I adjusted the heart rate monitor strap, applied some water to the sensors to ensure a good connection, and attached the monitor to my body. After a couple of clicks on my watch, the monitor was detected and my resting heart rate of 70 beats per minute was displayed on the screen.
I had read that it was important to determine my Maximum Heart Rate (MHR) so that I would be able to determine the various heart rate zones for my workouts. There is a simple formula that gives a generic MHR: 208 - (.7 x your age). Which in my case is 208 - 23.1 = 185.
However, there is also a more personalized method to determine MHR which is as follows:
1. Be sure you're well rested, well hydrated, and well warmed up.
2. Run hard and fast for 2 to 3 minutes. Jog back to your starting point. Repeat two more times, running a little harder and faster each time. On the third and last repeat, pretend you're running an Olympic race.
3. Check your heart rate during and immediately after the last repeat. The highest number you see is your maximum heart rate (MHR).
My track workout was to run 12 x 400m intervals with 1.30 rest intervals, which didn't really fit with 2 to 3 minute intervals required in the MHR test (each 400m interval takes about 1.30, so I'd really need to run 800m intervals for the test), so I decided that I would do the test next week instead.
I ran 11 x 400m and 1 x 600m at the track, all with 1.30 rest intervals. The weather was a cool 65F (18F) with no real noticeable humidity so I was able to run hard (average of 1:30 per 400m) and recover well between each interval. I ran a 600m interval at the end of the session to see how high I could get my heart rate and I registered 176 beats per minute. I was excited to get home and look at the graphs of my workout!
The graph shown above shows the pattern of heart rate increase and decrease during the first 10 intervals. The red line is the heart rate and the blue line is the pace that I am running. You can see that when the blue line goes flat (when I am running the 400m interval) my heart rate increases up to the peak just as I finish the interval. Then when I stop running hard and jog slowly back to my starting position, my heart rate rapidly falls. Of course, this is what I expected was happening, but it is nice to be able to see that the last 4 intervals on the graph are very similar and reflect that I was able to repeat the level of exertion over and over again.
I hadn't really been worried about my track workout paces being effected by the heat and humidity as they are basically running close to as hard as possible for relatively short distances and I can easily extend the rest intervals to allow me to recover for the next run. It had been the tempo runs that had been causing me the issues, and on Thursday morning, I got my first chance to try a tempo run with my heart rate monitor.
The books say to gain the most from a tempo run the heart rate should be between 87% (161bpm) and 92% (170bpm) of MHR, so that was my target. My workout was meant to be 2 miles easy warm up and then 3 miles at 7.22/mile followed by one easy mile. I had been able to handle 3 miles at 7.22/mile easily in the cooler months, and I know I can do it during 5K races in the heat and humidity, but the point of the tempo run is to train your body to handle a level of exertion that is just below the level that leads to fatigue - not to run a 5K race hard every week.
The weather on Tuesday at 7am was 65F with 90% humidity. I ran the first two miles easy and then increased my speed to something that felt like it was out of my comfort zone but that I would be able to maintain for 3 miles. I kept an eye on my heart rate which was 155bpm at the start of the hard 3 miles and gradually increased to 160bpm at 0.6 miles, 165bpm at 1.2 miles and hit a peak of 168bpm at 2 miles when I backed off a little bit to make sure I didn't go over 170bpm. My splits were 7.37, 7.37 and 7.41.
The graph above shows my heart rate and pace. I was really pleased that I was able to complete the 3 miles at tempo pace with more control than I have been able to in previous weeks. What I found really interesting was that even though I decreased my speed to a 9:00/mile for the last mile, my heart rate stayed above 160bpm, which probably means that I should run my last easy mile much slower.
The final workout of the week was a 13 mile long run. Easy/Long runs are meant to be performed in the 65% (120bpm) to 75% (138bpm) zone, and I had a feeling this was going to be much much slower than I am used to when I went outside to see the weather was 75F (23C) with 75% humidity at 7am.
It turns out that I would spend more time walking than running if I really wanted to keep my heart rate below 138bpm when the sun is beating down on a warm, humid morning. I started out at a slow 9:27 for the first mile and my heart rate quickly rose to 140bpm. I reacted by running slower (9:51, 10:19) and slower (10:55, 10:58) in an attempt to keep my heart rate as close to 140 as I could without having to walk. I managed to stay at around 145bpm for the first 10 miles, by which time the temperature was closer to 80F. I weighed my options of running slowly (around 11:20/mile) or walking and decided that I would continue running. I ended the 13 mile run in 2:21:46 with an average of 145bpm, which is much slower than I have ever run, regardless of the weather conditions and a full 2 minutes per mile slower than the pace required in my training program.
I have had a feeling for a while that I have been running my long/easy runs too fast and have not been getting the full benefits of them as a result - so at least now I have a tool that is going to force me to run them slower. We'll have to wait and see whether it makes a difference in the long run - I fully expect it will!
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