In strength & conditioning, it is common to see polarized opinions on the topic of unilateral training. Unilateral training is essentially exercises which use, at least predominantly, one limb for most of the force production. This can include single limb movements, split stance movements, or other variations which bias the loading toward one leg or one arm.
One one hand, most sporting movements are unilateral in nature, which would make it logical to assume that unilateral training can be good for athletes. In contrast, many coaches claim that due to the unstable nature of unilateral exercises, force production in unilateral training is low and therefore not useful for developing the explosive strength and power that athletes need.
In this article we will go over a meta analysis which looked at the influence of unilateral training on athletic performance, discuss some of their conclusions, and give my opinion on the utility of unilateral training in the development of athletic performance.
What This Article Will Cover
- Meta-Analysis On Bilateral And Unilateral Training
- Training Effects On Maximal Force, Jumping and Sprinting
- General Considerations For Using Unilateral Training
- Workout Examples Incorporating Unilateral And Bilateral Exercises
Meta Analysis On Bilateral vs Unilateral Exercises
Researchers from the Guangzhou Sport University in Guangzhou, China set out to assess the effects of unilateral and bilateral exercises on different aspects of athletic performance, including jumping ability, sprinting ability, force production, change of direction ability, and balance ability.
After a thorough search, 28 exercise science studies consisting of 651 athletes who trained two to three times per week for six to twelve weeks we included in the analysis.
Exercises used in the studies included resistance training, plyometric training, complex training, and eccentric overload training interventions.
Next, we will look at some of the conclusions the authors came to with regard to training for maximal force production, jumping ability, and sprinting ability.
Training For Maximal Force
In sports, maximal voluntary force production underlies all other force development related qualities. One's ability to produce power, exhibit a high rate of force development, and to move with explosive strength is all limited in large part by their maximal force capabilities. As such, training interventions which increase maximal strength are important.
In reviewing the previous research, authors in this meta-analysis found the following:
- Unilateral training recruits large and small, deep and superficial muscle groups.
- Unilateral training can stimulate the nervous system and recruit fast twitch muscle fibers.
- Unilateral training can improve muscle imbalances between left and right limbs, contributing to a reduction in sports related injuries.
Some evidence suggests that there may be a greater utilization of fast-twitch muscle fibers when performing unilateral training. For example, one study found that there was a greater resistance to fatigue when performing bilateral leg extensions, which was likely due to a greater utilization of easily fatigable fast-twitch fibers in the unilateral exercises compared to the bilateral exercises (Vandervoort et al., 1984).
The meta analysis stated:
“...there is a limitation of muscle neural activity in bilateral training that affects the maximization of muscle activation and the generation of maximal force.”
With this in mind, athletes looking to increase maximum force production can benefit from unilateral strength exercises, particularly if they seek to improve muscle imbalances, recruit fast-twitch motor units, achieve high levels of muscle activation with less absolute load, or who want to improve force production in more sport specific positions and movement patterns.
Jumping Performance
Jumping performance is relevant for sports performance in both a direct and indirect manner. Some sports rely on jumping as an integral aspect of performance, while other sports benefit from the training effects of jump training.
In this meta-analysis, researchers looked at the effects of unilateral resistance training programs on jumping performance and concluded the following:
- Unilateral and bilateral training elicit greater improvements in unilateral and bilateral jumping abilities, respectively.
- Unilateral training can improve neuronal activity in the untrained limb, due to the cross-education effect of unilateral training.
Both bilateral and unilateral exercises can improve the performance of movements through the stimulation of the neuromuscular system, such as:
- Increasing the number of motor units recruited.
- Increasing the release frequency of nerve impulses.
- Improving coordination.
Athletes who want to improve single leg jumping performance should incorporate single leg strength training exercises and single leg jumping activities in their training programs. Athletes who are injured on one side of the body can train the uninjured side, and still see positive training adaptations to the untrained limbs thanks to the cross-over effect of unilateral exercise.
Sprint Performance
Sprinting is another key aspect of athleticism that is fundamental to sports performance in a variety of sporting disciplines. Researchers in this meta-analysis assessed the research on the training effects of unilateral movements and bilateral movements on sprinting performance.
Based on the available evidence, researchers suggested that unilateral training is more likely to improve an athlete's straight line sprinting ability, due to the unilateral nature of sprinting being more biomechanically similar to unilateral training.
- Unilateral strength training can improve strength in both large and small, superficial and deep muscles of the body, as a result of the nervous system’s stimulation of a wide range of muscles during unilateral training.
- Unilateral training can improve the ability control pelvic and postural muscles, enhancing ones ability to balance properly throughout the stride cycle, also aiding in injury prevention.
It is suggested that athletes use plyometric training and complex training to enhance ground reaction forces and improve running economy.
Athletes who want to sprint faster can perform complexes consisting of unilateral exercises for strength, plyometrics and jumping exercises, and explosive strength training movements to facilitate the development of higher force production, motor unit recruitment, and to reduce limb-to-limb asymmetries.
General Considerations For Training
With all this said, we can confidently say that bilateral and unilateral exercises have a place in one's training program.
With regard to the use of unilateral exercises in training, athletes should consider the movement patterns exhibited in their sport, and come up with ways to strengthen the body to better handle these movements and positions through the use of unilateral exercise.
Because of the less stable nature of unilateral exercises, exercises must be performed with technical proficiency and used as a supplement to traditional bilateral training. Since lower absolute loads are used in unilateral training, athletes will incur a lower total stress load and be at less risk of significant injury when using unilateral exercises.
Transfer Of Performance
Because unilateral explosive strength exercises require more efficient neuromuscular control to maintain stability, unilateral training transfers better to unilateral explosive strength expression than bilateral strength training.
When we sprint, change direction, or jump off of one leg, we need not only the strength and power to exhibit explosive movements, but also the balance, coordination, and control do do these movements with skill and grace.
If you want to see your strength training transfer to something like sprinting, it would be wise to include exercises in your training program such as:
- Bulgarian split squats
- Single leg squats
- Single leg deadlifts
- Single leg box jumps
- Single leg long jumps
- Step ups
- Forward and reverse lunges
- Single leg leg press
Chronic Overuse Considerations
One thing to consider with unilateral exercises is that you want to make sure you do not perpetuate any chronic overuse injuries that may result from repeatedly doing similar movements at too high of loads. For example, if you perform a huge volume of sprints at the track and then go perform heavy split squats, the potential for irritating your groin may be high.
To avoid this, progress loads gradually when integrating unilateral exercises, and substitute bilateral exercises in when you feel your body is too sore in split leg positions to perform something like a split squat. Over time, you will get stronger at these exercises, become used to them, and should be able to perform them regularly without issue.
The most important thing is to gradually integrate more unilateral exercises and higher external loading in your training, so that you do not shock your body or drastically increase the training load on tissues which are highly utilized by sprinting.
Start with adding one or two single leg or split leg exercises into your program, and build from there.
Muscle Recruitment By Exercise Type
Generally speaking, bilateral training will activate large prime mover muscles to a larger degree, while unilateral exercises will activate stabilizing muscles more than a bilateral movement.
According to the research, unilateral plyometric training generates higher activation of vastus medialis, gastrocnemius, and soleus muscle during multi-joint movements.
Unilateral resistance training exhibits higher activation of external obliques, gluteus medius, and hamstrings, but less activation of the rectus femoris, gluteus maximus, and erector spinae.
This suggests that unilateral training challenges stabilizers and synergists more so than prime movers, which I see as a reason to include both forms of training in our training programs.
We need both the prime movers and the stabilizing muscles to be well trained if we want to sprint fast and jump well. Combining both bilateral and unilateral exercises into the same workout or week of training allows us to properly stimulate the tissues needed for performance, while also giving the body variety in movement pattern selection.
Example Workouts
To give you some idea of how you can train, here are some workouts that target the upper body and lower body muscles with strength and power training to improve athletic performance. You can get workouts like this by joining my online training group.
Workout 1
- 1 - Power Cleans - 4x3 up to 65%
- 2a - Bulgarian Split Squat (Single Leg Squat) - 5x3 per side up to 80%
- 2b - Single Leg Box Jump - 4x3 paired with the last 4 sets of split squats.
- 3 - Single Leg RDL - 4x6 with a light to moderate load.
- 4a - Single Arm DB Bench Press - 4x6 up to 70%
- 4b - Chin Ups - 4x8
Workout 2
- 1 - Prowler Sled Push - 6x10 yards with a 25% velocity decrement.
- 2a - Single Leg Deadlift - 5x3 up to 82%
- 2b - Single Leg Hinge Jump To Box - 4x3 paired with last 4 sets of deadlifts.
- 3 - Front Squat To Box - 5x3 up to 83%
- 4 - Single Arm Kettlebell Overhead Press - 4x8
References
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Zhang W, Chen X, Xu K, Xie H, Li D, Ding S, Sun J. Effect of unilateral training and bilateral training on physical performance: A meta-analysis. Front Physiol. 2023 Apr 13;14:1128250. doi: 10.3389/fphys.2023.1128250. PMID: 37123275; PMCID: PMC10133687.
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Vandervoort AA, Sale DG, Moroz J. Comparison of motor unit activation during unilateral and bilateral leg extension. J Appl Physiol Respir Environ Exerc Physiol. 1984 Jan;56(1):46-51. doi: 10.1152/jappl.1984.56.1.46. PMID: 6693334.