Building Better Bones – bone health for runners

Posted on 29th September 2023

Introduction

Bone health is an important topic for people of all ages, but it is not a one-size-fits-all issue. Many factors can affect bone health, including age, gender, physical characteristics and lifestyle choices. Each person’s bone health is unique to them so while generalised information is broadly applicable to all, please consider your own unique circumstances.

People who take regular exercise might labour under the misapprehension that the nature and degree of their physical activity provides them with the protection they need against poor bone health. Sadly, this is not the case for many individuals and when it comes to runners, a surprising number are diagnosed with osteoporosis, weak bones (see below), during their running career – worse news still is that endurance running can precipitate it. Some studies have shown than male runners are more susceptible to it than males participating in other sports and also to non-running males^{.[1] [2][3]} Estimates vary widely for female runners but range from 19 to 50% might be affected by low bone density especially during the perimenopause.

What is an endurance runner?

Endurance will likely mean something different to each of us. However if you run a few miles at a time you are likely to fall within the category of an endurance runner and here’s why.

There is no single definitive scientific study that provides an agreed upon, universal definition of “endurance running” with precise thresholds. The literature cites the following frequently assessed measures of the physiology, demands or characteristics of endurance running:

Endurance running is often compared and defined relative to other sport: in particular from sprinting and jumping type sports which rely more on anaerobic power than aerobic.
Distance run: studies vary but can start 3000m upwards with 10000m often used in studies
Duration of the activity with anything longer than say 10 minutes having a high aerobic requirement
Intensity: the ability to perform an activity at a sustainable pace for 30 minutes of more
VO2 max is used to define endurance: various rates cited at around 65-85% maximum oxygen uptake

Thus, an endurance athlete is someone who participates in sports or activities that require sustaining moderate to high levels of aerobic activity for prolonged periods of time and where training focuses on building cardiovascular capacity, muscular endurance, and fatigue resistance.

The key attributes of an endurance athlete include:

High aerobic capacity – the ability to take in, transport, and use oxygen for energy production over the course of the activity. This requires strong cardiovascular and respiratory systems.
Fatigue resistance – the ability of the muscles to continue contracting and generating force for extended durations without fatigue
Managing pace and energy expenditure to avoid fatigue
Muscular and metabolic adaptations such as increased capillary density, mitochondrial density, and glycogen storage that support sustained activity
Mental stamina – focus and discipline needed to maintain high effort over a prolonged period
Low power/high sustainability – a combination of power and endurance that enables sustaining moderate to high effort as opposed to short bursts of maximum effort.

The skeleton is often considered inert. Bones are hard, solid and don’t seem to move or change much and as we don’t see them growing or repairing themselves it’s easy to think of them as inanimate objects. In fact, we often don’t think about them much at all unless something goes wrong such as a fracture.

However, bones are dynamic and metabolically active tissues which are continually being remodelled very slowly in accordance with the demand of the stresses we place upon them. The adult skeleton turns over around every ten years so the skeleton you have today is not the one you had ten years ago. A baby’s skeleton turns over completely in the first year of life.

The skeleton has a number of functions: it provides structure to the body to enable us to stand and a framework for soft tissue attachments of ligaments, which hold bones together as joints; and muscles and tendons which work across those joints to enable movement. It also provides protection for the internal organs: the skull protects the brain; the rib cage protects lungs and heart and the pelvis protects the structures of the reproductive organs, the urinary system, and the blood vessels and nerves supplying the lower limbs amongst others.

As well as structural support, protection, and enabling movement, bones are important storage organs. They are the body’s reservoir for minerals such as calcium and phosphorus, absorbed and released into the bloodstream to maintain levels within a fine range. They store a vast number of chemicals and cells involved in bone remodelling and the immune system. The marrow inside bones is the site for production of blood cells and is also an important store of fat. Marrow fat quantification is used in some settings to determine whether animals have died of starvation. The skeleton is also involved in blood glucose control and regulation, and with the reproductive system.

What is bone health?

Bone health refers to the condition and strength of a person’s bones. Healthy bones are dense, strong, and resistant to fracture.

Bone mineral density (BMD), is a measure of the amount of bone mineral in a given area of bone and is a good predictor of bone strength and health; the greater the density, the stronger the bones and the less susceptibility to fracture.

Diagram: bone density through life

This diagram shows average BMD through life, pink for females, blue for males. Bones are actively growing throughout childhood and adolescence and BMD increases during this time. Peak bone mass is reached in the thirties after which is starts to decline gradually for both males and females. Bone formation and resorption are closely linked in a process of remodelling, in fine balance to maintain the mass and strength of a healthy skeleton. However, over the age of 30, this balance changes with less bone formation and greater resorption resulting in reduced bone strength, osteoporosis, and fractures. From around mid-40s, the rate of decline for females steepens rapidly as they enter the perimenopausal phase. This reflects the loss of oestrogen at this time and indicates the importance of oestrogen for female bone health. From aged about 60 onwards, the rate of BMD decline in females slows to around the same rate as males.

Low BMD can result in osteopenia (BMD less than normal peak BMD but not low enough to be classified as osteoporosis) and osteoporosis. Osteoporosis is a disease characterized by low bone mass and deterioration of bone tissue and leads to increased bone fragility and fracture risk.

Osteoporosis is also known as the ‘silent disease’. This is because it mostly doesn’t produce symptoms unless or until you sustain a fracture as a result of minimal trauma that would not typically cause a fracture in healthy bone. The prevalence of osteoporosis is 2% at the age of 50 and 50% at the age of 80. Data from my practice treating patients with hip fracture for over 20 years, the ratio of females to males presenting with hip fracture was 4:1 with an average age of 83. The lifestyle choices you make throughout life, your running career and beyond can have significant implications for your quality of life as you age.

Factors affecting bone health

Dietary factors contribute to overall health and bone health is no exception. In particular, one should aim to consume sufficient calcium and vitamin D.

Calcium is essential for many functions in the body and is maintained within a fine range. If blood calcium drops even fractionally, the body takes immediate measures to correct it and one of those is to signal to the bones to reabsorb calcium from them. Vitamin D is also involved in many functions within the body and on the current topic it helps your body absorb calcium from your food and reabsorb it from kidneys. If you have a low calcium and vitamin D intake you could be compromising your bone health. This applies to those who choose to restrict their diets, to those who have malabsorption conditions such as inflammatory bowel disease and, sadly, to those of us of not such young years as evidence suggests we absorb less as we age. In particular, those most at risk of poor bone health are children and perimenopausal females. Calcium needs: 1000mg/day consumed over the day to optimise absorption.

Vitamin D is essential for calcium absorption and bone health by promoting calcium absorption in the gut from our food and by ‘reclaiming’ it from kidney filtration. It has many functions in the body including for muscles, nerves and the immune system. Vitamin D is acquired primarily through our skin when exposed to UV sunlight but also from our diet from fatty fish, eggs, and fortified dairy products. The recommended daily intake of vitamin D for adults in the UK is: 10 micrograms (400 IU) per day. Health guidance recommends we should all take a vitamin D supplement all year round.

Excessive alcohol intake interferes with metabolic pathways and can increase your risk of osteoporosis.

Smoking is an independent risk factor for future fractures and increases the risk of osteoporosis. In one study male smokers aged over 65 years had a 30-40% increase of hip fracture.^[4]

However, the most important lifestyle factor influencing bone density is physical activity. In the developing skeleton the growing bones are more responsive to mechanical loading than adult bones and it’s crucial we encourage as much physical activity in these decades as we can.

A significant cause for concern is the findings of a Sport England survey in 2018^[5] that reported that over the age of 13 only 10% of girls meet the Chief Medical Officer’s recommendation on physical activity and it’s not much higher for boys. This has huge implications for later life – when peak BMD is less than the average level shown in the diagram above, the risk is that osteopenia and osteoporosis will occur at an earlier age when BMD naturally declines, and that raises the risk of fractures at an earlier stage in life.

The type of physical activity undertaken is important.

A ten year study of masters athletes aged between 37 and 85 years examined their bone health over time comparing those who were endurance (distance) athletes with those classed as power athletes (jumping and sprinting). The results suggested that bone mass is better preserved in male than female athletes and that power training is better for maintenance of bone mass than endurance training in older age. ^[6]

Whilst endurance runners steadily cover many miles over long periods of time, the ground reaction force required to provide the requisite stimulus to bone is not being achieved. Indeed, the constant repetition particularly running on tarmac, is producing micro damage at a rate faster than the body may well be able to repair and remodel it. This itself can lead to a loss of BMD, especially in those athletes who may not be consuming sufficient calories to fuel their activity needs (see RED-s below).

Those who regularly strength train and those who are sprint runners both deliver sufficient power stimulus to the bones to remodel strongly. This stimulus appears to be preserved throughout life with strength training being of benefit however late in life you start it. A 2018 study looked at postmenopausal females with osteoporosis and put them through a managed program of strength training.^[7]Over eight months they found that the degree of osteoporosis could be reversed.

What might training comprise to optimise bone health for life?

Think of four different types of activity focus: suppleness, strength, stamina and skill – working on each is important.

Suppleness needs movement that puts all of our joints through a full range of motion, something we do not achieve in the course of normal daily activities. It does not necessarily mean stretching although stretching can enable a joint to move to its maximum end of range for you. Maintaining the maximum rate of mobility through the joint is important for a number of reasons. Firstly, it enables the maximum possible stimulus for bone adaptation in all directions from your strength activities. Secondly, in those who develop any form of joint restriction condition, by keeping the soft tissues as mobile as possible can enable movement and slow any restriction and pain for longer – if you stop moving a joint, the tissues tighten up and become stiff and painful to move, as anyone who has had a broken bone immobilised will know.

Strength training at high intensity places a greater mechanical load and tension force on the bones compared to lifting lighter weights and this provides a greater stimulus for bone remodelling and adaptation. A number of studies^{examples[7][8]}have shown the benefits that can accrue in relatively short periods (months) of time. Typically, this would be done using weights of 85% of the weight at which you can only shift for one rep maximum (1RM). Generally, one would aim to perform 5 sets of 5 reps of 85% for each exercise. Squats, deadlifts and overhead press have been shown to improve BMD at lumbar spine and hip. If you’re new to resistance work then this type of training does need to be worked up to under appropriate guidance.

Stamina is the ability to sustain prolonged physical effort and is likely to be the activity modality runners will already have well developed. It depends on the body’s ability to circulate oxygenated blood and nutrients to working muscles without fatiguing too quickly but also allows continuation of the activity once fatigue does start to accumulate. Good muscular and cardiovascular endurance are key to good stamina.

Skill -running is an asymmetrical activity moving from one leg to the other and the skills required include balance and coordination. The ability to balance, control your body movements and change directions smoothly and fluidly are fundamental for safe movement. Balance is a function of three things: your vision, the function of your inner ear and proprioception. Proprioception is the body’s ability to know its position in space without needing to look and is informed by signals going to the central nervous system from receptors in muscles, joints and other tissues. Our ability to balance deteriorates as we age becoming a risk factor for falls. We can exercise to improve it although we can’t get it back to what it was in earlier years. You can assess yourself, right leg versus left. How long can you balance on each leg? Do this without shoes and socks on. Then try it on each leg with your eyes closed making sure you are close to something to hold on to. How many seconds?

Good exercises include:

standing on one leg while brushing your teeth – two minutes twice a day add up to 2 hours a month so it’s an easy habit without having to find time to do it. Practice also with your eyes closed.
Hopping – can also be done while doing teeth 😊
When putting on clothes, socks, shoes, raise the leg towards the body and balance on the other leg

Being overweight or obese is a risk factor for osteoporosis, thus maintaining a healthy weight is important. Healthy weight is defined as a body weight that falls within the healthy range for a specific height and body frame according to standard measures such as Body Mass Index (BMI) and body fat percentage. ^[13]

Genetics also has a large part to play in bone health with a family history of osteoporosis and hip fracture being a potential risk factor for you. Any concerns on this account should be discussed with your GP to assess your overall risk factors.

In summary, whilst physical activity is a prime requirement for good bone health, it does not stand alone: the ideal combination of factors would be physical activity, including weight bearing and resistance and strength work, adequate calcium and Vitamin D intake together with eating sufficient calories to fuel activity, not smoking, minimising alcohol intake and maintaining a healthy weight.

Relative Energy Deficiency in sport (RED-s)

RED-s is a condition of low energy availability (LEA) which can affect both male and female athletes of all ages. It can adversely affect many systems in the body with significant long-term health and performance consequences. In the context of bone health, consequences include osteoporosis and fractures.

The underlying cause is low energy availability due to the athlete not eating sufficient calories to fuel their needs for their basic daily activities and their sport. It can be intentional or unintentional either by actively restricting caloric intake or by training in excess of intake. A 2016 study found that there was a 20% higher prevalence of disordered eating in athletes compared to non-athletes.^[9]However, athletes with normal diets are still susceptible to RED-s if a high training load is not adequately matched with caloric intake.

Developing LEA and RED-S compromises the ability to adapt to training, reduces performance and is damaging to health.

It affects males and females and one of the causes is a misguided belief that the less you weigh then the faster you will be able to run. This can lead athletes to reduce their calorie intake.

Reduced nutritional intake can lead to nutritional deficiencies: insufficient calories to fuel the endeavour, insufficient nutrients such as calcium and vitamin D and disordered hormonal function leading to amenorrhoea (loss of menstrual periods in females). The resulting reduction in oestrogen adversely affects bone health leading to loss of bone mineral density and a tendency towards osteoporosis which predisposes to stress fractures.

Research in male endurance athletes shows low energy availability leads to negative impacts on bone density and markers of reproductive health like low testosterone and reduced libido^.[11]

The process takes months to develop, and it takes many more months from which to recover. The recovery process is not as simple as starting to replace those calories and eat a normal diet. Damage has been done and the body must be carefully rehabilitated and reconditioned. Healing fractures, improved body weight and restored periods are helpful cues that recovery is taking place but just because symptoms are easing doesn’t mean you’re back to normal. It may take years. It takes around two to four weeks for an area of bone to be resorbed but it takes four months for the body to lay down the new bone to replace it as it remodels. ^[12]

Summary: Bone health is a fascinating and complex subject. This article only touches the surface and any of the aforementioned topics is worthy of a lecture in its own right. I hope you’ve found something of use even if only to confirm that what you’re already doing is great, and that you’re already on the road to having a healthy skeleton for life.

Angela White (@therunninggranny)

is a retired trauma and orthopaedic surgeon with a special interest in hip fracture and osteoporosis
an Associate Lecturer in Bone Health
is Director of Going for Old CIC, a social enterprise promoting action for healthy ageing through life
develops and delivers bespoke health and wellbeing workshops e.g. Building Better Bones
started running at the age of 53 and discovered endurance running, completing events such as Lakes in a Day, Tour de Helvellyn and the Northern Traverse
in 2019 set a Guinness World Record as the Oldest Female (aged 60) to run John o’ Groats to Land’s End
Is a motivational speaker

References:

[1] Lower vertebral bone density in male long distance runners. Medicine and science in sports and exercise, 21(1), 66-70 https://pubmed.ncbi.nlm.nih.gov/2927303/

[2] Greater maintenance of bone mineral content in male than female athletes and in sprinting and jumping than endurance athletes: a longitudinal study of bone strength in elite masters athletes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7286845/

[3] Bone Health in Endurance Athletes https://pubmed.ncbi.nlm.nih.gov/23147022/

[4] Smoking and fracture risk: a meta-analysis. Osteoporosis International, 16(2), 155-162. https://pubmed.ncbi.nlm.nih.gov/15175845/

[5] Women in Sport: reframing sport for teenage girls https://womeninsport.org/resource/reframing-sport-for-teenage-girls-building-strong-foundations-for-their-futures/

[6] Greater maintenance of bone mineral content in male than female athletes and in sprinting and jumping than endurance athletes: a longitudinal study of bone strength in elite masters athletes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7286845/

[7]High-Intensity Resistance and Impact Training Improves Bone Mineral Density and Physical Function in Postmenopausal Women With Osteopenia and Osteoporosis: The LIFTMOR Randomized Controlled Trial https://pubmed.ncbi.nlm.nih.gov/28975661/

[8] Musculoskeletal responses to high- and low-intensity resistance training in early postmenopausal women. Medicine & Science in Sports & Exercise, 32(11), 1949-1957 https://pubmed.ncbi.nlm.nih.gov/11079527/

[9] Aspects of disordered eating continuum in elite high-intensity sports. Scandinavian Journal of Medicine & Science in Sports, 20(s2), 112-121. https://pubmed.ncbi.nlm.nih.gov/20840569/

[10] Prevalence of individual and combined components of the female athlete triad https://pubmed.ncbi.nlm.nih.gov/23247706/

[11] Parallels with the female athlete triad in male athletes. Sports Medicine, 46(2), 171-182. https://pubmed.ncbi.nlm.nih.gov/26497148/

[12] Normal bone anatomy and physiology. Clinical journal of the American Society of Nephrology, 3(Supplement 3), S131-S139. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3152283/

[13] Health Weight https://www.nhs.uk/live-well/healthy-weight/bmi-calculator/

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