Let’s say your 8th grader, ‘Ike’, is a terrific baseball player. At 13 years old, Ike is the youngest player in his league but competes successfully against players who are already playing junior varsity baseball in high school.
Ike is having a lot of fun playing baseball, and it is his goal to keep it going through high school and play varsity baseball as a junior and senior.
Ike is 5’6″ tall and weighs 130 pounds, so his weight is in the 75th percentile for his age. Conservatively, he’s on pace to be 6′ tall by the time he’s a high school senior, and to maintain his 75th percentile weight, he will need to gain about 45 pounds (to around 175 pounds). It turns out that 175 pounds is a fairly typical weight for the current varsity seniors on his high school team.
Right now, Ike eats about 2600 calories per day to maintain his weight. This is fairly standard. Moderately active teenage athletes (training and playing 5-9 hours per week) need to consume about 20 calories per pound to maintain their current weight.
Ike wants to grow at a steady pace over the next 1,400 days or so (that gets him to the middle of the summer before his senior year). How many EXTRA calories does Ike need to eat over the next 1,400 days?
Over 750,000. That’s 750,000+ EXTRA calories, above and beyond what he would consume if he just ate his current 2,600 calories a day for the next 1,400 days.
So is this really a problem, don’t teenage boys just naturally eat a lot? Sure. Hormones drive teenage boys to eat a lot and grow a lot. The average 13-year-old male weighs 100 pounds. The average 17-year-old male weighs 140 pounds (CDC BMI calculator – http://bit.ly/2Ja6YyG).
However, the challenge for teenage athletes is much larger.
First, athletes train. Training requires extra energy. Sedentary people need to consume 12-13 calories per pound of body weight to maintain their current weight. Athletes who train 5-9 hours per week need more like 20 calories per pound of body weight. During periods of very high exertion, it’s more like 25 calories per pound. For maintenance. Not growth. Maintenance. (Estimated Daily Energy (Calorie) Needs for Competitive Athletes, http://bit.ly/2J6FUQH.)
Second, Ike already weighs a lot so he needs to eat more just to maintain. He is not trying to go from 100 pounds to 140 pounds, he is trying to go from 130 pounds to a minimum of 175 pounds. And he doesn’t want to just gain 40 pounds. He wants to gain at least 45 pounds. More would be better, less would be worse.
Third, Ike has to keep eating all the time. As a baseball pitcher, Ike works hard at strengthening the muscles in his lower arm, shoulders, and hips. If Ike does not eat enough and does not carry enough body fat, he is vulnerable to catabolism – the body’s irritating habit of burning muscle for fuel when other sources are not available. If gaining muscle to support vulnerable joints lowers injury risk, then losing some of this muscle is highly undesirable, even dangerous.
In part II, where we come up with that number of ‘750,000+ excess calories.’