Running specialization for young athletes: when should you become a year-round runner?

As my bio states, one of my areas of interest as a coach and writer is long-term development for young athletes: what is the best way to take a talented young runner and maximize his or her ability, both in high school and college/beyond? I've been thinking a lot recently about the idea of specialization—at what age is it appropriate or optimal to become a full time distance runner who trains year-round instead of doing other sports?

Perhaps eight or ten years ago, opinion in the running community leaned pretty heavily towards early specialization.  AAU track meets were (and to some extent, still are) popular for runners in elementary and middle school, and high school cross country programs saw a lot of growth in numbers when they started integrating a middle school "feeder program."  In the past few years, however, it feels like momentum is swinging back towards not having runners focus exclusively on running until a lot later—continuing to be multi-sport athletes throughout all of high school, in some cases.  I think the genesis of this was the success of runners like Grant Fischer, who played soccer up until his senior year of high school, plus backlash against hyper-early specialization in big-money sports like football and hockey, where training can completely take over your life, even at a young age. 
Coaches pushing ever-younger kids into two, three, or four-hour daily practices, plus the pressure of performing well at such an early age, can have some real negative consequences on enjoyment of the sport for a young athlete.  At the same time, missing out on too much of the fundamentals will definitely put you at a technical disadvantage, at least temporarily, compared to your competitors. 
This is true for most team and skill-based sports, but what about running? As distance runners, we trade in technical proficiency for raw physiological fitness, and because our sport is a repetitive, high-impact one, we can't put in long hours of training at a young age like swimmers or lacrosse players can.  The typical middle school or high school runner runs cross country and track, perhaps doing a bit of summer running before cross country, but does not train at all over the winter.  Maybe he or she plays basketball, swims, or does indoor soccer.  At what point should we encourage a promising young distance runner to fully commit to the sport? And are there any disadvantages to dedicating yourself to distance running at an early age?
When is the latest you should commit to year-round running?
There's no denying that having a strong lifetime mileage base is important in distance running.  The age of the top runners in the world for each event is proportional to the race distance: The best 1500m runners are 23-24, the best 5k and 10k runners are 26 to 28 years old, and the best marathoners are often in their thirties.1  The older you get, the more lifetime training you can accumulate, and the stronger your aerobic system can be. 
Additionally, a particular race distance has a certain minimum level of training that is required to in order to run it well.  Barring a few supremely talented exceptions, nobody runs a great 10k off thirty miles a week.  The question for the high school runner, then, is "How many consecutive training cycles are required to reach an adequate training level for 5k cross country and 3200 meters?"
For the vast majority of high school boys, I believe that it is necessary to reach at least sixty miles a week in training to run your best at 5k cross country and 3200m.  This is also about the level of training you'll need to be able to do to move forward with higher training volumes in college.  It's very difficult, and dangerous, to move from 40 miles a week as a senior in high school to 75 or 80 miles a week as a freshman in college, but that's often what is asked of you at the NCAA level. 
If you've never trained in the summer or winter before, it would be reckless and to try to run sixty miles a week volume immediately; that's why we need to build up to it over several training cycles—ideally, continuous ones (i.e. starting a new training cycle immediately after finishing an older one).  To peak out at sixty miles a week by fall or spring of senior year, we need at least three consecutive six-month training cycles to get there in a reasonable way, preferably four.
If you start doing off-season training for the first time the summer after your sophomore year of high school, an aggressive buildup can take you up to a peak of sixty miles a week by the start of your senior year, like so:
Peak mileage
Summer / Junior year XC
Winter / Junior year track
Summer / Senior year XC
However, I would strongly prefer a more reasonable buildup involving four training cycles to get to the same volume. It's safer from an injury perspective and doesn't require everything to go right like the above buildup does.  It also allows you to reach 65 or more if you are so inclined.
Peak mileage
Winter / Sophomore year track
Summer / Junior year XC
Winter / Junior year track
Summer / Senior year XC
Now, if you've been doing summer training for longer in your high school career, you can prolong your multi-sport career a little longer and get to 60 miles a week by your senior year, but I still think you should carry a full year's worth of training into the summer before your senior year.
Why? First, this allows you to carry much more of your cross country fitness from your junior year into the spring, which lets you leapfrog ahead of runners who took the winter off.  This will have a compounding effect on your preparations for your senior year of cross country.  Second, if you have any aspirations of running in college, even at the DII or DIII level, your junior year of track is extremely important from a recruiting perspective.  Running fast times as a junior will put you on the radar for college coaches.  Third, you have the experience of a full year of running so there's less new territory to navigate as a senior.  You'll have a better sense of what kind of workouts you can do on the roads during the winter, what kind of gear you'll need when it's cold and rainy or snowy, and how to handle the long blocks of sometimes-monotonous training in the dead of winter or the humid doldrums of summer. 
For these reasons, I strongly recommend committing to year-round running no later than the summer before your junior year of high school.  As always, there will be some exceptions to the rule: hyper-talented athletes who had a lot of success despite playing basketball in the winter or doing swim training over the summer.  But I still contend that these runners would be even better (at least in high school) if they had begun year-round training earlier.
Are there any disadvantages to year-round training at a young age?
There are three aspects to consider when we approach this question. 
First among these is physiology.  As stated above, the age of elite runners at various distances demonstrates that more lifetime training volume is superior, at least in the distance races, so it should be trivial to see why doing several years of good training (an important qualifier, and a topic for another day) will allow you to be more successful in high school, college, and beyond. 
However, what constitutes good training is also dependent on age, independent of what coaches call "training age" (how many years you have been training).  Even if they have both been training for three years, a fifteen-year-old can't and shouldn't do the same training volume as an eighteen-year-old can, so training for younger runners needs to be calibrated by actual age, physical maturity, and training age. 
Puberty throws a wrench into the equation as well.  Most followers of distance running know that it can be a struggle for girls to adapt to the changes that come with puberty, but as a coach, I've seen the same things happen with boys, too.  Though boys do have an advantage in handling puberty—for them, puberty virtually guarantees they'll be stronger, more powerful, and more muscular once they come out the other side—but they still struggle with awkward mechanics as they grow taller. 
Your running economy is tightly linked to efficient use of muscle fibers; many hours of training refine your ability to recruit exactly the right number of fibers at the right moment to move yourself forward.  But when you're growing (especially growing rapidly), these muscle recruitment patterns are all wrong.  Your leg is half an inch longer, so the same muscle recruitment patterns don't produce the same results.  Because of this, you have to re-learn efficient muscle movements, and your running economy will deteriorate temporarily.  A stronger cardiovascular system, which often comes along with puberty, can counteract this somewhat, but rapid growth can still prove problematic on a performance level for both boys and girls.
Structural concerns are another problem—injury susceptibility is another issue to consider. Your body adapts to the stresses of running in a very specific way.  For example, if you train in traditional running shoes, you may be able to handle a lot of volume in your usual shoes without any issues, but if you switched to an ultra-thin minimalist shoe, you might suffer a metatarsal stress fracture or Achilles tendonitis.  It's not that the absolute amount of stress on your body changed; it was how that stress was distributed.  In the same fashion, changes in your body size, limb length, and so on will probably increase your injury vulnerability until you've adapted to the new way stress is distributed in your body.  This is all, of course, in addition to the usual injuries that are related to growth: Osgood-Schlatter disease, Sever's disease, and other apophysitis-type injuries that are directly related to growth.
With these considerations in mind, it becomes clear that maintaining a heavy training load throughout puberty will, in many cases, not be optimal.  I think it is very beneficial to be doing some running on a regular basis as your body grows, as this will gradually and incrementally introduce you to new stresses, but some runners, especially those who grow rapidly or unevenly, may need to scale back their training volume or avoid year-round running to stay healthy.  At the same time, it doesn't make a lot of sense to completely avoid running until you're done with puberty, since you're losing out on a lot of physiological benefits that aren't tied to body dimensions.
But, to return to our initial question, what about specialization? One of the prime benefits of doing other sports, then returning to running, is that you improve your athleticism, strength, coordination, and injury resistance.  Coaches who have spent a lot of time working with high school athletes can tell you that runners who only run often lack the quickness, agility, and coordination of a multi-sport athlete.  In terms of injury resistance, one study of competitors at the USATF National Championships found that successive years of playing ball sports (e.g. football, soccer, basketball) during childhood and adolescence was associated with a substantial decrease in the incidence of stress fractures.2  The same phenomenon has been observed in military recruits.3  Ball sports involve large-magnitude impacts that put a wide range of stresses on your bones, instead of the steady moderate impact of running; this leads to greater bone strength overall. 
Now, there's nothing magical about ball sports that grants them the exclusive power to develop agility, coordination, athleticism, and bone strength.  It would be fairly easy to develop a strength, agility, and plyometrics routine that trained the same skills in a much more efficient manner than playing 12 hours of soccer a week. Indeed, I'm working on one right now for the boys I coach at Edina High School! But, unless you were doing it in a team setting, it might not be as fun or engaging as soccer or basketball.
Finally, there are mental, emotional, and psychological considerations when it comes to specializing in running at a young age.  Some of this fall under the umbrella of "all your eggs in one basket"—there's a real risk of associating your identity and self-worth inextricably with running.  If you primarily identify yourself as a runner, then things can really fall apart when your running isn't going well (or isn't going at all, in the case of injury).  Even hugely successful runners have rough patches, and being too obsessive about your running at a young age won't be good for your mental or emotional health. 
Everybody's different—some people can begin training extremely hard at a young age and still be easy-going and not overly invested in the minutia of their day-to-day performances and the occasional setback, while others will struggle with obsessiveness their entire career, even if they start at a later age when they have a stronger sense of identity independent of running. 
One goal should be to keep running from completely taking over your life year-round.  Running has a distinct advantage over other sports in this area, since even very high levels of training don't have to gobble up all your free time: a middle school kid playing travel soccer practices far more than even the most dedicated high school distance runners ought to—and I'm a high-mileage coach! Running 25 or 30 miles a week as a 13-year-old takes a far smaller time commitment than playing Pop Warner football or little league baseball.  Even 60 miles a week only averages out to an hour of running per day.
Managing emotional and psychological health and developing a strong, resilient spirit is a much bigger topic than I can cover in this post, but I still wanted to raise the issue. 
These concerns also have a lot to do with the people you surround yourself with.  Do your parents, coaches, teammates, and friends help push you in a positive direction? Or do they put excessive pressure and expectations on you? Sometimes, kids who get involved with the sport very deeply at a young age end up mentally burned out, either from external pressure at a young age (coaches, parents) or their own high expectations for themselves.  Paradoxically, this problem is worse when you have a lot of success early on in your running career.  We shouldn't neglect emotional, mental, and psychological well-being when considering the optimal age to specialize in running. 
Guidelines for specialization
The current level of competitiveness at the high school and college running level puts a fairly strict limit on how long you can wait until you train year-round.  With the possible exception of supremely talented runners, I believe you are losing too much ground to other runners if you do not commit to year-round training by the summer before your junior year of high school.  Since most semi-serious distance runners do "summer mileage" anyways, this really means you don't have to stop being a winter sport athlete until the winter of your junior year.  However, I prefer, and recommend, starting up with year-round running the winter of your sophomore year of high school.  Getting in several consecutive training cycles while you're still in high school allows you to maximize your track performances junior and senior year, plus your level of preparedness for college training.
Undoubtedly, there are some runners right now who are training year-round at a younger age than this.  In the 1990s, you could get away with not training year-round at all in high school and still be a very competitive runner because performances were worse across the board.  If performances continue to improve, it may be necessary to begin year-round training at an earlier age to stay competitive.  If, as many people say, 8:50 is the new 9:00 for boys 3200m, it may take another year or two of full-time training for a 9:00 talent to reach 8:50, and hence full time training must start earlier.  Only time will tell.
As for what age is too early for specializing as a runner, it's a more individual matter.  Continuous blocks of heavy training loads should typically be avoided until the athlete is well on his or her way through puberty, especially if you know the athlete is growing rapidly or is predisposed to growth-related problems like Osgood-Schlatter disease or Sever's disease.  This doesn't necessarily mean young athletes can never do long runs or high-volume workouts; rather, they need to modulate the occasional exposure to a strong stimulus with longer blocks of short, easy training or just spent playing other sports.  Exposure to some running at an early age is ideal, since you want to get the ball rolling on developing basic fitness and running economy, but realize that you can't keep all of these gains as the athlete's body is growing.  I whole-heartedly endorse participating in middle-school track and cross country for these reasons!
If a young runner decides to specialize early (9th grade or earlier), there are a few important considerations to keep in mind.  First, from a strictly pragmatic standpoint, he or she should be doing some type of ball sport, strength/agility training, or other non-running activity to build a strong, athletic, injury-resilient body.  This doesn't necessarily have to be an organized activity; even something like skateboarding or pick-up basketball will probably work.  Just make sure you don't just run.
Next, having a parent, coach, or older teammate provide some rough guidelines for training is helpful, but you don't want to get too involved in specifics at a young age, and you especially don't want to get obsessive about race results and performances.  Too much pressure and outside involvement at a young age is never a good thing.  In fact, it's probably better to let a young runner explore running by himself and allow him to make a few mistakes than it is to risk being too involved by trying to make sure he follows the "perfect" training program. 
I don't think I would ever actively discourage a young runner from specializing early.  If you really love running, and that drive is coming from you, why not? If you're helping a young runner who wants to specialize early, my only recommendations are to try to encourage him (or her) to do some type of strength, agility, and athleticism training in addition to running, and to try to guide him towards a mentality that is passionate, but not obsessive, about training and racing. 
For more on training for young athletes, check out my first eBook, Basic Training Principles and my full-length book, Modern Training and Physiology available on Kindle and in paperback!
1.         Schulz, R.; Curnow, C., Peak performance and age among superathletes: track and field, swimming, baseball, tennis, and golf. Journal of Gerontology 1988, 43 (5), P113-120.
2.         Fredericson, M.; Ngo, J.; Cobb, K. L., Effects of ball sports on future risk of stress fracture in runners. Clinical Journal of Sports Medicine 2005, 15 (3), 136-141.
3.         Milgrom, C.; Simkin, A.; Eldad, A.; Nyska, M.; Finestone, A., Using Bone’s Adaptation Ability to Lower the Incidence of Stress Fractures. American Journal of Sports Medicine 2000, 28 (2), 245-251.

About the Author

John J Davis, PhD

I have been coaching runners and writing about training and injuries for over ten years. I've helped total novices, NXN-qualifying high schoolers, elite-field competitors at major marathons, and runners everywhere in between. I have a Ph.D. in Human Performance, and I do scientific research focused on the biomechanics of overuse injuries in runners. I published my first book, Modern Training and Physiology for Middle and Long-Distance Runners, in 2013.

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