How Nerves Handle Stress

Eric Marquette

Hello and welcome back to Fall 2025. I’m Eric Marquette, your host. Today we’re exploring an often-overlooked part of our movement—how our nerves hold up under stress. I mean, most of us think of tight muscles or aching joints when we feel discomfort from, say, a long day at the desk or a bout of over-enthusiastic gardening. But our nerves, especially the ones running all through our limbs—those peripheral nerves—they’re constantly adapting to stress too. Now, before getting into what happens under strain, let’s unpack their structure a bit.

Eric Marquette

So, peripheral nerves are long, cable-like structures, and they’re more sophisticated than you might guess. At the center, you’ve got axons, which are the conductors of the nerve signal—sort of like electrical wires. These axons are bundled together with the help of three main protective layers. First, the endoneurium wraps each axon, giving it insulation and support. Then, several axons are grouped into fascicles and protected by the perineurium, which is the main load-bearer when it comes to mechanical stress. That’s the bit that really helps nerves handle stretching and compressing. And finally, all those fascicles are held together by the epineurium—the outermost sheath, which also houses blood vessels and connective tissue, allowing the nerve to glide and even absorb compressive forces.

Eric Marquette

Now, nerves aren’t rigid. When you move—let’s say you extend your elbow or flex your wrist—these nerves can elongate, glide, and change shape to a remarkable degree. That’s what we refer to as nerve strain, excursion, and transverse contraction. Strain is basically the percent lengthening of a nerve as it stretches. Excursion describes how far a nerve slides relative to its surrounding tissue, and transverse contraction is how the nerve’s cross-sectional area shrinks as it stretches out. Such flexibility is what allows us to go about daily life—typing, reaching, stretching—without damaging these essential cables. But it's crucial to note that too much strain, or the wrong kind, can push nerves beyond their healthy range. For physical therapists, having a handle on these characteristics—how much strain is “safe,” how nerves adapt to load, and the mechanics behind all that—is essential for treating injuries and helping patients recover normal movement.

Eric Marquette

Actually, one thing that tends to surprise students and even some clinicians is how the arrangement of joints along a nerve’s path changes the nerve’s compliance—its ability to stretch and return. Nerves crossing major joints like the elbow or hip tend to have more give, more flexibility by necessity. Factors like the number of fascicles or the surrounding connective tissue also come into play, but it’s certainly not a one-size-fits-all situation. The more we understand about nerve biomechanics, the better we can customize care, whether it’s for injury prevention or rehabilitation.

Eric Marquette

So, let’s get into what actually happens when nerves are exposed to different types of physical stress. We’re not just talking about an accidental jolt or over-stretching during yoga—although those absolutely count. Think of all the forces nerves encounter day in, day out: there’s tensile stress when you stretch, compressive stress when a nerve is squashed between structures, and even shear stress as tissues move past one another. Mueller and Maluf’s Physical Stress Theory really hits home here—the idea is that nerves respond to whatever physical stress they experience, and their reaction depends on just how much, how often, and for how long that stress is present.

Eric Marquette

At one end, if stress is very low—say, during prolonged immobilization like when an arm is in a cast—nerve tissue starts adapting downwards. It gets less tolerant to even normal levels of activity. There’s actual structural change—loss of myelin, collagen build-up, the nerve fibers themselves getting smaller. On the other hand, a little more stress than usual doesn’t necessarily damage the nerve. It might actually increase its tolerance. But there’s a threshold. Too much, for too long, and you end up in the injury territory—damage, demyelination, impaired blood flow, and reduced function.

Eric Marquette

Take acute or excessive stretch—enough strain for a short time, like 11% or more lengthening, can permanently damage nerves. It actually doesn’t take much; for some people, normal clinical stretches can get close to this, and they report pain or tingling, which is an early warning. Interestingly, when nerves are stretched at a slow, steady rate—like with gradual limb lengthening in medical procedures—they generally cope much better than if rapidly yanked or pulled.

Eric Marquette

Repetitive movements and especially compressive forces are where we see some everyday modern problems. A classic example—and this comes straight from an office consult I had not long ago—involves those long hours at the computer. I was chatting with someone with fairly classic carpal tunnel symptoms. Turns out, simply resting your wrist on the desk or a mouse boosts the pressure in the carpal tunnel enough to restrict nerve blood flow. All those little adjustments, like keeping the wrist extended or the fingers flexed, can increase stress on the median nerve by quite a lot. Over time, that steady pressure adds up. You get numbness, pain, and—if it goes unaddressed—potentially lasting damage.

Eric Marquette

The lesson? It’s not just major injuries we have to worry about. Even modest, repetitive stresses—sustained or repeated awkward mouse use, for instance—can shift a healthy nerve into dysfunction if we’re not careful. Therapists, and honestly anyone with a computer-heavy job, should really keep this spectrum of stresses in mind.

Eric Marquette

Knowing all that, what can we do about it? Understanding nerve biomechanics gives therapists a kind of roadmap for intervention. If a nerve’s been stuck at low stress for weeks—like after immobilization—the goal is slow, careful remobilization. Watch for warning signs: pain, numbness, or even things like exaggerated reflexes. Those are cues to back off and let the nerve adapt gradually. On the flip side, with compression issues—like carpal tunnel syndrome—treatment is all about reducing those external stresses and inflammation, improving blood flow, and teaching the nerve to slide and stretch again smoothly.

Eric Marquette

Let’s take carpal tunnel as a concrete example. The standard playbook includes postural correction—think keeping the wrist neutral as much as possible. Nerve gliding exercises are huge here; they encourage the nerve to regain its normal excursion and strain without overdoing it. Patient education is equally crucial. People might need to rethink how their desk is set up or change the way they grip the mouse. Sometimes it’s small tweaks that make the biggest difference—raising the chair slightly, switching to a vertical mouse, taking microbreaks throughout the day.

Eric Marquette

One question I often discuss with colleagues: what signs should prompt a therapist to tweak a treatment plan? Besides obvious pain or paresthesia, watch out for plateaus in recovery, or maybe an increase in swelling or weakness. These are indicators that the nerve’s tolerance for stress is still limited, and the approach needs updating. And from the patient’s perspective, the more you understand your own symptoms and daily stressors, the better you’ll get at managing them—before they snowball into something requiring more drastic treatment.

Eric Marquette

I might be rambling a bit here, but if there’s one thing to leave you with, it’s this: our nerves are adaptable, but only up to a point. By respecting their limits—and knowing how they respond to different types and levels of physical stress—we can keep them functioning optimally, whether we’re rehabbing from injury or just trying to get through another workday pain-free. Thanks for sticking with me, and we’ll get into more of the science and practical tips for nerve health in our next episode.