What is a Unilateral exercise?
Unilateral means “one sided”; an exercise performed on one side of the body, or with one limb. Bilateral means “both sides”; an exercise performed with both sides of the body or with both limbs. For example, A piston would be considered a unilateral exercise, where a squat would be considered a bilateral exercise. Unilateral exercises can be great for many reasons like correcting asymmetries between sides, or increasing metabolic burn during a workout. We will discuss the three major benefits of unilateral exercise, and show you how they compare to bilateral exercise in some cases:
Unilateral exercises have a narrow base of support. This is because they are performed with one limb rather than both. Because of this, they require more neuromuscular input to maintain balanced. These exercise require a faster rate of force production (RFD) from muscles. This means that rate at which the muscles are “turned on” to do their job, can be made quicker by performing unilateral exercise.
One study even cited that rate of force production (RFD) can improve 40-60% in sub-maximal AND maximal loads! Even more fascinating than that, was that the rate of force development improved in the arm being trained (obviously), but also, equal improvements in RFD were found in the un-trained arm. How is that possible you ask? Our neurological system has the ability to send cross-over messages to the same muscle on the other side of the body. So benefits are being made even on the untrained side, when you are doing a one-sided exercise. How great is that?
Now, why not do bilateral exercises and work on both at the same time right? Well, bilateral exercise does improve RFD with increased load. This means the more weight you load the exercise with, the more feedback will get out to your muscles. While bilateral exercise also improves power output, it doesn’t do so to the extent unilateral exercise does, and nor does it lead to cross-over contributions from side to side.
It’s obvious that unilateral exercises will challenge balance more since they have a smaller base of support. Last week’s blog discusses the interaction of the three systems involved in balance: vision, vestibular, proprioception. Last week’s blod explained that when we minimize one of the three systems, we rely more on the other two. Therefore, by narrowing the base of support in these exercises we rely more heavily on vestibular and visual input, and we can train these balance mechanisms.
One article studied visual input on balance comparing bilateral and unilateral exercises. The study showed that closing your eyes in unilateral exercises results in more balance disturbances than bilateral exercises. That is because we are relying more heavily on vision when balancing during unilateral exercises. So, by minimizing two of the systems (vision by closing eyes, and proprioception by small base of support) you are challenging balance much more so than you can with bilateral exercises. Therefore, unilateral exercise is a much better option to challenge, train and improve balance.
3. Increases Muscle Building
Eccentric training is widely considered a great way to build muscle. A muscle functioning eccentrically can resist 15-30% more load. Unilateral exercises are shown to improve power, but also overall strength when used eccentrically. A recent study showed that unilateral eccentric exercise improved muscle strength on trained limb ( and untrained limb!!). The neuromuscular cross-over affect to the other limb influences power output, AND overall strength– WOW! So once again, unilateral exercises are benefitting the un-trained limb without even performing exercise on it. Therefore, you will gain bilateral strength with unilateral exercise.