You can group most strength training exercises into two categories: bilateral and unilateral exercises.
Some people claim bilateral exercises are superior, whereas others claim that unilateral exercises are better for improving your health and fitness.
For example, many people think that if you want to get as strong as possible, you should focus on bilateral exercises. That’s because they allow you to lift the most weight possible, so they’re best-suited to helping you gain strength.
On the other hand, if you want to perform better on the field, track, or court, many would say you should focus on unilateral exercises. This is because unilateral exercises train your muscles in ways that more closely resemble the types of movements performed during sports, making them more likely to boost your athletic performance.
Are these ideas correct, though, or is there more to the unilateral vs. bilateral exercise debate than most realize?
In this article, you’ll learn the difference between bi- and unilateral exercises, the benefits of each, how to include them in your program, and more.
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If you perform a lot of bilateral barbell exercises, it’s common for your dominant side to “take over” or “pick up slack” from your non-dominant side. Over time, this can lead to an imbalance, where your dominant side becomes bigger and stronger than your non-dominant side.
During a unilateral exercise, both sides of your body must lift the same weight independently, which helps you identify and even out any size and strength imbalances you might have.
One of the best ways to optimize the muscle-building effects of strength training is to lift heavy weights. And while bilateral exercises allow you to lift more weight per set, unilateral exercises may allow you to lift more weight overall. This is because of something scientists call the bilateral deficit.
The bilateral deficit is the inability of your brain to instruct your muscles to generate maximal force when both sides of your body work simultaneously compared to the force they generate when each side works separately.
For example, let’s say you do a one-rep max biceps curl test with each of your arms separately. You curl 45 lb with your right arm and 40 lb with your left. Theoretically, if you add these two numbers, you should get your barbell curl one-rep max (95 lb).
However, because of the bilateral deficit, it’s highly likely that your barbell biceps curl one-rep max will be slightly lower—maybe 80 or 85 lb.
Therefore, when you do a unilateral exercise, you can lift a little more total weight than you can with a similar bilateral exercise, which is generally better for muscle and strength gain.
When you train unilaterally, less of your body is involved in the exercise. Having fewer moving parts to focus on allows you to develop a greater mind-muscle connection with the muscles you’re trying to train, which may aid muscle growth in some scenarios.
Some coaches gush about the benefits of unilateral exercises for sports performance, claiming that there’s no reason to train bilaterally if you’re an athlete.
For example, in a meta-analysis conducted by scientists at the Shanghai University of Sport, researchers found that unilateral exercises are slightly better than bilateral exercises for improving unilateral and bilateral jumping, agility, and speed.
Thus, if you play a sport that requires power, agility, and speed (most sports, basically), it’s smart to include unilateral exercises in your program.
Unilateral exercises help you maintain or gain strength in an injured arm or leg thanks to the cross-education phenomenon, a bizarre neurophysiological process where an increase in strength in one limb helps to increase the strength of the other, even when you don’t train it.
For example, if your left biceps is injured, training your right biceps should help maintain or increase strength in the left arm without training it directly.
In one study, participants who only trained one arm increased their biceps curl one-rep max by 9% in the arm they trained and 7% in the arm they didn’t. In other words, by training their right arm, their left arm became 80% as strong, despite not doing any work.
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One of the best ways to get stronger is to train with heavy weights.
Bilateral exercises are better suited to training with heavy weights than unilateral exercises because they allow you to use both hands or legs to push, pull, and squat the weight.
The exercises that allow you to handle the heaviest weights, such as the squat, deadlift, and bench and overhead press, are also easier to perform bilaterally. You can perform unilateral variations of these exercises, but they’re unwieldy and awkward, especially when the weights get heavy.
Because you use both hands or feet when you train bilaterally, you tend to have more control over the exercise than when you train unilaterally, making bilateral exercises safer.
What’s more, bilateral exercises often involve a rack. Using a rack allows you to get into a safe and efficient position before bearing any weight, which isn’t always possible when you do unilateral exercises.
As we’ve already seen, unilateral exercises effectively boost athletic performance.
That doesn’t mean bilateral exercises don’t, though.
Bilateral exercises are inherently more stable than unilateral exercises because they allow you to distribute weight evenly over both sides of your body. As such, they require less coordination and balance and thus tend to be easier to learn and perform, especially if you’re new to weightlifting.
Bilateral exercises allow you to train both sides of your body simultaneously, significantly shortening the time you spend training. It’s no wonder, then, that researchers investigating the most time-efficient way to train recommend emphasizing bilateral exercises over unilateral exercise in your program.
Neither is better or worse than the other. Both have slightly different benefits, so use whichever suits your circumstances and goals.
For instance, if you’re training to become as strong as possible (to compete in powerlifting, for example), emphasizing bilateral exercises makes most sense since these exercises allow you to lift the most weight.
Likewise, if you’re new to weightlifting and want to smooth out your learning curve while staying safe, or you have little time to train and want to get in and out of the gym double-quick, using bilateral exercises for the majority of your training is probably the best option.
If, on the other hand, you’re training around an injury, keen to correct muscle or strength imbalances you have, or struggling to feel your target muscles working during an exercise, it’s prudent to prioritize unilateral exercises.
As for which is best for boosting athletic performance, it’s basically a toss-up.
Of course, there’s no reason to choose just one. The best solution for most people—strength athletes and sportspeople included—is to do both types of exercise in your program.
A good way to do this is to make your main strength-building exercises (typically the exercises you perform first in each workout) bilateral and the remainder of your program a mixture of uni- and bilateral exercises.
Here’s an example of how this might look for a leg workout:
- Back Squat: 3 sets of 4-to-6 reps with 2-to-3 min rest
- Romanian Deadlift: 3 sets of 4-to-6 reps with 2-to-3 min rest
- Lunge: 3 sets of 6-to-8 reps with 2-to-3 min rest
- Leg Curl: 3 sets of 6-to-8 reps with 2-to-3 min rest
(Note: For the leg curl, you could train both legs simultaneously or each unilaterally.)
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Many people think that unilateral exercises are superior to bilateral exercises for training your core because they’re inherently less stable, which means your abs have to work harder to stabilize your torso.
While some research suggests this is true, other studies show that your abs are highly engaged during bilateral exercises, making it difficult to know whether the slightly higher ab activation in unilateral exercises will have any meaningful effect on long-term muscle growth.
It’s hard to say which unilateral exercises are “best,” but here are my favorites . . .
Unilateral chest exercises:
- Single-Arm Dumbbell Bench Press
- Single-Arm Incline Dumbbell Bench Press
- One-arm Push-up
Unilateral back exercises:
- One-arm dumbbell row
- Meadow’s Row
- Single-Arm Lat Pulldown
Unilateral shoulder exercises:
- Single-Arm Overhead Press
- Single-Arm Arnold Press
- Cable Side Lateral Raise
Unilateral leg exercises:
- Bulgarian Split Squat
- Single-Leg Romanian Deadlift
Unilateral arm exercises:
- Single-Arm Triceps Pushdown
- Single-Arm Overhead Triceps Extension
- Alternating Dumbbell Curl
- Incline Alternating Dumbbell Curl
Most people will benefit from doing at least one unilateral exercise for each major muscle group. Typically, I recommend using a bilateral exercise for your first exercise in each workout to build strength, then doing a mixture of bi- and unilateral exercises for the reminder of the workout.
For example, here’s how this might look for a back workout:
- Deadlift: 3 sets of 4-to-6 reps with 2-to-3 min rest
- Pull-up: 3 sets of 4-to-6 reps with 2-to-3 min rest
- One-arm Dumbbell Row: 3 sets of 6-to-8 reps with 2-to-3 min rest
- Alternating Biceps Curl: 3 sets of 6-to-8 reps with 2-to-3 min rest
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