Heather Marr is an NYC-based personal trainer and The Model Trainer Method creator, whose A-list client roster includes some of the world’s most famous supermodels. Ahead, she reveals the difference between unilateral and bilateral exercises.
What's the Difference between Unilateral & Bilateral Exercises?
Unilateral exercises use one arm or one leg to perform the move. Exercises include the Bulgarian split squat, one-arm dumbbell row and a one-arm dumbbell press. The limb is working independently. Bilateral exercises require you to use both arms or both legs to perform the move. Exercises include the barbell squat, barbell row and the bench press. The limbs are working in unison. Both types of exercises provide a host of benefits and may be used in a variety of training programs.
Most people are not perfectly symmetrical. Implementing unilateral training into programming can, however, narrow the gap. By training each limb separately, you can ensure that they're both getting worked equally and one side is not overcompensating for the other. The more symmetrical our physiques are, the better we look of course, but also the less imbalances we have. This not only reduces our risk of injury but can increase our overall strength as well.
By eliminating or reducing imbalances, we are able to more evenly distribute the workload between limbs when performing a bilateral exercise. Take a back squat for example. Most people are not going to distribute the workload equally between limbs and will have their dominant side handling more of the load. By incorporating exercises like lunges and single-leg pistol squats into programming, you will see an improvement in your patterns in those bilateral moves.
Both types of exercises are excellent for working your core. Unilateral moves are less stable which means that your core stabilizers have their work cut out for them. Try doing a standing one-arm shoulder press and you'll quickly discover that your core is on fire trying to keep you from toppling over. The downside to this, of course is that the loads you're able to lift will not be as heavy. The instability becomes a limiting factor. When performing bilateral exercises, you are able to use maximal loads and exert more force during your lifts, which requires a capable midsection. A perfect example of this is performing a set of heavy conventional deadlifts. By the last rep of any vigorous set, you'll certainly be feeling those abs. For those with certain limitations and medical issues, we see that although the weight used for unilateral moves is less, it may still provide an edge. You’re able to load the target muscles while maintaining a reduced load on the spinal column when necessary.
The bilateral deficit is basically when your expected numbers for maximal force just don't add up. Let's use the single leg Romanian deadlift as an example. Assuming I can lift 75 lbs. per leg, you would think that when performing a Romanian deadlift using both legs, I would be able to load 150 lbs. This is not always the case. When both limbs are working in unison, the load used in the working set may be lower than the combined weights of the limbs working independently. Neural capacity, velocity, joint dysfunction and technique are just some of the factors in play that are still being explored.
Most people would do well to incorporate both types of exercises in their strength and conditioning workouts. Unilateral exercises are not just for rehabilitation and sports-specific training. They complement bilateral exercises and can make for a well-rounded program. The ratio between moves and choices of exercise selection can be specifically geared towards goals.