Spinal flexion is best for abs so any of those ab crunch machines

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Just work abs a lot, very often, with weight. Abs is 3 layers of muscle so you need to work it real hard to get results

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2-3x a week for 2-3 sets of 6-15 reps. Decline/GHD/cable/machine crunches all work well. No need for leg raises unless you want to, ensure standardized form though throughout your sets and avoid using momentum.

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