For most of the year, I have a rough sense of what a good workout looks like in terms of pace. An easy long run through Fort Clinch singletrack comes in around 9:30 to 10:00 per mile. A solid tempo effort on the Parkway sits somewhere in the 7:30 to 8:00 range. I’ve run these routes often enough that I mostly check my watch to confirm what I already feel.
Then late April arrives. Not all of April — the first two weeks are still fine. But somewhere around the third week, the numbers start lying.
I’ll head out at 6 AM thinking I’m going to run an easy 8-miler. Same route I’ve done fifty times. By mile 3, I’m working harder than the pace suggests I should be. Heart rate that belongs at 140 is sitting at 155. I’m sweating through my shirt twenty minutes earlier than usual. The effort that used to produce 9:30 now costs 10:30, and even that feels like more than easy.
This isn’t fitness loss. This is Florida.
What’s Actually Happening
Heat and humidity don’t just make running uncomfortable. They change the physiology. When your core temperature rises, your body diverts blood to the skin for cooling — blood that would otherwise go to working muscles. Your heart compensates by beating faster, even at the same pace. Add humidity, which impairs evaporative cooling and keeps core temperature elevated, and you get a compounding effect.
I’ve found that a humid morning in the high 60s with a dew point around 65 adds somewhere between 30 and 45 seconds per mile of equivalent effort on a sustained run. By late April on Amelia Island, you’re already feeling this on anything over six miles. The dew points that were sitting in the low 50s through March are now pushing into the mid-60s, and they’ll keep climbing through August.
So if you’re still targeting March pace numbers in late April, you’re either running harder than you realize, or you’ve started wondering what’s happened to your fitness. Neither is productive.
Switching to Heart Rate
Starting in late April, I run most of my easy and moderate efforts by heart rate. I keep that through September. The logic is simple: heart rate is a more honest signal of effort than pace when heat is a factor. Pace has too many variables stacked against it once temperatures and humidity climb.
For easy runs, I target 135 to 145 BPM — roughly Zone 2 for me. What that translates to in terms of pace depends on the morning: could be 10:00, could be 11:30. I’ve stopped caring which. The purpose of an easy run is aerobic stimulus without recovery cost, and pace won’t tell me if I’m hitting that. Heart rate does.
For longer efforts along the beach or through the Egans Creek Greenway, I’ll set a ceiling and let pace drift naturally. If it’s 80 degrees and full sun, I’m not chasing a number. I’m staying under 150 and finishing well.
For actual workouts — tempo, fartlek, anything structured — I lean on effort perception more than heart rate, because heart rate lags and workout intervals move fast. But I still use it as a check: if my HR at what should feel like a tempo is pushing into territory I’d associate with a sprint, I dial back.
The Practical Adjustments
A few things that make heart rate training workable in Florida heat:
Get out earlier. The difference between 5:30 AM and 7:00 AM in late April is significant. Dew point, air temperature, and direct sun all affect effective effort. I schedule long runs for 5:45 AM when effort quality matters. If I sleep in and don’t make it out until 8, I cut distance and run purely by feel.
Accept slower paces early in the season. The first few weeks, you’ll run noticeably slower at the same heart rate. That’s not regression — it’s your body adjusting to thermal load. In my experience, after four to six weeks of consistent heat exposure, pace at a given heart rate creeps back toward where it was. Runners who fight this adjustment by pushing pace end up overtrained by July. I’ve done that. It’s not worth it.
Pre-hydrate on longer runs. Once we’re past mid-April, I drink 16 to 20 ounces before any run over an hour. Not because I’m thirsty — because pre-hydration gives you a buffer before fluid loss starts compounding your heart rate. Running dehydrated in heat drives HR up faster than the heat alone does.
Route for shade and breeze. On Amelia Island, the north end beach gets a consistent ocean breeze and stays cooler than inland roads. The canopy sections inside Fort Clinch are noticeably different from the Parkway in the open. I route harder efforts through shaded or breezy corridors when I can. Running a tempo on the south end of Amelia Island Parkway at 8 AM in late April, full sun, is not the smartest use of effort.
What This Looks Like Week to Week
A typical late-April Tuesday for me: out the door by 5:45 AM, usually heading toward the Fort Clinch loop or north along the beach. Heart rate target is 140 to 145 for the first five miles, then I’ll let it climb to 150 to 155 for a mile or two in the middle if the legs feel good. Total distance comes out to 8 or 9 miles. I stop checking pace splits by May.
That adjustment is what makes Florida summer training sustainable. I’ve had some of my best quality long runs in late summer, in conditions that would have wrecked me if I’d kept chasing pace targets. The runners I know who struggle through June and July are usually the ones who keep expecting March-effort numbers from an August morning.
The heat takes your pace. That’s just the deal. Run by heart rate, get out early, route smart. The fitness is still there — it just shows up on different terms.