This is an excerpt from Training Young Distance Runners-3rd Edition by Larry Greene & Russell Pate.
Research shows that, pound for pound, normally active 6- to 8-year-olds have V\od\O2max values as high as, or sometimes even higher than, recreational adult runners who train 30 to 40 miles (about 48 to 64 km) a week. The view that young children are physiologically capable of running long distances is backed by world age-group records for races as long as the marathon (26.2 miles, or 41.2 km). The records for 8-year-olds are 3:34:30 for boys and 3:13:24 for girls; for 11-year-olds the records are 2:47:17 for boys and 2:49:21 for girls. Many adult marathoners have trained at high levels for years without reaching these marks. Research also shows that young children adapt physiologically to endurance training in ways that improve running performance. Before puberty, for example, children who perform moderate levels of endurance training experience about a 10 percent increase in V\od\O2max, slightly less than the 15 percent increase observed, on average, in adults.
From this information, you might conclude that young children are indeed capable of training for and competing in long-distance races. Before you start planning programs for 8-year-olds, however, consider the following other important points:
- Neither scientific nor anecdotal evidence suggests that distance runners must start training at a young age to reach their greatest potential. Most world-class runners did not begin training until they were in their mid to late teens. And, with very few exceptions, the children who held age-group records for the 5K through the marathon did not develop into elite adult runners.
- Research consistently shows that, before puberty, physiological adaptations to training aren't always correlated with performance in long-distance events. For prepubescent children, the factors that best predict distance running performance are simply related to physical maturity: taller, stronger, and faster children lead the pack in distance races, just as they excel in other sports such as basketball, baseball, and soccer.
- Although many children have naturally high levels of aerobic fitness, making them physiologically capable of performing low-intensity endurance activities, they are limited in their capacity to generate energy for high-intensity activities. The body has two primary systems for producing energy during exercise: the aerobic system, which operates when a sufficient amount of oxygen is available to the muscles, and the anaerobic system, which operates when the oxygen supply cannot keep up with the muscles' demand during high-intensity activity. One of the most consistent findings in pediatric exercise science is that the anaerobic system is not fully developed until children have passed through puberty.
- Physically immature youth who undertake high volumes of intense training are at relatively high risk for injuries, abnormal growth and maturation, and psychological burnout.
Considering these points, we recommend that children not begin regular and specialized training for distance running at least until the early stages of puberty, around ages 11 to 13 (see table 1.1). By no means are we saying that kids under 11 shouldn't participate in running events such as 1- or 2-mile fun runs at school or in community races. We encourage children of all ages to run for fun and health. Instead, we advise holding off on regular training, which we define as more than three days a week over periods of several months, and specialized training, which means focusing only on running as opposed to other sports and physical activities.
While children are experiencing major physical changes during puberty, we recommend limiting the volume and intensity of training. One reason is that normal pubertal development can improve running performance on its own. For example, the growth spurt of the lungs and heart, which occurs at an average age of 11.5 years in girls and 13.5 years in boys, boosts the delivery of oxygen-rich blood to the muscles, which naturally increases V\od\O2max. Another example is the elevated level of growth hormone, which enables stronger muscle contractions, increasing running speed and efficiency.
Not all developmental changes automatically improve running performance, a point that also supports curbing early training. Consider rapid growth in height. At the average age of 10.5 for girls and 12.5 for boys, the growth rate increases dramatically from approximately 2.2 inches (5.5 cm) per year to approximately 4.1 to 4.7 inches (10.5 to 12 cm) per year. The highest rate of growth, which is called peak height velocity, occurs at around age 11.5 for girls and 13.5 for boys. Now consider the 13-year-old boy who grows 2 inches (5 cm) over a single summer - suddenly he's all legs. The growth spurt should improve his running by increasing leg length and thus stride length. However, he now has trouble coordinating his longer legs because the nervous system, which controls movement, doesn't immediately adapt to changes in limb length. Also, during the growth spurt body parts grow at different rates. The feet and legs, for example, usually lengthen faster than the trunk, making many teenagers seem gangly or awkward in their movements. These developmental changes may actually cause the runner to temporarily perform worse because his uncoordinated stride wastes energy and leads to fatigue.
Rapid limb growth also means that children who train intensely for distance running are at risk for muscular and skeletal injury. Bones lengthen at each end in soft tissue called epiphyseal growth plates. During puberty, the growth plates are weaker than hardened bone and susceptible to fractures under the heavy, repetitive stresses experienced in long-distance running. The growing athlete's joints and muscles are also susceptible to injury because muscle mass and strength develop more slowly than bone. Eventually, the epiphyseal growth plates ossify, or harden, and muscle mass increases. Until these two critical growth processes are complete, however, children are at increased risk of injury from excessive training.
Excessive training before puberty can also affect hormones in ways that may interfere with normal maturation and optimal health. Estrogen, for example, is a hormone that ensures healthy growth and development in girls. This hormone plays a major role in menstruation, which is a normal process of maturation in girls and young women. Under certain conditions, including suboptimal nutrition, estrogen is not produced at regular levels during puberty in female runners. As a result, they may experience delayed menarche or irregular menstrual cycles. In chapter 3 we discuss a major health problem called the female athlete triad, which encompasses suboptimal nutrition, abnormal menstrual function, and weakened bones. Compared with normally active girls, those who train excessively for distance running are at risk for this condition.
Fortunately, most young runners avoid harmful levels of training. They naturally stop pushing themselves before reaching their limits. However, we've known at least a few young runners who were self-motivated to push to extremes, and we've known coaches and parents who pushed young runners too far. For these children, running injuries are fairly common.
Another concern for those who specialize in running at a young age is psychological burnout. Take the 10-year-old who's running 40 miles (64 km) a week and racing 10Ks on a regular basis. Eventually, she may grow tired of running, especially because improvement depends on increasing training loads over time. If a child is running 40 miles (64 km) a week at age 10, at age 16 she'll need to run 70 (113km), or maybe even 90 or 100 miles (145 or 161 km), to keep improving. That much running leaves little time for activities other than school, sleeping, and eating. When training becomes that consuming, it isn't fun anymore, and most young people drop out of running.
Most girls and boys, by the ages of 12 and 14, respectively, have experienced key developmental changes that enable them to safely begin a low-mileage, low-intensity training program, leaving lots of room for gradual improvement over time. Again, we're not saying that younger children should avoid participating in distance running altogether. Instead, our advice is to delay specialized training on a year-round basis. Beginning at age 7 or 8, children who enjoy running may participate in fun runs and organized track and field programs that last a few months each year. Future distance runners will benefit from participating not only in middle-distance races (up to 1 mile, or 1,600 meters), but also in sprinting, jumping, and throwing events. When track season is over, they should participate in soccer, basketball, and other youth sports they enjoy. We recommend multisport participation because it's important to develop all-around physical fitness before beginning specialized training for track and cross country (see developmental principle 3).
Learn more about Training Young Distance Runners, 3rd Edition.