High Volume Training Affects Immune System In Endurance Athletes


Alyssa Bialowas

Exercising regularly and moderately improves your overall health, which is said to help boost and strengthen your immune system, defending the body against infections. However, overdoing it with strenuous repeated exercise can reduce immune function, and endurance athletes have a notably depressed immunity, especially when it comes to upper respiratory tract infections. When elite endurance athletes do get colds, they tend to last longer on average, especially after a long race. For this reason, it is important for endurance athletes, or any athlete for that matter, to remain healthy and ready to train and compete.

A team of researchers from the School of Sports Science at Umea University in Sweden set out to observe whether high training volumes are associated with a low number of sick days in elite endurance athletes. Seven elite athletes participated in the study, composed of cross-country skiers, biathletes, and long-distance runners. All the athletes formerly performed at the top national or international level in their respective endurance sport, and were between the ages of 17-24 years old. The subjects reported a training period that lasted between 3-16 years, with continuous observation taking place throughout the course of the study.

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The Study

The athletes who participated in the study were directed to keep a rigorous record of their training in a log book. The athletes detailed how many hours and kilometers they trained for, the number of days that they were injured, and the number of sick days they took off training over the course of the study. The training logs were updated daily, and when participants were sick or injured, they did not train that day. Some of the injured and sick days included examination by a physician, but most did not. Researchers analyzed the raw data from the training logs in 12 month intervals, and counted the sum of hours and kilometers trained. A minimum of 3 years of logged training were required for inclusion in the study.

Analyses were performed and the results indicate that the number of training days reported missed by an athlete is negatively correlated to the volume of training of elite endurance athletes. This finding is in line with previous suggestions that elite endurance athletes with a high training load is tied to a low incidence of self-reported injury and sick days. The subjects had trained an average of 462 hours per year, were sick on an average of 15 days, and 21 average injury days were reported. 

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Moderate physical activity lowers the risk for infection, and as described in the results of the study, intense endurance training has a similar effect in elite distance athletes. However, moderate athletes that over-train report an increased number of self-reported upper respiratory tract infections. Elite training and competition requires an immune system capable of withstanding infections and sickness. The balance between training and rest and the relationship to injury is clear for elite endurance training programs. 

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Malm, C., Martensson, S., Nordebo, K. (2014). “High Training Volumes are Associated

with a Low Number of Self-Reported Sick Days in Elite Endurance Athletes.”

Journal of Sports Science and Medicine, 13, 929-933. 

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