Specifically, you are activating your transverse abdominis (TVA), a deep inner core muscle. Focus on drawing in your abdominal muscles towards your spine as you slowly raise each arm and/or leg. To minimize stress on your shoulder, point your thumb up as your raise each arm.
First set: Raise your arms only
Second set: Raise your legs only
Third set: Raise opposite arm and leg (Right arm/Left leg and Left arm/Right leg)