A monofin is a type of swimfin typically used in finswimming and free-diving. It consists of a single surface attached to footpockets for both of the free-diver's feet.
Monofins were introduced in 1972, by a Ukrainian finswimming club, and have been used for finswimming competitions since, allowing monofin swimmers to reach speeds of 12km/h.
Monofins can be made of glass fibre or carbon fibre. The diver's muscle power, swimming style, and the type of aquatic activity the monofin is used for determines the choice of size, stiffness, and materials.
To differentiate between the use of monofins and conventional fins, the latter are sometimes referred to as stereo fins or bi-fins. The monofin swimmer extends arms forward, locking hands together, locking the head between the biceps. The undulating movement starts in the shoulders, with maximum amplitude towards the hips, the legs almost don't bend to transfer the movement to the monofin. This technique is called the dolphin kick.
Monofins can be used to swim:
By slowly oscillating the surface of the monofin when submerged, freedivers can generate large amounts of thrust even with small or slow movements. This preserves energy which helps with breathholding (apnea).