Single-Leg Leg Extension

The single-leg leg extension is the unilateral version of the standard leg extension, performed one leg at a time on the same machine. Saeterbakken 2021 found that unilateral leg extension produces greater peak force and activation per leg compared to the bilateral version — a manifestation of the bilateral deficit. This makes the single-leg extension useful for identifying and correcting left-right quadriceps strength asymmetries.

Execution

1. Set up the machine identically to the bilateral version; sit with the non-working leg hanging free or resting to the side
2. Extend the working leg to full extension under controlled speed
3. Hold briefly at the top contraction, then lower under control
4. Complete all reps for one leg before switching

The Bilateral Deficit

When both legs extend simultaneously, each leg produces less force than it would working alone. For the leg extension specifically, Saeterbakken 2021 confirmed that switching to unilateral work increases per-leg neural demand — making single-leg variations appropriate for trainees who have plateaued on bilateral leg extensions or need to address asymmetries.

When to Use

• Asymmetry correction: When left-right strength differences are identified in bilateral testing
• Rehabilitation: Post-injury limb retraining
• Volume accumulation: Unilateral volume with less systemic fatigue than bilateral

For primary quadriceps development, the bilateral leg extension is more time-efficient. Include single-leg work when asymmetry is a concern.

For system-specific training applications, see each system's lens entry.