It’s interesting. There’s always that stat about Villa winning the league in the 80s using 14 players all season. They didn’t make changes for cups either. That’s incredible now to think about.
Liverpool named the same starting eleven 48 times out of 80 in the early 80s. The most a certain starting eleven has played for Klopp in all his seasons is 5 times. That’s not consecutively that’s ever.
One thing we can all agree on is medical and sports science is also infinitely better than it was in the 80s too. Also back then only one sub so no chance to rotate and rest players in a game. Another thing we can say is tackles were rougher and you could still go in from behind and two footed. So how on earth has ir become harder to stay fit now vs then?
Pre season tours, more meaningless internationals, the European cups effecting more teams and for more games there’s a number of reasons I guess.
The one that always interest me though is the ending of the keeper being able to pick the ball up from a pass back rule. I remember speaking to a pro who straddled both eras and him talking about the increase in fitness levels that were needed on that rule change. He said he was glad to finish playing and that it actually finished friends of his from playing full stop.
He was adamant that the constant ball in play without those periods players used to create to slow the tempo down or give them an in game break was a dramatic effect on intensity levels and changed the game into an endurance sport. As fans we hated the pass back teams and those elongated periods of play where teams did it but did outlawing it create something else?
Who knows but thought it was interesting.
You hit a major one with the difference in fitness required in those older days vs the modern sport, even with increased rotation I would suspect that both the peak stresses on one's body and the overall stress from playing a full game are higher today (there's probably some stats that could be used to quantify this, e.g distance covered, top speed, number of sprints...).
Bit of a hot take since I don't have any data for or against it, but another factor may be injury prone players being filtered out. As you point out, substitutions used to be more limited, so being able to reliably make it through the game was more important than nowadays where a player that picks up a minor injury every 3 matches that takes them out early and miss a match or two may still be worthwhile if they're brilliant for those 3 (Stanislas up until his last few seasons, for example, would have been washed out of any top flight side if only a single substitution was allowed).
Your question near the end about if the back pass rule change created "something else" is both a bit interesting while also nigh tautological and reminds me of a similar situation in the sport of curling. Interesting, in that we can debate whether football with backpass or football without backpass are "better", more fun to watch, more fun to play, etc. Nigh tautological, in that adding the backpass rule football with it and football without it are by definition different and therefore "something else" (though the above debates are much more interesting, just being a pedant here).
The parallel with curling is when they introduced a rule called the Free Guard Zone 2-3 decades ago. Basic goal of curling is that teams take turns trying to land their stones closest to the center of a scoring circle, with points at the end of the round going to the team with the stone nearest the center and the number of points being how many stones they have closest to the center before the other team's nearest. Being the team throwing last is a major advantage to scoring in a round, and this advantage goes to whatever team did not score in a round. Importantly, if no teams have stones in the scoring area at the end, this is called a blank, and the throwing last advantage stays with the current team. This is repeated for 8-10 rounds, and the winner is the one with the most points at the end.
As the sport became more professional, some players got really good at the throwing the stone accurately at high speeds such that, if they had the advantage of throwing last, they could reliably guarantee that no stones would score in an end and they would keep that advantage. In the most egregious of situations, you'd have a team start with the last stone advantage, knock out all the stones for 9 rounds in a row, and then in the last round knock out all the stones until the very last one, where the opponent has a single one in and it is relatively trivial for them to hit it out and score. This, of course, is not very fun to watch - like the periods of backpass in football before the backpass rule. You'd either need teams that both don't use this tactic to be entertaining or rely on the game only being interesting when a team makes a mistake, which became rarer as players got better at it.
So curling introduced the Free Guard Zone, this meant that for the first X number of stones thrown, if they were in a certain area between the thrower and the scoring area, it was illegal to knock them out until X stones were thrown. This way, if a team wanted to put stones in play they were guaranteed a chance to have multiple stones and the opponent could not trivially hit them out one at a time.
Professional curling definitely changed with the introduction of the Free Guard Zone (which has gone through variations to encourage stones in play since then as players got better at hitting multiple stones at once), from what had become a very straightforward hitting heavy game to the modern game combining lighter weight play behind guard stones and complex hits involving numerous stones. It was definitely fun for fans, but there was initial resistance from some players - as you'd expect, some of the best hitting teams were not a fan of their special skillset no longer being enough. But curling had gone through changes before then: before players got consistently good at those hard hits, light weight play behind guards had been staple play.
Similarly in football, before the backpass rule the sport had already undergone numerous changes. Some purely in tactics, from the early dribbling heavy English style to this thing called "passing" that some crazy Scots decided to do. Others, like offside, have gone through multiple iterations.
The most interesting parallel to me here is that the backpass and free guard zone rules were both put in to encourage offensive play that is entertaining for spectators and both paralleled increasing professionalism in the sport (yes, football players were already paid professionals, but the standards expected of them and their pay would increase dramatically in the modern version). Some players at the time of the rule change rebelled or quit as they couldn't or wouldn't acquire the new capabilities or skills, but neither change made the sport less skillful - if anything, I'd argue both increased the needed skill of players and teams.
Well, that was quite the tangent, but I guess it was a bit of fun.
