Exercise: the smallest amount that still works

Everybody knows exercise is good for them, and a great deal of the advice is
pitched at people who are already doing some. If you are starting from nothing,
the most useful fact is this: **the biggest single gain is between zero and a
small amount**, not between a good amount and an excellent one.

The dose-response curve is steep at the bottom and flattens out. Going from
sedentary to about ninety minutes of moderate activity a week buys a
disproportionate share of the benefit. Going from there to the full
recommendation buys more, but less per hour invested.

That is worth knowing because the official numbers can read as a threshold you
either meet or fail.

The targets, for reference

For adults, the usual recommendation is:

• 150 minutes a week of moderate-intensity aerobic activity, or 75 minutes
  of vigorous, or a mix.
• Muscle-strengthening work on two or more days a week, covering the major
  muscle groups.
• For older adults, balance training as well, because falls are the thing
  that actually removes independence.

"Moderate" has a practical test: you can talk but not sing. "Vigorous": you
cannot say more than a few words without pausing for breath.

What it actually does

The list of conditions where regular activity helps is long enough to sound
like overstatement, but the evidence for each is reasonable:

• Cardiovascular — lower blood pressure, better cholesterol profile, lower
  risk of heart disease and stroke.
• Metabolic — better insulin sensitivity; among the most effective things
  known for preventing type 2 diabetes.
• Musculoskeletal — stronger bone, preserved muscle mass, less back pain.
• Mental health — moderate effects on depression and anxiety, comparable in
  some trials to first-line treatments for mild cases.
• Cognitive — associated with slower cognitive decline with age.
• Sleep — falling asleep faster and spending more time in deep sleep.

Strength training deserves separate mention because it is the part most often
skipped. Muscle mass declines from roughly the thirties onward, and that
decline is what eventually determines whether someone can get out of a chair
unaided in their eighties. Nothing else substitutes for resistance work.

Sitting is its own problem

Long uninterrupted sitting carries risk that a single workout does not fully
offset. The finding that matters practically is that breaking it up helps:
a few minutes of walking every half hour has measurable effects on blood
glucose, independent of whether you also exercise.

So the first change for a desk worker is not a gym membership. It is standing
up more often.

Starting from nothing

Start below what you think you can sustain, and increase slowly. The most
common failure is not lack of willpower but an opening week ambitious enough to
produce injury or exhaustion, followed by stopping.

Anything that raises your heart rate counts — walking briskly, cycling to get
somewhere, stairs, gardening, carrying shopping. Structured exercise is
convenient, not required.

And it is never too late. Trials in people starting in their seventies and
eighties still show gains in strength, balance and independence.