When performing unilateral exercises your body weight plays a much greater role in the level of resistance. For example, try comparing an unweighted two legged squat with that of a pistol squat. The pistol squat it is significantly harder because of the way your loss of balance forces you to work extra hard to complete the movement.
The benefit to your vertical jump of performing an exercise such as the pistol squat is that it is a more functional way to train.
Increased Development of Functional Strength
Double leg training doesn’t necessarily translate into unilateral strength. For example there would be many athletes that can squat 2.0x or more their own body weight for reps but struggle to perform even one deep pistol squat.
Obviously if you are training in a more functional way, you will develop more functional strength. This is very much the case with unilateral training.
Greater Recruitment and Development of Stabilizers
One of the things we love about unilateral training is how it forces you to really work hard to maintain balance. This balancing work is done by the recruitment of extra stabilizer muscles.
The development of these muscles results in a stronger, more explosive, and more injury resistance athlete.
How To Incorporate Single Leg Training Into Your Program
On the whole we feel the benefits of this type of training is best for sports specific training, but That said I still absolutely love two legged varieties and the tremendous whole body training they provide. So how do we go about getting the best of both worlds?
Some of the techniques we like using are alternate single leg and double leg training days. For example, if you are still a beginner and trying to develop your base levels of strength (i.e. you are mostly just weight training with minimal plyometrics and jumping) you could do two heavy double leg days per week (performing traditional squats and deadlifts) with a more explosive single leg only day somewhere in between. I usually do two to three days of single leg exercises and the same for upper and total body.
The same sort of logic can be applied to your plyometrics. Depending on what sort of jumping you are trying to improve, you might perform one day of single leg jumps such as power skipping and the 123 jump, and on another day just use two legged jumps. Obviously if you are more of a two foot jumper you may want to focus more on double leg exercises, but if your sport requires you to run and jump then the one legged will be of great benefit to you.