The calf gets the attention. It is not the whole story

The calf on an affected side is smaller in essentially every treated clubfoot, and the difference persists for life regardless of training. Measured differences of one to three centimeters in circumference are typical. It is not disuse. The muscle was built smaller, and it was built smaller before anybody touched it.1

Imaging in Ponseti-treated children found the plantarflexor muscles smaller on the affected side and the Achilles tendon larger, with the size of the difference showing no relationship to age.2 Less muscle, more tendon, and the proportion set early.

What this costs is push-off. The calf drives the final propulsive phase of every step, so a smaller one means less power from that side, every stride, forever. On a walk to the shops that is invisible. Over a marathon, or a duty day in boots, it is the reason one leg tires first.

Worth training anyway. Strength and endurance respond well even where size does not. See what training actually reaches.

The peroneal muscles run down the outside of the lower leg and turn the foot outward, against the tibialis anterior and posterior pulling it in. That balance is the whole story here, and when it tips the clinical name for it is dynamic supination: the foot rolls inward as it swings through, most visibly in a child learning to walk.3

What nobody has published, as far as I can find, is a study measuring evertor strength in treated adult clubfoot. The imbalance is well documented and this specific muscle group is not, so treat what follows as mechanism and experience instead of measurement.

The consequence is a foot that resists turning outward and has less active defense against rolling inward. If you roll your ankle more than seems reasonable, or feel unstable on uneven ground, the evertors are a plausible contributor and a cheap one to test. Unlike the calf, nothing about this group is structurally fixed, so it responds to targeted work the way any undertrained muscle does.

This muscle runs down the front of the shin and lifts the foot upward. In many treated clubfeet it is comparatively spared, which matters because it is one of the few things pulling against the tight structures behind.

It is also the muscle most often moved surgically. A tibialis anterior tendon transfer relocates the tendon to a more outward position to correct dynamic supination, and it is typically done between ages two and a half and five, on a foot that is still flexible.34 If you had one, the muscle now pulls somewhere nature did not put it, and that is the design, not a complication.

These are the small muscles within the foot itself, controlling the toes and supporting the arch from inside. This is the least studied corner of an already thinly-studied subject: the clubfoot literature concentrates on the calf and on the tendons that get transferred, and the intrinsics are largely absent from it.

What can be said is that a high-arched foot concentrates pressure under the ball and the heel instead of spreading it, and that toes which claw make that worse. Intrinsic work is unglamorous, slow, and low-risk. I do it, it seems to help, and I am not going to dress that up as evidence.