Steps
- Lie flat on the floor (or exercise mat) on your back with your arms extended straight back behind your head and your legs extended also. This will be your starting position.
- As you exhale, bend at the waist while simultaneously raising your legs and arms to meet in a jackknife position. Tip: The legs should be extended and lifted at approximately a 35-45 degree angle from the floor and the arms should be extended and parallel to your legs. The upper torso should be off the floor.
- While inhaling, lower your arms and legs back to the starting position.
- Repeat for the recommended amount of repetitions.
Tracking it in OneRep
Add the jackknife sit-up to a routine and your previous weight and reps sit beside every set, so the decision to add load is made by what is already on the screen rather than by memory. Exercise history and volume trends are one tap away, and logging works offline for the gyms where signal does not reach.
Because OneRep tracks food on the same timeline, a stall on this lift can be read against what you were actually eating that month — which is the difference between a programming problem and an eating one. More on that in tracking progressive overload without a spreadsheet.
Where the instructions come from
The steps above come from free-exercise-db, a public-domain exercise dataset. They are general guidance, not coaching for your body: if a movement hurts, stop and get someone qualified to look at it.