The debate many coaches have about single-leg versus double-leg exercise is like arguing about whether you should eat only carrots or only broccoli. In reality, each vegetable offers a unique flavor and provides a certain set of nutrients, so just include them both in your diet.

Throughout the week, your strength training workouts should include at least one the following:

  1. A single-leg hip oriented exercise, such as a single-leg Romanian deadlift or a Romanian deadlift lunge.
  2. A single leg knee-oriented exercise, such as an upright-torso lunge or knee tap squat.

Don't think of single-leg and double-leg exercises as interchangeable. You'll still want to do lower body lifts with both legs. Why? Because compound lower-body movements place you in a wider base of support, force you to use both your legs and your hips together, and coordinate many muscles in order to move big loads, which is very metabolically taxing.

In contrast, unilateral leg-training exercises force you into a narrow base of support, which works your legs and hips in a slightly different manner – a manner that's often closer to how your legs work during sports since many athletic actions (think running and cutting) are single-leg dominant.

Of course, they also force you to focus on controlling and using one side at a time, which is great for strengthening your weaker, less coordinated side.

The Science

Single-leg performance during sidestep cutting may be a better indicator of how an athlete will move in sport activities, and therefore may be a better predictor of injury risk than bilateral drop jump testing (1). Although this example applies better to the sporting realm, the following studies can also be applied directly to your workout planning.

One study suggested using single-leg performance to detect deficits in unilateral force development, while another study showed that a 15% or greater variance in closed-kinetic chain strength (or movement control in single-limb performance) between the right and left leg is a good indicator of increased injury risk (2,3). Meaning, if one leg is significantly stronger or more controlled than the other, you're at a greater risk of injury.

Also, because weakness and fatigue in single-leg landings increase the risk of injury, it may be beneficial to regularly incorporate single-leg training exercise variations in your program to improve single-leg control, strength, and strength endurance (4).

Related:  Lost Strength – The Missing Exercises

Related:  7 More Single Leg Exercises You've Never Tried

References

  1. Kristianslund, E, and Krosshaug, T. Comparison of drop jumps and sport-specific sidestep cutting: Implications for anterior cruciate ligament injury risk screening. American Journal of Sports Medicine41(3): 684-688, 2013.
  2. Myer, GD, Martin, L Jr., Ford, KR, Paterno, MV, Schmitt, LC, Heidt, RS Jr, Colosimo, A, and Hewett, TE. No association of time from surgery with functional deficits in athletes after anterior cruciate ligament reconstruction: Evidence for objective returnto-sport criteria. American Journal of Sports Medicine40(10): 2256-2263, 2012.
  3. Rohman E, Steubs, JT, and Tompkins, M. Changes in involved and uninvolved limb function during rehabilitation after anterior cruciate ligament reconstruction: Implications for Limb Symmetry Index measures. American Journal of Sports Medicine 43(6): 1391-1398, 2015.
  4. Brazen, DM, Todd, MK, Ambegaonkar, JP, Wunderlich, R, and Peterson, C. The effect of fatigue on landing biomechanics in single-leg drop landings. Clinical Journal of Sports Medicine 20(4): 286-292, 2010.