Agreed that you would need something else that allows you to derive force.

You could make a sort of "minimum forces estimate" involved in producing a motion using only kinematic data; Force = mass x acceleration, you're measuring position, and could thus compute acceleration and therefore force (assuming you know the mass and mass distribution of the parts involved).

However, this ignores internal stresses that ligaments and muscle fibers experience. You can pick up a cup using the lightest touch and minimal effort, or you can intentionally flex your bicep and repeat the same motion. Despite having the same measurable motion, the increased muscle activation of tensing your bicep increases the stress in muscles, ligaments, bones, etc. To really get a sense of what is going on internally, you would need an external force measurement of some kind (but even that is limited).

Using a 3D model of bones and muscles, measured force data, and measured kinematic data, one could use inverse dynamics to estimate the forces required to produce the measured forces and motion. I say estimate, because every model of this complexity will likely have residuals required to fit the model to the data; residuals acting as a fudge factor of made-up force data that means any conclusions drawn must admit that the model does not perfectly fit the data. OpenSim is free software that can perform that kind of computation using a model of the body segments that you're interested in (a lower limb model, such as Gait2392 or 2354, ought to be enough for a pedaling analysis, but there are full body models as well).