The Lower Kinetic Chain: Why the Knee Never Works Alone

The injury after the injury

A runner develops knee pain. At first, it only shows up after long runs. Then it begins showing up during them. Hills go first, then running altogether — and without quite noticing it, the runner starts moving less in ordinary life too. The knee injury was the first problem. The loss of activity is the injury that compounds.

Cardiorespiratory fitness declines. Muscle and bone receive less load. Balance becomes less practiced. Insulin sensitivity worsens. Each of these makes movement feel a little harder, which gives the body one more reason to avoid it — until what began in a single joint becomes a whole-body trajectory.

This is why Portico organizes exercise around three pillars: aerobic fitness, strength, and balance. Aerobic training builds the engine. Strength gives the body the capacity to absorb and produce force. Balance teaches that capacity to show up at the right moment, in the right direction. Lose the structure that supports movement, and the aerobic work eventually goes with it.

Inactivity is the real threat, not age.

This article isn't about what happens when training load rises too quickly, technique changes abruptly, or recovery gets ignored — any tissue can be overloaded, including a strong one. It's also not a rehabilitation plan for an existing injury. The question here is more fundamental:

What keeps the lower body durable enough to preserve activity across a lifetime?

The answer begins by looking beyond the place that hurts.

The knee is the middle, not the whole system

The knee is one of the hardest-working joints in the body. Each time a foot lands, the knee briefly carries roughly three times body weight while walking and closer to three and a half times while running. For a 150-pound person, that's north of 500 pounds passing through a joint about the size of a fist. Over a single 30-minute run at a typical cadence of 160 to 180 steps per minute, each knee does this roughly 2,500 times. It's a bit like carrying another adult on your back and landing on one leg, again and again, for half an hour straight.

The knee is built for exactly this. A smooth, low-friction surface lets the bones glide against each other. Pads of tougher tissue inside the joint spread the load out so no single spot takes the full hit. Bands of tissue keep the joint from moving too far in the wrong direction, while the muscles above and below it constantly adjust tension to keep everything steady. It's genuinely impressive engineering.

But the knee doesn't work alone. Above it, the hip controls the direction the leg travels. Below it, the foot and ankle decide how the body meets the ground. If the hip can't keep the leg well-aligned, or the foot can't adapt properly to the surface it's landing on, the extra stress has to go somewhere — and it often gets passed to the knee, sitting right in the middle.

This is sometimes called the kinetic chain: force moves through the hip, knee, ankle, and foot as one connected system, not as separate events at each joint. A single stride isn't a foot movement, then a knee movement, then a hip movement. It's all one motion.

The point isn't that the knee is blameless. It's that knee problems are rarely just about the knee. More often, they're about a system where the hip or the foot isn't pulling its weight — and the knee, stuck in the middle, is where that shows up first.

The hip: the steering system

The hip moves more freely than almost any other joint in the body — forward and back, out to the side, and in rotation — which means it needs real strength to stay controlled through all that range.

Most of that work falls to the glutes. They drive the push when you stand up, climb, or accelerate, and — just as important — they keep the pelvis level whenever your weight is balanced over one leg. That's not a rare position. It's most of walking, and all of running.

When the glutes aren't strong enough for the demand, the pelvis can drop and the leg can cave inward as it lands. That changes how force travels down to the knee, which is one reason hip strengthening shows up so consistently in knee pain treatment.

A durable lower body needs a hip that can produce force, resist caving inward, and hold the pelvis steady on one leg. Improve hip strength, and the benefits carry down the whole chain — not just to the hip.

The foot: an adaptive foundation

The foot is one of the most intricate structures in the human body. Each foot has 26 bones and 33 joints — together, the two feet account for roughly a quarter of all the bones in the human skeleton — plus more than 100 tendons and ligaments, packed into an area not much larger than a sheet of paper. By age 50, the average person's feet have carried them an estimated 75,000 miles — the equivalent of circling the Earth roughly three times.

All of that machinery exists to do two things that sound contradictory.

When the foot meets the ground, it has to adapt: its joints move, its arches give way slightly, and its tissues absorb energy as they take the shape of whatever is underneath them. A fraction of a second later, at push-off, the same foot has to do the opposite — lock into a stiff, stable platform that can drive the body forward. It shifts from shock absorber to rigid lever within the length of a single stride.

The arches make this possible. The arch running from heel to forefoot acts something like a spring, flattening under load and springing back as the load releases. A second arch, running across the width of the foot, adds real stiffness to the structure. Hold a slice of pizza flat and the tip droops down under its own weight. Fold that same slice slightly along its length — just a bit of curve — and it goes rigid, holding its shape all the way to the tip. The foot's crosswise arch does the same thing to the middle of the foot: the curve itself is what creates the stiffness.

A tough band of tissue on the sole, along with the foot's ligaments and the shape of its bones, forms the passive half of this system. Muscles handle the active half: some sit entirely inside the foot, others reach down into it from the lower leg, and together they fine-tune how much the arch gives and how fast it stiffens back up.

What actually triggers that stiffening is worth understanding, because it's the part most people don't know: the big toe. As the heel lifts at push-off and the big toe bends upward, it pulls on that tough band of tissue running under the arch — the same basic action as pulling a rope through a pulley. This is the windlass mechanism: as the big toe extends, it tightens the plantar fascia, which draws the heel and forefoot closer together and raises the arch, locking the foot into the rigid lever it needs for an efficient push-off. For this to work, the big toe must be free to bend, and the foot must be able to feel and grip the ground. A toe that's cramped, numb, or held stiff by footwear can't complete the motion — and when it can't, something else further up the chain ends up compensating.

What matters, ultimately, is capacity: can the foot tolerate load, adapt to the ground, and shift into a stiff, usable lever the moment it needs to?

How shoes quietly weaken the foot

That capacity depends partly on what's on your feet. Most modern shoes share three features: heavy cushioning, a toe box narrower than the actual shape of the forefoot, and a heel raised higher than the toes — what's usually called heel-to-toe drop. Each one works directly against the mechanism from the last section.

A narrow toe box squeezes the toes together and often crowds the big toe inward — out of the straight position it needs to extend fully and trigger the windlass mechanism. A raised heel shortens how far the big toe has to bend at push-off, so the windlass fires less, and the foot's own spring does less of the work. Heavy cushioning dulls the feedback the foot uses to sense the ground and adjust its muscles moment to moment, and it absorbs load the arch and its muscles would otherwise be handling themselves.

None of this does damage in a single wear. But feet respond to what's asked of them, same as any other tissue: ask less of them, and their natural capacity quietly shrinks — a little every day, over months and years, without ever feeling like an event. And because almost nobody trains their feet directly the way they might train their legs or arms, there's nothing pushing back against that decline. It just accumulates.

That weakness doesn't stay in the foot. A foot that can't adapt, stiffen, and push off well hands more of that job to the ankle and knee, and asks the hip to compensate for what the foot no longer does on its own — the same chain the earlier sections described, just running in the wrong direction.

None of this makes shoes the enemy, or means the fix is to throw them out. It means we need to stop getting in the foot's way and let it do the job it was built for — which is where we go next.

A protocol for the whole kinetic chain

The hip and the foot aren't separate projects. They're already covered by two of Portico's three pillars.

The hip is built through Portico's Strength protocol. In practice, that means movement that loads the hip through its full range and teaches it to hold the pelvis steady over a single leg, trained consistently and progressed over time. Follow the protocol as programmed, and the hip strength this article describes comes with it — no separate plan needed.

The foot is built through Portico's Balance protocol. That means direct, deliberate work for the foot's own small muscles and the toes themselves — the kind of targeted control that ordinary walking and running never ask for — trained until the foot can hold its own under load. Follow the protocol, and the foot capacity this article describes comes with it too.

Shoes are the one piece that's on you to choose. Look for a wide toe box — one that lets the toes lie flat and the big toe stay straight — and a low or zero heel-to-toe drop. Cushioning matters less than people think — some is fine, but more isn't automatically better, and we'd rather see less cushion than more. Get the toe box and the drop right, and you've covered most of what matters.

Toe spacers are worth adding here too — even wearing them for short stretches during normal daily activities helps. They give the toes room to spread that most shoes never allow, which is what lets them actually splay and strengthen under the balance work above.

A hip trained for control, a foot trained for capacity, and a shoe that doesn't work against either one — that's the whole kinetic chain.

What Portico does with it

Portico treats exercise as more than minutes logged or calories burned. The real outcome is durable participation: whether the body can keep walking, lifting, running, climbing, and recovering across the decades.

The three pillars from the start of this article are what make that possible. Aerobic training builds the engine — but an engine is only useful if the structure around it can carry the load. That's what strength training builds: the tissue capacity to absorb and produce force. Balance is what puts that capacity to use, coordinating it moment to moment so it shows up at the right time and in the right direction. Recovery is what gives all of it room to actually adapt.

Together, the three pillars protect one thing: the continuity of movement. Aerobic work preserves cardiovascular capacity. Strength supports the joints, bones, and tendons. Balance connects the nervous system to the ground. The hip, knee, and foot are where all three meet in daily life — which is exactly why this article started there.

Healthspan is not only the number of years without disease. It's the number of years your body still lets you participate.

The knee matters. So do the systems above and below it. Train the chain, preserve the activity, and the benefits travel far beyond the joint.