Revista de Medicina Desportiva (English) September 2018 | Page 28

Physical Activity and Mortality:
the Potential Impact of Sitting
Peter T. Katzmarzyk, Russell R. Pate
Translational Journal of the ACSM, 2017; 2(6):32-33.
Summary: Dr. Basil Ribeiro
The Physical Activity Guidelines
for Americans, published in
2008, refer that for obtaining
health benefits it is necessary
to carry out 150 minutes per
week of physical exercise of
moderate to intense intensity.
It is a magical number that
applies to everyone, regardless
of the time spend seated in the day-
time. The authors of this comment
add a very important information
and also, somehow, challenge this
value.
Based on published studies, the
average self-reported time the
Americans spent seated is equal to
4.7 hours/day (2014), which is under-
estimated, because the objective
measurement with the accelerom-
etry indicated the value of 7.7 hours/
day (2008). For the Australians it was
found the value of 8.8 hours/day
(2015). Regardless of these values,
it is known that there are jobs that
require the sitting position for many
hours a day, but it is also realized
that after the job, in all professions,
the sitting time is high.
The authors wanted to interpret
on their own way the results pub-
lished at the Lancet, in 2016 by Eke-
lund, U. et al, from a meta-analysis
(13 studies), where 1005791 people
participated, were followed between
2 and 18 years, and the mortality
was considered for all causes. In this
period, 8.4% of the people died. Of
course, and according to common
knowledge, the negative effect of
sitting was directly attenuated with
the increase of the physical exercise
levels. The practice of moderate-
intensive physical exercise during
60 – 70 minutes/day effectively
eliminated the risk of death from all
causes. These results are not surpris-
ing and are in accordance with the
current sports medicine wisdom. But
the authors wanted to know more
and questioned whether the levels
of sedentary life would influence the
relationship between the practice of
physical exercise and the mortality,
Figure 1 – Association between the weekly levels of physical exercise of moderate
intensity-intense according to the seating levels (2.5, 16, 30 and 35.5 MET.h.week-1
correspond approximately to 5, 25-35, 50-65 and 60-75 minutes of moderate-intensive
physical exercise).
26 september 2018 www.revdesportiva.pt
that is, if the relationship is the
same on the subjects belonging to
groups with different hours of daily
sitting.
From the data of the meta-analy-
sis of Ekelund, U. et al, these authors
worked the numbers differently and
produced this figure/graph. Again,
and very naturally, it was found a
relationship between the practice
of physical exercise of moderate
intensity-intense and mortality
from all causes, that is, the higher
the volume, the lower the risk of
death. But the graph, stratified by
the number of hours of daily sitting,
has another reading. The authors
refer to the example of the person
who performs 25-35 minutes a day
(16 MET·h·week −1 ) that still have
an increased risk of death, which
is higher than the reference value
for all levels of sitting time, even
for values less than 4 hours per day.
What the authors intend to say is
that “people who remain seated for
long periods on a desk during the
working day should have a strong
incentive, not only to get up, but also
to substantially increase the volume
of physical exercise of moderate-
intense intensity”. They also men-
tion that complying with such
150 minutes/week substantially
decreases the risk compared to the
person who performs little exercise
weekly, but the 150 minutes will not
minimise the risk (Hazard Ratio).
The comment ends with two very
strong opinions:
1. Moderate-intensive physical
exercise levels shall be increased,
irrespective of the number of daily
hours remaining seated;
2. Persons who are obliged to
sit for a long time must strive the
higher levels of physical exercise
and not the lower ones (the 150 min-
utes will certainly not be enough).