Vicky Stiles, Brad Metcalf, Karen Knapp and Alex Rowlands
We don’t yet know whether it’s best to do it all at once, or little and often, but what we do know is that if a woman’s day-to-day activity contains 1–2 minutes of weight-bearing, high-intensity activity, similar to a medium-paced run for pre-menopausal women or a slow jog for post-menopausal women, she will have better bone health than women who do less. The benefits of high-impact activity on bone health are nothing new. What is novel about our findings is that better bone health is linked to such a short amount of daily activity, albeit at an intensity of the running variety.
Good bone health means that the conditions in the body (nutrition, hormones, mechanical stimulation from exercise) are right to either build or maintain bone mass, which helps prevent bone thinning (osteoporosis) and fracture risk in older age. We’ve known for a long time that weight-bearing activity is generally considered good for bone health but, so far, studies of bone health and day-to-day activity levels in women have not been able to tell us exactly how much time (or, rather, how little time) we need to spend doing an activity at a particular intensity to benefit bone.
To more accurately measure the day-to-day activity that is beneficial to bone, we accessed a national health database in the United Kingdom (UK Biobank) of about 100 000 research participants. Each participant gave consent to have their heel bone health measured using ultrasound and their physical activity accurately measured over the course of a week using a wrist-worn activity monitor. This monitor enabled the UK Biobank to collect detailed data on participants’ physical activity levels, which means that, as researchers, we don’t have to rely on asking people in a questionnaire to try to recall the amount and intensity of activity they’ve done over the past week. Measuring activity beneficial to bone health requires a lot more accuracy than questionnaire data allow.
Activity monitor data have been around for a while, but to look in more detail in relation to bone health, we broke these data up into small snippets of time that capture how people tend to go about their daily activities. We wanted to make every second count; because short snippets of high-intensity activity are more beneficial to bone health than longer, continuous periods of high-intensity activity, we were careful not to ignore short bursts of activity throughout the day. We counted the number of seconds spent in different activity intensities, ranging from doing nothing (sedentary) up to an intensity of activity well beyond a full-out sprint, which, not surprisingly, does not typically occur in many people’s day-to-day lives.
The results of this analysis showed us that women who spend just 1–2 minutes of their total daily activity at an intensity equivalent to running have on average 4% better bone health than those who do less than a minute — which, for the majority, actually means spending no time in activity of this intensity during the day. Those who spend more than 2 minutes of their day at an intensity equivalent to running have on average 6% better bone health than those who do less than a minute.
A note of caution: this study was cross-sectional, meaning we cannot be sure whether the high-intensity physical activity led to better bone health, or whether those with better bone health do more high-intensity activity. However, we’re always motivated to think about how we might encourage those who do little physical activity to do more and, for bone health, doing more could mean just 1 to 2 minutes of running throughout the day.
As we’re confident that the healthy-boned sample in our study were not typically “runners”, we are now wondering how this 1–2 minutes of activity at an intensity equivalent to running came to pass, and whether it was done all at once or in snippets throughout the day. While we’re pondering exactly how many people really do run for the bus each day, your time is probably better spent thinking about the type of daily activity in which you might be tempted to engage, should you wish to do more. If you are after any pointers, the UK’s National Osteoporosis Society suggests starting with a walk. While you’re out and about, we would add that you might consider substituting a few walking steps with a few running steps, a bit like you would if you were to quicken your pace to catch the bus.
Stiles VH, Metcalf BS, Knapp KM, Rowlands AV. A small amount of precisely measured high-intensity habitual physical activity predicts bone health in pre- and post-menopausal women in UK Biobank. International Journal of Epidemiology 2017. doi: https://doi.org/10.1093/ije/dyx080.
Vicky Stiles is a Senior Lecturer in Biomechanics at the University of Exeter. She is interested in the development and use of activity monitors to measure characteristics of daily activity that are important for better bone health in the general population and characteristics of training load that are important for reducing the risk of injury risk in different sports. She is a member of the Physical Activity and Health Across the Lifespan (PAHAL) Research Group and Human Movement Science (HMS) Research Group at the University of Exeter.
Brad Metcalf is a Senior Lecturer in Physical Activity and Health at the University of Exeter. His current research interest is in developing novel metrics from accelerometer data that capture the different patterns in which people accumulate their activity. He spent many years working for the EarlyBird Diabetes Study as both a physical activity researcher (examining the longitudinal associations between physical activity, obesity and metabolic health in children) and as the senior statistician. He is a member of the Physical Activity and Health Across the Lifespan (PAHAL) Research Group at the University of Exeter.
Karen Knapp is an Associate Professor in Musculoskeletal Imaging at the University of Exeter. Combining a passion for research and education with her clinical background, Karen uses research-led teaching to inspire students. With a background in teaching undergraduate and postgraduate students from Masters level through to professional doctorates and supervising PhD students, Karen is keen to engage at all levels of higher education. Karen’s primary research interest is in bone health, osteoporosis and associated conditions, along with developing and testing computer-aided detection (CAD) software in vertebral fracture patients. Karen is actively involved in the National Osteoporosis Society and the Society and College of Radiographers.
Alex Rowlands is a Senior Research Fellow in Physical Activity, Sedentary Behaviour and Health with the NIHR Leicester Biomedical Research Centre (Lifestyle Theme), based at the Diabetes Research Centre, University of Leicester. His research focuses on the objective measurement of physical behaviour (physical activity, sedentary behaviour and sleep) using accelerometry-based wearable monitors. He is on the Scientific Committee of the International Society for the Measurement of Physical Behaviour (ISMPB).