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