I Wore a Down Jacket in the Summer to Heat Train. It Was a Disaster.

In 2024, I rode 1,000km from Reno to Las Vegas, with the big draw being a chance to cruise through Death Valley. What sounded great on paper turned into 30 mph headwinds and temperatures up to 110°F (43°C). On the 3,000-foot climb out of the valley, I could only manage about 500 feet of elevation at a time before collapsing under a scrubby bush for 10 minutes to rest and regroup. Needless to say, I was looking for redemption.

What is heat training?

I wanted another crack at the desert adventure, but I certainly didn’t want to relive that heat horror, so I decided to try heat training. It’s essentially repeated exposure to enough heat stress to force your body to adapt. For more scientific insight, I reached out to Brian Maiorano, Coach Liaison at CORE Body Temperature, to find out what’s actually happening inside your body during the process.

“When you consistently cause the body stress by raising your heat strain index, it says, hey, I don’t like this. This is causing me more work,” Maiorano explained. “Your body then adapts by creating more blood plasma. And that extra blood plasma is what allows you to start sweating earlier and start sweating more profusely.”

It’s that increased plasma volume that gives you a more effective sweat response, helping your body better manage the physiological stress of exercising in the heat. Sounds ideal. So how do you actually do it?

Can you heat train outside?

I don’t own a bike trainer. I’m the type of cyclist who would ride through a hurricane before I sit on a hamster wheel. (Spoiler alert: we did hit the tail end of a hurricane in the desert, but more on that later). So when it came to heat training, my only option was outside. My inspiration was that now-iconic social media video of Tom Pidcock heat training for Worlds, so I basically recreated it. I wore a full wool winter kit, topped with a CORE Body Temperature Tyvek suit. Over that, I added a Rapha down jacket with the hood up, plus thick restaurant freezer gloves—the kind you saw Jonas Vingegaard using at the fish factory. I added sweat shorts over the Tyvek suit to help block the wind, winter shoe covers, a wool cap, my puffy hood, and finally my helmet.

It was giving Beastie Boys in the “Intergalactic” music video. I looked absolutely deranged. I was also hot, and that was the goal. I used this setup to bike outside three times a week for three weeks, and each session lasted one to two hours.

According to Maiorano, the strategy I had in mind was possible. “You can do it on a road bike,” he says, but the focus needs to be getting “your layering more dialed in to prevent the wind evaporation.” In other words, the challenge isn’t necessarily creating enough heat; it’s keeping your body from getting rid of it. On a road bike, the constant airflow helps sweat evaporate and cool you, which is exactly what you’re trying to limit. Maiorano explains, “Try a normal cycling kit, but then over top of that, a snug rain jacket and snug rain pants. And then thermal layers on top of the rain jacket. The reason you don’t want the thermal layers underneath is because you’re the one generating the sweat. If you get the thermal layers wet trapped inside the rain jacket, they’ll get soaked and cool you off. So thermal layers on the outside.” You’ll notice, this was my first of many mistakes.

How do you measure the adaptations?

A CORE sensor will certainly do the trick but I started my training block without one. The sensor tracks a metric called a heat strain index, which combines your core temperature and your skin temperature. “The heat strain index goes from 0 to 10,” Maiorano explains. “For heat training, that magic spot is 3 to 7. You just want to get in there and hold that for 45 minutes, 60 minutes, 90 minutes if you’re really looking for an intense session.”

If you don’t have a sensor, Maiorano says he used to tell his athletes to “go cook yourself, but don’t overcook yourself.” The obvious problem: What exactly does that even mean? A sensor gives athletes a target, but over time it can also teach you what an appropriate heat session feels like. Maiorano compares it to riding with a power meter: eventually, you can probably guess your power within a few watts without looking down. Heat training can work the same way.

How did it go?

The honest answer? Not great. My husband Richard was following the same heat-training protocol as I was. In fact, he even had hotter weather to train in during an elusive San Francisco summer heat wave while I was travelling. But on day one of our three-day trip, 109 miles into a 160-mile day, he was puking in the bushes with temperatures hitting 109°F. Day two is where the wheels fell off for me.

I was riding in the remnants of Hurricane Rachel, battling a diabolical headwind through Death Valley that had me, Josh Ross, Mike Levy, and other friends doing everything we could to hold 10 mph in a full echelon across the road. After three hours of unrelenting wind, my speed had dropped to 8 mph and I was done. I sat under that well-known Death Valley scrubby bush and tried to regroup. After what felt like an eternity—which was probably only 10 minutes—I got back on my bike and was immediately dizzy, with zero power in my legs. Game over.

Sadly, I didn’t even make it to the 3,000-foot climb out of the valley, which I had originally thought would be the true heat-training test. Instead, I got to test whether my iPhone satellite feature would work to get an SOS text to our friends running SAG. Desert: 1. Lisa: 0.

Was it the heat that actually did me in? According to Maiorano, on an ultra-endurance ride, it’s not that simple. Heat, fatigue, and fueling can compound on each other. Overheating increases cardiovascular strain and can interfere with digestion and fueling, while inadequate fueling can further compromise performance.

“Overheating and lack of fuel will reduce the body’s ability to clear lactic acid,” Maiorano explains. “So you can cross over that lactate threshold at a much lower heart rate or power than you normally would.” In other words, between the headwinds, heat, fatigue, and fueling, who knows what put the nail in my coffin. Realistically, it was probably a combo platter of everything.

Learn from my failure

I asked Maiorano if he thought I could have done anything differently. No shocker here, but he thought there was plenty. If you are prepping for a massive ride in the heat, here is the playbook I should have followed.

First, stop overcooking individual sessions. “The idea behind doing a heat session in the heat zone we prescribe is, yeah, it’s hard, it can be miserable while you’re doing it. But the next day you should be recovered to do your regular training,” Maiorano noted. This makes a lot of sense, since I was pedaling squares and feeling like hot garbage for two days after each heat-training ride. Second, consistency beats intensity. “If you were only doing two sessions per week… you may not have been doing it enough to gain super high adaptation over the long term,” he explained. I had managed to hit both ends of the failure spectrum: I got too hot in individual sessions, but wasn’t consistent enough overall.

Third, track your sweat rate. Maiorano recommended measuring sweat loss during normal rides versus heat sessions to understand exactly how much extra fluid and electrolytes you need to replace. Finally, give yourself a proper runway. “You can get fully heat adapted within six to eight weeks without a big stress,” Maiorano says. “I mean, you can do it in two if you really need to, but a more comfortable level is six to eight weeks.”

As for me, I plan to try this again. Some rides you can walk away from. This isn’t one of them. Not only did both my husband and I have issues in the heat, but we also encountered the hurricane and never made it to the third day because of weather warnings. My plan is to go back in March 2027. This time, I’ll start earlier, give myself the full eight weeks to adapt, and stop treating every session like I’m roasting myself to medium-well. Will it change the outcome? I guess we’ll find out. But one thing won’t change: I’ll still be riding around San Francisco looking like an idiot.