You can hear a bad backstroke kick from the other end of the pool. Two feet breaking the surface, knees cycling like someone pedalling underwater, plenty of white water and almost no forward movement. The swimmer in the next lane barely disturbs the surface and goes past.
Backstroke is the second leg of the 200 individual medley, the event I swam at two Olympic Games for Brazil and won at the 2015 Pan American Games in Toronto in 1:57.06. I have spent a long time on my back with my eyes on the ceiling, and the kick is the part of that stroke most swimmers get backwards. It is not a leg exercise. It is what holds the rest of the stroke in place.
What does the backstroke kick actually do?
Three jobs, and only one is pushing you forward. The US Masters Swimming backstroke kick guide lists them: "These include creating propulsion, improving your body position, and helping with rotation."
Take those in reverse order of how swimmers rank them. Body position first, because "A good body position can reduce how much resistance you encounter as you move through the water." A kick that keeps your legs up buys speed by subtraction, not addition. Then rotation: "Your kick can also help with body rotation." The legs set the rhythm the shoulders turn to.
Propulsion comes last on that list, and the guide is honest that it is modest. That ordering is the lesson. Kick harder, drop your hips doing it, and you have paid for propulsion with drag. Same hole as in why your hips sink in backstroke, reached from the legs.
Why is kicking from your knees the worst backstroke kick mistake?
Because it is the most common one. The guide does not hedge: "The most common backstroke kick mistake is kicking from your knees."
What should happen is a sequence, and the order matters more than the effort. "Start your up-kick from your hip, and then bend your knee slightly." Hip first, knee second, only slightly. Coming down the leg does the opposite: "Perform your down-kick with a straight leg." The guide repeats it: "Your leg should be almost completely straight during your down-kick."
So the knee bends a little going up and not at all going down. If your knees keep breaking the surface you have inverted it, flexing the knee to start the movement, so the lower leg sweeps back through water already moving back and the heel pushes nothing.
The research agrees. A systematic review of the determinants of backstroke performance reports that "Faster backstroke swimmers were characterized by a greater kicking frequency", coming "coupled with specific segmental differences related to a lower knee range of motion in the upkick and downkick positions". More beats, less knee.
How big should the backstroke kick be?
Smaller than you think, and the guide gives a target you can see: "Kick within the shadow of your body."
The principle: "Backstroke kick should be done over a relatively small range of motion." Then the instruction worth writing on your hand: "Keep your kick small and fast to optimize your speed in the water."
The alternative is a named fault. "The second major issue is kicking too big, which leads to extra drag with little to no extra propulsion". That is why big kickers are slow kickers. A bigger kick is not a stronger kick. It is a wider frontal area dragged through the water for nothing.
Effort is the next fault listed: "Another common mistake is kicking too hard." Adults told the kick matters attack it, the legs fill up inside 50 m, and the kick disappears while the stroke falls apart around it. Small and fast is a rhythm you can hold.
Does the up-kick or the down-kick drive you forward?
The up-kick, almost entirely: "Your up-kick provides the majority, if not all, of the propulsion you get from your kick while swimming backstroke."
That one sentence reorganises how you practise. The down-kick is not propulsion, and not wasted either: "The purpose of your down-kick is to set up your up-kick." It sets the leg long and low so the upward snap has range to work through.
So the propulsive direction is up, with the top of the foot, closer to flicking a ball off your instep than to stamping. Drive down hard and you are working the half of the cycle that does not pay.
What do your ankles have to do in backstroke?
Stay loose and stay pointed, which is harder on your back than it sounds. The guide notes that holding the foot pointed backwards for long stretches is demanding, so "Flexible ankles can really help here."
The review's table sets the strokes side by side in its own shorthand: "and ↓ ankle vertical range of motion in front crawl than in backstroke." One included study, and the direction is worth knowing: a stiff ankle costs you more here than in the freestyle kick.
The other ankle fault is a shape problem: "Some swimmers turn their feet out to kick, using a breaststroke-like action." Point the toes, do not splay them.
How does SwimRead read this part of your swimming?
It does not read backstroke at all, and you should know that before you film anything.
The SwimRead home page says that "The current beta supports freestyle filmed from the side of the pool", and that "Backstroke, breaststroke, butterfly, underwater footage, starts, and turns are not supported analysis modes in this beta." What it does do is read freestyle: "On-device pose detection estimates up to 33 body landmarks in sampled video frames", from a clip the page describes as "Aim for 10 seconds of continuous freestyle", filmed as "Film in landscape from the side, keep the whole body visible, use a stable camera and standard lens". The output is a set of measurements rather than a verdict, since "These estimates are not validated technique grades."
So on backstroke you are the analyst. Phone on the deck, film from the side, and look for two things: do the knees break the surface, and do the feet stay inside the width of your body.
What should you drill this week?
The US Masters Swimming backstroke kicking drills page names the fault each one attacks, which is why I use them in this order.
- Kickboard over the knees. Eight by 25 m. "By placing a kickboard over your knees while kicking, you'll get constant feedback", aimed at the fault above: "Many swimmers inappropriately bend their knees while kicking." If the board gets hit, the knee started the kick.
- Vertical kick. Four by 20 seconds in deep water, hands on your chest. It "will help you learn to move your hips when you kick, rather than just your knees."
- Boat kick. Six by 25 m: "kicking on your back with your arms at your sides and your hands resting on your hips." It "encourages you to round your back slightly", the posture that keeps your hips up.
- Film one length from the side. Watch the surface line, not the swimmer. Knees up means hips first next time.
My free swim pace calculator turns those 25s into a pace per 100, so you can check whether a smaller, faster kick is quicker and not just tidier. Pair it with the backstroke catch and both ends of the stroke are covered.
SwimRead is free while in beta, invitations go out as beta spots open, and paid plans will come later with beta testers told before anything changes. For a reading of your freestyle, join the beta and leave your email.