In case it escaped your notice, humans work better on two legs than on all fours.
Walking upright requires specific evolutionary adaptations of the skeleton and muscles. Changes included increased lumbosacral angle, a shorter and broader pelvis, formation of spinal curves, and use of core stabilising muscles, to name but a few (Essentials of Physical Anthropology, 2008).
The earliest fossils indicating bipedalism are approximately 3.5 million years old, and over almost this entire period walking has been the primary means of locomotion. To find food people walked, to escape drought people walked, to avoid tribal conflict people walked, to trade people walked... If you wanted to do anything over the past 3.5 million years, you walked.
It's reasonable to say most of us don't walk as much as our ancestors did, if any. By comparison, despite the gym and despite sport, we are fairly sedentary beings. This means large proportions of time sitting.
Think how much time you spend doing the following:
- Work desk
- Watching television
The effect of all this sitting? The elephant in the room; increased mortality (Warren et al, 2010).
Sedentarism affects lifespan more than alcoholism, smoking, obesity, and high bloody pressure.
An American study showed that retired men who walk more than two miles a day had half the mortality rate of those who walked less than one mile a day (Hakim et al, 1999).
Sitting for long periods puts a large amount of load on your lumbar discs, primarily because your core muscles are relaxed (Adams and Hutton, 1985).
Shortening of the hip flexor muscles which places increased load on your low back when you stand (Link et al, 1990).
Weakened core muscles make spinal injuries more common and rehabilitation more difficult.
Ligaments that stabilise your spine stretch when you sit, meaning they can't do their job as effectively.
Because of the C-shaped curve caused by sitting, the weight of you head is placed anteriorly. This puts more demand on the posterior muscles of your neck which can fatigue and cause pain. This can also cause headaches (Sato, 1984)
Tight hamstrings as a result of prolonged sitting have been linked to a number of knee problems (piva et al, 2005).
Adams M, Hutton W. Gradual disc prolapse. Spine 1985; 10:524-531
Hakim AA, Curb D, Petrovitch H, Rodrigues BL, Yano K, Ross W, et al. Effects of walking on coronary heart disease in elderly men: The Honolulu Heart Program. Circulation 1999; 100:9-13.
Jurmain R, Kilgore L, Trevathan W (2008). Essentials of Physical Anthropology 7th ed. Belmont: Wadsworth.
Link C, Nicholson G, Shaddeau S, Birchand R, Grossman M. Lumbar curvature in standing and sitting in two types of chairs: relationship of hamstring and hip flexor muscle length. Physical Therapy 1990; 70(10):611-618.
Piva S, Goodnite E, Childs J. Strength around the hip and flexibility of soft tissues in individuals with and without patellofemoral pain syndrome. Journal of Orthopaedic and Sports Physical Therapy. 2005; 35:793-801.
Sato H, Ohashi J, Owanga K, et al. Endurance time and fatigue in static contractions. J Human Ergol 1984; 3:147-154.
Warren TY, Barry V, Hooker SP, Sui X, Church T, Blair SN. Sedentary behaviours increase risk of cardiovascular disease mortality in men. Med. Sci. Sports Exerc. 2010; 42(5):879–85.