Strength Training · Aquatic Conditioning
Deep-Water Jackknife
The Deep-Water Jackknife is a flotation-supported leg lift that trains your abs and hip flexors as you raise both legs from an upright floating position.
- Intermediate
- Compound
- Moderate injury risk
- Rest 45 sec
How to do it
- Fasten the flotation belt snugly around your waist before entering the water.
- Float upright in deep water with your arms submerged beside you.
- Raise both legs forward toward hip height with your knees slightly bent.
- Lower your legs back beneath your hips.
- Regain a stable upright position before starting the next repetition.
Form cues
- Make small hand sweeps for balance.
- Exhale as your legs rise.
- Keep your ribs over your pelvis.
Common mistakes
- Swinging the legsMove slowly in both directions so momentum does not rock your body.
- Leaning too far backKeep your chest mostly upright rather than tipping backward to get your legs higher.
- Forcing the rangeLift only as high as you can without arching your lower back.
Safety
Losing balance or having the belt slip can put your face underwater. Fatigue or an overly large leg lift can also strain your lower back.
- Exercise in a lifeguarded pool, never alone.
- Do not rely on the flotation belt as a life jacket; it does not replace swimming ability.
- Check that the belt stays in place during upright flotation before starting.
- End the set if you cannot keep your mouth and nose comfortably above water.
Choose a supported shallow-water version if you are uncomfortable in deep water, and seek physiotherapist advice if leg lifts cause back or hip pain.
Muscles worked
Primary muscles
Secondary muscles
Equipment
- Aquatic Flotation Belt
Sets and reps
- Sets
- 2–3
- Target
- 8–12 reps
- Rest
- 45 sec
Start with fewer repetitions if maintaining steady flotation is challenging.