I think he is refering to the second stage = etape. There are stages in hurdles race.

"Second souffle" se dit "second wind", so I don't think it's that. However, for me the difficulty is what he means when he says holding on "to" : does he mean "until" or "through" the second stage? Colloquially "to" is often used instead of "until", the sense being "through to", through being understood. Alternatively does he mean "maintenir" (le rythme) through the second stage?