Why Does Heart Rate Decrease as Fitness Improves?

Question: I’ve noticed that my heart rate at lactate threshold decreases as my fitness increases. This seems counterintuitive. I would think that a better-trained athlete should be able to push to a higher heart rate before reaching lactate threshold. — Justin M.

Coach Fred Matheny Replies: The question that occurs to me is, How do you calculate your lactate threshold? Are you getting a lab test done with actual measurements of blood lactate? Or do you mean the intensity you can sustain for about an hour?

Generally, as fitness increases, the percentage of max heart rate that you can sustain also increases. So if you can handle 85% of your max for an hour early in the season, you might increase that to 90% in June.

Also, the power you can generate for a period of time increases at a given heart rate as you increase fitness. So, if you can sustain 250 watts at 160 bpm in April, you might be able to sustain 270 watts at the same heart rate in the summer after suitable training. This means that after training, your heart rate at 250 watts would be lower.

To restate your question slightly, yes, your heart rate at a given power output decreases as you get fitter.