You can train your cardiovascular system, work on your conditioning and push yourself through hard workouts.

But have you ever thought about the position your lungs are trying to work in?

Breathing is mechanical. Your rib cage needs to expand and your diaphragm needs room to move. The position of your head, neck and thoracic spine can change those mechanics.

How a Rounded Thoracic Spine Compresses the Lungs

Your lungs don’t have muscles of their own. They fill the space your rib cage and diaphragm create for them. That space depends heavily on the shape of your thoracic spine.

When the thoracic spine flexes forward into a rounded posture, the chest cavity loses space. Add a forward head position on top of that curve and the compression compounds, pulling the chest further from the open position it needs for a full breath. Research on hyperkyphosis backs this up directly: more severe forward curvature is tied to less rib cage mobility and reduced lung expansion, and correcting that curvature with targeted exercise has been shown to improve chest expansion again.

This isn’t just a cosmetic issue. Researchers have measured it directly. In one study, simply placing healthy adults into a forward head posture reduced lower rib cage movement along with measures of lung function, including forced vital capacity and peak flow. A recent systematic review looking specifically at forward head posture found similar results across multiple studies.

In other words, the shape of your spine sets a ceiling on how much air you can move, before conditioning ever enters the picture.

How Thoracic Alignment Changes Rib and Diaphragm Mobility

The ribs don’t just sit passively on the spine. Each one attaches to the thoracic spine through two small joints, the costovertebral and costotransverse joints, and those joints need to glide for a rib to move properly. The upper ribs are built to lift up and out, like a pump handle. The lower ribs are built to flare side to side, like a bucket handle. Both movements are what let your chest cavity expand in three dimensions instead of just one.

When a thoracic segment gets stiff or shifts into a fixed, flexed position, the rib attached to it loses part of that motion. Multiply that across several segments and the whole rib cage starts moving as one rigid block instead of an expanding structure. You can still breathe, but you’re breathing through a smaller, less efficient space.

The diaphragm takes the same hit. It’s a dome-shaped muscle that depends on a certain resting length and position to generate force. When the thoracic spine loses its natural curve and the rib cage drops and narrows, the diaphragm’s dome flattens out. A flattened diaphragm has less room to descend and less mechanical advantage when it contracts, so it has to work harder to move the same amount of air.

So the ribs lose their expansion, the diaphragm loses its leverage, and your breathing muscles end up working against your own posture instead of with it.

What Does That Mean for Performance?

Think about the last time you were deep into a hard workout, running up a hill, playing a long point on the tennis court, or trying to recover between rounds of an exercise.

Breathing efficiency matters.

I’ve also seen this clinically in patients with significant hyperkyphosis. Exercises on the ground can feel incredibly difficult because of the position they’re forced to work from. As we improve their posture and thoracic mechanics, they’ll sometimes come back bewildered by how much easier it feels to breathe, move and exercise.

Some even tell me they simply have more energy.

They came in thinking we were working on their pain. They didn’t expect breathing to change too.

Research more broadly supports the idea that body position affects pulmonary function, with many studies finding better respiratory measures in more erect positions.

That doesn’t mean posture is the only thing determining how well you breathe or how conditioned you are.

It means there may be a mechanical piece of the equation you’ve never considered.

You train your lungs and cardiovascular system. Don’t forget about the position you’re asking them to work from.