Sedentarism: it's bad for us to sit too much, but what about too little?

The study in question – published this year in Journal of Sport and Health Science – was carried out by experts at various international institutions, including: Nanchang University, the Chinese Academy of Medical Sciences and Chinese University of Hong Kong (China), University College London (UK) and Simon Fraser University (Canada).

It involved 41,733 adults aged 35-70. The researchers assessed time spent sitting, levels of exercise and sleeping habits, identifying any relationships between the data and all-cause mortality and cardiovascular events.

The results showed a very particular link between the risk of death and time spent sitting: the risk was lowest for those who sat for four hours a day, but increased for those sitting for less then two hours and for more than six.

In other words, the data appear to indicate that the risk is highest at the extremes but lower under intermediate conditions.

The paradox of demanding work

While it's clear why there is an increased risk of death and of heart disease for those living sedentary lives, why does the risk rise for those who sit very little?

This can be explained by the study sample: of the people who stated they sit down for less than two hours a day, over 60% had physically demanding jobs. They weren't necessarily people who had chosen especially active or healthy lifestyles: many underwent hours of intense, strenuous activity each day.

This is the so-called “paradox of exercise”: moving a lot doesn't necessarily mean moving well. According to the research, therefore, for individuals who are very active because of physically exhausting jobs (and only for them!), replacing 30 minutes of physical activity with 30 minutes of sitting is paradoxically associated with a reduced risk of death and heart disease.

The risks of sedentary lifestyles: sitting down too much is in any case bad for us

The research does not put into question the overall body of scientific evidence.

The World Health Organization recommends that adults limit sedentary behaviour and emphasises that replacing time spent sitting with exercise, even of low intensity, is always beneficial.

For example, at least 150-300 minutes per week of moderate aerobic exercise is recommended for adults, or 75-150 minutes of vigorous exercise, as well as muscle strengthening at least two days per week.

Sitting down and physical exercise: the type of movement also matters

The research therefore highlights the importance of context. It can be misleading to only assess how much a person moves, without also considering how, why or in what condition they move. The same number of hours of exercise can indeed impact us very differently, depending on whether it is exercise during free time or physically demanding work.

A farmer who spends eight hours working in the fields could technically be considered “active”, but that type of continuous exertion, dictated by necessity, can be harmful – for our bones and joints, for example – and over the long term is more damaging than sedentary behaviour.

Genuine exercise to replace sedentary behaviour, on the other hand, should follow certain criteria: it must be appropriate for the person’s physical condition, gradual, and ideally under the supervision of an expert.

Move more, but allow time to recover

For those who work at a desk and spend much of the day sitting, therefore, the message remains to regularly break up long periods of inactivity. For those who perform very demanding manual work, on the other hand, the research seems to suggest that recovery should not be viewed as time wasted: enough rest and sleep is just as important to a healthy lifestyle as exercise.