They’re inexpensive and all you need to spice up your current ab routine. You don’t even need a fitness brand model (although plenty exist from maker like Bender Ball, Spri, and others). Get a small squishy ball, about the size of a cantaloupe and watch this video to see how fast you can blast your abs into submission. Form is key of course, so listen to my cues and keep those ab muscles “braced”. Safety tip: unless the ball is between your shoulder blades, it’s safest not to lay all the way back so you don’t hyperextend your lumbar spine. If you need a break, sit up. If you need a little extra balance support, spread your arms out to the side and place your hands on the floor. Hands in the air or behind the head is harder.