Are Unilateral Exercises Better Than Bilateral Exercises?

Proper exercise selection is one of the core features of any effective strength training program.

Traditionally, bilateral exercises make up the bulk of most training routines, with lifts such as the squat and bench press taking precedence over unilateral exercises.

These lifts have been a staple of strength-focused programs for decades. When we talk about strength and power, we typically refer to bilateral movements, the ones that use both limbs in unison, as opposed to unilateral exercises which work one limb at a time.

Though the ‘big lifts’ get most of the love, single-limb exercises can often be a superior choice for developing strength, hypertrophy and power while maximizing training longevity. 

In fact, we’re often much stronger unilaterally than we are bilaterally.

As an example, take someone whose 5RM squat is 100kg. You’d expect that, when tested unilaterally, each leg’s 5RM would be 50kg, but that’s not actually the case. What you end up seeing is that each leg can actually produce more than half the force generated bilaterally. In our example, that could mean a split-squat of 60, 70 or even 80kg!

This phenomenom is known as the bilateral force deficit (BLD), and it is perceived to be a neural discrepancy in maximal force output between unilateral and bilateral movement.

The deficit refers to the difference between the sum of maximal strength in each limb (for example, the sum of the strength in each leg during a split-squat, 70kg + 70kg = 140kg) and the maximal force output in a bilateral exercise (100kg).

When the bilateral deficit is present, each limb contributes to more than 50% of the force production seen in a bilateral movement.

How can this be? Though the explanation for the bilateral deficit remains largely unknown, researchers have theorized that neural drive differences in unilateral versus bilateral movement may be at play. Others have proposed that differences in the force-velocity relationships of single-limb and double-limb lifts may contribute to a discrepancy in force production outcomes. There have also been references to postural and muscular imbalances, poor technique, among other kinematic factors.

The truth is, we don’t really know why the deficit exists, we just know that it does.

What does this mean to athletic performance? Could it be that we are limiting our strength gains by relying mostly on bilateral movements?

As is always the case, the answer heavily depends on context. For the athletic population, unilateral training offers a range of benefits that often can’t be matched by bilateral movements.

For starters, unilateral exercises more closely mimic sport-specific movements, which can translate into better on-field performance.

But it doesn’t just end there. Here are a few more reasons why every strength enthusiast should consider focusing on single-limb training:

 – Unilateral training gets the job done, and more. By effectively recruiting the target muscles (ex: quads) and increasing recruitment of stabilizing muscles (the lateral and medial hip musculature in a single-leg squat), we can train more muscles at once.

– Increased need for core strength, stability and balance, often due to a smaller base of support (ex: one foot on the floor vs. two).

– Immediate feedback with regards to limb symmetry (or lack thereof), which can be helpful in injury-prevention.

– Single-limb exercises require less external load compared to their bilateral counterpart.

– Unilateral training is a great way of overloading target muscles without taxing other areas of the body. For example, single-leg exercises may be an efficient way to gain or maintain strength and muscle mass while decreasing spinal loading in the presence of low-back injuries.

So, should you ditch the back squat and focus on split-squats instead? Not necessarily, but if your goal is to attain maximal strength while steering clear of injuries, it may be worth reevaluating your exercise selection to include more single-limb training where appropriate.

To your strength,

Barbara M.

 

References

Mullican, K., & Nijem, R. (2016). Are Unilateral Exercises More Effective Than Bilateral Exercises? Strength and Conditioning Journal, 38(1), 68-70.

 

About The Author

Barbara M.

Since 2013, Barbara has been helping women of all fitness backgrounds get stronger, leaner and more confident, both inside and outside the gym.

Her passion lies in educating, empowering and encouraging women to find out what they’re capable of, and more.

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