Dead point

A dead point is one of the extreme positions of the piston in the cylinder of a steam engine or internal combustion engine at the time of its reciprocating motion. When the piston stops at a dead point, an external action is required to start the movement. To prevent jamming of the engine at a dead point, various methods are used: the use of several cylinders, the dead points of which are divided into different positions of the output shaft; in steam locomotives with a compound machine - special steam distribution schemes. To smooth the passage of dead points during engine operation, flywheels are used.

There are two dead points:

• The top dead center is the position of the piston in the cylinder corresponding to the maximum distance between any point of the piston and the axis of rotation of the crankshaft (usually the top position of the piston connected in a vertical crank-slide mechanism (KPM)). In this position, provided that the valve mechanism of the gas distribution system is in the compression stage, maximum compression of the gases in the combustion chamber is created .
• The bottom dead point is the position of the piston in the cylinder corresponding to the minimum distance between any point of the piston and the axis of rotation of the crankshaft (usually the lower position of the piston is connected in a vertical crank-slide mechanism . Piston movements below are impossible due to KPM kinematics.

Dead point - (biomed.) State of the body during intense exercise. It occurs a few minutes after the start of intense muscular work. An unpleasant sensation appears, accompanied by shortness of breath, a feeling of tightness in the chest, dizziness, a feeling of pulsation of the vessels in the head, a desire to stop working.

The reason for the “dead point” is that at the beginning of the training session it takes some time for the cardiovascular system to reach a certain level of its functioning and to be able to adequately supply the working muscles with oxygen. And with excessive intensity of the onset of training, a mismatch arises between the oxygen requirements of the muscles and the ability of the cardiovascular system to adequately provide the body with oxygen. As a result, from the very beginning, decomposition products, primarily lactic acid, accumulate in the muscles. Accordingly, in order to avoid the “dead point”, it is necessary to gradually increase the intensity of the training session.

If the state of the “dead center” has nevertheless come, then it can be overcome by great volitional efforts. If physical work continues, this state will be replaced by a feeling of sudden relief, which most often manifests itself in the appearance of normal (comfortable) breathing. Therefore, the state replacing the “dead center” is called the “second breath”. The emergence of a “second breath” means that the body has adapted to perform physical activity and is able to satisfy working muscles in their energy needs.