The study compared legs of single amputees. Having a fixed human leg also constrains the artificial limb in length and in rebound speed so that the runner can run synchronized. With 2 artificial legs, the length and rebound speed can be optimised for the runner without the constraint of having to match a human leg.

The abstract says “force” but it is not clear whether this is a peak force, or a measure of the total power applied during ground contact. IOW, as YouRang indicates, if a lesser “force” is exerted for a longer time, due to greater artificial leg springiness, the total power applied may be higher. The actual paper presumably would clear up this ambiguity.

The abstract also says, “Some elite unilateral trans-tibial amputee sprinters appear to have learned or trained to compensate for AL force impairment by swinging both legs rapidly. ” Bilateral amputees, ie with both legs replaced, may be able to swing their legs even more rapidly since the legs are much lighter. Lance Armstrong was noted for his high cadence compared with other elite cyclists. A higher cadence uses more energy, but can apply more power for a given maximum muscle strength.

tOM

2. Surely, yourang, surely your well-proposed theory has not been considered by scientists, none of whom would be well-versed in physics due to the fact that they’re scientists.