Have been performing a post-mortem on my run, comparing to my last effort. A bit of background - I'd been aiming to run 38 minutes, having achieved that in a parctice 3 weeks prior. The practice was at 6am in cool conditions, with little wind.
My conclusion has been one of my body working much harder in the heat, but I still couldn't understand how my heart rate got so high so quickly compared to all previous runs. Stryd is used to measure the average 'power' in watts I put into my run. My April practice run (38 min 10K) stats are shown in screenshot 1.
...whereas my Bristol 10K average watts consumed is much lower, as is my cadence (how many steps I take in a minute), as illustrated in screenshot 2.
Conversely, in my practice run my heart rate (purple) took a good 35 minutes to settle above 180bpm, so my body wasn't too stressed (screenshot 3).
...yet in the Bristol 10K race, my heart rate was consistently 180 and higher after just 10 minutes, in spite of running at the same or marginally slower pace (screenshot 4).
Physically, I felt I was at a similar level of fitness. The two runs were only a few weeks apart, and I’d trained regularly in the interim. I had a cold, but have run with a cold often during the past 6 months and it hasn't effected me THAT much. The only attribute I can find that was dramatically different was running in the sun, in a much higher level of heat.
I always imagined the effects would be dehydration - not an actual dramatic difference in heart rate for the same level of performance. But according to this, heat effects heart rate: https://www.runnersworld.com/race-training/training-in-the-heat
"Furthermore, both temperature and humidity increase heart rate and amplify these effects. At 60 to 75 degrees, heart rate increases by two to four beats per minute. From 75 to 90 degrees, heart rate increases up to 10 beats per minute, and humidity increases it even more. Perceived effort is accordingly much greater as both the temperature and the humidity rise. "
Guessing then that my body just isn't strong enough to cope with that pace at that temperature and humidity. I had no idea at the time, so ran the target pace until my body completely overloaded, and in doing so made myself pretty sick. I had to walk on two occasions. The first due to nausea. The second shortly before the finish, when my chest tightened up alarmingly (screenshot 5).
Has anyone else experienced such an alarming difference in heart rate when running the sun?