Long-Distance Hike Alters Cardiovascular Function and Body Composition

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There is an ongoing debate as to whether one can exercise “too much.” A moderate to high amount of aerobic and strength training is fantastic for our body — improving cardiovascular health, body composition, and metabolic and mitochondrial function, to name a few of the myriad effects of exercise.

While I’m in the camp that in general, more exercise will lead to more positive health benefits, there is no denying that somewhere, a point exists where a plateau occurs or perhaps a point at which exercise actually begins to exert detrimental rather than favorable effects on health.

Where that line exists is unknown and will probably never be a concern for 99.9% of the population.

Should we want to study the negative effects of “too much” exercise, investigating how extreme feats of endurance impact the human body is a great place to start.

This brings us to a recently-published case study (a report of a study done on a single individual) that investigated the effects of a long-distance hiking expedition on vascular function, arterial stiffness, and body composition in a young, healthy male.

This wasn’t your everyday backwoods hike. The individual in this case study completed a thru hike of the Pacific Crest Trail (PCT) — a 4,265 kilometer (2,650 mile) trail that extends from the US-Mexican border up to the US-Canadian border; during which one will experience 250,000 meters of elevation change.

A thru hike means completing the PCT in a single season — which the individual in this study did between May and August of 2019. Of note, he also completed the hike 30% faster than the average hiker.

As far as extreme daily exercise goes, a PCT thru hike is probably near the top of the list. Just look at some of these statistics from the journey:

To maintain weight and intake the necessary calories to support his daily exercise, the hiker had to consume what the paper refers to as a generally poor (Western-style) diet consisting largely of fast-food meals (when he stopped in town to recover), along with energy-rich snacks like beef jerky, candy bars, pre-packaged pastries, chips, and nuts. He had to carry all of his food with him after all, so convenience and portability was crucial.

Thus, not only did this case report investigate the effects of extreme exercise on cardiovascular function and body composition, but extreme exercise paired with a calorically-dense yet nutrient-poor diet consisting of largely processed foods. The hiker reportedly consumed around 5,500 calories per day to meet the requirements imposed by the daily exercise volumes!

Before and after the hike, measurements were made of the hiker’s vascular function, aortic stiffness, body composition (bone mineral density, body mass and body fat %), blood pressure, and heart rate.

How did the journey impact the hiker’s physiology?

Vascular function was negatively impacted — with a reduction in brachial-artery vasodilation from 6.97% before the hike to 5% after the hike. The individual’s aortic/arterial stiffness was increased after the hike, suggesting that negative structural changes may have occurred to his arteries as a result of the trek. However, systolic and diastolic blood pressure were unchanged from pre to post hike.

Only minor changes to body weight and composition occurred during the hike. Body weight was reduced by around 1%, total bone-mineral density was reduced by around 0.6%, and body fat percentage was increased by 3.45% compared to baseline.

Interestingly, the hiker’s spine and pelvic bone mineral density seemed to be uniquely impacted by the hike, with reductions in bone mineral density of 5.17% and 3.76% in these areas, respectively. Again, when whole-body bone mineral density scores were analyzed, no significant changes were found.

The hiker also seemed to experience a fat mass redistribution. While fat mass in the arms and legs was reduced throughout the duration of the hike, fat mass in the trunk region was reported to increase.

What could account for the negative vascular changes? Even though aerobic exercise causes favorable improvements in vascular function, a hike such as the one completed here probably crosses the line from being a beneficial stressor to a detrimental one. The extreme cardiovascular stress and lack of recovery probably combined to, at least temporarily, reduce vascular function in the hiker.

There is also the chance that the “poor diet” consumed during the hike exerted negative effects on the vascular system. So-called “Western” diets are associated with worse endothelial function and cardiovascular health, so the highly-processed food intake may have also contributed to worse vascular outcomes. The paper speculates that it is likely the combined effects of extreme exercise AND a poor diet that led to the adverse cardiovascular effects. I won’t argue with that.

Body mass and composition were likely unaffected because the hiker was diligent about maintaining caloric intake, even if the calories consumed came from suboptimal food sources.

Carrying a heavy pack, using trekking poles to engage his arms, and maintaining a daily push-up routine were also strategies that likely prevented negative changes to lean mass throughout the hike, and may also have resulted in the minor loss of fat mass in the arms and legs. The heavy pack may have also prevented a major loss in bone mineral density by serving as an additional weight-bearing stimulus.

Even while consuming around 5,500 calories per day of generally processed foods, the hiker was able to maintain or even slightly reduce his body weight. I know this wasn’t the goal of the study, but perhaps one CAN outrun (or “out hike”) a poor diet.

Case reports such as this one are interesting and informative, despite the fact that we can’t draw major conclusions from data on a single individual. I love the fact that a team of researchers had the idea (and am jealous they had the opportunity) to study an individual in a unique physiological context such as this one.

Sure, it’s fun and necessary to conduct studies in “normal” individuals to see how human physiology works in the majority of people, but it’s also great to get a glimpse into what happens when physiology is truly pushed to the limit — life at the extremes.

Study cited

Heinbockel TC, Craighead DH. Case studies in physiology: Impact of a long‐distance hike on the Pacific Crest Trail on arterial function and body composition in a highly fit young male. Physiol Rep. 2021;9(5). doi:10.14814/phy2.14767

PhD candidate at the University of Florida — Science writing with a particular focus on exercise and nutrition interventions, aging, health, and disease.