Can you offer a reference for this claim? Here's a counter-claim: "A normal resting heart rate for adults ranges from 60 to 100 beats a minute. Generally, a l

Can you offer a reference for this claim? Here's a counter-claim: "A normal resting heart rate for adults ranges from 60 to 100 beats a minute. Generally, a lower heart rate at rest implies more efficient heart function and better cardiovascular fitness. For example, a well-trained athlete might have a normal resting heart rate closer to 40 beats a minute." Source: Mayo Clinic, http://www.mayoclinic.org/healthy-living/fitness/expert-answers/heart-rate/faq-20057979 http://www.mayoclinic.org/healthy-living/fitness/expert-answ...