I support the runner-on-second experiment.
. Given a brief 60-game season, I think it's a great time to try stuff like that.
Obviously pandemic and compressed training window amplifies the issue. But I think long extra-inning games are problematic every season. Relief pitchers are routinely stressed, and often talk about pitching tired. When a team plays a 15 inning game, suddenly there are a bunch of additional innings that need to be absorbed by perhaps overtaxed arms. The long extra-inning games can't be anticipated, either; if a team knew one was coming, the pitching coach might better plan accordingly.
No sure my memory is accurate, or my correlation to health issues is accurate. But to consider two recent Cubs relievers:
1. Morrow was effective, but given his past health issues, Theo wanted him on a very controlled usage plan. But then came an extra inning game, Maddon wanted to win, and in went Morrow on a day he wasn't really supposed to pitch. His career ended shortly thereafter. (I may not be remembering right... and maybe his arm demise wasn't directly attributed to that outing anyway...)
2. Kimbrel has had his mid-season start, and was maybe starting to get used and save some games. He'd already been used too often in the last several days, but then they had an extra innings game with the Giants. Maddon wanted to win, in went Kimbrel, and he was kind of a mess the rest of the way. Coincidence, maybe; or maybe not?