Building the Bridge
The bridge concept is a way of thinking about what needs to happen under the foot to prevent the arch from collapsing. The bridge concept builds on the neutral heel and foot tripod ideas.
The arch of the foot can be thought of like a bridge, with one end being the heel and the other being the base of the big toe. If you read the previous guides, these points should be familiar to you as they are two of the foot tripod points.

Both ends of the bridge need to be stable to prevent the foot pronating and the arch flattening.
Heel position
The heel is stabilized by keeping it in a neutral position. It’s common for people with flat feet or excessive pronation to stand with their heels in an everted position.

In the beginning, I used a mirror and video of my heels from the back to help find the neutral heel position and retrain my feet to move into the position when standing.
Aside from getting in the habit of holding a neutral heel and keeping weight on the outside edges of the feet when standing or walking, an exercise that targets this motion is the sole to sole exercise that’s seen in the intermediate routine.
Tight calf muscles can also contribute to the heel everting, so gaining calf flexibility and ensuring the heel stays in neutral while doing calf stretches is also important.
Big Toe Stability
Before, when I walked, I noticed that the big toe was not doing much. I’ve seen this referred to as a “lazy big toe” and that description is pretty accurate. My big toe would sort of flop down on the ground. I wasn’t using muscles to engage the ground. Instead, the big toe was forced into the ground by the weight of the foot collapsing inward.
It’s mainly the knuckle of the big toe (the 1st MTP joint) that stabilizes the front of the bridge and this is one of the points of the foot tripod. But the toe itself also plays a role. Creating stability here is often a difficult task, but it can sometimes produce amazing results in terms of preventing the arch from collapsing.

When the big toe is stable, neither of the strips of paper shown in the picture will be easily pulled out from under the toe. One strip of paper you can see is under that big toe joint. The other is under the toe itself. This is showing that the big toe should remain flat and not curl when it’s pressing against the floor.
What I find works best for getting a feel for putting pressure down through this point of the tripod is to lift all the toes up and just work on feeling for the floor under the big toe joint. This can be done sitting or standing and then progressed by adding in a shallow squat or by balancing on one leg while keeping a stable tripod position. After getting the hang of things, the same activities can be tried with the toes lowered.
But remember, the contact point under the base of the little toe must be maintained. This can be done by ensuring weight is kept toward the outside edge of the foot so the foot doesn’t roll inward.
Exercises to Help with the Bridge
Some exercises that help with getting the whole toe down are Toe Yoga (particularly the big toe tapping part) and the Toe Spread Out.
For further strengthening, one of the best exercises for this is heel raises done with a focus on pressure down through the big toe.
I also find it helpful to practice taking a few short steps with only the big toe down and the other toes held up, making sure to press down enough to prevent the foot from rolling in.
And this concept of the arch bridge can be a helpful reference in other situations, like with sidestepping, going from sitting to standing, and even with the short foot exercise.