My daughter said this on the trail and stopped me in my tracks.

If my daughter said while hiking, “My pack is too heavy,” I would stop and adjust the fit or redistribute the weight to make her burden easier. Her words would tell me that something about her external load wasn’t quite right. However, on a recent hike in Yellowstone National Park, what my daughter actually said that stopped me in my tracks was, "I don't have the headspace for this hike."


Her words were communicating to me that her load was too heavy, but not her external load. She was feeling the weight of her internal load. Internal load is the inherent load within the body. The factors that contribute to the internal load are psychophysiological, meaning, they are hard to measure and easy to ignore. Such factors include:

· Fitness level

· Overall state of health

· Mental health status

· Stress

· Nutrition status

· Hydration status

· Amount of fatigue

· Quality and quantity of sleep

· Genetics

· Climate and environment – such as heat or cold stress or demanding terrain

· Mood

· Hormonal status

· Perception of exhaustion - how tired one feels

· Perception of effort – how hard the hike or activity feels

· Body composition

· Age

If internal load is hard to quantify, then what’s the best way to measure it? One way is through the rating of perceived exertion (RPE). The RPE is a feedback tool that allows you to designate how hard a workout or activity feels (see figure 1). When your RPE and your exercise demand or activity don’t mesh, your internal load may be elevated. Consider a day when a hike or a jog has felt much harder than it should. You may have experienced this during hot and humid weather, or when you’ve not slept well the night before. As a result, your RPE for what should be an easy activity for you is higher than usual.


Figure 1: Rate of perceived exertion



Another indicator of the internal load is the recovery heart rate. This measure determines how quickly your heart rate returns to its resting rate after you’ve stopped exercising. Heart rate recovery is also a measure of fitness. To determine your recovery rate, take your pulse at the end of your hike or activity, and then again one minute later. If your heart rate remains elevated or doesn’t go down as quickly as usual, it may indicate that your internal load is high.

Why consider internal load?

Training outcomes are a result of both internal and external loads. If you’ve calculated your external load to have specific outcomes, but don’t factor in your internal load, you can overload your body’s capacity to do the external work. Training and performance errors like this are the leading cause of athletic injuries. Therefore, you likely increase your risk for injury out on the trail if you don’t make accommodations for your internal load.

It’s important to consider internal load when planning a hike, especially a strenuous one where your external load will be high. For instance, when taking on a 14’er, start looking at your internal load at least a month before and adjusting areas that need attention. Make sleep a priority and pay attention to eating healthy, nutritious foods to fuel your body instead of empty calories. Incorporate a meditation practice into your lifestyle to reduce stress.

Other examples of causes of high internal load when on the trail include GI issues during a thru hike. Sick hikers should plan on low mileage hiking for the next couple of days to offset the body’s load from dealing with illness. Stressful life events can also alter mood and decrease energy. Consider postponing or cutting short a big backpacking trip if you’ve experienced significant stress or trauma.

In the instance with my daughter, she was expressing fatigue due to our hectic travel schedule. Late nights, restaurant food, and daily hikes were starting to take their toll. To address her internal load, we stopped, had a rest and a snack, talked about how she was feeling and scheduled a day off. She felt refreshed, heard, and ready to continue the rest of the hike safely. Sometimes merely acknowledging how you feel is enough to lighten your internal load.

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