Reply To: Underwater (Double leg) Kick
Rushall’s technique macrocycle advocates a narrow fast kick with a still upper body. This flies in the face of conventional wisdom (which doesn’t bother me at all), but also what the best swimmers in the world are doing and what seems to be more effective in my swimmers (a wider kick trying to generate more propulsion and slightly more upper body movement).
He was more than likely advocating for minimizing movements during the era when everyone was doing full-body super-undulation. That style has faded away. Kick from the hip and keep the upper body “quiet” and streamline if not still. Sprinters can get away with moving the upper body more if the tradeoff is generating more force from the kick than the frontal drag from the upper body’s drag shadow.
As for the feet distance, Rushall didn’t do a ton of writing on turbulence. He was mostly focused on drag reduction and combating the lift force theory (which he was 100% correct on, we aren’t a wind-powered hydrofoil). From my own testing, the feet should be about hips distance apart. This is backed by research in a number of other areas: 1) injury reduction and efficiency in cycle pedaling where pedals contain spacers to align with the hips, 2) separating the fingers by 5-6 mm during the swim pull to increase the compression surface of the hand (increasing the turbulent area around the hand) and 3) the law of least resistance – when an object travels through a medium it will find either the shape or path of least resistance.
What all this means is that when the feet are together they are probably pressing against mostly the same water and it is flowing around a smaller object. When the feet are separated enough there are 2 turbulent pockets that compete for flow around the feet. Widening the feet outside of the hips creates a muscular or biomechanical inefficiency and increases the leg drag shadow.
What I notice in my own training is that when my kick gets tired the feet start to get closer together to use the same pocket of pressure which allows them to travel through the water easier. This is just like the wrist bending back or the elbow “dropping” during the pull when you start to fatigue. A vertical forearm with a stiff wrist is harder to maintain but also generates more force and thus more power.
As for underwater swimming, there has been a lot of research on this. Push off the wall at 12-18 inches, streamline glide at a 10 degree down angle for 4-6m to about 3-4 feet underwater (depending on pushing power), start kicking when you feel your speed drop to your kicking speed, then rotate to a 5-10 degree up angle with smallish-fast kicks. You should feel like the kicking and buoyancy are accelerating you to the surface.