Updated: Aug 15, 2020
A few days ago, I was climbing at 10,700 feet on a trail alongside mountain goats and overlooking numerous mountain lakes. The steep climb up was strenuous, and as I neared the top, I had to stop every so often to rest. Less than 48 hours later, I ran at sea level on a flat trail with a heat index of 100 and a humidity of 68%. Completing the same distance as my hike, I also had to rest and walk during that run. Can you guess which one was harder?
When we talk about how hard a task is, we mean the amount of perceived effort we put into the activity. Despite how hard we feel a task is, it doesn’t always reflect the actual difficulty associated with the work. Our internal load contributes to how much effort we sense the task requires.
Heart rate is, however, an objective measure of how much effort goes into a task. While heart rate is also dependent on internal load, it gives us a gauge of how much work we are doing. Therefore it helps us know how hard we have to work during an activity.
Altitude, heat stress, and heart rate
Oxygen saturation in the air decreases as altitude increases. Therefore, you don’t breathe in the same amount of oxygen with each breath at 8,000 feet of elevation as you do at sea level. That means that the amount of oxygen available in your bloodstream also decreases. Thus, your respiratory and heart rate get faster at altitude to increase the amount of available oxygen in your blood. Your body tries to make up for the ‘quality’ of each breath and heartbeat by increasing their number.
If your baseline resting heart rate is elevated, it makes sense that your activity heart rate will also be higher at altitude than close to sea level. That’s why cardio training, outside of just hiking, is important for hikers. It’s critical for you to reach a higher heart rate zone during training to condition your heart to endure the stresses of altitude.
While altitude increases heart rate, so does heat stress. For those training in the heat, the primary method of cooling is through the skin. Therefore, heart rate increases to, among other things, drive more blood to the skin where it can dissipate heat.
So which is harder – hiking in heat or altitude? The answer lies in your cardiac response. How well trained is your heart, and how efficiently does it deliver oxygen to your muscles?
If you are in tune with your body, you don’t need a fancy heart rate tracker to monitor your body’s response. Pay close attention to the talk test and keep your activity at a level of talking comfortably but not singing. If you’re talking in a breathy way, stop to rest. Another sign is cramping or tightness in muscles that indicate a lack of oxygen delivery. Again, if you feel this, stop and rest. Slowing down your pace and decreasing step length also reduce effort and eventually, heart rate.
As for which felt harder, the heat wins, hands down. While my perception of effort was greater, it was also more difficult to keep my heart rate in an acceptable zone in the heat than at altitude. Whichever situation you find yourself in, stay aware of your heart’s response to the challenges and adjust for whatever internal load stress it may also experience.
Need guidance on setting up a training program that conditions your heart for your high-altitude trek? Contact me and let's get you on your way to conquering your dream trail!