lever arms.

Since multi-joint exercises are practically the only ones consistent with high intensities of load (<8 RM), it follows that they are better for generating mechanical tension since this mechanism depends on the load. Actually, there is little clarity about the causes of mechanical tension, since it appears to depends not only on the intensity of load, but also on intensity of effort or relative time-under-tension (the latter is generally a consequence of the former) (16.17). For example, a moderate intensity of load (8-12 RM) to failure can generate more local mechanical tension than a high load (5-6 RM) with 3-5 repetitions in reserve (RIR). 

In other words, for the same intensity of load and effort, a multi-joint exercise would not increase the local mechanical tension on the target muscle, but rather, it would redistributes it on the additional muscles involved. According to this contention, if the intensity of effort is maximal (muscular failure) or matched, the mechanical tension on the prime mover muscle will be similar with both a high (5-6 RM), moderate (8-12 RM) or low load (15-20 RM) (18). In addition, with certain single-joint exercises a muscle can be overloaded more with much less weight (2), invalidating the idea that greater external load is an indicator of greater local mechanical tension.

6. Greater time-efficiency

A typical proposed advantage of multi-joint exercises is the so-called time-efficiency, i.e. the ability to get a complete muscle stimulation in less time, since more muscles are involved in one exercise (1,2).

As seen above, the additional muscles involved in multi-joint exercises often do indirect work, which is often (but not always) not strictly optimal (5). This implies that if the interest is to maximize the hypertrophy of a muscle involved as a synergist in a multi-joint exercise, the addition of single-joint exercises that involve it as a prime mover (direct work) is often required.

The comparison between single- and multi-joint exercises for hypertrophy concerns the efficiency in producing this adaptation at the local level, not the efficiency to get a general stimulus in less time regardless of its quality. The priority of a bodybuilder is not to do the work in less time, but to optimize hypertrophy of a given muscle, even if that takes longer.

The argument about time-efficiency instead assumes that the priority is to select the exercises that allow to stimulate more muscles in less time; while being true, this often leads to sacrifice the quality of local work on at least some of the muscles involved. Another aspect taken for granted by this reasoning is, in fact, that indirect work would have the same quality of direct work, but this is generally not the case (2,5,7).

For a bodybuilder, who is interested in optimizing local hypertrophy, the choice of a multi-joint exercise regardless could even worsen time-efficiency, because the lower quality of the indirect stimulus should be compensated by adding more specific/direct exercises (2) (also because the indirect/suboptimal work would often not be counted as an actual complete set).

Hasty generalization

From the arguments above, can be concluded that the inherent efficiency of an exercise to develop hypertrophy should not be assessed on the basis of the number of involved joints, but on the basis of an accurate case-by-case assessment. Critics of single-joint exercises instead tend to commit the hasty generalization fallacy, not assessing their suitability on the basis of the context, but on the basis of a mere belonging to the category.

Contextualizing, it can be realized that many times a single-joint exercise can be more efficient than a multi-joint exercise, in other cases it can be the opposite, while in others, the efficiency can be similar. But in spite of what is believed, the first case among those described is very common.

In many cases, the indirect work done by the synergistic muscles in a multi-joint exercise imply a suboptimal length-tension relationship (LTR); in other cases the segment moved by a synergistic muscle does not oppose to a significant resistance; in others, the weak muscle in the chain during the lift determines form failure before the target muscle reaches optimal stress/tension thresholds. The common denominator is that, for various reasons, the local mechanical tension on the target prime mover is not optimal.

What does the research shows?

In research there are some research teams highly critical about the inclusion of single-joint exercises (1), while others express more balanced opinions, recognizing the potential merits of this category (4,5).

To demonstrate the presumed dispensability of single-joint exercises for hypertrophy, detractors have conducted a long series of studies comparing the performance of only multi-joint exercises, or their combination with single-joint exercises (1,4,5,18). The few studies in this series where the volume was matched, showed no significant advantages by adding a single-joint exercise (direct work) (19). Depending on the point of view, that can be interpreted as an advantage or in contrast, a disadvantage.

Beyond the important limitations reported by other authors (4,5,19,20), these studies did not compare the “absolute” hypertrophic potential between single- vs multi-joint exercises, but only between indirect work (multi-joint), and the combination of indirect and direct work (multi-joint plus single-joint exercise). The real purpose of these studies was more correctly to figure out if only indirect multi-joint work was enough to optimize the hypertrophy of some synergistic muscles using some exercises.

That is very different from the absolute comparison between single- and multi-joint exercises where the muscle always acts as a prime mover. Simply put, to provide an absolute answer it is not ideal to compare the biceps hypertrophy between row vs curl (i.e. between indirect vs direct work), but it would be ideal to compare the pectoralis major hypertrophy between bench press and chest flyes (direct work in both cases). This is because indirect/synergistic work is a confounding variable with respect to multi-joint movement per se, which should be assessed when the muscle is a prime mover in both cases.

Unfortunately, only one study among the many published to date has attempted to establish the inherent hypertrophic potential between single-joint and multi-joint exercises, that is the Paoli study (21).

The Paoli study (21)

The Paoli study is the only one published with a more appropriate study design to compare the hypertrophic potential of single-joint vs multi-joint exercises. Two groups of 18 amateur (non-resistance trained) soccer players performed two different split routines for 8 weeks: one performed only single-joint exercises and the other only multi-joint exercises. Both stimulated all the major muscle groups.

After the study period, a similar increase in lean body mass (FFM) was observed, leading scientists to conclude that multi-joint exercises do not have benefits for this purpose. A closer look at the data reveals that the multi-joint group had a slight advantage in the FFM increase, which is however considered not significant.

One of the problems was the lack of direct muscle measurements given the use of DXA: therefore, the single muscle groups hypertrophy was not examined. Furthermore, multi-joint exercises involved other additional muscles that were excluded or just less involved in the single-joint group (arms, glutes, spinal erectors), likely explaining the minimal advantages observed in the first group (19).

Finally, the multi-joint group was still forced to use only indirect work for some muscles such as those of the arms (push and pull) and the hamstrings (deadlifts), without considering the disparity between rest periods, intensity of load and, for some muscles, also of muscle-specific volume (due to indirect work, which penalized some limb muscles).

So, although the idea of ​​comparing only single-joint and only multi-joint exercises is the only way to study the inherent hypertrophic potential of the two exercise types, this study did not exclude many confounding factors that influenced the results, and did not directly measured local hypertrophy, not allowing to extrapolate a clear answer.

The ideal comparison

To compare the hypertrophic potential between a single-joint and a multi-joint exercise, the standardization of many variables is needed. Perfect standardization should include exercises of similar biomechanics, with the result of excluding or minimizing many confounding factors. 

The variables to match should be range of motion (ROM), joint angles, anatomical plane, strength/resistance curve, degree of stability, length-tension relationship and certainly the function: prime mover and not synergistic or stabilizer. This without considering all the of the basic training variables, such as intensity of load (RM), intensity of effort (muscle failure/RIR), volume, frequency etc.

If all these variables are not standardized, it is not possible to establish the inherent hypertrophic potential of a single- or multi-joint exercise for a prime mover muscle through direct work.

Here are some ideal examples:

• Pectoralis major: dumbbell bench press vs dumbbell chest flyes;
• Quadriceps: roman chair squat vs leg extension;
• Front deltoid: dumbbell military press vs dumbbell reverse lateral raises;
• Lateral deltoid: upright rows (to chest) vs dumbbell lateral raises;
• Posterior deltoid/medial trapezius: wide grip dumbbell row vs dumbbell reverse flyes;
• Pectoralis major/triceps long head: PJR pullover vs. straight arms pullover;
• Latissimus dorsi: narrow grip lat pull-down vs pullover machine;
• Triceps: barbell JM press vs bar push down (prone grip);
• Biceps: barbell multi-joint curl (shoulder flexion) vs arm blaster barbell curl (locked shoulder);

Looking at these examples, many will likely conclude that would not be significant difference in the hypertrophic potential of the prime mover muscle between the multi-joint and the single-joint exercise, precisely because in both cases all the variables that affect local work and mechanical tension are practically matched (except few exceptions), including direct work. In other words, mobilizing more than one joint in one movement per se likely does not make an exercise more effective for hypertrophy of a muscle when it is still a prime mover.

Conclusions

Although direct scientific evidence is lacking to date, a extrapolable conclusion from the arguments above is that hypertrophy is, above all, the consequence of a local mechanical load of a given magnitude, regardless of whether this is achieved with a movement that rotate one or more joints.

To try to convey these concepts, many authors use expressions such as: the target muscle “does not know” if the resistance is given by a single- or multi-joint movement, as well as “does not know” if it is contracting isolated or together with additional muscles.

Key points:

• The greater central nervous system activation and the greater motor control do not determine the local muscle activation and mechanical tension;
• The involvement of more muscles in multi-joint exercises does not determines local muscle activation and mechanical tension;
• The possible greater anabolic hormone response induced by the multiple muscles involved does not seem to be a significantly determining factor in muscle hypertrophy;
• Strength is specific to the exercise, and therefore it also improves in response to single-joint exercises;
• The greater load that can be lifted with multi-joint exercises is not proportional to local muscle activation and mechanical tension, and in some cases the opposite is true;
• The priority of a bodybuilder is not to train more muscles in less time, but is to optimize the hypertrophy of the target muscles, justifying the choice of single-joint exercises;
• There is no evidence that a muscle undergoes greater hypertrophy with a multi-joint exercise than a single-joint one, especially if in both cases it acts as an agonist;

Resistance exercise, from isolation exercises to integrated, multi-joint exercises, should not be looked at as mutually exclusive. Rather, they should be viewed as complementary training components, because each type of resistance exercise offers unique benefits the other types may lack.  (Tumminello & Vigotsky, NSCA PTQ 2018) (22)

All roads lead to tension.  It’s just a matter of how you get there. (Lyle McDonald) (23)

Riferimenti:

1. Gentil P et al. A review of the acute effects and long-term adaptations of single- and multi-joint exercises during resistance training. Sports Med. 2017 May;47(5):843-855.
2. Brignole D. The Physics of Fitness: The Analysis and Application of Biomechanical Principles in Resistance Exercise. Ogman Publishing. 2016.
3. Aragon AA. Compound versus isolation exercises: Bret Contreras weighs in on the surrounding issues. AARR. 2014 Sep.
4. Ribeiro AS et al. Comment on: “A review of the acute effects and long-term adaptations of single- and multi-joint exercises during resistance training”. Sports Med. 2016 Dec 19;47(4):1-3.
5. Schoenfeld BJ et al. Calculating set-volume for the limb muscles with the performance of multi-joint exercises: implications for resistance training prescription. Sports (Basel). 2019 Jul 22;7(7). pii: E177.
6. Israetel M, Hoffmann J, Wesley C. Scientific Principles of Hypertrophy Training. e-book, 2020.
7. Schoenfeld BJ, Contreras BM. Do single-joint exercises enhance functional fitness? Strength Cond J. 2012;34(1), 63-65.
8. In the chest flyes, the biceps brachii is fixed at the radial insertion thanks to the the locked elbow, allowing it to better perform its secondary function of horizontal shoulder flexor (especially the short head). The triceps instead becomes a weaker stabilizer especially in the final parts of the concentric phase.
9. Another example is the comparison between straight-arms single-joint pullover and the PJR pullover (multi-joint): in both cases the same musculature is involved, but in the first case the single-joint heads of the triceps work isometrically, in the second case dynamically. Other examples are the comparison between nordic hamstring (single-joint) and glute-ham raise (usually multi-joint); between a pulley row and a straight-arm pull-down (although the latter is more unstable); between a reverse lateral raise and a dumbbell military press.
10. Kraemer WJ, Ratamess NA. Hormonal responses and adaptations to resistance exercise and training. Sports Med. 2005;35(4):339-61.
11. Schoenfeld BJ. Postexercise hypertrophic adaptations: a reexamination of the hormone hypothesis and its applicability to resistance training program design. J Strength Cond Res. 2013 Jun;27(6):1720-30.
12. Schroeder ET et al. Are acute post-resistance exercise increases in testosterone, growth hormone, and IGF-1 necessary to stimulate skeletal muscle anabolism and hypertrophy? Med Sci Sports Exerc. 2013 Nov;45(11):2044-51.
13. Slater GJ et al. Is an energy surplus required to maximize skeletal muscle hypertrophy associated with resistance training. Front Nutr. 2019 Aug 20;6:131.
14. Schoenfeld BJ et al. Strength and hypertrophy adaptations between low- versus high-load resistance training: A systematic review and meta-analysis. J Strength Cond Res. 2017 Dec;31(12):3508-3523.
15. Biceps curl, push down, calf raise, pullover, leg curl. nordic hamstring, leg extension, pullover, hip thrust are examples of exercises that an advanced athlete can realistically perform even at 5-7 RM. That depends on the joint health, as well as on the conditioning and adaptation of passive structures in general.
16. Schoenfeld BJ et al. Effect of repetition duration during resistance training on muscle hypertrophy: a systematic and meta-analysis. Sports Med. 2015 Apr;45(4):577-85.  
17. Burd NA et al. Bigger weights may not beget bigger muscles: evidence from acute muscle protein synthetic responses after resistance exercise. Appl Physiol Nutr Metab. 2012 Jun;37(3):551-4.
18. This is actually a very general concept, but it is possible that, for the same intensity of effort, a multi-joint exercise causes less local stress on the agonist muscle, due to the premature failure of a synergistic muscle.
19. Krieger JW. Do isolation movements improve hypertrophy over compound movements? An evidence-based guide and meta-analysis. weightology.net. 2019.
20. The hypertrophy measurements were inaccurate or were taken on individual muscle sites; the comparison was never done between exercises where the target muscle acted as an agonist in both cases; in many of these the volume was not matched; when the volume was matched, direct work was not matched; only some multi-joint exercises and only some muscles were considered, with the inability to generalize the conclusions; the studies were conducted by the same research team, with the risk of bias and the need of replications by other teams with other research designs.
21. Paoli A et al. Resistance training with single vs. multi-joint exercises at equal total load volume: effects on body composition, cardiorespiratory fitness, and muscle strength. Front Physiol. 2017 Dec 22;8:1105. 
22. Tumminello N, Vigotsky A. Are the seated leg extension, leg curl, and adduction machine exercises non-functional or risky? NSCA PTQ. 2017;4.4:50-53.
23. McDonald L. Muscular Tension Part 2. bodyrecomposition.com, July 17, 2019.