I've been self-coaching for 3 years now. It's been interesting. I feel like I have a good handle on base training and strength work, but I struggle with trusting my own judgement on periodization and tapering.
Quote from Lydiard:
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"I'm always telling young athletes; "If you look back last year at your performances and one day you went out, the previous year, you ran your best time of the year; everything went right. If you knew WHY you ran so well that day and this year you can put your training together, so on the day of the Japanese Championships or the Olympics or the big race you are training for, you can produce your top form; then you know something about training. But until you can do that, you don't know anything about training. You are just a good athlete who, one day, would run a good race but you don't know when.
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I've had several races where I completely blew away my expectations and felt awesome and ran really, really well. The problem is in duplicating that. A lot of times for me this occurs in the "middle" of my season, when I'm still maintaining peak mileage and running "strength" workouts. I'll just show up to a race with no real expectations, and then, bam! - a new pr. And it's very possible that I won't match the performance later on in the season when I am trying to peak.
What I do know is that when I get too caught up in workouts - doing intervals with limited recovery, running against the clock, pushing tempos too hard - my racing performances usually suffer.