Stress Fractures and

Bone Loss in Distance Running: 

Answers to your Questions

This article was written for UltraRunning Magazine (ISSN 0744-3609) March 2012, page 25-26.

Question:  What is the best strategy to ensure that an ultrarunner is maintaining energy balance and avoiding long term bone loss and stress fracture?
 

There is no simple formula for the calculation of how many calories one must consume to balance energy expenditure.  Age, size, body composition, hormonal levels, psychological state, and training status (volume, intensity) all influence an individual’s metabolic rate and energy requirement.  Although appetite satisfaction and body weight stability are oftentimes considered adequate indicators of energy balance they may be unreliable as exercise tends to suppress normal hunger cues and there are many counter regulatory mechanisms designed to spare body mass in the presence of an energy deficit (just ask you dieting friends!). 

 

A good place to start is to record your daily intake of food and calorie containing beverages over three days time.  The daily totals can be calculated with a commercial software package or summed manually.  This level of intake should be compared to your total energy expenditure that includes your resting energy expenditure (amount of energy that is required for sustaining basic metabolic processes) and exercise.  Resting energy expenditure can be approximated by multiplying your body weight in pounds by 11. The most practical means to determine exercise expenditure is to utilize a heart rate monitor with a calorie counting function.  Heart rate monitors that require gender, weight, height, and activity input are best. 

 
Question:  What is the optimal diet strategy to maintain energy balance and maximize bone health?


Historically, most sports nutritionists have recommended that endurance athletes consume high carbohydrate fare as carbohydrates are considered the most important fuel source during exercise.  However, it is important to consider that the human body is able to adapt to a variety of diets and more recent scientific evidence reveals that the amount of carbohydrate versus fat that is metabolized during exercise by individual athletes is highly variable.  Certainly, a greater reliance on fat as an energy source is an advantage in ultrarunning as the body’s carbohydrate supply is limited and requires extensive replenishment to maintain performance. 

A simple strategy that many endurance athletes have found useful is to start with consuming protein (either animal or vegetable sources) at a level of 1 gram per pound of body weight and supplement their typical carbohydrate intake with the addition of enough fat calories to balance their energy requirement. 

This level of protein intake is somewhat higher than what is typically recommended by nutritional experts but is consistent with studies that have demonstrated reduced levels of protein turnover, muscle damage, and improved recovery following exercise in addition to better bone health. 

Because fats are more energy dense than carbohydrates it is often easier for endurance athletes to balance high energy expenditure by increasing their fat intake.  Monounsaturated fats such as those found in extra virgin olive oil and many nuts have been demonstrated to be both protective of cardiovascular disease and improve certain indices of bone strength.  Omega 3 polyunsatured fatty acids found in fish (sardines, salmon), walnuts, krill oil, and flax seeds are known to reduce inflammation, improve exercise performance, and reduce the rate of bone loss.         

 
Question:  What level of calcium supplementation is safe as I have recently read that calcium supplements have been linked with increased risk of heart attack and stroke?


A report by Bolland and Colleagues published in the British Medical Journal (April 2011) concluded that calcium supplements with or without vitamin D modestly increase the risk of cardiovascular events, especially myocardial infarction.  This finding of course raised the question about the prudence of recommending calcium supplements for the prevention of osteoporosis and fractures.  In response, other researchers have stated the conclusion of Bolland is flawed as there were several limitations including the risk factors for myocardial infarction were not available for 65% of the participants and the majority of the heart attacks were self reported.  In addition, there were a high percentage of overweight participants, more subjects on thyroxine and more males on calcium than on placebo.

Based on the lack of agreement by the scientific community making a well informed decision based upon your unique circumstances is indicated.  There are a multitude of studies indicating that low calcium intake is strongly correlated with reduced bone mass and stress fractures in athletes and that increasing calcium intake through supplementation may be an effective strategy.  Unfortunately, many supplements are known to have poor absorption and lack the health promoting effects of whole foods.  The current level of recommended intake for the general population has been set at 1,200 mg per day with a safe upper limit being 2,500 mg.  Unfortunately, many endurance athletes fail to meet even lowest level of suggested intake through diet alone and may therefore benefit from the prudent use of supplements.

Calcium citrate is considered to be the best source of supplemental calcium as it is better absorbed and more easily tolerated than calcium carbonate.  Calcium absorption is limited to less than or equal to 500 mg per dose and therefore calcium intake should be spread throughout the day.           


Question:  I have been performing body weight exercises including push-ups, planks, and stability exercises, for strength; are they adequate to prevent bone loss or induce new bone strength?  


Although body weight training and calisthenics are an excellent way to improve overall health and perhaps exercise performance, the types of exercises you have described are generally inadequate for improving bone strength.  Scientific studies reveal that in order for appreciable bone mass to be increased heavy resistance exercise or high impact loads (such as those induced with box or depth jumps) are necessary.  In general resistance loads need to be greater than or equal to the 8 repetition max (8 RM) level.  The repetition maximum refers to the maximal amount of weight that can be lifted with strict technique that specified number of times.  Typical muscle endurance protocols using light weights that are performed to failure have been found to be ineffective in terms or increasing bone density. 

 
Question: I was diagnosed as having a spiral type fracture of the tibia; is this a common type of running related of stress injury?    


The orientation of a spiral fracture implies that the line of force creating the injury is that of rotational torque about the legs vertical axis.  This type of stress is seen in the lower extremities of individuals that have elevated levels of what biomechanists refer to as free moment (FM).  Runners that exhibit high levels of pronation of the lower extremity and collapse of the knee toward the midline during the stance phase of running are typically at greatest risk for this sort of injury.  Fortunately, this mechanical pattern may be amenable to modification with a variety of strategies.  Some individuals with a leg length inequality demonstrate this pattern on the side of a longer lower extremity while others may have mobility limitations or weakness of certain stabilizing muscles. 

Individuals with an anatomic leg length inequality may benefit from the use of a shoe insert while those with mobility loss or weakness will improve with a targeted rehabilitation program.  Strengthening the hip external rotator and abductor muscle groups are especially effective in terms of improving lower extremity stability and reducing the likelihood of sustaining a spiral stress fracture.  

Question: Having a history of stress fracture I have reduced the frequency of my running to 2-3 days per week and supplemented it with non impact exercise including cycling and indoor rowing.  Do you feel this is a good strategy?


The frequency of skeletal loading is a very important determinant of adaptation.  Scientific experiments that have examined bone strength as a product of various exercise frequencies have reported that daily exercise, even at relatively small volumes, is oftentimes superior to exercise protocols that involve fewer weekly sessions.  Although there may be significant increases in markers of cardiopulmonary fitness with a program of cross training, running less than three times per week would most likely not enable your musculoskeletal system to adapt to the demands of running as optimally as a program that involved more running days per week.  It is important to note that the volume of running per week is not nearly as important as the frequency of running in terms of adaptation.  On practical terms, running 40 miles per week over 6-7 days per week would most likely result in a stronger skeleton than running the same number of miles over only 2-3 days per week.   

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