Hot Temperatures - Should You Adjust Your Power On The Bike?
One of the biggest opponents athletes have is heat, no matter if it is during training or on race day…it can be equally challenging. According to research conducted by Stanford University, humans achieve only 20-30% mechanical efficiency cycling with the majority of the energy being produced being lost as heat. Taking this a step further, anaerobic threshold power output declines as air temperature increases. Putting this into perspective, how does this information impact training and racing approaches? We provide you with two options including additional insight.
Option 1: You could drop your efforts to reflect a lower, calculated power ranges. If your threshold for example is 275 watts at 73 degrees Fahrenheit, you could expect that at 90 degrees F it would drop to approximately 256 watts reduce it by 6.5% (Tatterson et al, 2000). This represent a decrease in threshold power of 6.5% at a higher temperature.
Option 2: You could rely more heavily on your perceived exertion in hot weather and training/race situations as you normally would, accepting that the power data for those given performances might be lower than expected or when comparing to previous weeks efforts.
To help you make your choice let’s see what happens when training in hot conditions.
More blood to the skin
You have about 1.2 to 1.5 gallons of blood (about 7% of body weight) in your body and it has to supply oxygen to every cell, including your working muscles. The circulatory system also transports heat, and when core temperature rises your body increases blood flow to the skin to accomplish both, convective and evaporative cooling. You can see that these two imperatives (oxygen delivery and heat dissipation) compete with each other for resources. As a result, your cardiovascular system is forced to work harder, and you notice an elevated heart rate for a given effort.
Fluid loss accelerates
When you work hard you generate heat. When you are exposed to hot environments your convective cooling system is less effective because there isn’t a big temperature gradient between skin and air temperatures. Consequently, you are more reliant to cool yourself via sweat and the floodgates open up. Everyone reacts differently, with men and women responding inversely, but you can lose up to 1.5 liters (or 0.396 gallons) of fluid per hour in hot conditions. As you acclimate to exercising in heat, your plasma volume will increase, you’ll start sweating sooner, you’ll sweat more profusely, and your sweat will contain fewer electrolytes per unit of volume. So, if you know you have a race in hot conditions don’t stay indoors when temperatures outside are hotter than you’d like. If you can’t train in the heat still acclimate yourself. Since these alternatives are a different subject please reach out if you need advice.
Now let’s go back to the question if you should you proactively reduce your power ranges for hot-weather workouts and competitions?
Should you adjust Cycling Power Ranges for Temperature?
No. Surprised? Why is that? It is difficult to accurately correct for temperature-related decrements in performance in real time and in the real world. You have to take other factors into consideration such as a decrease in air resistance at higher air temperatures, which can save you watts. You also don’t know your exact hydration status or core temperature in real time. There are some promising software solutions that may be able to better correct for these variables and minimize the percent error in the future, but with current technology if you back off based on calculations you’re basically just guessing. Utilizing, and cross referencing your power, perceived exertion and even heart rate can provide a good picture as to how you are pacing, but it takes practice to calibrate your brain to this strategy. The more you pay attention to these variables during training, the more valuable, and accurate, you become at pacing yourself on race day.
Hot-Weather Performance Strategies
At a race, it’s important to remember that everyone is competing in the same heat. Even though some athletes will cope better than others, all will be affected by the heat. Your best option is actually the least technical. Train in the heat to acclimatize prior to competition, optimize your cooling strategies, and focus on learning to correlate your perceived exertion to your power data. On race day, use your perceived exertion (it’s more accurate than you think) and determination to dig deep and do what you have to do; just understand that your actual power outputs may be 5-7% lower than you expect for that exertion level when temperatures are high.
In training it’s the power output that leads to the adaptation. You can achieve “normal temperature” power outputs in high temperature environments, but you will generate a lot of heat. That means that you might struggle to dissipate it, which means you won’t be able to achieve those necessary power outputs for as long. When air temperature is hot (80+ Fahrenheit) and 10-15 or more degrees hotter than the temperature you’re acclimated to, shorten threshold intervals and, if you’re able to maintain the appropriate power output for these shorter intervals, add an additional interval so the total time-at-intensity remains the same. (Remember to put comments into TP immediately after those workouts so we can adjust accordingly. If you don’t communicate it to us in a timely manner and the data does not indicate any abnormalities, we’ll progress upcoming sessions). For high-intensity interval sessions, like VO2 max workouts, you don’t want to reduce the duration of each interval, but can break up your intervals into sets, so you can complete the same total time-at-intensity for the workout. Again, your timely input & comments are necessary if you want to adapt and progress appropriately.
Any further questions you may have please reach out. For now, we’ll see you at the group workouts & races over the upcoming weekends, we are currently spoiled with the hot conditions to acclimate ourselves.