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Why your arms cross your body when you sprint

The arms are usually the symptom. Fixing them without fixing what they are balancing rarely holds past ten metres.

It is one of the first things anybody notices from the side of the track, and one of the least useful things to shout. The athlete hears it, tidies the arms up for two strides, and it comes back the moment they stop thinking about it.

What the arms are actually doing

Legs swinging front to back try to twist the pelvis, and the arms exist to cancel that twist. Swung forwards and backwards they do it neatly. Swung across the body they stop cancelling and start contributing, so the shoulders rotate, the hips follow, and the foot lands slightly off the line the athlete is trying to run down. It is not the ugliest fault in sprinting but it leaks speed in a way nothing else on the video explains.

Where the crossing comes from

• Shoulders held high and tight. A shrugged shoulder has very little range front to back, so the arm takes the only path left to it, which is across.
• The elbow opening up. A long lever swings wide, and wide becomes across.
• A trunk that cannot hold the pelvis still. If the hips are rotating, the arms cross to balance them, and in that case the arms are doing their job, badly but honestly.

What StatLap can and cannot see here

The sprint event reports trunk lean against a zero to twenty degree range, elbow angle against the roughly ninety degree norm, overstride (how far the foot lands ahead of the hips), and knee fold and extension. The elbow angle is the one that touches this. When an elbow drifts open across a run, the crossing is usually already there or on its way.

But the crossing itself is a movement across the body, and a side-on camera is the one view that cannot see it. This is a case where a coach standing at the end of the lane beats the app outright. Film ten metres from the front or from behind if what you want to see is the arm path; use the side view for the elbow, the trunk and the strike point.

What to do about it

Seated arm swings set the ninety degree lever and stop the hands crossing the midline, which is why they are the drill the elbow finding sends you to. Do them long enough to be boring. If the hips are the real cause, arm drills alone will not hold, and the fix is trunk work plus a strike point that is not out in front of the athlete.

If the overstride number is bad too, start there. An athlete reaching for the ground rotates, and the arms will keep crossing to balance a problem that is not in the arms.

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