There is actually some evidence that, in a sprint, humans might be able to run faster on all 4 limbs than on 2
https://pubmed.ncbi.nlm.nih.gov/27446911/#&gid=article-figur...
That record progressed
2008 18.58
2015 15.71
2.87 seconds over 7 years. https://en.wikipedia.org/wiki/Kenichi_Ito_(athlete)If we check in on more recent progress since then, we find the current record is 15.66 set in 2022. https://web.archive.org/web/20241222175947/https://www.guinn...
Another 7 years, for an improvement of 0.05 seconds, or about 850 years of linear improvement to reach Bolt's 9.58 seconds.
Anyone wanting to bet on beating Bolt by 2048?
Trail runners often run with poles on up or down hills. Not sure about top speed, but from experience the poles definitely help with endurance.