As someone who trained as a Sports Trainer (ASMF) Level II - one thing to not forget is the dangers of 'overtraining'.

The 'many short bursts rather than one long session' is basically good advice. But if you train EVERY day with NO REST DAYS at all, you can push yourself too hard. With muscle training (weight resistance lifting) one rule of thumb was to have regular periods of rest to allow the muscles time to rebuild/relax. With guitar, it is a little different from weight lifting, but taking one day off a fortnight, a few days to a week off after a month or so, etc, would be in line with advised medical theories.

True, missing a day will make the next practice time seem harder (so lower your expectations a little that first day back!), but if you push yourself too hard, you may easily end up with RSI type injuries, which will mean that you will then unwillingly take an enforced break of maybe months before you will be able to play again.

You are more likely to 'overtrain' like this at the beginning, as your body will gain more strength in time, and be capable of more work before fatiguing. RSI is related to excess muscle fatigue. If you don't do the particular specific muscular exercise for many months or years, you will have to start off at a lower level than when you stopped, and build up again, but you will retain some of what you gained, so you will 'strengthen up' somewhat faster than originally.

'No Pain - No Gain' is bullshit! Discomfort is maybe ok if not too severe, pain is right out - that means soft tissue damage!

'Moderation in all things, except moderation itself.'

Robin