You always need to consider your own resting pulse rate (mid-to-high 40s for me now; lower 40s when I was younger and more fit) in determining your personal max heart rate. I have always paid far more attention to recovery rate -- how long does it take me to get back below 90, then 70, then 60?
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069