Leg Muscle Wasting as You Age? Take a Look at the Low Back Nerves
POSTED ON 3/26/2018 IN Spine BY Christopher Centeno
Have you ever noticed that thinner older people have flatter butts and skinnier legs compared to young people? According to new research, this isn't just your imagination, but a real physiologic effect of aging. One that again shows us how much the nerve supply of the low back impacts our legs without us knowing it's happening.
What We Already Know About the Low Back Nerves and How They Affect the Legs
Knee pain and irritated back nerves have been studied for years, and connections have existed for a long time. If you have knee pain, oftentimes the cause stems from the low back, not the knee itself. Specifically, the part of the spine that supplies nerve signals to the legs. Take, for example, the L5 nerve; this one stretches all to the foot, so a pinched nerve at the L5 level could present as foot pain and if unaddressed could lead to plantar fasciitis or even bunions. Your hamstrings are another muscle group that can be directly affected by a nerve issue in the low back. You might first notice tight or swollen hamstrings that becomes chronic and painful, and this should be a red flag that something might be wrong with your lower back. Low back nerves also travel through the hips and buttocks. One study found that, despite what many doctors believe, butt pain can be an indication of a problem in the low back. Another study found connections between hip replacement complications and low back issues that existed prior to surgery. The study concluded that hip replacement patients who also had a low back problem (e.g., arthritis, herniated disc, etc.) had double the risk of complications after surgery.
The Link Between Irritated Low Back Nerves and Leg Muscle Wasting
The new study examined muscle mass in four groups of men (168 total): young men, old men without muscle wasting, men in pre-stages of muscle wasting, and men with muscle wasting. You'll see the medical term sarcopenia in the study, which specifically means a reduction in the muscle mass (or muscle wasting) with aging. The results? By age 75, active nerves in the legs decreased by 30% and from there decreased by as much as 60%, and this was associated with those with muscle wasting. The older group without muscle wasting and the one in the pre-stages both had better chances of reinnervation, meaning other active nerves picking up the slack for a part of the body where nerves have failed. This means the healthier a muscle is, the greater the chance nerve supply can be restored. Once this muscle has experienced significant wasting (sarcopenia), however, there is nothing left to restore nerve supply to. So researchers concluded that this muscle wasting with aging is actually caused by nerve loss from the spine and into to those areas. In other words, when the muscles experience nerve loss, they can't thrive, and they will soon begin to waste away. Why? Without nerve signals from the spine to communicate with the leg muscle to tell it what to do, the muscle essentially goes dormant, and if we don't wake it back up soon, muscle wasting begins. So addressing the problem in the low back to get the nerve supply back on track before muscle wasting sets in is key.
Shouldn't I Have Low Back Pain if I Have Nerve Issues and Leg Muscle Wasting?
Oftentimes, when there is a low back nerve issue that has begun to cause muscle wasting, the first problem you might notice is in the buttocks muscles (which will flatten out) because the nerves in the lower spine that innervate the buttocks are the first to go. You may then notice, especially with aging, that your leg muscles are beginning to weaken or waste away. On the surface, it seems logical that if the problem is rooted in your back, you would have to have accompanying back pain, but in reality, you may have back pain, but you may not. You may also have pain or other irritations, such as the muscle wasting, anywhere along that nerve branch. Once nerve loss becomes an issue in the muscle, however, there may be no pain anywhere, just a weak and shrinking muscle.
How Can I Prevent This?
The first answer is easy, exercise! Other studies I've covered show that elderly people who exercise at high levels have muscles that more closely resemble those from younger people versus their same age peers. In addition, if you have low levels of low back nerve irritation, with or without back pain, then you may want to get that checked out. In our experience, things like using the growth factors isolated from your blood platelets (platelet lysate) can help when precisely injected around those nerves. The upshot? This study isn't surprising as I see this every day in my older patients. Just keep moving and pay attention to your body. The "no pain, no gain" mantra pushed by Jane Fonda in the '80s was never a good idea (Jane ended up with multiple joint replacements). If you notice your legs or butt wasting away, your body is telling you that it needs help!
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