But with a narrower kick depth, the frequency of kicking with the Apollo (both split and taped versions) was significantly higher and the efficiency was lower (5%) compared with the Attack fin (7%). The two fins with a higher energy cost also had higher drag and lower efficiencies. This indicates that kick depth and kick frequency have to be optimized to minimize the energy cost and accounts for the similar performance of the Attack and Apollo fins. Fancy Features Slow Fins Down The researchers determined that length and width of a fin’s leading or trailing edges, surface area, weight, and flexibility did not significantly influence the energy cost of swimming. The type of material and the use of winglets (flanges), longitudinal splits, vents, or ribs alone didn’t increase the velocity of water down the fin, and in fact may decrease it, thus leading to lower thrust and economy.