One of the interesting facts about land mammals is that their life expectancy is the same – if you measure it in terms of heartbeats. All land mammals will live for about 1 billion heartbeats. A shrew has a heart rate of 600 bpm (beats per minute) and a life expectancy of just three years. An elephant with their 30 bpm heart rate can expect to live over 60 years. The hearts of each animal will beat 1 billion times in their expected lifetime.

Humans, of course, are the exception – we can last for about 3 billion heartbeats. I’m not sure why – maybe medical technology, nutrition, who knows. Marine mammals don’t follow the pattern either, but let’s stick with ourselves and our 3 billion heartbeats. There are 525,600 minutes in a year, and the average human has a resting heart rate of 72 bpm, so divide that into 3 billion and you get a life expectancy of 79.3 years.

I was talking about this topic with a co-worker when he asked me “So how many days of your life did you burn up by running that ultramarathon?” Holy cow. My heart rate was probably around 150 bpm for the 12 hours it took me to run 50 miles, so in half a day I used up just over a day’s worth of heartbeats! More than that, I ran for 180 hours total in 2006 – that’s 7.5 days of extra heartbeats spent on running! Is it really worth it?

Before I started running three years ago, my resting heart rate happened to be the average 72 bpm. Let’s assume that I lived my first 28 years at that heart rate, which means I used up 1.06 billion of my life’s heartbeats in that span. Now let’s assume that I keep running (or cycling or otherwise keeping in good shape) for the rest of my life. My current resting heart rate is about 56 bpm, so if I keep that up for my remaining 1.94 billion heart beats, I would live another 69 years… to the age of 94!

By getting into (and staying in) good shape, I increased my life expectancy by 15 years! Each year I spend as a runner costs me one week of heartbeats, but the improved fitness adds 13 weeks to my life expectancy for a net of +12 weeks. Another way to look at it: Every month of regular running adds one week to my life! Diving deeper yet… assuming I run 3.5 times per week, that means that each run adds 12 hours to my life. How’s that for a good investment?

Yes, it’s worth it. Assuming, of course, that my clock will tick 3 billion times…