Stress Fractures and the Growing Athlete
By: Theresa Lugatiman, PT, DPT
Board Certified Women’s Health Specialist
Our body has a system of checks and balances. Whatever energy our body gets from food is distributed proportionately. When there is caloric deficit, available energy is diverted to the survival functions of thermoregulation, cellular maintenance and movement, shutting-off supply for growth, immunity, and reproductive function. With prolonged inadequate caloric intake, growth and hormonal operations are skipped for the more essential purpose: staying alive.
With bone formation highest at age 10 to 14, energy availability is crucial for adolescent athletes who may have inadequate caloric intake or may be overworked. Bone strength is affected by diet, weight-bearing activities, and genetics. One can make the most out of nutrition and appropriate weight-bearing activities for optimal bone growth.
What happens then? Bone rebuilding is the balance of deposition and resorption. Without deposits, overdraft occurs from resorption, leading to bone thinning. Bones that accept weight like the foot (metatarsals), the spine, pelvis, the leg bone (tibia), the hip (femoral neck) and kneecap may develop stress fractures. With low energy availability, muscle bulk is lost, affecting athletic performance. Muscle has the ability to absorb mechanical stress. If muscles are weakened, loads are displaced to the skeletal structures, increasing risk for stress fractures.
Energy availability is the balance-tipping factor in reversing Female/ Male Athlete Triad, or Relative Energy Deficiency in Sport (RED-S). The warning signs of lack of energy, the absence of menses for three months (amenorrhea), and low bone mineral density increases risk for osteoporosis and fractures. Low caloric intake can lead to hormonal imbalance, which can affect bone growth. Stress fracture risk is highest for 16-17 year-olds and symptom screening is suggested for teens with Body Mass Index (BMI) below 17.5 kg/m2. Endurance athletes and athletes participating in weight-limited sports may be susceptible to RED-S. Overtraining affects male athletes, leading to symptoms of the male athlete triad (low energy availability, impaired bone health, reproductive suppression). Overtraining per week is identified as running 108.0 +/- 4.5 km or exercising more than 450 minutes. Female athletes show lack of energy, bone loss and menstrual dysfunction with food intake less than 30 kcal/kg of fat free mass/day. On a good note, increasing caloric intake or decreasing exercise frequency to improve BMI to >18.5 kg/m2 can restore menstrual function. This increases bone deposition, and can reverse symptoms over time. Oral contraceptives may regulate menstruation, but does not increase bone density.
All points lead back to adequate food intake.
In the long haul, we can only splurge so much of what are our bankable bony assets. A decade after menopause, bone loss rate is 1% to 3% each year, increasing another 0.5% to 1% after the age 70 for women and 80 for men. How much you have saved up matters. This is why calcium and vitamin D supplements are suggested in pre-menopause. The goal is to accumulate as much deposit, before it’s too late.
With proper guidance, teamwork between a registered dietitian, the adolescent athlete, the coach or trainer, the physician, and the parents, can reverse symptoms of RED-S in as early as a few months and normalize bone health within a year. It’s time we contribute to our bone banks. We don’t want bone overdrafts for our adolescent athletes now, do we?
Source of values and related read:
De Souza MJ, Koltun KJ, Williams NI. The Role of Energy Availability in Reproductive Function in the Female Athlete Triad and Extension of its Effects to Men: An Initial Working Model of a Similar Syndrome in Male Athletes. Sports Medicine. 2019;49:125-137. doi:10.1007/s40279-019-01217-3