One hundred and ten years. According to Dr Kelly Starrett, that's how long the human musculoskeletal system is designed to last. Why, then, does this system fail for so many people so much earlier? KStarr, as he is affectionately known, attempts to answer this question in his book Deskbound.
In his book, KStarr focuses on the biomechanical problems of sitting, and strategies to avoid and fix these problems. However, deeper research into the topic reveals risks on a far greater scale. In addition to worsening your posture, wearing down your musculoskeletal system and reducing your athletic performance, sedentary behaviour can cause widespread damage to your health.
The evidence is clear and continues to mount. The World Health Organisation ranks physical inactivity as the fourth greatest risk factor for global mortality. A large cohort study in the US found that sitting more than 6 hours a day increased the relative mortality risk by 94% in females and 48% in males. Sitting time was associated with increased mortality risk independent of physical activity.1 In the UK, working-aged adults spend significant amounts of time sitting, and alarmingly this is often more time than they spend sleeping (whether this is due to excessive sitting or a lack of sleep, the health risks of this behaviour are without question).2
To put it simply, sitting too much is killing us.
There is much that could be written on the subject. One could write about how sitting can increase cancer risk (especially colon, endometrial, and lung).3 The cognitive benefits of activity could be explored: sitting results in less dense grey matter and worse academic performance in children 4 and is associated with decreased cognitive functioning in adults. 5 The correlation between sedentary time and diabetes and metabolic syndrome is also unmistakable. 6 In the interest of brevity I shall leave these topics untouched for now.
It is unsurprising that sedentary behaviour can degrade so many systems. Humans are designed to move and for millennia this has been vital for survival. From the perspective of evolutionary biology, it therefore follows that humans thrive in conditions of movement. Fundamentally, humans excel at physiological adaptation. From the day you are born until you die, your body is adapting to your environment to give you the best chance to survive. This ongoing process explains why exercising for an hour a day is insufficient - your choices during the other twenty three hours cannot be overlooked.
What is the solution? At an individual level we need only to move more and sit less. At a societal level it becomes more difficult, lifestyles have advanced and progressed to minimise rather than maximise movement. Thus we require a profound cultural shift in the way we live and make decisions. This type of change takes time, though I am confident that society is moving in the right direction.
1 Patel A.V., Bernstein L, Deka A, Feigelson H.S., Campbell P.T., Gapstur M.S., Colditz G.A., and Thun M.J. Leisure Time Spent Sitting in Relation to Total Mortality in a Prospective Cohort of US Adults. American Journal of Epidemiology. (2010) 172(4): 419-429
2 Kazi A, Duncan M, Clemes S, and Haslam C. A survey of sitting time among UK employees. Occupational Medicine (London). (2014)
3 Schmid D and Colditz G. Sedentary behaviour increases the risk of certain cancers. Journal of the National Cancer Institute. (2014) 106(7)
4 Chaddock L, Voss M.W., and Kramer A.F. Physical Activity and Fitness Effects on Cognition and Brain Health in Children and Older Adults. Kinesiology Review. (2012) 1: 37-45
5 Singh Manoux A, Hillsdon M, Brunner E, and Marmot M. Effects of Physical Activity on Cognitive Functioning in Middle Age. American Journal of Public Health. (2005) 95(12): 2252-2258
6 Van der Berg J.D., Stehouwer C.D.A., Bosma H, et al. Associations of total amount and patterns of sedentary behaviour with type 2 diabetes and the metabolic syndrome: The Maastricht Study. Diabetologia. (2016) 59:709-718