Going out for a run.

[Mid Life Crisis Marathon Man]

Here's a very revealing extract from an article in the current Marathon & Beyond magazine:

Run on soft surfaces
Another way you can reduce the pounding on your hip, knee, and ankle joints is by running on soft surfaces. Grass fields and sawdust or dirt trails greatly reduce our impact with the ground. This impact, known as ground reactive force (GRF), is one of the most pernicious side effects of our sport.

The high GRF from running on roads causes far more muscle soreness and
inflammation than trail running. A survey (Beckstead et al. 2005) given to trail runners on their training habits and surfaces was most revealing. A typical comment from ultra trail runners in the survey was that their legs are not nearly as sore after a 50-mile trail race compared with running a marathon on the road.

The ultrarunners also reported that their body recovered slower after a marathon. Electron microscope photos of muscle biopsies taken from the legs of marathon road runners look horrendous. Postmarathon muscle tissue is a war zone: widespread disruption to the muscle sarcomere, breached cell membranes that allow the contents and intracellular proteins to spill out into interstitial spaces and the bloodstream, swollen muscle fibers, and damage.