Over the last 50 years the training of distance runners has evolved from a process of trial and error testing, to specific event-centered progressions that are deeply based in the scientific method. Exercise physiologists, cardiologists, and endocrinologists, working with training theorists, have provided a wealth of empirical evidence for coaches to use as a resource for their training plans. Training for the demands of the specific race distance, while maintaining healthy athletes is now the focus in the endurance events, including cross country.
One of the biggest influences in recent cross country training evolution has come about as the result of scientific study in the field of sports medicine. Studies of the immune and skeletal systems of distance runners has given even a serious high school coach cause to ponder changes in training as the continued health of the runner has moved from hope and prayer, to actual action protocols.
Maintaining a healthy runner is a primary goal of a coach at any level. While usually not a primary physician, the coach is nonetheless who the athlete talks to first about health problems related to running. These concerns generally fall into two categories: stress issues in the skeletal system and depression of the immune system. Both of these have been problematically linked by scientists to running volume in excess of 25 miles per week. This is the point scientists consider a runner to be “high mileage”. These are the athletes of The Healthy Runners Project (M. Fredricson., Stanford, 2014).
Studies show that about 25% of male and 32% of female high school/high mileage runners will exhibit skeletal problems in the bones of the foot. These problems range from bone bruises to stress reactions to actual stress factures. All are debilitating. Recovery from a bone bruise is a couple of days of lessened training volume. Recovery from a stress reaction has a training protocol that calls for a 50% decrease in training volume for about 21 days, coupled with cryotherapy after the workout each day.
Stress fractures are a more serious problem for cross country runners. The occurrence of a stress fracture is defined as a failure to withstand sub-maximal forces over time. A few facts are, in order:
1.) Athletes who participate in weight bearing sports have about a 10% greater bone mass than non-athletes,
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2.) 90% of peak bone density should be attained by males age 18 in females and age 20 in males,
3.) Diet and sleep play a large role in achieving maximum bone density, and
4.) High impact loading (lunges, skipping, etc) are important in achieving high bone density in athletes.
Cross country training is mostly a low impact form of activity. An athlete running at 5k pace is putting about 3 times their body weight on each step. A somewhat medium training intensity on a 6 mile run is likely to be about 2 times body weight on each step. Scientists have reported that at least 3.5 times body weight is needed regularly to achieve maximum bone density. This can be accomplished by frequently training faster then 5k pace (ex. 800 meter pace), or by adding in high impact weight bearing exercises and drills each day as part of the warm-up routine.
Some studies have shown that high school cross country runners who played basketball regularly from age 11-13 were much less likely to get a stress fracture later, while those that swam regularly (age group swimming club) were much more likely to get a stress fracture during later high school cross country. Other studies showed that “assisted” activities like bicycling and Nordic skiing improve the athlete’s aerobic characteristics, but lower the bone density of the foot. That is an adaptive combination that will be potentially dangerous as the athlete switches to a training protocol of all running. The Healthy Runner Project attempts to forewarn coaches of these dangers.
Several studies support the prediction that a male or female high school cross country runner training in excess of 40 miles per week has nearly a 100% chance of having a stress fracture of the foot if they have ever broken a bone for any reason (even falling out of a tree) as a young child. This is an important red flag for coaches.
One study reported that a glass of skim milk before bed decreased stress fracture incidence by 66%. If a stress fracture does result the treatment is 7-8 weeks of inactivity.
Immune system depression usually manifests itself in an upper respiratory tract infection (URTI). Studies have shown that runners who train at 50 miles per week are 7 times more likely to contact a URTI then those at 20 miles per week. Further studies have shown that an URTI will affect training for 8 days on the average. Some studies support the supplementation of 20-30 mg of zinc each day prior to symptoms of URTI to shorten the duration of the infection. One study showed a decrease from 8 days to about 5 days. Zinc supplementation was not shown to lower the incidence of URTI, and it must be taken before symptoms appear.
Sleep studies have shown that 8-9 hours of uninterrupted sleep reduces the incidence of URTI and length of URTI symptoms. Studies of both URTI and stress fracture incidence in high school cross country runners indicate that 8-9 hours of sleep is crucial in limiting the appearance of both.
Sleep is important to humans. It is the time of the 24 hour cycle that glycogen is replaced in the liver. It is the time that the skeletal system remodels and rebuilds itself through the action of osteoblastic and osteoclastic activity. Not only is sleep an important physical and psychological stress reliever, but it also brings the hormones that cause stress back to equilibrium. Sleep has been shown to be an important factor in endocrine system health.
Several studies support a 50% reduction in stress fractures of the foot for those cross country runners that slept 9 hours each night as a regular routine. One important and landmark study showed that going to bed at the same time every night (within 15 minutes) lowered the incidence of URTI in the general population by about 40%. The human body works best when there regular rhythms.
Training Resource: Training Model for High School Cross Country
An important factor in The Healthy Runner Project is to chart the athlete’s serum ferritin. An annual test at the local clinic is suggested. While the normal range for the general population is 12-240 ng/L, to get a cross country runner within the 35-70 ng/L value would be a great accomplishment. Recent studies have shown that ferritin is required not only for oxygen carrying hemoglobin protein, but for enzymes that are required by the aerobic system to function properly under load.
The Healthy Runner Project supports the completion of the following worksheet by each athlete to assist the coach in maintaining the good health of the cross country team members. Each athlete should fill it out over a 5 day period as part of what is required for the first week of practice. It is not overly invasive. Assure the athlete that it will be used to assist the coaching staff it setting up their individual training program.
Click here for worksheet: Healthy Runner Project worksheet