For sprinting I don't know that there is, given that muscles are capable of exerting more force than their weight.
If there are absolute limits, they are probably in the ligaments. See my answer above about baseball pitchers.
Maybe. https://en.wikipedia.org/wiki/Ulnar_collateral_ligament_reco...:
“Some baseball pitchers believe that they can throw harder after ulnar collateral ligament reconstruction than they did beforehand. As a result, orthopedic surgeons have reported that parents of young pitchers have asked them to perform the procedure on their uninjured sons in the hope that it will increase performance. However, many people, including Frank Jobe, believe that any postsurgical increases in performance are most likely the result of the increased stability of the elbow joint and pitchers' increased attention to their fitness and conditioning. Jobe believed that rather than allowing pitchers to gain speed, the surgery and rehab protocols merely allow pitchers to return to their pre-injury levels of performance.”
(I don’t see that header “misconceptions” follow from that paragraph, which says “some people believe A, others believe not-A”)
Also, even if ligaments can’t be trained to be stronger and can’t be replaced by something stronger, longer arms should lead to faster throws for the same forces on those ligaments, wouldn’t it?
Longer arms: maybe. The tallest pitchers aren't the fastest, though. And there will probably never be a human with a 10 foot wingspan.
There have always been pitchers with unhittable fastballs, but often they can't control them and they walk too many batters.