Does exercise reduce pain?

Short answer

It does. With regular exercise, long-lasting back pain dropped 15.2 points out of 100 and knee arthritis pain 12 points. Even one session dulled pain, but in people with widespread body pain, hard exercise made them more sensitive.

Does exercise reduce pain?
'Exercise is a natural painkiller' — really?
Many people say their aches feel better after a workout. Yet it is just as common to hear that you should rest when something hurts. We looked separately at the effect of a single session and the effect of exercising regularly for weeks.
Even one session helped
One bout of cardio clearly dulled pain
We looked at studies that measured pain in the lab, using pressure or heat, in people without pain. After one session of aerobic exercise, pain sensitivity dropped a lot across 7 studies of 236 people. One session of strength training reduced it a little, and holding a position under load (static exercise) did not.
How hard do you need to go?
In people without pain, harder meant a bigger effect
An analysis pooling 13 studies of a single aerobic session found the pain-dulling effect was largest after high-intensity exercise. Low-intensity exercise had almost no effect, and session length, long or short, made no difference. Pain sensitivity dropped not just in the exercised body part but also in parts that did not exercise.
But with widespread body pain
Hard exercise made people more sensitive
In fibromyalgia, where pain spreads across the body, hard aerobic exercise or moderate static holds made people more sensitive to pain. Aerobic exercise at a comfortable or moderate pace dulled pain. In 114 people with long-lasting muscle or joint pain, one session of static holds did not reduce pain.
What about exercising regularly?
Long-lasting back pain fell 15.2 points out of 100
We looked at 249 trials of exercise for back pain lasting more than 3 months. Compared with doing nothing or usual care, pain was 15.2 points lower on a 100-point scale. It was 9.1 points lower than other treatments too, and no different from hands-on manual therapy.
Knee arthritis pain fell too
Cardio had the biggest effect
Across 44 trials, exercise cut knee arthritis pain by 12 points out of 100, and pain was still 6 points lower 2 to 6 months after the program ended. An analysis comparing 217 trials with 15,684 people found cardio such as walking, cycling and swimming reduced pain the most at 4 and 12 weeks.
Did exercise ever make pain worse?
Side effects were mostly muscle soreness
A review of 264 studies with 19,642 people found no outcomes that got worse because of exercise. Most reported side effects were muscle soreness, which faded after a few weeks. In back pain trials, side effects were reported in 33% of exercise groups and 29% of comparison groups, a similar rate.
Bottom line: exercise reduces pain
What worked was exercise kept up for weeks
Even one session dulled pain, and exercising regularly for weeks lowered back pain by 15.2 points and knee arthritis pain by 12. In widespread body pain, though, hard exercise made pain worse. In widespread body pain, what reduced pain was cardio at a comfortable pace.