Completely shutting down the legs and trying to power through the water with just arm strokes is simply inefficient.
How often have you heard triathletes tell each other they should “save” their legs for the bike and run by not kicking during the swim? The theory is that you should let your arms do all the work so that your legs will be “fresh” for the remaining two disciplines.
Yes, you should conserve energy during the swim for the remainder of the event. But completely shutting down the legs and trying to power through the water with just arm strokes is simply inefficient. Imagine running without the use of your arms—even without attempting it, it’s clear that running this way would be more difficult.
The same biomechanics are applied to the freestyle swimming stroke. The downward kick of one leg provides a counterbalance to the stroke of the opposite arm. The kicking motion can be passive but still efficient, just like the relaxed arm swing of a distance runner. There is also no right or wrong way when it comes to the frequency of the kick. A two-beat or six-beat kick (or any variation of the two) can be successfully employed during a triathlon swim as long as the action requires minimal energy.
Unlike a competitive pool swimmer, a triathlete is not trying to gain propulsion from the kick. This is where we get the idea of conserving energy for the bike and run. A powerful and forceful kick requires a lot of energy to perform and only produces a small fraction of propulsion. Instead, a triathlete should be looking for a passive kicking motion that requires little energy but places the body in a better position to produce power during each arm stroke.
How to train your kick
Do kick sets. Build the strength and muscle memory for an efficient and gentle kick so that it becomes natural.
Limit training with a pull buoy. Learn how to keep your body afloat by using your legs.
Disconnect your stroke rate from your kick. Practice swimming with a higher stroke tempo but maintain a passive kick.
Train in your wetsuit or neoprene shorts. When your body position rises in the water, the kick does not become obsolete. Continue to kick to provide core stabilization for your strokes.