No marathon runner can fight for an hour without rest, just like any boxer.
In 1885,
James Kelly and Jonathan Smith fought non-stop for several hours each round, with the only breaks being when one or the other or even both were knocked down, whereas modern boxing rounds only last three minutes with one-minute-long breaks in-between; in fact, their first round stretched onto two hours. The entire fight was six hours long, spread across a total of seventeen, grueling matches where, quote: in the eighth round, "Kelly let go the right but received on his nose from Jonathan, the claret flowing very freely from Kelly’s snuffler", in the twelfth round, "Kelly still [bled] from the nasal organ", in the fourteenth round, "Kelly [was excited], and perhaps somewhat annoyed at the obstinacy of his nose, which WOULD bleed", and in the fifteenth round, "... nearly an hour was occupied in sparring, feinting, stepping [back,] etc."
Tl;dr — James Kelly and Jonathan Smith fought brutally across seventeen rounds for a total of six hours, with their first round lasting two hours and their fifteenth lasting one. A few highlights include Kelly taking a blow to the nose in the eighth round and continuing to fight while bleeding until the seventeenth, and the two of them continuing to launch back-and-forth blows at one another despite being "considerably contused" — bruised.
They only ever collapsed shortly after the colossal battle; at this point, though, their bodies were "
bloody and swollen".
In 1893 — at this point, one-minute-long breaks were established —
Andy Bowen and Jack Burke fought vigorously across one hundred and ten matches over seven hours. Throughout the fight, Bowen, seemingly invulnerable, completely steelwalled Bowen despite being the stronger slugger. And, most notably, at some point during the fight, Burke broke every bone in both of his hands from relentlessly pummeling the "Iron" Bowen, and continued to fight back against him; albeit, with a weaker offense. In the end,
they both emerged bloodied, bruised, and battered but still standing, even after seven hours.
Just pointing these cases out.