Most runners don't think about connective tissue until it hurts. We have a general awareness that our bodies contain support structures like bones and ligaments to prevent us from collapsing into blobs of Jell-O, but that's where our curiosity ends.

Until our first case of Achilles tendinitis. Or plantar fasciitis. Or IT band syndrome. Or until we sprain an ankle, tear cartilage in our knee or suffer a stress fracture. Then we become experts. We visit doctors or podiatrists, learn about the particular connective tissue we've injured, begin a lengthy course of physical therapy and curse the day we overlooked the importance of strengthening this vital tissue. Because here's the scary truth: Once connective tissue damage is done, it's difficult—sometimes impossible—to undo.

What is Connective Tissue?

Connective tissue is exactly what it sounds like: tissue that connects your body's muscles, organs, blood vessels, nerves and other parts to one another. It supports, surrounds, strengthens, stores energy for, cushions and protects the components of your running body. It's the glue that holds you together.

Connective tissue is a catchall phrase for tissues that take many forms, from the gel-like areolar tissue, which binds skin to muscle, to the rock-solid bones that comprise your skeleton. Connective tissues most associated with running include bone, tendons, ligaments, cartilage and fascia.

Connected Training

Most connective tissues adapt to training, but there's a catch: They adapt at a much slower rate than muscle. When you allow your muscle development to outpace connective tissue adaptation, the result can be injury. Runners begin training and their muscles improve rapidly. Encouraged, they increase the intensity and length of their workouts. The next thing they know, they've got Achilles tendinosis, tibial tendinitis or stress fractures in their feet. Their connective tissue couldn't cope with the increased workload, even though their muscles seemed fine.

Some connective tissues won't ever improve much with training. For these tissues, such as cartilage and ligaments, your emphasis needs to be on injury prevention. You must strengthen muscles that directly affect the tissues (often smaller muscles overlooked in traditional strength-training routines) and use stretching and massage to reduce tissue tension.

Most of all, training connective tissue requires patience. Getfit-quick schemes rarely produce fast fitness; they produce injury.

Focusing on bones, tendons and fascia, the following pages explain how to build your connective tissue so that you can run stronger and avoid injury.

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Bones: Structure Under Remodeling

Your adult body contains 206 different bones. These bones form a balanced and symmetrical skeletal structure that puts even the best Lego toys to shame. They're also your primary defense against gravity, with your femur (thigh bone) alone capable of supporting up to 30 times your weight.

Of course, we runners tend to push gravity defiance to the limit. A single step during a distance run creates an impact force approximately two to three times your body weight. Lucky for us, bone is a living tissue that undergoes constant renewal. Under normal conditions, about 4 percent of your bone is broken down and replaced through a process called remodeling. When you run, this process goes into overdrive. Just as your body strengthens muscle fibers by replacing damaged myofilaments, it also uses remodeling and modeling—a separate process that fortifies bone with extra bone tissue—to create bigger, stronger, better bones.

But rebuilding and fortifying your bones takes time. At the beginning of remodeling, cells called osteoclasts dig out old, damaged bone tissue, leaving tiny cavities in your bones. It then takes three to four months for other cells called osteoblasts to fill those cavities with new bone. In the interim, you're left with porous bone that's susceptible to injury. During this phase, runners who push too hard for too long often end up with a stress fracture as their reward.

If you do get a stress fracture, the wait begins again. It will take three to four months for your body to repair the fracture. Training too soon risks re-injury.

Training To Build Bone

Training bone begins with nutrition. Poor nutrition leads to weak bones. In fact, deficient calcium in your diet can force your body to mine bones and teeth (which contain 99 percent of your body's stored calcium) for the mineral. If you are diagnosed with a stress fracture, pool running is your best cross-training bet. Resistance training triggers improvements in bone strength, but intermediate and advanced runners might need to increase their usual volume of reps and sets by 25 to 50 percent to continue strengthening their connective tissue.

Ten Foods For Happy Bones

Most of us know we need calcium and vitamin D for healthy bones, but our skeletons are hungry for more than just a glass of milk. A good set of bones requires a constant and adequate supply of protein, magnesium, potassium, phosphorus, fluoride and vitamin K. Each of the following 10 foods is unusually abundant in at least several nutrients that give your bones a boost:

1. Almonds

2. Bananas

3. Canned sardines

4. Orange juice

5. Raisins

6. Roasted pumpkin seeds

7. Soy products

8. Spinach or broccoli

9. Wheat bran

10. Yogurt

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Tendons: Organic Cables

Tendons connect muscle to bone, transmitting the force generated by muscles to move your joints—and hence your body. But tendons are far more than organic cables. They are active, responsive and vital partners with your muscles, so much so that the two tissues are regularly referred to as a muscle-tendon unit.

Muscles don't end where tendons begin. There is no line drawn. Instead, there is a transition area, the muscle-tendon (or musculotendinous) zone, where muscle gradually gives way to tendon. In this zone, muscle fibers and tendons merge, operating as a unit. It is only at the outskirts of this zone that tendons finally emerge as the glistening, white, fibrous cords that eventually connect to bone.

The Meeting Point

The point at which individual muscle fibers meet tendon, the myotendinous junction, is your muscle's weak link. It's here that most muscle strains occur. Powerful eccentric contractions cause damage either at this junction or directly above it. If you're lucky, damage will be limited to a few fibers and some short-lived soreness. If you're unlucky, a complete muscle tear might require surgery and physical therapy. The good news is that the muscle-tendon zone gets a rich blood supply from muscle fibers, resulting in a healing rate that almost parallels that of muscle.

Achilles tendon injuries, the plague of runners (especially those aged 40 and over), range from mild tendinitis to complete rupture. Achilles tendinitis is an overuse injury that is accompanied by painful inflammation. Achilles tendinosis, on the other hand, involves degenerative damage at the cellular level that produces chronic pain without inflammation. Until the late 1990s, almost all Achilles pain was thought to result from tendinitis. Now, it's understood that most Achilles pain is generated by tendinosis.

The best treatment for Achilles tendinosis is eccentric heel dips, a remedy discovered by Swedish orthopedist Hakan Alfredson. Alfredson was a runner who developed severe Achilles pain. In a podcast with the British Journal of Sports Medicine, Alfredson explained that he'd asked his boss to perform surgery on the tendon, only to have his boss reply, "If we operate on you, you need to be on sick leave. And we cannot afford that here at the clinic . . . I won't ever operate on your Achilles tendon."

Desperate to get the operation, Alfredson attempted to rupture his Achilles with a high-volume bout of heel dips. Instead, he got better. A 2012 study published in the British Journal of Sports Medicine investigated the long-term effects of heel dips. Researchers questioned 58 patients who'd previously treated their Achilles tendinosis with 180 heel dips per day for 12 weeks. The study reported that almost 40 percent of the patients remained pain-free five years later. The researchers also noted that two similar studies on the long-term effect of heel dips showed even better results, with 88 percent and 65 percent of those patients reporting little or no pain. It's not calf strengthening that does the trick. It's stress on the tendon itself, and subsequent adaptations, that lead to healing.

In the absence of proactive treatment (like heel dips), damage done to tendons in the white fibrous zone--that bloodless stretch preceding the interface with bone--has a gloomy outlook. A 2013 study from Denmark tried to determine the tissue turnover rate (the time it takes to regenerate completely new tissue) for this zone. Previous estimates ranged from two months to 200 years. The researchers chose subjects who'd lived during the nuclear bomb testing from 1955 to 1963, when atmospheric levels of carbon-14 were highest. They then measured existing levels of radioactive carbon-14 in the subjects' muscles and Achilles tendons. Tested muscle was clear of carbon-14. In contrast, tested tendon showed levels of carbon-14 that hadn't changed in the decades since atomic testing. So when can you expect damaged tendon tissue to regenerate? According to this study: pretty much never.

Tendon Training

Running and resistance-training exercises contribute to tendon stiffness. Wobble board and resistance band/tubing exercises further strengthen the entire kinetic chain (muscles, connective tissue and nerves from hip to toe); this helps to prevent tendon inflammation and damage. Active Isolated Stretching (AIS) is useful for working the muscle-tendon zone because it sidesteps the stretch reflex that can lead to strains in this area.

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Fascia: Woven Cocoon

Imagine that a spider with supernatural powers lies within you. And imagine that this spider spends its days spinning a single continuous web that cocoons your body beneath the skin, a web that spreads inward, surrounding and penetrating every muscle, nerve, organ and bone—every structure, cavity and tissue in your body. That'd be one heck of a web. Minus the spider, that web—a continuous weave of collagen and elastin fibers that grows thicker and thinner and that appears as membrane, sheet, cord and gristle—is your fascia.

Once considered the Saran Wrap of the body, fascia has recently been nominated for a status upgrade by some researchers. They view fascia as a reactive tissue. They believe it contracts and relaxes like muscles (albeit at a slower rate), recoils like tendons, provides sensory feedback like nerves and links all 650 muscles into a single working unit. Oh, and they blame it for the vast majority of chronic pain and injury in runners.

Robert Schleip, Ph.D., head of the Fascia Research Project, in a 2009 interview for Men's Health, described fascia as an instrument for "structural compensation." In other words, fascia is responsible for posture. When we climb stairs or slouch at our desk, we create alterations in our posture that can become permanent. In this model, fascia is like a sweater. Tug on one part of the sweater and the entire garment moves. Tension in one area can therefore affect every aspect of posture. Adhesions that build up between fascial surfaces due to injury can create chronic pain that radiates throughout the body. Seen this way, plantar fasciitis is no longer an injury of the foot; it could just as easily be caused by problems with the hips, back or shoulders. Schleip and others in the field believe that myofascial release exercises and specific stretches can improve posture, reduce pain and resolve injury.

Improving The Web

You don't have to be a true believer like Schleip to recognize the value of stretching, foam rolling and range-of-motion exercises. These exercises can include everything from resistance training to plyometrics and form drills.

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This post was excerpted and adapted from Build Your Running Body: A Total-Body Fitness Plan for All Distance Runners, from Milers to Ultramarathoners, copyright Pete Magill, Thomas Schwartz, and Melissa Breyer, 2014. Reprinted by permission of the publisher, The Experiment.

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