Jackknife Sit-Up

Muscles worked by the Jackknife Sit-Up

Primary

AbsRectus Abdominis

Secondary

Hip FlexorsHip Flexor MusclesObliquesOblique Abdominals

Also called: abs, six-pack, rectus abdominis, abdominals, stomach muscles.

Equipment

No equipment — this is a bodyweight exercise.

How to do the Jackknife Sit-Up

1. Lie face-up on the floor with arms extended overhead and legs extended straight.
2. Simultaneously lift the torso and the straight legs off the floor.
3. Reach the hands up toward the feet as the feet rise — meet above the hips.
4. Lower the torso and legs back to the floor under control.
5. Repeat for the recommended number of repetitions.

Form tips

• Arms and legs move at the same speed — avoid a kick-first cheat.
• If the lower back arches on the return, slow down and don't fully touch the floor.

At a glance

Jackknife Sit-Up in German & Spanish

Descriptions, instructions and tips ship in all three languages in the JSON.

Related exercises

• Ab Wheel Rollout
• Ball Pike
• Barbell Ab Rollout
• Bench Leg Pull-In
• Bicycle Crunch
• Bird Dog Hold
• Boat Pose
• Cable Crunch

Exercise data (JSON)

The record below is exactly what exercises.json ships for this exercise — names, descriptions, instructions and tips in English, German and Spanish.

{
  "id": "jackknife-sit-up",
  "name_en": "Jackknife Sit-Up",
  "name_de": "Jackknife Sit-Up",
  "name_es": "Abdominal navaja",
  "description_en": "A full-body crunch performed from a floor-hover position, lifting both legs and torso simultaneously to touch hands to feet.",
  "description_de": "Ein Ganzkörper-Crunch aus dem Bodenschwebestand, bei dem Beine und Oberkörper gleichzeitig angehoben werden, um Hände und Füße zu berühren.",
  "description_es": "Un crunch de cuerpo completo realizado desde el suelo, levantando las piernas y el torso simultáneamente para tocar las manos con los pies.",
  "category": "strength",
  "force_type": "dynamic",
  "mechanic": "compound",
  "difficulty": "intermediate",
  "body_part": "core",
  "primary_muscles": [
    "rectus_abdominis"
  ],
  "secondary_muscles": [
    "hip_flexors",
    "obliques"
  ],
  "goals": [
    "hypertrophy",
    "endurance"
  ],
  "tags": [
    "core",
    "calisthenics"
  ],
  "is_unilateral": false,
  "is_bodyweight": true,
  "instructions_en": [
    "Lie face-up on the floor with arms extended overhead and legs extended straight.",
    "Simultaneously lift the torso and the straight legs off the floor.",
    "Reach the hands up toward the feet as the feet rise — meet above the hips.",
    "Lower the torso and legs back to the floor under control.",
    "Repeat for the recommended number of repetitions."
  ],
  "instructions_de": [
    "Leg dich auf den Rücken, Arme über dem Kopf gestreckt, Beine gerade.",
    "Hebe Oberkörper und gestreckte Beine gleichzeitig vom Boden.",
    "Strecke die Hände den Füßen entgegen – Treffpunkt über den Hüften.",
    "Senke Oberkörper und Beine kontrolliert wieder ab.",
    "Wiederhole die empfohlene Anzahl an Wiederholungen."
  ],
  "instructions_es": [
    "Acuéstate boca arriba en el suelo con los brazos extendidos por encima de la cabeza y las piernas estiradas.",
    "Levanta simultáneamente el torso y las piernas rectas del suelo.",
    "Lleva las manos hacia los pies mientras estos suben — encuéntralos sobre las caderas.",
    "Baja el torso y las piernas de vuelta al suelo con control.",
    "Repite el número recomendado de repeticiones."
  ],
  "tips_en": [
    "Arms and legs move at the same speed — avoid a kick-first cheat.",
    "If the lower back arches on the return, slow down and don't fully touch the floor."
  ],
  "tips_de": [
    "Arme und Beine bewegen sich gleich schnell – kein schummelhafter Beinkick.",
    "Wenn der untere Rücken beim Absenken durchhängt, langsamer werden und nicht ganz ablegen."
  ],
  "tips_es": [
    "Brazos y piernas se mueven a la misma velocidad — evita hacer trampa levantando primero las piernas.",
    "Si la zona lumbar se arquea al bajar, reduce la velocidad y no toques completamente el suelo."
  ],
  "met": 5.0,
  "images": {
    "flat": {
      "start": "images/flat/jackknife-sit-up-start.webp",
      "peak": "images/flat/jackknife-sit-up-peak.webp"
    }
  }
}

Fetch just this exercise

const { exercises } = await fetch(
  "https://exercise-dataset.com/exercises.json"
).then(r => r.json());
const ex = exercises.find(e => e.id === "jackknife-sit-up");

Free for personal and commercial in-app use with attribution (“Exercise data by RepDB”) — see the license and ready-made attribution snippets. Redistributing the data as a dataset or API is not permitted.