What is the most effective way to improve the efficiency of swimming strokes?

By applying "hydrodynamic".

Hydrodynamics is a branch of material science that deals with the movement of liquids and the powers following up on solid bodies submerged in liquids and in movement in respect to them. Liquid hydrodynamics assumes a part in a swimmer's general execution, in light of the fact that the powers delivered in and by water can either increment or decrease a swimmer's speed.

si fuera 2 en colombia, entonces sería 10 pm en rusia

balearic sea - is a body of water in the mediterranean sea around the balearic islands. baltic sea - is a mediterranean sea of the atlantic which is enclosed by scandinavian and baltic countries. barents sea - is a marginal sea in the artic ocean located off the northern coast of norway and russia.