The "anti-extension" category of core training consists of any exercise where you're actively resisting extension at the lumbar spine. These exercises are great for developing stability at the core, lumbar spine, and pelvis. If you're doing them right, they'll really tax your external obliques, along with your rectus abdominus to some extent. You can use TRX straps, Blast Straps, or gymnastic rings for these.

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Some people will say that these exercises feel easy, but usually they just aren't doing them correctly. To get the most out of these movements, focus on the following:

1. Keep your chest up throughout. Don't allow yourself to "crunch" over. This is where you're using too much rectus abdominus to stabilize instead of your obliques. Stop it!
2. Think about tensing your obliques throughout. Engage your obliques on the sides by thinking "tall and skinny" not "draw your navel into your spine."
3. On exercises where you're combating full extension, think about cuing the obliques and squeezing your glutes as well. This will really crank up the intensity.

Note: If these are really tough for you, don't lose hope. Years of crunching variations have made most people very rectus dominant, so you have to work extra hard to keep your chest up/out, as well as your neck in neutral position.