May: Dirt

   It is practically a dare. To dedicated road runners, a dash through the woods seems vaguely illicit-tempting for its sensory indulgence and for its perverse, unfamiliar perils. You could be ambushed by elves or twisted ankles. Is it really even a workout at all?

   Never mind the ways trails work the imagination. Ponder the muscles that turn shockingly sore the day after. How can this be? Even craggy desert paths and fire roads provide softer landings for your feet than asphalt or concrete. Trail running should be easier on the body. Yet uneven and loose path surfaces along with sudden climbs and descents punish muscles that rarely come into play during a workout on the street. This is why trails are good for you. In fact, precarious footing and dramatic climbs force you to run with parts of your body that normally just fly along with the ride. For example, you'll intuitively shorten your stride on trails to prevent slips and spills. Your stabilizer muscles-the obliques in your torso-work harder to maintain your balance. You'll feel them the day afterward in your back, soinetimes in your hips.

   Femoris muscles (hamstrings) and the gastrocnemius and soleus muscles (calves), which launch you from step to step on predictable pavement, suddenly play second banana to less-developed quad and ankle muscles, which catch your step, then hoist you into position for the next step. There are 38 muscles and 214 ligaments in each of your feet, playing new roles in all this catching and hoisting. After a hard trail run, you will feel every sinew.

   Trails also make you strong by slowing you down. Hard pavement turns you into a human basketball; the energy you exert in each domnward step rebounds, catapulting you forward. On softer terrain, much of this energy is absorbed by the ground. It's squandered (tiy ~ n n i n gal ong a sand dune if you think this is hooey). Not only are your steps less efficient on trails, but there are more of them, thanks to a shorter stride. And to keep up with all these added labors and inefficacies, your cardiovascular system must work harder. In other words, you'll cover less distance at slower speeds, and you'll become pooped faster.

   Are you depressed yet? Road runners will never find joy on trails until they abandon the fixed delight in speed that comes from the snap of pavement under their feet. Time-through-distance goals are loosey-goosey notions off road, where even a light rain can create enough step-sucking mud to dramatically alter your performance from workout to workout. Far better are time-through-intensity goals: 10 minutes of sprinting followed by 5 minutes of recovery, and so on.

   The psychological landscapes change, as well. Every step must be planned (you wouldn't want to twist your ankle or trample an elf). Picking a line through trail obstructions and uncertain footing becomes an obsessive, gratifying skill. The singularity of purpose we bring to road running seems quaintly limited on trails, which engage a broader range of muscles, senses, and imagination. Even if it's just a diversion from your normal workouts, a little time off road will make you a better runner.