I guess you may have heard of "Zone training" and may be even "Power Training"? I used to do all my training with a Heart Rate Monitor (HRM) and then kept a careful watch on my Zones - how much time I spent in various heart rate zones with the theory being that I could control the amounts of work in each Zone, the better to manage my training.
So, in any given week I might be able to say "I've done 6 minutes of Zone 5 (near maximum heart rate) training, and 2 hours of Zone 2 (fairly low level exercise)" and then compare that to other weeks, and perhaps increase or decrease my time in various Zones according to my training needs.
Trouble is I never really got to manipulate my training in this way:
1) It's quite complicated. The software you use to record the amounts can produce graphs of what you are doing - but what does it all mean? And what should you do next?
2) The numbers could jump around, so you could have 6 mins in Zone 5 one week, and 12 minutes the next - just by accident.
3) It was a distraction. You felt like you were managing your training when really you were just recording it, and in the meantime you would be ignoring the signs from your body about what the real effect the training was having.
Eventually, when the HRM chest strap ran out of batteries I didn't bother renewing them, and had my best year on the bike ever. That was several years ago and I'm still training without an HRM.
Italian events and European climbs