Single-arm freestyle explained: one arm pulls, the other rests in front or at the side. Find side differences in pull, head and rotation. With milestones.
In single-arm swimming only one arm pulls, the other rests stretched forward or lies at your body. The honest answer to "Why should I swim with just one arm?": because only then do you notice that your two sides are not the same. And they are the same for almost nobody.
A study of 28 freestyle swimmers from elite to beginner level over 100 m showed: most swam with asymmetric arm coordination, on one side a break in propulsion, on the other an overlap. This was often linked with the preferred breathing side and handedness profile. In less skilled swimmers, breathing amplified the asymmetry on the breathing side [1]. The drill shows you your own profile.
The Swim Wales plan calls the single-arm pull with the arm at the body a drill that is often neglected, although it is critical for the balance of rotation and propulsion and prevents one-sided overuse of the body [2]. It takes time and discipline [2].
Be realistic: you learn the basic form in one session. Balancing side differences takes weeks (experience, not a study value). This guide covers the freestyle variant. Backstroke and single-arm butterfly are separate topics.
One arm rests stretched in front, you kick in side position. The plan asks you to stretch from fingertips to toes and rotate hip and shoulder to about 45 degrees without changing head position [2]. Milestone: 25 m, the head stays calm.
The other arm does the pull. Catch with the fingertips, pull to the hip, bring the arm loosely forward. The resting arm stays in front. Milestone: 4 × 25 m per side with a flowing, even pull.
Now the resting arm lies at your body, not in front. This is harder because you lack the long line. The plan names exactly this drill "Single Arm Pull (arms by side)" [2]. Milestone: you hold your body position without sagging, the rotation stays even.
The plan points out that this drill shows how too much head movement disturbs the stroke [2]. Your head turns only as far as the body rotates. Milestone: on video the head sits as if on a rail.
Count the strokes per length left and right and have yourself filmed. You can also measure how far you roll. If one side rolls less or the hip hangs, you have your topic. Rolling can differ here: freestyle swimmers show roll asymmetries, but research has not found a performance disadvantage from them so far [3]. Milestone: you know your weaker side and have a task for it.
Swim 25 m single-arm, then 25 m normal freestyle and watch your weaker side. Milestone: both sides feel more alike in normal freestyle than before.
Do a side test: 4 × 25 m right, 4 × 25 m left, each with stroke counting. The difference is your hint. If you need three more strokes on the left than on the right, that is a lead (not a diagnosis): perhaps the left hand slips. Then the weaker side gets the first lengths of your warm-up for two weeks.
It isolates pull and rotation per side and shows differences between left and right. The Swim Wales plan calls it critical for the balance of rotation and propulsion [2].
Yes. Most freestyle swimmers coordinate their arms asymmetrically, often linked with the preferred breathing side and handedness [1]. That does not mean something is wrong, but you can improve it.
At the start yes, because it simplifies breathing. Later you take it off to feel the effect of head position on the pull [2].
The drill can be transferred to backstroke and butterfly, but the details differ. This guide is limited to freestyle.
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