Canadian Health Authorities Release New Physical Activity Recommendations

So what were the recommendations?

For kids: 

Children and youth 5-17 years of age should accumulate an average of at least 60 minutes per day and up to several hours of at least moderate intensity physical activity. Some of the health benefits can be achieved through an average of 30 minutes per day.

For adults: 

For a reduced risk for premature mortality/CVD/diabetes/stroke/osteoporosis, it is recommended that individuals should participate in 30 min or more of moderate to vigorous exercise on most days of the week. Greater health benefits appear to occur with higher volumes and/or intensities of activity.

Now as some have noted, the minimum guidelines for kids have decreased from 90 min/day to 60 min/day.  However, I think it's extremely important to point out that the recommendations do not suggest that people do less exercise.  Kids are not supposed to do 60 minutes a day, they are supposed to do a minimum of 60 minutes a day - which is obviously a very important distinction.  But some have still questioned why even the minimum guidelines would be reduced.  Luckily, that issue is nicely explained in the kid guidelines paper (emphasis mine):

There is strong
and consistent evidence based on experimental studies for several health
outcomes that participating in as little as 2 or 3 hours of
moderate-to-vigorously intense physical activity per week is associated
with health benefits. Evidence from observational studies also
demonstrates dose-response relations between physical activity and
health, with differences in health risk between the least active (or
fit) and the second least active (of fit) groups. Thus, it would seem
appropriate to set minimal physical activity targets that reflect a low
level of physical activity (see Recommendation #1). Furthermore, the
current recommendation of 90 minutes more per day (Canadian) or 60
minutes per day (US, UK, Australian) may be quite intimidating,
particularly for children and youth who are very inactive. From a
behaviour modification perspective, having a target that seems out of
reach may actually undermine physical activity participation [115].

That being said, with the exception of
injuries, the dose-response evidence from observational studies for
several health outcomes suggests that more physical activity will be
better, and that additional health benefits can still be achieved at the
higher end of the physical activity spectrum. Therefore, it would
also seem appropriate to set higher physical activity targets (60
minutes and up to several hours) that would elicit more pronounced
health benefits for those children and youth who are already somewhat
active (see Recommendation #1). This approach is consistent with
recommendations made by the U.S. National Association for Sports and
Physical Education[116] and the Australia Department of Health and
Ageing [117], both of whom have recommended that children and youth
participate in at least 60 minutes, and up to several hours, of moderate
to vigorous intensity physical activity every day.

This type of dual message provided in
Recommendation #1 will hopefully encourage children and youth who are
very inactive to engage in at least a modest amount of physical
activity, while at the same time encourage moderately active children
and youth to achieve even greater benefits by becoming more active.
The minimal and optimal doses of physical activity required for good
health in children and youth remain unclear, and more carefully
conducted dose-responses studies are warranted in the pediatric age
range.

I can see why there would be some genuine debate over whether it is
better to have "optimal" targets which may be hard for many to reach,
versus having "softer" targets that are only associated with some
benefits.  From my reading, the current guidelines try to cover both
bases - they explain the minimum amount that is associated with
measurable health benefits, but they also explain that doing more is
better.  Or, as I read in one press
release:

The papers outlining the recommendations synthesize a tremendous amount of information, so if you're looking for a thorough review of the evidence on the link between exercise and any number of diseases, they're a great place to start.  You can find all of them here.

Travis