If you feel like getting your blood moving - and with longer lasting effect than lifting dumbbells - go outside and lift stones. Make a dry stone wall - that is, one laid without mortar.
A well-constructed stone wall can last centuries. Use it to create a terraced surface where a short, steep and dangerous-to-mow grassy slope once lay. On level ground, use a stone wall to better define your terrace or driveway, or to create a garden "room." A stone wall also makes a nice backdrop against which to show off your bed of flowers or shrubbery.
And the wall itself can be a thing of beauty.
Even though about a ton of stone is needed for every 30 square feet of wall face, you only have to move those stones one at a time. Or a barrowful at a time. When you purchase or gather stones, make sure to get only those that are no heavier than you can comfortably move around.
Also, purchase or gather some basic tools. Gloves help prevent nicked or crushed fingers when working with stone. A metal pry bar or crow bar is useful for those final nudges a stone needs to settle it home. Occasionally, a stone might need to be cut, which you do by scoring it with a masonry chisel and hammer, then using the hammer solo to clink the far side of the cut. Wear goggles when cutting stone.
The mechanics of building a stone wall can be boiled down to a half-dozen or so basic principles.
Start out - most logically - from ground level, with a good foundation. Dig out the ground to a half-foot, less if drainage is good, and pour a couple of inches of gravel into the resulting trench. This gravel-filled trench creates a solid, immobile base on which to build.
Then, build on that theme of a good foundation by generally using your largest and flattest stones lowest in the wall. As you work upward, taper the wall in on both faces of a freestanding wall, or on the outside face of a retaining wall, to make the wall less inclined to collapse. For the same reason, lay flat rocks so they have a slight inward tilt.
Every time you put a rock in place, its fit with its neighbors should be secure, perhaps helped along with shims of small rocks or handfuls of packed soil or fine gravel.
For both appearance and strength, avoid lining up a joint in one course with a joint in the course immediately above or below it.
In addition to the space it defines, a stone wall opens up new opportunities in gardening.
Alpine and rock garden plants thrive in the warmed microclimate and good drainage provided by crevices packed with bits of soil. Or use the wall as a "shelf" on which to display potted plants.
The test of your wall will be next year at this time, when you see how it stood up to the ground shifting from frost.
If all rocks stay in place, your wall will get prettier with age as it cozies up in its surroundings with the embrace of plants and kisses from mosses and lichens.