Biomechanical principles of movement
The centre of gravity refers to the point at which all weight tends to be concentrated, signifying that the body is balanced in all directions. The centre of gravity can move, for example, when an individual moves their limbs. Knowledge of this can allow individuals to optimise their techniques and maximise their efficiency of movement. An individual will remain balanced if the centre of gravity remains over the base of support.
The base of support of an individual is the area encompassed by all body parts in touch with the floor. When standing, the base of support includes the area covered by each foot and the total area in between. This is why it is essential to widen your stance on several standing free weight exercises and when sitting down to perform an exercise – to ensure that your centre of gravity falls between your base of support to maintain balance.
An individual standing with correct posture with arms by their side would have the centre of gravity at approximately the height of their navel, about midway between the front and back of the body. By raising their arms above their heads, the centre of gravity would move slightly upwards.
Arms represent approximately 11% of total body mass (quite a small proportion) and therefore only has a small effect on the position of the centre of gravity. If a larger body part were to be moved (for example, the trunk which equals approximately 50% of total body mass), there would be a more noticeable increase in the change of centre of gravity. If lifting a heavy weight, the centre of gravity will shift – the heavier the weight, the greater the effect
If an individual is carrying too much weight around the stomach for example, this would move the centre of gravity potentially outside their base of support making them unstable. They would compensate for this, however, by altering their posture which can lead to problems. Individuals with poor postural alignment, such as those suffering from lordosis or kyphosis, will also have an altered centre of gravity.