A basic hard punch is actually generated from the feet and hips. The basic way of throwing a heavy punch is depending on your stance and how your feet is positioned.

In Boxing; the key form of throwing a punch is by having one leg back and one leg forward. While the back leg is pushing forward, the body is gaining body mass through out its weight. The next step to the punch is rotating the hips to the left or right (depending which punch is being thrown). By this movement, you are gaining an amount of energy from the feet all the way up to your hand through out one motion. In science, this is known as "connectic linking".

Preferably, the vertical punch is mostly recommended in the action of throwing a "Heavy Punch".

The vertical punch is mostly used in most arts such as Isshin Ryu - Karate, Also in the Five animal form of Shaolin Kung Fu; Quan Fa, and The Adhart Techniques of the Shaolin "Luohanquan", while other kung Fu styles such as XingYiQuan, BaJiQuan, even TaichiQuan also use a similar form.

The reason behind this is that the punch is launched from the side, by keeping the elbow close to side the of body (ribs), while the shoulder is lowered and relaxed. Using the weight that the power that is generated from the feet (Connectic Linking), while using the vertical punch (which makes a better bone alignment of the wrist and arm), the power is distributed at a better rate.

The vertical Punch is preformed by having the hand turned to its side. Leaving the Thumb in the top position, but still wrapping the the Index and Middle Finger with the thumb. Some practitioners may not wrap the two fingers, but actually have the whole Thumb laying on the top of the index finger. It depends how comfortable you are and how the certain martial art school teaches it.

Story- Little Red Ridding Hood.

Rotkãppchen

Once upon a time, there was a little girl who hadn't seen her mother in seven years. She was forced to dress in iron clothes and was told "when you wear out those clothes, you can go back to your mother." The girl robbed her clothes on the wall trying desperately to tear them. When they had finally been torn she got some milk and bread as well as a little cheese and butter and set out for her mother's house.
In the woods, she met a wolf who asked her what she was carrying. "Milk and bread and a little cheese and butter", she answered. When the wolf asked for some the girl said no, saying it was a present for her mother. The wolf asked whether she'd be taking the path of pins or the path of needles. When the girl said she was going to take the path of pins the wolf hurried off down the path of needles and ate up the little girl's mother.
The girl finally reached her mother's house. "Mother, open the door", she said. "Push on the door. It's not locked." answered the wolf. The girl undressed and approached the bed where her mother lay in a strange position with a hood over her face. "Mother, what big ears you have. Mother, what big eyes you have. Mother, what big claws you have. Mother! What big teeth you have!" And then the wolf ate up Little Red Ridding Hood.

In yet, today was another day when I was walking down the street, when I found a penny.