Muscle Medicine: The Revolutionary Approach to Maintaining, Strengthening, and Repairing Your Muscles and Joints (4 page)

The tough outer layer of the joint capsule is made from another kind of cartilage, fibrocartilage. Some joints have special fibrocartilage shock absorbers inside the capsule—the labrum in the shoulder and hip, and the meniscus in the knee. In the spine, fibrocartilage makes up the disks, filled with mucoprotein gel, that act as shock absorbers between the vertebrae.

Inside, and sometimes outside, the capsule, strong bands of tissue called ligaments connect the two bones together and hold them in place, allowing for controlled movement. (The ligaments in the knee are the most numerous and also the most often torn.) The common denominator for all these structures, what really makes the system work, is collagen: a tough, rubbery, and altogether amazing material that is the building block of all the connective tissues in the body—cartilage and ligament, as well as muscular fascia and tendon.

No question, the joints are impressively engineered; the detail can be mind-boggling. But it’s worth remembering that the muscles are very effective shock absorbers, possibly absorbing up to—or more than—half the force you generate, whether you’re eluding tacklers on the football field or sitting at the desk. Between the muscles and the joints, it might seem as if nature had devised a bulletproof system for moving around in the world, barring a car accident or a severe sports injury, impervious to breakdown. If you’re over thirty-five or forty, you know that’s not true. We’ll take up that story in the next chapter.

SYSTEM MALFUNCTION: WHEN THINGS BREAK DOWN

If
you want to hold someone or something accountable for muscle and joint problems that pile up as people age, blame evolution. A couple of million years ago, our animal ancestors changed from walking on all fours to standing tall on two, but the human musculoskeletal system has never really fully adapted. The adult human head is a real cannonball, weighing eight to twelve pounds. If you have poor posture, that weight can contribute to problems in the neck area. The entire trunk weighs down on the lower back. Our frames still haven’t made their peace with gravity.

Age really exposes the design flaws. If you have the good fortune to escape joint injury when you’re young, the middle and senior years are when you’re most likely to bump against the shelf life of the materials you’re made out of. (This wasn’t such an issue for most of human history when the average life span was a fraction of what it is today.)

BONES

Let’s go back to the three basic components of the human frame: bones, joints, and muscles. Owing to its mostly mineral composition, bone is fairly rigid and, not surprisingly, fractures if it’s subjected to sufficient impact. But bone is living material. With the exception of broken bones in seniors (or smokers or anyone else with low bone density), a fracture stimulates the bone-building osteoblast cells to patch up the break so completely, it heals stronger than new. Men’s skeletons rarely slow them down until well into their senior years, when the osteoclasts, the “breaking-down” cells, leach so much mineral out of the bones, they become vulnerable to fracture. In the most common scenario, the bony vertebrae of the back suffer microfractures, causing the spinal column to compress, taking off a few inches of height. In women, bone health, like so many other things, is influenced by the sex hormones. When estrogen levels drop off dramatically during menopause, women are vulnerable to dangerous bone thinning or osteoporosis. For senior women, a fractured hip is a potentially life-threatening injury. (We’ll talk about ways to protect bone density with diet and exercise in chapters 5 and 6.)

JOINTS

The joints have a tough job. They must stabilize the bones as they move inside the joint capsule, and they bear the heaviest responsibility for supporting the weight of the body. The routine act of climbing or walking down stairs places on the knee a load equal to three or four times your body weight. As we described in the previous chapter, the joints can handle these forces thanks to connective tissue that runs in and around them—tendons, ligaments, and cartilage—all composed mostly of collagen. Collagen’s spongy, matrixlike structure permits these connective tissues to compress and expand, responding to the forces placed on them with just the right balance of firmness and flexibility.

Some joint trauma is so severe, it makes no difference how young and lithe you are. Twist your knee a certain way as your skis slide out from under you and you’ll tear your ACL. But as you age, your connective tissue loses water and becomes less supple, making you more vulnerable to injury from the accumulation of everyday stresses and strains. The two most common examples of this are probably the
injuries to the disks in your lower back and the meniscus cartilage in your knee. Both are shock-absorbing structures made of fibrocartilage that dries out over time. When the tissues deteriorate, it doesn’t take much—a single awkward twist, and you’ve cracked (or “herniated”) a disk, or torn that flat, C-shaped meniscus inside the knee. If you’re over forty and you’ve escaped this fate, you probably have at least one or two friends who haven’t.

Injuries to the structures inside a joint are almost always serious because the tissue there heals so poorly, or not at all. The orthopedic surgeon steps in where nature can’t. If you tear your ACL, you do without or you get it surgically repaired. It’s a case-by-case proposition. Some knee ligament and meniscus tears will heal, slowly, but only in young patients. (The robust circulation of youth pumps up the otherwise modest blood supply to these areas.) The tendons, the connective tissues that attach muscle to bone, are also slow healers. In the case of severe tendon tears, the surgeon surgically repairs them to bone.

But the mother of all nonhealers is the articular cartilage, the tissue that cushions the ends of the bones inside the joint. Inside the joint capsule, there is no blood supply—the cartilage is nourished by the synovial fluid. When the cartilage sustains damage from trauma at any age, or from wear and tear as it gets older and drier, it has minimal or no ability to heal itself. No joint is immune from nicks and scratches over time. But in the larger joints such as the hip, the knee, and the shoulder, the damage can cross a threshold and become self-perpetuating. As the cartilage thins, the bones inside the joint capsule begin to move abnormally, further injuring the cartilage and setting off the body’s inflammatory response. Eventually, the cartilage can completely disappear, until bone is rubbing against bone, producing pain, restriction of movement, and injury to the bone tissue itself. This is very bad news for the joints as it can result in osteoarthritis. (Rheumatoid arthritis is a different beast. Not as common as osteoarthritis, it’s an autoimmune disease in which the body’s own defenses attack the joints, usually smaller, finer ones such as the fingers and wrists.)

It’s a grim-sounding scenario. But the important thing to remember is that even though genetics and injury can play their part, the choices you make may determine whether you cross the finish line with your original joints intact. Low-impact movement is your friend, a sedentary lifestyle is not. (We’ll discuss this in more detail in
chapter 6
and in the individual “Hot Spots” chapters.)

MUSCLES

Let’s turn our attention to the muscles that power all that useful movement. If joints are, sometimes, the weak links in the musculoskeletal system, the muscles that drive them are their most resilient defenders. They absorb much of the physical force to which the body is subjected. (Recall the jolt your knee took when you didn’t see the curb coming and your foot smacked down on the road surface before your leg muscles had the chance to flex and cushion the shock.) When the muscles are firing strongly, they can compensate for a joint whose internal moving parts are not at the peak of health. Here’s a dramatic example. Not long ago, we treated a talented recreational marathoner. In his last race, everything had been going according to plan until late in the race when he’d been shut down by hip pain. We were floored when his X-rays revealed he had advanced osteoarthritis in his hip. His trained athlete’s muscles were functioning at such a high level, he was running marathons when a sedentary person with the same degree of the disease would have spent the past five years hobbling in pain. Of course, our marathoner is an extreme case and a cautionary tale as well. (A hip replacement and the end of his running career were in his near future.) Your goal is to have healthy muscles that support healthy (or healthy enough) joints.

We know from the research literature that joint damage by itself is often not the whole story behind pain and restriction. In a famous 1994 study published in the
New England Journal of Medicine,
64 percent of the subjects, none of whom suffered from back pain, had significant disk abnormalities that turned up on their MRI exams. Similar studies have looked at meniscus tears in the knee, which, according to one Harvard paper, are found in one out of three people over the age of forty-five, only a fraction of which cause symptoms.

Now let’s look at muscle fiber. Like connective tissue, muscle ages over time, losing water and suppleness and becoming more vulnerable to injury. Unlike bone, which usually heals better than new, muscle tears heal themselves with a second-rate patch material: scar tissue made from collagen that is stiffer and weaker than the original fibers. But in contrast to connective tissue, muscle has a great blood supply. It’s packed with capillaries that bring in oxygen and nutrients, allowing the tissue to heal quickly (if imperfectly), and the healthy muscles can grow bigger and stronger in response to healthy stress.

If no effort is made, muscle mass and muscle endurance will decline about 1 percent a year after the age of forty. All of the body’s systems decline with age, but nothing bounces back like muscle responding to exercise. In one famous study by a University of Arkansas researcher, some hundred-year-old study subjects doubled their strength with a program of light weight training. (Certainly, American swimmer Dara Torres has opened a few eyes, defeating competitors less than half her age with her three silver medals at the Beijing Olympics.) Muscle is the human equivalent of a renewable power resource like wind or solar energy. Connective tissue, especially articular cartilage, is more like oil, nonrenewable. When it starts to run out, you scramble to adapt, and when it’s gone, it’s gone.

To power the body and protect the joints, muscles have to respond to a command from the nervous system with a simultaneous contraction and relaxation of the agonist and the antagonist. When they can’t, its often the result of muscle dysfunction or injury, the two major categories being traumatic and chronic injury. In the case of trauma, the damage is the work of a moment: a trip, a fall, a car accident. The most common example of muscle trauma is a strain—or a “pulled” muscle—when the muscles fibers overstretch and tear. How many tear determines the severity of the strain. (As a matter of terminology, muscles suffer
strains,
and ligaments, when they are stretched and ripped, suffer
sprains
.) In the simplest cases, a muscle is asked to contract too hard or for too long, and something “gives,” for instance when an outof-shape recreational athlete decides to start the season with wind sprints and pulls a hamstring muscle.

TRAUMATIC VS. CHRONIC MUSCLE INJURY

But what if the muscle pull isn’t a one-shot deal? Let’s say you keep suffering muscle pulls in the same place. Or the joint and the surrounding muscle get achier and weaker from the stress of everyday life. Now we’ve entered the realm of chronic injury. Something has gone awry in the way the muscles and the joints work together that produces constant irritation. The most common forms of chronic trouble are labeled repetitive stress injuries. Think about performing the same small, rapid movement over and over without giving the muscles a chance to rest and recover, for example, clicking a computer mouse all day. Little tears develop in the muscles and the connective tissue; the area becomes inflamed and then chronically sore. These