Here is Day 4. I'm in Urdhva Dhanurasana aka "upward bow or wheel". This pose strengthens the arms, wrists, legs, butt, abs and spine! It also stimulates the thyroid gland which controls many aspects in the body (trust me I've had thyroid issues before, no bueno).
Day 3: Parivrtta Janu Sirsasana aka "revolved head-to-knee". This stretches the spine, shoulders, and hamstrings so it's a great pose for after "Leg Day" if you're an avid cross fitter or workout enthusiast in general. It also stimulates the liver and kidneys.
