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Endurance sport is one of the greatest tests of mental and physical toughness. During a marathon an athlete, on average, will complete 160-200 steps per minute. Whilst running has numerous benefits for our health and wellbeing, it can be monotonous loading on the skeletal system. Bony stress injuries account for up to 20% of running related injuries per year. It is believed that one reason for this is the repetitive overloading on runners’ bones. In comparison, activities involving irregular movements seem to foster greater bone health. The ultimate goal should always be injury prevention, so, should runners incorporate directional movements into their training repertoire for bone health?
Bone is an alive, adaptable, and dynamic structure. Our bone density increases as we grow and by 30 our density is at its peak. After this age we can only maintain what we have. Bone health refers to our bones’ mineral density and quality and is the result of a plethora of factors. In otherwise healthy runners, energy availability, biomechanics, training load and recovery, all play important roles in creating good bone health. Poor bone health can increase the risk of fractures during one’s developmental years and later in life.
There are two main theories that address the way in which our bones are loaded during running. The muscle-bone unit theory refers to the pulling forces created by a muscular contraction. The other references the ground reaction forces through bone when the foot contacts the ground, producing torsional and compressive load. Both mechanisms create macro-trauma which stimulates tissue production and shapes bones geometric structure. However, like other tissues in the body, the activity needs to be progressive otherwise the bone may become accustom and stop adapting. These principles may be used to help runners who may otherwise be stunting adaptation through habitual running load.
In general runners’ bones are healthier than sedentary people. Unfortunately, runners consistently demonstrate lower bone mineral density (BMD) when compared to matched individuals who partake in high impact and irregular movement based sports. A summary of the research of athletes (aged 14-30) found soccer, basketball and volleyball players as well as gymnasts, all displayed greater BMD than those who only ran. A study of young soccer players demonstrated that female players had healthier tibiae than runners and both genders had better density at the spine, femur and calcaneus. In separate studies of track athletes and infantry recruits those who also regularly participated in basketball had up to an 82% reduction in stress fracture risk. Interestingly, in masters athletes those who participated in sprinting had greater BMD than their peers who competed in long distance running. The benefits of diverse loading in youth were also found to protect runners later in life with some up to 50% less likely to sustain a stress fracture.
What seems to be more unclear is the ideal dosage for bony loading. Bone regeneration cycles are suggested to take 3-8months. Studies of humans, mice and turkeys found significant changes after as little as 3 weeks of a jump program. Repetition amount also widely varied between studies from 30 - 350 cycles per week. A study of adolescent females found that a 9-month plyometric program improved only greater trochanter bone strength. Another found plyometric training only benefited those who participated in low osteogenic sports such as swimming. Studies on structure found that rate, magnitude and activity resulted in site specific changes, however, no optimal values for load were presented. No well-known study was found to investigate an irregular, directional and high impact, loading program for the reduction of fracture risk in endurance runners.
It is important to note there are many other factors which influence bone health that have not been explored here. The body needs a plentiful supply of vitamin D and Calcium to build strong bone. To create an optimal environment for this rest and good sleep are also essential. For distance runners who are constantly in a state of low energy availability, bone loading has been found to have little strengthening effects and can be somewhat detrimental if added in addition to their normal training.
Runners want to run. Convincing them to do otherwise continues to remain a great challenge for clinicians, however, it would seem that some variety may strengthen their bones. Youth runners should be encouraged to participate in a variety of sports. Once specialisation occurs, a runner may benefit from incorporating direction and plyometric loading into their training. Unfortunately, the optimal dosage for this is largely unknown.
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About the Author
Emily completed her Bachelor of Physiotherapy (Honours) – Advanced Research at Monash University in 2015. Her honours thesis examined the relationship between body composition and musculoskeletal pain. Emily is currently completing her Post Graduate Certificate in Sports Physiotherapy at La Trobe University, with the goal of subsequently completing a Masters in Sports Physiotherapy.
Emily’s clinical areas of interest include running related injuries, female athlete health and bony stress injury. Emily has had experience working with Athletics Victoria, Athletics Australia and numerous school athletes teams. Emily currently works full time in a private practise clinic and provides physiotherapy for her old school’s firsts sports teams. Outside of physiotherapy Emily enjoys competing in 400m hurdles at a national level and enjoying the Melbourne food culture.