A 2004 study published in the Journal of Applied Physiology opens with an intriguing story. One day in 1984, a Miss Emily M. Brown squeezed a rubber bulb as strongly as possible with her left hand. She then spent the next thirteen days training her right hand, performing ten maximal contractions each day. When the strength of her left hand was measured again on the thirteenth day, it had increased by 43%. 

 

Seeing as Miss Brown had only trained her right hand, the authors of the report could only conclude that somehow the training of the right hand had created strength gains in the left. 

 

Miss Brown, though she was probably unaware of it at the time, was doing what we now call unilateral training. Training limbs individually, rather than engaging both sides together, is a popular and highly beneficial technique. Unilateral exercises are now widely recognized as an important part of any strength-training routine. Read on to learn why.

 

Breaking Muscle Shop

lunge, lunge exercise

 

Reduce Your Bilateral Deficit

When it comes to strength, the whole is usually less than the sum of its parts. In most cases, the total strength of both of your limbs used together is actually less than the sum of the strength of the individual limbs. 

 

While this seems strange - logic says two working together should be stronger than one - myriad studies have confirmed this phenomenon of “bilateral deficit.” No one knows why this is true. What we do know is that working the individual limbs through unilateral exercise can reduce bilateral deficit .

 

Train Away Imbalances

Everyone has a weak side. In fact, studies have shown that strength differences between limbs can be as high as 25%. Bilateral training allows your dominant side to compensate for your weaker side, hiding imbalances that could later cause injury. 

 

Unilateral exercises allow you to train away these asymmetries. When doing these exercises, start with the weaker side. After working that side to fatigue, do the same number of reps on the stronger side. While you won’t be working to fatigue on the stronger side, you’ll be bringing the weaker side up to meet it, enabling you to strengthen both sides equally as you go forward.

 

"When doing these exercises, start with the weaker side. After working that side to fatigue, do the same number of reps on the stronger side." 

Part of this is thanks to the phenomenon discovered by Miss Emily Brown and her rubber ball. The authors of the 2004 study reached a similar conclusion to the 1984 study, discovering that when one limb is trained unilaterally, the untrained side experiences strength gains amounting to around half of those on the trained side.  Other studies have found strength increases in the untrained limb ranging from 8% to as high as 22%.

 

So even as you strengthen your weaker side, your stronger side benefits. Meaning, you won’t lose out despite the fact you’re not bringing the stronger side to full fatigue. This concept also comes in handy in the event of injury. Even if one side is out of commission, unilaterally training the other can help improve strength in the injured limb. Just don’t overdo it to the point of causing major imbalances.

 

Improve Core Strength and Stability

Unilateral exercises knock you off balance, recruiting the deep stabilizing muscles of the body to engage and pull you back to center. One 2005 study on unstable and unilateral exercises found that:

 

[U]nilateral shoulder press produced greater activation of the back stabilizers, and unilateral chest press resulted in higher activation of all trunk stabilizers, when compared with bilateral presses.

 

The researchers concluded that “trunk strengthening” can be a side benefit of performing exercises unilaterally. Another study on core muscle activity in various types of resistance exercises definitively concluded that for those seeking to strengthen their core, unilateral exercises were superior to bilateral exercises. Developing these core muscles is important for developing balance and stability, protecting your spine, and cultivating integrated, functional strength.

 

trunk, core

 

Build Functional Strength

Our athletic and day-to-day activities rarely require bilateral movement. Kicking a soccer ball is a unilateral movement - balancing on one leg while the other applies force. Carrying a grocery bag is typically a one-handed operation. Even walking and running are, at their core, unilateral movements - one foot and then the other. 

 

In fact, when looking to simulate functional muscle recruitment patterns required for athletics and daily living, professionals often prescribe unilateral exercises. Cultivating unilateral strength translates into our other activities, increasing adaptability and building functional strength. 

 

Ready to Try Unilateral Training?

Try working these unique unilateral bodyweight exercises into your program. Remember: work your weaker side to fatigue, then do the same number of reps on the other side. Repeat for 2-3 sets on each side.

 

Missing Arm Hold

Holding up the weight of your body through one-side of your upper body engages the muscles of the chest, shoulder, and arm in new and dynamic ways. Be sure to keep your body parallel with the floor to engage the core muscles. Your breathing should be steady, slow, and even throughout the exercise. If you’re losing your breath, you’ve gone too far.

 

 

Leaning Tower Push Up

By altering a normal push up by placing one arm on the ground, you’ll shift the focus to the pec, dramatically increasing the difficulty for one pec muscle. Inhale to lower and exhale to push back up.

 

 

One-Legged Squat

Balancing on one leg turns a squat into a killer experiment in stability. You’ll cultivate core strength and balance while totally burning out your legs. Don’t worry about going all the way down at first. Start at halfway and then go lower as you build strength and balance. Inhale to lower and exhale to rise.

 

 

One-Legged Bridge on Sun

Because you have to recruit extra muscle fibers to maintain your position on the stability ball, this exercise creates serious strength through the glutes. As with any balancing exercise, focus is key. Keep the breath steady, even, and calm.

 

 

If you have questions about any of these exercises, please post them to the comments below. Give them a try and let us know how it goes!

 

Check out these related articles:

 

References:

1. Timothy J. Carroll, et. al., "Contralateral effects of unilateral strength training: Evidence and possible mechanisms," Journal of Applied Physiology 101 (2006). Accessed August 8, 2015. doi: 10.1152/japplphysiol.00531.2006.

2. André Luiz S. Teixeira, et. al., "Bilateral Deficit in Maximal Isometric Knee Extension in

Trained Men," Journal of Physiology Online 16 (2013). Accessed August 8, 2015.

3. Cresswel and Ovendal, "Muscle activation and torque development during maximal unilateral and bilateral isokinetic knee extensions," J Sports Med Phys Fitness 41 (2002): 19-25, accessed August 8, 2015.

4. Christianne Pereira Giesbrecht Chaves, et. al., "Bilateral deficit in leg flexion and extension and elbow flexion movements," Revista Brasileira de Medicina do Esporte 10 (2004). Accessed August 8, 2015. doi: 10.1590/S1517-86922004000600007.

5. "Unilateral v. Bilateral Movements," HL Strength (2014). Accessed August 8, 2015.

6. DG Behm, et. al., "Trunk muscle electromyographic activity with unstable and unilateral exercises," Journal of Strength and Conditioning Research 19 (2005). Accessed August 8, 2015.

7. Atle Hole Saeterbakken and Marius Fimland, "Muscle activity of the core during bilateral, unilateral, seated and standing resistance," European Journal of Applied Physiology (2011). Accessed August 8, 2015. doi: 10.1007/s00421-011-2141-7.

 

Photos courtesy of Shutterstock.

Topic: