This is a question I hear a lot, "why is my heart rate higher/lower than this guy I train with?"
Every individual’s Heart Rate (HR) is highly unique to that person, comparing one person’s heart rate to another is comparing apples and oranges! A person’s HR is determined largely by genetics and also by environmental factors (such as medications, hydration, sleep), so what’s really important is knowing your own HR, how it reacts to efforts, and what your normal baseline is for different training zones.
Maximum HR, percentage of maximum at threshold, rate of increase/decrease and resting HR is going to vary (sometimes greatly) between any two riders you compare. Rider A may have a maximum HR of 195bpm and a threshold HR of 180bpm while Rider B has a max HR of 205bpm but a threshold HR of 175bpm. Is Rider A stronger because their threshold HR is higher, or is Rider B stronger because they have a higher max HR?
The answer is neither, the stronger rider is the one that is able to pedal their bike fastest :) Only knowing their HR doesn’t actually tell us anything about their relative strengths except where those riders’ physiology happens to land their HR’s.
What about if Rider A has a resting HR of 46bpm while Rider B has a resting HR of 54bpm, is Rider A fitter? Again, we have no idea, because a resting HR number doesn’t tell us how fast the riders can pedal a bike! An individual can assess if their own fitness is improving if their personal resting HR is decreasing over time (indicating a strengthening of the cardio vascular system), but comparing between riders gives no relevant comparison.
So next time the guy on the local group ride starts bragging about his threshold HR, just politely smile and say “that’s nice” and keep watching our own HR.