Does arm action out of the blocks matter as much as leg drive?
Loose or early arm swing can pull a sprinter upright before the drive phase is finished, which makes this an arm problem with a leg-shaped symptom.
Coaches drill the legs out of the blocks: shin angle, hip height, push back instead of up. The arms get a single instruction, pump them, and then get ignored. That is a mistake, because the arms are not just along for the ride.
What the arms are actually doing
In the drive phase a sprinter's trunk is held down and forward by the legs pushing back into the track. The arms are what keep that trunk from twisting. Every time one leg drives back, the opposite arm punches forward to cancel the rotation it creates. Take that counterbalance away, or time it badly, and the trunk has nothing holding it down, so it rises. That is one of the more common hidden causes of standing up on step two or three: not weak legs, but arms that popped the trunk upright before the legs had finished their job.
What goes wrong, and what it looks like
- The lead arm punches too high, too early, which lifts the chest with it.
- Both arms swing wide instead of straight front to back, so the trunk has to rotate to follow them.
- The arms slow down to match a leg that is already decelerating, instead of driving the leg faster.
Where the Film Room can and cannot help here
The block start setting on the Film Room reads drive-phase trunk lean, whether the hips climb instead of driving out, and back-leg extension at clearance. All three of those are downstream of the arms, without the Film Room ever looking at the arms directly. A high trunk-lean number on a start that looked like a leg problem is worth rewatching with the arms in mind before reaching for another leg drill.
A single 2D camera reads the plane it is pointed at. Arm action that is driving a trunk fault happens at the shoulder, off to the side of a side-on lens, so the Film Room will show the trunk rising without being able to tell you the arm punch that caused it.
Time your next meet with the phones you already have
Timing, the Film Room and the speed gates are free forever, with no account. A Club plan, $71 a month, puts your meets on your own results page, and one plan covers every phone.
Related
Why your sprinter's back leg never fully extends out of the blocks
The rear leg is supposed to finish straight at clearance, and when it does not, the fix is almost never in the leg itself.
Read →Why does my sprinter drift sideways out of the blocks?
Side-on video can confirm the drive phase looks fine and still miss the one plane where this fault actually lives.
Read →Why does my sprinter's arm swing look so wide?
Wide, flapping arms are usually a symptom of tension somewhere else, and it is a fault a side-on camera is not even positioned to measure.
Read →