I live in the suburbs of Philadelphia, and every summer running in the heat and humidity proves to be a challenge for me. Even getting out by 5:30 in the morning does not always seem to improve conditions substantially. When running tempos and intervals in warm, humid weather, I always struggle to hit the times I feel I should be able to make and end up frustrated. My question to you is: is it comparable to do these types of runs at a similar effort level and/or heart rate that I would expect under more ideal conditions? Or should I just plan to add a certain amount of time (e.g. 5, 10, 20 seconds) to each mile or interval? Should tempos and intervals each be handled differently? Any light you could shed on this would be much appreciated. Thanks for your help!
Before relocating to San Diego a few years ago, I spent my summers running workouts in the heat and humidity of New England, so I understand your seasonal struggle when it comes to hitting target paces during some of your toughest workouts. And while it’s certainly frustrating when the numbers on the watch don’t seem to make any sense, don’t let this fool you into thinking that you’re not as fit as the last mile split in your most recent tempo run.
Just as runners living at altitude have to adjust their target paces and heart-rate zones to account for the elevation and lack of available oxygen, so too do flatlanders who have to deal with high heat and oppressive humidity. Studies have shown that when the temperature rises above 65 degrees, your heartrate will also rise by about 10 beats per minute and performances will slow. If the humidity is also high, add another 10 or so beats to that number. My own experience tells me that under these types of conditions, my average pace will often be off by 10 to 20 seconds per mile at the same effort level. What does this mean? In short, slow down.
If your average heartrate on a typical tempo run performed under near-ideal conditions is in the range of 165 to 170 beats per minute, on a hot, humid day, trying to maintain that type of effort will yield a number in the neighborhood of 190. While you do everything in your power to stay “on pace,” you’ll also be working dangerously close to your max heartrate and exerting yourself at an effort level that’s much greater than it should be for that given workout–or is even safe, for that matter. The best thing to do in this sort of situation is to aim for your normal heart-rate numbers (or, if you don’t wear a heart-rate monitor, the same effort level) keeping in mind that, in the end, your average pace will be a few ticks per mile slower than usual. For example, if the pace of your tempo runs is typically 7:00 per mile, under oppressive conditions the same sort of heart-rate (or effort) might turn out to be 7:15 per mile. This is OK! Your body doesn’t know the difference between a 7:00 mile and a 7:15 mile, but physiologically, you’re still getting the same benefit. The same principle applies to interval workouts — slow down, but keep the effort level the same.
Hang in there, and don’t let the heat and humidity hamper your training!