ActivTrax

Jack Knife

Primary Muscles: Lower Abs, Upper Abs
  • Instructions
  • In Brief
  • Key Points

  1. Start Position Exhale as you slowly crunch, simultaneously raising your upper and lower body.
  2. Middle Position Continue to crunch your upper and lower body until they are both approximately at a 45-degree angle to the mat.
  3. End Position Now continue to raise your upper body closer to your feet, using your arms to assist you. Keep your lower body stationary. Hold for 1/2 a second, squeezing your abdominals. Note: Do not jerk your body or use momentum.
  4. Return to Middle Inhale as you slowly return to start position.
  5. Return to Start Do not let your legs touch the mat. The small of your back remains in contact with the mat and you have maintained the tennis-ball-sized gap between your chin and chest. Repeat the movement for the recommended number of repetitions.

Instructions

  1. Start Position Exhale as you slowly crunch, simultaneously raising your upper and lower body.
  2. Middle Position Continue to crunch your upper and lower body until they are both approximately at a 45-degree angle to the mat.
  3. End Position Now continue to raise your upper body closer to your feet, using your arms to assist you. Keep your lower body stationary. Hold for 1/2 a second, squeezing your abdominals. Note: Do not jerk your body or use momentum.
  4. Return to Middle Inhale as you slowly return to start position.
  5. Return to Start Do not let your legs touch the mat. The small of your back remains in contact with the mat and you have maintained the tennis-ball-sized gap between your chin and chest. Repeat the movement for the recommended number of repetitions.

Key Points

  1. Throughout the entire range of motion:

    • Keep your head aligned with your spine.
    • Keep your chin aligned with the middle of your chest.
    • Keep your arms extended, and elbows bent outward.
    • Keep your legs together and extended, and maintain a slight bend in your knees.
    • Concentrate on using your abdominals to perform the exercise.
  2. At end position, do not jerk your body or use momentum.

  3. Keep the small of your back in contact with the mat to alleviate unncessary stress on your back.

    • Do not perform this exercise if you feel discomfort in your lower back.