Guhit, a Filipino word for line, is always the target of the triangle force in serious fighting for offense when one attacks and for defense when one protects. A line can be a force or a target of force. Blade weapons, for instance, are symbolized by a line. Arms, legs, and even the entire body is a line. They are strong forces.
There is a line in the human body that is weak and vulnerable to attack. That imaginary line is from the throat to the groin, and solar plexus and navel in between. Those for points within that line if hit by a punch, a kick, or a stick will definitely make a person curl down or even drop facing down.
Getting kicked in the groin or punched in the stomach does not necessarily kill but it would make someone drop on his knees and remain defenseless and immobile. The throat area and the solar plexus are the lethal ones. They are the dead points in the body line. Every fighter should protect that line from his opponent's strike, kick, punch, hit, or thrust. He should always be aware about that line when he is in a fight.
There are also lethal points in the head, but the latter can move, avoid, skip, bow down or lean back. The four points in the body line, lalamunan (throat), sikmura (solar plexus), pusod (navel), and harapan (groin) cannot do what the head and neck can, so arms, hands, legs, and feet are used to protect them. The forces that protect that line are triangles-- the weak is shielded by the strong.
For the throat and solar plexus, arms and hands are used respectively while with navel and groin, feet and knee are put into use. Of course, this is not a rule. A hand can be used too to protect the navel and the groin, but one needs to rely on a habit to protect himself during adrenaline rush. Quick thinking is important in a tight situation.
When cornered and punched on the solar plexus or throat, for example, hands cannot really strongly cover the vital point but arms can. Using hands has only two mini-shields while using arms have six-- upper arms, lower arms, and hands. The same story when it comes to groin and navel with feet, lower legs and thighs.
To avoid confusion, using triangular connection of points in defense is a good thing. The groin is best protected with knees and the solar plexus with hands. There is a reason why a fighting stance is usually in a side body position with one foot forward. The groin is protected by the leg and the solar plexus by the arm that way.
Even the feet on the ground is in a triangular position for force, weight, and balance to counter the line separating two fighters. In any aspect of martial arts, even in grappling and stickfighting, the play of force between a triangle and a line is always present and obvious. Even when someone falls after getting punched, he can use his arms or hands on the ground for leaning to regain balance and to avoid a total knockout. That in itself is a triangle avoiding a line.
If triangle is life, line is death.