We want to know what’s really happening inside the leg — especially in the muscles that power your every step. Think of it as looking under the hood of the body: we’re opening up the engine room of movement.

That means measuring exactly how the muscles work: their activity, how they contract and release, the forces they generate, and how all of this shifts when the outside world throws challenges at you — whether that’s a change in terrain, unexpected impact, or simply fatigue setting in.

Our focus is on four key muscles in the lower leg: the tibialis anterior, the soleus, and the two gastrocnemius muscles (inner and outer calf). Together, they orchestrate the movement of the ankle. The soleus and gastrocnemius push the foot down, while the tibialis anterior pulls it back up. Among these, the soleus is the true powerhouse: it does most of the heavy lifting when pushing the foot down. The gastrocnemius muscles assist, but their signals mainly help us fine-tune the calculations alongside the soleus and tibialis anterior.

There’s another reason we pay special attention to the soleus: our computational model captures its activity with remarkable accuracy. This means that even if the gastrocnemius signals are a bit noisy, we can still generate a reliable estimate of the ankle’s movement and force. In short, by tracking the soleus, we get a strong and trustworthy window into the mechanics of running itself.

We measure it in two ways:

First, we place small sensors on the skin to capture the electrical signals coming from the nerves — this tells us how and when the muscles are activated (EMG).

Second, we use lightweight wearable motion sensors (IMUs) that track the body’s movement in space. That way, we don’t just know what the muscles are doing, but also how that translates into actual motion. Together, these systems let us connect the invisible signals inside the body to the visible performance on the outside.

Most existing technology in this field was built for healthcare and rehabilitation. Valuable, yes — but sports push the body in ways that are very different from recovery. High intensity, long duration, unpredictable environments: the demands are completely new. That’s why we need tools that can keep up — robust, accurate, and built for athletes who go to the limit. And because our measurements have to run not for minutes, but for hours and days, durability and long-term reliability become just as critical as precision.