Why does my sprinter's arm angle open up in the last part of a race?
A tight elbow angle takes active effort to hold, and most athletes have never been taught to keep holding it once they get tired.
Watch a 200 or a 400 back on video and the pattern is easy to see once you look for it. In the first 60 metres the elbow sits at roughly a right angle, sharp and controlled. By the final straight it has opened out, closer to a slow pendulum than a driven lever.
Why it happens at the elbow first
Holding the arm at close to 90 degrees through a full sprint takes continuous muscular effort. It is not a passive shape the arm falls into, it is a position the athlete actively maintains, pulling the arm back through a tight bend rep after rep. As fatigue sets in and the legs slow down, the arms slow with them, and the easiest way for a tired body to keep swinging the arms at all is to let the bend open and swing them more like a pendulum, which costs less active effort per swing but moves less deliberately.
Does it actually cost speed, or is it just what tired looks like
Both, a little. A longer lever at the elbow swings slower for the same effort, which can quietly add to the very fatigue that opened the angle in the first place. But some opening late in a long sprint is normal even at the elite level, and a coach chasing a perfectly rigid elbow angle for 400 metres is chasing something that is not really the goal. The more useful question is not whether the angle opened, but whether the trunk and the stride fell apart along with it, or held together while the arm simply did less work.
What the Film Room shows you here
The sprint setting reports elbow angle against the roughly 90 degree norm, read frame by frame across the whole clip. That turns 'the arms looked tired at the end' into an actual number you can watch drift as the race goes on, rather than a guess about which part of the race it started in.
The camera reads the angle. It does not know why it opened. A gassed athlete with good technique and an untrained athlete with poor technique can produce the same elbow number in the last 50 metres, and telling conditioning apart from technique is a judgment call for a coach watching the rest of the stride, not something the angle alone will decide for you.
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Related
Why your sprinter's form falls apart in the last 20 metres
Every sprinter slows down late in a race. The question worth answering is whether the posture is failing on top of that, and costing more.
Read →Why do my sprinter's shoulders creep up around their ears?
Tight shoulders do not make anybody faster, they burn effort the legs needed and shorten the arm swing that was driving the stride.
Read →Why doesn't my sprinter's knee come up in recovery?
A trailing recovery leg is a longer lever that takes longer to swing through, and the cause is rarely the knee itself.
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