How Much Exercise is Enough?
Like many the COVID pandemic has me working at home, sitting at my desk, tapping away at my computer for maybe 9-10 hours per day. In an office environment my level of movement is greater than being at home as I would get up and move around to talk with people, go from one room to another, walk to the coffee station etc. whilst at home I mainly sit and tap with the occasional 10 step walk to the kitchen to refresh my coffee.
We are told that sitting is the new smoking. A national heath-bomb that has serious impacts on our bodies and results in ailments such as cardiovascular disease, diabetes, stroke, osteoporosis, back-pain to name just a few. This got me thinking as to how much movement and exercise, as a species, we should be doing. I exercise quite a bit - when I am not sitting! Maybe 3 times per week in the gym, a few 5km runs and some walks. Is this enough to counteract the impacts of sitting?
It turns out that as a species, Homo sapiens is pretty sedentary. Not too much different from our ancestors or indeed or large ape cousins. Indeed there is significant value to animal species in not moving, as it preserves calories. Standing uses more calories than sitting. For our ancestors this was really important as they needed to preserve calories for food gathering or for avoiding becoming prey of another species. As a species though we have evolved to be better at standing than sitting - unlike our ancestors and ape cousins our lower spine has a curvature that positions our centre of gravity above our hips when we stand and that makes us very stable in the upright position - have a look at a gorilla or chimpanzee walking - you can see that it is inherently unstable.
Humans and apes have very low physical activity levels (PAL) compared to other animals and especially mammals. PAL is calculated as the ratio of how much energy you spend in a day divided by the amount of energy you would use to sustain yourself if you never left your bed. Many of us have a PAL in the range of 1.4 to 1.6. If you are above 2.0 then you are most likely vigorously active for several hours per day. It has been estimated that our hunter-gatherer ancestors had an average PAL of 1.9. Most mammals have PALs in excess of 3.3! Another way of thinking about this is that if you are a typical person who barely exercises then an hour or two of walking per day will make you as physically active as our hunter-gatherer ancestors. By the way, chimpanzees have a PAL of about 1.5 - they sit around a lot during the day.
So, as we can see from the PAL numbers, we humans and our ancestors and cousins, avoid wasting scarce energy on discretionary physical activities. However, the problem for us humans is how we spend our non-physical active time. We sit on soft sofas, we slouch, we sit on chairs with back supports, we sleep on very comfortable beds - we sit inactively! Our ape cousins and ancestors and indeed human tribes such as the Hadza people in Tanzania sit very differently - they squat or sit with their legs out in front and most importantly they sit without back support - this engages the core and strengthens the back. Additionally, whilst sitting apes are actually quite active - eating, grooming, minding the young etc. Humans are quite physically inactive - watching tv, sitting at a screen, popping sugary snacks in our mouths.
It looks like then that as a species we have evolved to sit just as much as we have evolved to be physically active. The secret seems to be then to sit actively without being inert for too long (include a sitting-to-standing exercise) but also to ensure that sitting doesn't get in the way of physical activity.
