As an adrenalin junkie I spent most of my twenties diving headfirst out of high flying objects, throwing myself off bridges and plummeting down the side of skyscrapers. The majority of my 'leisure' time was spent being upside down.
Jim Morrison, Janice Joplin, Jimi Hendrix, Kurt Cobain, and most recently Amy Winehouse, should have considered spending more of their lives inverted, and a little less 'bottoms up'. Being upside down is nothing but good for you. At 27 years old and looking at the current global status of people with more than a few screws loose, I am alive.
Which brings me to the topic at hand, why does no one teach the handstand push up? This is the most natural shoulder exercise, and benefits the mind and body enormously. Your blood supply is reversed which means your veins and arteries are working against gravity, forcing them to become stronger. A rush of fresh blood to the head, that's absolute tonic for the mind and brain.
Handstand push ups develop incredibly powerful shoulders, why are we wasting time on the shoulder press at the local sweat shop? There is no excuse not to do this exercise, it requires no equipment, heavy machinery or any space at all, you can perform this exercise inside your closet if you must.
It works your upper body pressing muscles, developing strength Conan would be jealous of. When in this pose your body instinctively positions itself in a position healthiest to the shoulders, and raising your feet above your body transfers body weight through your hands in a concentrated way. A handstand push up is the equivalent of shoulder pressing your body weight, many athletes cant even accomplish that. It can take you years and many deep heat rubs to get to this level of strength with a barbell, but handstand push ups can get you there in a few months.
Not only do they develop absurdly strong muscular shoulders but they teach total body control, and kinesthetic awareness in all your other training movements. Strength, stamina, power, agility and health all in one exercise.
Today's gyms are placing orders for bosu balls, balance boards and other trivial pieces of balloon, because of the supposed benefits of balance, stability and core conditioning they administer. I remember reading about the Roman gladiators, preparing for battle, strengthening their cores with a bosu ball. Handstand push ups offer you all that, plus total body coordination and muscle control.
Being upside down also causes the balance organ in your ear (vestibular system) to adapt to the motions and become increasingly more efficient for your everyday life. This form of upper body training heightens and strengthens every single muscle in your upper body all at the same time and improves your upper body resistance exercises.
Strength is not something that you find under a Christmas tree in a box, or on a shelf in your local Glomail store. Strength is a skill - practice it often if you want to improve it.