The 220-age formula is just an estimate, and not a very good one at that. I think most people would say that their max HR is higher than this calculated value. If you reached 173 during your 5K and were not feeling like you were about to die, my guess is that your max HR is probably in the high 170s. Knowing your max HR is only relevant if you intend to use it for HR zone training. However, IMO, knowing your lactate threshold is probably more beneficial for this purpose. There are tests you can do to estimate it. Lactate threshold is not a function of your max HR.

@pondee629 - I am 61 years old, and have wrestled with the same type of thoughts about max HR since I became a runner at age 55. The last 10K I ran (USATF Masters 10K Championship in Dedham, MA on April 30), my HR resembled your numbers: Average 157, max 172, fairly stable to slightly rising for most of the race, highest near the end when I was trying to put on a finish line kick uphill. I went anaerobic enough near the end to feel like I needed to puke, but did not actually do so. Also turned in a PR time, breaking 40 minutes for a 10K the first time in my life. Clearly, 220 minus age isn't working for me any better than it does for you.

Last time I saw my doctor, I asked how to tell what my max HR should be. She verified I was interested for training, and didn't offer any way to measure it. Just go by feel, she said.

So . . . My HR goes over 165 during any 5K I run as a race and during a lot of speed intervals. It doesn't go that high on easy runs. The highest I've seen it was 189 (at age 60). This was at the top of "the wall" on the third loop of the 8K USATF XC Club Championships in Tallahassee last December. At that point, I felt like I could no longer run; but that was the crest, and it was downhill to the finish, so I did manage some sort of finish line kick.

I take 185 to be a reasonable working number for my max HR. In addition to the experience at Tallahassee, when I use 45 for resting HR and 185 for max HR, the HR zones feel like the descriptions to me. In particular, Zone 5 comes out to anything over 170; and that's where I can tell by feel that I can't keep it up for very long. On solo easy runs, if I don't deliberately moderate my pace my HR will hang out in the upper 120s and 130s; the calculated bottom of Zone 2 is 129. That makes sense to me.

I don't really know where my lactate threshold HR is. I estimate lactate threshold running by pace, using my race times and the Jack Daniels calculator. This is imprecise; but it's also affected by weather, terrain, and current conditioning level. I only need it to be close enough.

I think the 220 minus age formula was designed for sedentary people who are just beginning an exercise program, to prevent them from working themselves into a heart attack. It's way too conservative for well trained runners.

There is significant individual variability in HRmax, with a standard deviation of 7-11 BPM. In addition, the 220-age equation is used because it's very easy and close enough, but the actual decline with age is less and this equation tends to underestimate the actual HRmax of older individuals.

http://www.sciencedirect.com/science/article/pii/S0735109700010548

At the wrist I get a 10 to 20 beat difference compared to the chest strap. For others this might not be the case. I find that the wrist is accurate when not running and is consistent when running, but just a lot higher.

A little late to the party myself. I'm turning 64 in just a little over a week. Got into using an HRM from the very beginning of resuming running at the age of 59, so I have all sorts of data as it applies to me.

First, max HR is, as noted above, highly individual. I've run a range of 30-minute critical power tests where I run as consistently and as fast as I can sustain over a 30-minute period. Since it is an outdoor test, environmental factors can play a role in how I feel relative to HR. At the end of the test I usually max out at between 184-195 bpm. I use 190 bpm as a useful maximum to set the top end of my HR zones. If I recall correctly, the program that I use takes the average of the HR over the last 10 minutes of the run to establish the Lactate Threshold HR (top end of Zone 4) and I show a very consistent pattern in HR when I run one of these tests.

OTOH, the end of race scenario actually tends to push my HR into these max values. The highest end of race values I have seen are 199 bpm at the end of a marathon after a nearly 300 yard sprint to the finish to overtake 5 people in front of me. But typically my race values will max out somewhere between 185 and 190 depending upon site-specific factors. Of course, my resting HR is way down in cadaver range (~47 bpm).