from Wikipedia

Handstand

A handstand is the act of standing erect, but upside down, with one's hands on the ground and feet in the air. The basic handstand has legs extended vertically with no knee bend, hands roughly shoulder-width apart, and head facing forward, but there are numerous variations. Performing a handstand requires good upper body strength.

Handstands are performed in many athletic activities, including break dance, fitness competitions, circus acrobatics, cheer leading, and martial arts like Capoeira. In yoga, the handstand is known as Adho Mukha Vrksasana (downward-facing tree pose). Handstand dives are one of the main categories found in competitive platform diving. Some variation of the handstand is performed on every gymnastic apparatus, and many tumbling skills pass through a handstand position during their execution.

Posture

A basic straight-leg static vertical handstand consists of five key points of posture.

1. Locked Arms - Hands placed flat on the ground shoulder-width apart, elbows locked, maintaining straight arms.
2. Tucked Head - The face is not pointed towards the ground, but straight forward, as if one were upright.
3. Hollowed Hips - Prevents the spine from curving by thrusting the hips over one's center of gravity. If performed lying flat on the ground, this posture would maintain contact between the small of the back and the ground.
4. Locked Legs - Knees locked, legs kept together or in a "V" and straight.
5. Pointed Toes - Feet pointed straight, continuing the line the legs.

Handstand variations, or handstands utilizing apparatus, will require a break from these standard points of posture in order to maintain balance. The handstand is maintained by subtly shifting the body's weight towards the fingers or the heel of the hand.

Variations

Popular variations of the handstand include positions with the legs extended in a side or front split, legs in a front split with knees bent ("stag split" ), with back extremely arched, legs slightly bent and toes touching back of head, and one-handed. Dancers in the breakdance community employ many handstand variations as freezes or one-handed kicks.

Handstand push ups, in which one raises and lowers the body while holding a handstand, are a test of upper-body strength.

Swimmers sometimes do handstands underwater, by rolling forward, placing the hands on the bottom of the pool, and raising the legs and feet out of the water. Underwater handstands may be a game or contest between swimmers to see who can maintain the handstand the longest.

While learning the handstand, it is most common to hold the pose against a wall or other surface for support and balance.

Risks

The handstand is a fairly safe pose when performed correctly and is comparable to a headstand. If possible, avoiding transitioning from a headstand to a handstand for safety reasons. Either can produce momentary dizziness or vision changes, especially for those with conditions such as high blood pressure. Such individuals sometimes choose a smaller inversion like the "legs up the wall" pose as a substitute.

When falling backwards, tuck your head and allow your body to smoothly roll. Once this is mastered there is very little risk involved.