TRX Jacknife Twist
Step 1 Start in a straight arm plank position, with the hands directly underneath the shoulders and the abdominals drawn in.
Step 2 Exhale and tuck the knees towards one elbow while keeping the upper body still.
Step 3 Slowly, and with good control, return the legs to the start position before repeating on the other side.
Primary muscles targeted are the Abs and Obliques.