Balance + Stability
Balance in involves the centre of mass and base of support. In terms of surfing the centre of mass is the mid point of your body and base of support is the area of contact underneath the surfboard. Usually, the bigger or wider your base of support is the more stable you become, this makes it easier to balance. Therefore, bigger boards are easier to ride. Also, you want the centre of mass and base support to be close to achieve a sturdy position when surfing waves. Having more control of your body and the board can also help to maneuver on the waves.
In relation to the technological developments in surfing, the design of the surfboard has increased surfers ability to balance and remain stable. This was done through creating friction on the top of the surfboard. Another important feature of the surfboard is the shape, having a point at the end allows the board to cut through the waves, rather than nose diving forwards.
Factors that affect stability are body mass, friction between the body and the surface or surfaces contacted, base of support and position of the centre of gravity.
Friction
To increase stability of the body, it is necessary to increase friction between the body and surface it is in contact with. In surfing, this is achieved by waxing their board and therefore increases stability. The development of wax used in surfing has created greater friction, therefore greater stability for the surfer.
However it is important to reduce friction on the bottom of the board. This is to generate less friction between the water and board allowing more maneuverability.
Inertia
The biomechanics law of inertia is, an object will remain in a state of rest or constant motion unless acted upon by an external force. The more mass an object contains, a greater force is required to change the state of motion. In relation to surfing, the force of the water pushing against the bottom of the board as you turn. The force of water underneath the board and against the fins, counteracts the force of inertia, this prevents you flying over the board as it surfs along the wave. Different board shapes and fins will also help you train to balance against inertia. Boards with single and twin fins allow the force of inertia to affect your movement in turns.
Biomechanics Of Surfing 