Are jack knives effective?
The jackknife is an excellent way to work your rectus abdominis (your ‘six-pack’ muscles), but it’ll also require the work of your deeper core – your transverse abdominis – which is notoriously tricky to target.
How many jack knives should I do?
Try to keep your arms and legs as straight as you can as you lower them, although it might be hard to not bend your knees slightly. Repeat 10-12 reps per set and aim to complete 2-3 sets. After your first set of 10-12 reps, allow yourself to rest for about 30-45 seconds.
Are jackknife crunches effective?
Jackknife Crunches are a great core and lower body exercise that can strengthen your abs while burning fat.