One of the biggest reasons has been the improvement and emergence of training technology, such as power meters, GPS, and most especially training analysis software. With more data to analyze, we've even come up with metrics to assess training which didn't exist just a few years ago. When training is better analyzed, and mistakes, plateaus or injuries are avoided, training becomes more consistent and new higher performance levels are achieved.
Talent will get you far, but attention to the details of training will get you to your potential. The metrics provide the details of your training.
One of those metrics which has emerged in the recent past is Efficiency Factor, (EF). EF is simply the watts produced per beat of heart per minute, or EF = Watts/HR. So if you can produce 200 watts at 100 bpm, your EF is 2.0.
This metric does an excellent job at assessing aerobic conditioning, especially if you use your HR monitor with your power meter. If you begin the aerobic base-building phase of your training with some easy rides, by the end of the phase you should see the power you can produce at easy, aerobic efforts, increase. Or you should see that for the same power output, your HR is lower.
This time of year is perfect for tracking your EF, and seeing if you're improving your aerobic efficiency. It gives you something to judge the quality of your training, build your confidence with, and get some satisfaction from all the effort you put in through the winter.
This metric isn't very reliable for assessing training on hard rides, such as group rides with attacks, or big climbs, hill repeats, etc. You will have long recovery periods, sitting in, attacks of high output, etc. These have too much variance in a workout to really give you a consistent stimulus to base any inferences on of EF for the effort.
How do you assess this? TrainingPeaks will do it for you, just click on the "Map & Graph" button for your workout, and it comes up in the metrics on the right. (See example below).
(Click on image to enlarge)