To Swim Like a Fish

Is This New Swim Stroke the Fastest Yet?

The surprising performance and physics of the fish kick.

Basically, the "dolphin" kick turned sideways.

. . .Once perfected, the fish kick may be hard to beat.

Although these ideas remain debated to this day, the fish kick has continued to gather fans. Luc Collard, a professor of sports science who has experimented with many different ways of swimming underwater—including swimming the fish kick with the arms down, along the swimmer’s side—says it may just be the fastest. “Its potential is impressive.” Raúl Arellano, a professor of physical education and sports at the University of Granada, agrees. “Lateral kicking is found to be quicker in some swimmers,” he says. “The hypothesis is that these vortices are not perturbed by the water surface and the pool bottom.”

Vortices are an inevitable consequence of moving through water. Some are counterproductive, impeding the swimmer’s motion. Others help propel the swimmer forward. “Vortices represent the transfer of momentum from a body into the water and vice versa,” says Atkison, “and thus can both propel swimmers forward and also slow them down.” The dolphin kick is more likely to send helpful vortices up to the pool surface, where they dissipate into waves, and down to the pool floor, where they create turbulence. The fish kick, by comparison, is more likely to send these vortices sideways, parallel to the water’s surface, where there are no obstructions. “Anything that makes waves on the surface is detrimental to swimming efficiently,” says Rajat Mittal, a computational scientist at Johns Hopkins University. “If you are swimming within a foot of the surface, there is a bigger chance that [you] will create waves on the surface than by kicking sideways.”

Atkison also believes that the fish kick is able to produce larger and more propulsive vortices when the swimmer finds herself in shallow waters. While the dolphin kicker draws in the water for her stroke from the volumes above and below her body, which are limited by the pool surface and floor, the fish kicker draws in water laterally and relatively without restriction.

However, the dolphin kick does not always suffer from these disadvantages. Swimming at a depth below 1 meter greatly reduces any surface turbulence and any difference in the volumes of water drawn, and Olympic and World Championship pools now are at least 2 meters deep. The fish kick is also inherently more difficult. “The problem is that the swimmer cannot control its swimming direction and body position as compared with ventral underwater undulatory swimming,” says Arellano. All that being said, though, once perfected, the fish kick may be hard to beat.

I wonder what happens when multiple people in a race start using the "fish" kick. Will the vortices from the leading swimmers interfere with the adjacent, and slightly behind swimmers, or will the vortices be like drafting cars; allowing the swimmers not setting the pace to use the energy left behind and save energy for a final push?