It's not your imagination--your training routines definitely got harder when you landed in a warmer climate.

You’ve been looking forward to your winter getaway since well before Halloween. But if you feel like your training routines suddenly got a lot harder on those first days after landing in Aruba, or Miami, or St. Thomas, you’re not alone. It’s not just your imagination making you feel as if you are slower than usual, affecting your motivation and your results. You are actually performing everything at a slower pace than you did just last week, back home where the temperature was hovering in the lower forties.

There’s a physiological reason for that heat-induced slowdown. In room temperature, and climates you are used to, your body delivers blood to muscles as you exercise; some is delivered to the skin to help dissipate the heat that your muscles generate. But on those first days in a hotter climate, your blood has to fight a war on two fronts: It has to maintain the blood levels to your muscles while also increasing blood flow to your skin as a way to combat the increased heat. As a consequence, your heart rate goes up and you begin to feel like exercise is strained.

To deal with this issue, your body does an amazing thing: For a very short time—about the first three to six days that you’re working out in the heat—it makes more blood. This increase in the volume of blood allows it to better service the muscles and the skin at the same time.

Research has shown that other subtle adaptations occur over the next 14 days—if you continue to work out in hot weather—that acclimatize you to the heat. Taken together, all of this makes your workout feel normal again: Your heart rate decreases, your core body temperature decreases, and your sense of exertion goes down. You also become a more efficient sweater, which means you become better at transferring heat from your body’s core to the skin and away into the air via sweat evaporation. At such times your significant other may not appreciate your very sweaty skin but sweat evaporation is the absolute key to cooling off.

Of course, the biggest challenge many athletes have in this situation is accepting that they can’t rush the acclimatization process. Research indicates that the fitter you are to start with, the more quickly you’ll adapt to the heat and be able to hit your splits again. But if you’re sleep deprived, which is the only part of heat acclimatization you can control, you’re not going to acclimatize as well. Likewise, top experts and a research review in the journal Sports Medicine make clear that pounding back excess water and electrolytes do not help you acclimatize faster. Sitting in a sauna won’t help either. All that does is make your body more efficient in dealing with saunas. To acclimatize to exercising in the heat, you actually must move around in the heat. There’s simply no other way around it. 

A great vacation workout: running on the beach.