Instead of exercises like situps or crunches that mostly train your core by contracting and releasing your abdominal muscles while lying down, exercises in the plank and hollow-body positions train core stability. This means you have to hold and maintain a contraction and good spinal alignment, often while there are forces opposing it.

These stability exercises train your transverse abdominal muscles, which are deep in your core and help with posture and back health. They also keep your entire midsection from bulging out. (Think of how your stomach sticks out when you slump).

This is a Tabata workout, which was named after Japanese scientist Izumi Tabata, who found that high-intensity interval training that was 20 seconds on, 10 seconds off improved " both aerobic and anaerobic systems simultaneously ." Watch the video above or see the directions below for exactly how Speer's workout is done.

Directions: Perform the exercises in the order listed 20 seconds of work with 10 seconds of rest.

1. Pushup, max reps

2. Hollow hold

That's 1 round. Do 3 to 5 rounds.