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(Pw:Hr) or Aerobic decoupling (i.e cardiac drift) is probably the most useful training metric for cyclists who want to accurately quantify fitness, adaptation to heat and proper hydration, and have a good indicator for long climbs and time trials.
Fast group rides, and the positive effects of drafting, often allow an individual to produce a higher power output at a significantly lower heart rate. This can lead to negative power to heart rate ratios, as opposed to a solo ride with an increasing heart rate and a decrease in power output, measured over longer periods of time. This is a good thing and should encourage the newbie or the grizzled old lone wolf to join in on weekly fast group rides.
Personally, I have found the Pw:Hr metric extremely useful in determining proper levels of hydration during and after exercise. A secondary benefit is looking back at an interval session and determining when the intervals had reached a point of ever declining returns for one’s effort. Knowing when to quit is just as important as knowing how hard and how long an interval should be, for a given purpose, as we develop as riders.
Long before the extensive use of heart rate monitors and power meters, individual athletes relied on perceived effort for determining pace and intensity during a ride. I still record my rate of perceived effort on a 1-10 scale, but often see glaring differences between what my mind and body is telling me, and what my actual input (power) and output (heart rate) really is. Rarely does a committed cyclist NOT work hard on the bike. In fact, most coaches need to restrain new riders from training until exhaustion and eventually dropping out of racing altogether.
Do yourself a favour and postpone that purchase of a fancy set of carbon racing wheels and a thousand dollar Garmin GPS. Instead, go out and buy yourself a decent power meter and a heart rate monitor. You will never regret your decision, and you will be faster for it in the long run 🙂