Arm swing in running: elbows at about 90 degrees, loose hands, nothing crossing the midline. What studies show, how to practice it and which mistakes cost energy.
The honest answer up front: a good arm swing means: shoulders low, elbows at about a right angle, forearms swinging in the running direction without crossing the body's midline, hands staying loose. That is how the running-drill collection of the Swiss Federal Office of Sport (BASPO) with Swiss Athletics describes it [1]. Your arms are not decoration, they are your metronome.
Does it measurably help? The evidence is honestly mixed. A review of technical factors in running economy lists maintaining arm swing as rather beneficial but explicitly warns against deriving a general "ideal technique" for everyone [2]. In a computer simulation, a runner model with active arm swing used the least energy per distance, 5.52 versus 5.82 J per kilogram and meter with fixed arms [4]. That was a simulation, not a measurement in people. And in a small experiment (eight people, oxygen measured in six), consumption was the same with straight and bent arms while running [3]. In plain words: arms joining in probably helps. Whether 90° is the only right angle, nobody knows for sure.
How hard is it? You grasp the principle in five minutes. In experience terms you need a few weeks until the swing stays loose even when tired.
BASPO starts standing: shoulders low, upper arms swing smoothly back and forth, the elbow angle ideally stays at about 90 degrees [1]. The motion starts at the shoulder. Milestone: you can swing for 30 seconds without the shoulders rising.
The forearms swing in the running direction without crossing the body's midline [1]. Imagine holding a handbag on each side that you swing forward and back ("handbag movement" in BASPO) [1].
The hands are loose, the wrists stay stable [1]. Imagine holding a raw egg or a bag of chips in your hand that you do not want to crush. Anchor: fists cost forearm tension you do not need for propulsion.
As a progression you raise and lower the heels in rhythm with the arms [1]. This lets you feel that arms and legs are coupled. Milestone: 20 seconds in rhythm without the hands twitching.
Only after standing and walking do you run 30 meters easily and pay attention only to the rhythm of the arms. According to BASPO, running drills last 10 to 20 minutes per session, 20 to 30 meters per pass, 2 to 3 repetitions [5]. Raise the pace only when the rhythm sits at slow speed.
Film yourself for ten seconds from the front. Do your elbows point outward or do your hands cross the middle? You see that better from the front than from the side. If the hands swing at about navel height forward and behind the hip, the picture is consistent.
Shoulders low, elbows at about 90 degrees, forearms swinging in the running direction without crossing the midline, hands loose [1]. That is a teaching picture, not the only possible style.
In a simulation, active arm swing saved energy compared with fixed arms [4], and a review lists maintaining arm swing as beneficial [2]. In a small experiment (eight people, oxygen measured in six), consumption was the same with straight and bent arms [3].
The reason is not conclusively clarified. One experiment found that bent arms lower shoulder torque by about a third but raise elbow torque [3].
BASPO recommends 10 to 20 minutes of running drills per session, 2 to 3 repetitions per exercise [5]. For arm swing alone, two minutes before a run is often enough.
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