Instructions

1

Sit on a chair or bench with torso upright, back supported, feet flat on floor, hands gripping sides of seat for stability

2

Position legs so knees are bent at approximately 90 degrees with feet planted on ground, engage core and maintain neutral spine

3

Slowly bend knees further, bringing feet up and thighs toward chest in a controlled lowering motion, feeling hamstrings and glutes engage as hip flexes

4

Extend legs forward by straightening knees against gravity, lifting feet up to full knee extension, then return to starting bent position with control

PRIMARY MUSCLESRectus Femoris

SECONDARY MUSCLESVastus Lateralis, Vastus Medialis, Iliopsoas, Rectus Abdominis

EQUIPMENTBody weight

DIFFICULTYBeginner

Overview

If you want to isolate and overload the Rectus Femoris, the Seated 8 Leg Crunch is an excellent addition to your routine. The mechanics of this Strength exercise specifically bias the Waist, while the use of Body weight allows for a smooth, natural resistance curve.

Benefits

Acts as a highly scalable Strength movement, perfect for both beginners and elite athletes.
Utilizes Body weight to create sustained mechanical tension, forcing deep muscle adaptation.
Significantly enhances the structural integrity and power of the Rectus Femoris.

Common Mistakes

Losing core tension, leading to poor spinal alignment and reduced power output.
Shrugging the shoulders or compensating with secondary muscles rather than isolating the Rectus Femoris.
Failing to achieve a full range of motion, which drastically limits Rectus Femoris engagement.
Using excessive momentum to swing the Body weight rather than controlling the eccentric phase.

Muscle Anatomy

The primary driver is the Rectus Femoris. However, the movement also recruits Vastus Lateralis, Vastus Medialis, Iliopsoas, Rectus Abdominis to maintain control of the Body weight.

Exercise Variations

Dumbbell Seated 8 Leg Crunch
Cable Seated 8 Leg Crunch
Banded Seated 8 Leg Crunch

Seated 8 Leg Crunch