Bent Leg Jackknife | Illustrated Exercise Guide

Primary muscles: Abs
Secondary muscles: Core, upper back, hip flexors, quads, hamstrings
Equipment: No equipment
Exercise for the opposite muscles: Back extensions

BENT LEG JACKKNIFE INSTRUCTIONS

1. Lie on your back with your legs straight and your arms extended back.
2. Raise your torso and bend your knees simultaneously, and then hug your knees with both hands.
3. Return to the starting position and repeat.

PROPER FORM AND BREATHING PATTERN

Use your core strength to keep your upper body stable, and maintain a neutral spine during the entire exercise. Breathe out as you bring your knees toward the chest and squeeze in the abs. Breathe in as you return to the starting position without ever letting your hands and feet touch the floor.

EXERCISE BENEFITS

The bent leg jackknife fully engages the abdominal wall and helps to strengthen and tighten the core. This exercise also challenges your back muscles, improves posture and prevents lower back pain and injury.

DEMONSTRATION

SETS AND REPS

Start with knee hugs and v sits to acquire proper exercise form. As you gain core strength, progress to the bent leg jackknife and do 2 or 3 sets of 10 to 12 reps.

CALORIES BURNED

To calculate the number of calories burned doing the bent leg jackknife, enter your weight and the duration of the exercise:

RELATED CORE EXERCISES

Try these other core exercises to tighten, sculpt and strengthen your abs, obliques, lats and lower back:
Pilates swimming
Rope climb crunches
Oblique V crunch
Downward dog crunch