By Greg Hagley, PT, DPT
Several years ago I packed my too-damp hiking boots into a box for a move. A few weeks later, I unpacked them. It looked like I’d left them there for a decade. The leather had hardened, cracked, and shrank. The once well-fitting shoe squeezed my forefoot. It took several hikes and a lot of leather treatment to breathe life back into the boots. The upper gradually loosened and the leather regained its softness.
After an extended break from running our feet and legs suffer a similar fate as my boots did. In fact, research suggests that one of the best predictors of running injuries is being new to running. New runners’ legs are not accustomed to the impact or ground reaction forces (GRF) that come with every stride. Taking more than 3 to 4 weeks off from running leads to similar deconditioning. Even if you are an experienced marathoner, you may be setting yourself up for the same injuries a novice encounters.
Each spring my clinic is filled with people who took the winter off, fished their shoes out of the closet on the first warm day and found themselves injured. Sure, they may have cross-country or downhill skied all winter, but it’s not the same: Snow sports don’t make the spring-like demand on muscles, tendons, and joints that running does.
It takes time for our legs to adapt to the impact of running. These forces are unforgiving causing needless pain and overuse injuries to those who return to running too quickly. They reward the consistent runner. If you start running hard after a winter hibernation muscles are likely to become strained, tendons will ache, and bones may fail.
What Happens to Your Body?
Two muscle groups commonly injured in new and returning runners are the hamstrings and calf muscles (triceps surae). Both of these muscle-tendon units carry a significant eccentric load that is not common in other endurance sports.
Why? When we run our muscles contract both concentrically and eccentrically. During a concentric contraction, our muscles work as they shorten. Cycling, for example is a concentric activity. When we lift our hamstrings or run up hill, we make concentric contractions.
Conversely, during an eccentric contraction, muscles work while they lengthen. Think of running downhill: When we run, the ground reaction forces (GRF) create a large eccentric demand on your calf muscles and Achilles tendon as they slow down the impact as your feet hit the ground. Our hamstrings also function eccentrically when they slow down our forward swinging leg right before ground contact. Our calf muscles have their largest eccentric load as they cushion our landing. Picture a shock absorbing spring extending and then contracting.
While muscles strengthen relatively quickly, tendons adapt much more slowly to eccentric training stresses. Fast adapting tissues have a good blood supply: think red meat or the center of the hamstring muscle. Slow healing tissues have a poor blood supply. In a runner, these often include the proximal tendon of the hamstring just below the buttocks and the middle of the Achilles tendon.
And those are where we often see injuries.
That’s because tendons in the muscle-tendon complex respond to training stresses much more slowly than the muscle does on its own. For example, it might take several weeks for the muscle belly of the hamstring to strengthen after a strain. However, it can take 6 months for its proximal tendon to heal.[i] The same holds true for the Achilles. Tendons take a long time to build, but can weaken relatively quickly.
Bones are also subject to large forces when running. A running plan that progresses too fast can lead to a stress fracture anywhere from the pelvis to the metatarsals in your feet. Similar to muscles, bones are constantly in flux. They are continually remodeled to adjust to structural and metabolic stresses. When sedentary, bones act like a bank where the structural building blocks, calcium and phosphorus, are cashed out to provide fuel for other metabolic processes in the body. The inverse is also true. When active, bones perceive the stress and they react by designing supportive structures to maximize strength for the specific stress.
What Should You Do?
What to do with this information? The right answer for you depends on many factors such as your running history and goals. Are you a dedicated, competitive runner? Or, do you run to unload work stress and keep your dog fit? Regardless of how you answer those questions, I’ve listed several principles to consider when making your winter running plans.
- Keep running. Be consistent with whatever amount of running you choose over the winter. Our body responds better to frequent running in small doses, rather than a few longer runs. Running a minimum of 3 to 4 times per week can keep muscles and tendons supple and springy. This frequency of running will ease the transition to a higher running volume in the future.
- Follow the 10 to 20 percent rule. Well-read runners are familiar with the time-tested 10 percent rule, whereby you increase your mileage by 10 to 20 percent each week. The slow adaptation of muscles, tendons, and bones to training is the physiological foundation for the time-tested rule. But don’t go more than that: One large study of novice runners found a significant increase in injuries when the runners increased their weekly mileage by more than 30%. If you would like to build your running fitness in the spring, it is much easier to build from a winter weekly mileage hovering around 30 miles rather than starting from 0!
- Take a relative break. While this sounds contradictory to the first recommendation, I suggest an active rest rather than going cold turkey. Our bodies need to be renewed. It is normal and good to have a period when you cut back on your running and exercising. If you decide to go this route, I recommend running one to three times per week for a shorter distance while on this active rest. When you decide to run more, follow the 10 percent rule.
You an also mix it up by substituting a run our two per week with a snowshoe run, which has less of an impact on your tendons and bones. This requires a smaller snowshoe than what is used for winter backcountry hiking and works best on packed trails.
But most important, stay in touch with your running shoes this winter. You’ll be rewarded in the spring with legs that are run-ready.
Greg Hagley, PT, DPT is a doctor of physical therapy at Dartmouth-Hitchcock Medical Center in Lebanon, NH specializing in the treatment of running injuries. When not at work you can most likely find him outside. He has qualified for the triathlon Age Group World Championships in both the Olympic and 70.3 distance as well as completed several American Birkebeiner cross-country ski marathons.