The most common masters training mistake Anthony hears about on the podcast is too much hard work. Riders feel guilty doing easy rides, equate fatigue with progress, and end up doing four or five 'hard' rides a week — none of which are properly hard, and all of which prevent recovery. The result is a permanent state of grey-zone fatigue and a flat FTP.
Two hard sessions a week is the right answer for almost every masters cyclist. The polarised model Stephen Seiler describes works even better with age, not worse — because the recovery cost of true high-intensity work is higher, you do it less often but make each session count. Typically that's one threshold session and one VO2max or repeated-effort session, with everything else either zone 2 endurance or full recovery.
Three hard sessions a week is the upper limit, and only sustainable for short blocks (4-6 weeks) under careful recovery management. The third session pushes total weekly stress significantly, and most masters cyclists trying to hold three for longer than 6 weeks end up with elevated resting HR, falling HRV, and stalled gains. Any coach Anthony has interviewed will say the same — three is a ceiling, not a target.
Four hard sessions a week is overtraining, full stop. There's no version of this that works for an amateur masters athlete training 8-12 hours a week. The body cannot recover, the quality of each session degrades, and the fitness gains that would have come from two well-recovered sessions are forfeited. The masters cyclists who keep gaining year-over-year are the ones who do less hard work, but more recovery and more strength.