A bit of background on my online training
Over the last 25 years or so I've found that indoor training is the key to improving my fitness and performance in time trials. Away from the vagaries of dealing with terrain and motor traffic, I can focus on the workout rather than survival. 25 years ago, power meters weren't readily available, and one's focus was on heart rate as a measure of exercise intensity. Indoor trainers offered adjustable resistance, but little else. In those days I found the structured plan in Pete Read's The Annual Manual (the Black Book), which presented a month by month plan for training on an indoor trainer, to be highly effective.