I mean yeah it's not exactly a novel observation, but there is some subtlety in /how/ you attach springs to your legs which seems to be the primary contribution

I mean yeah it's not exactly a novel observation, but there is some subtlety in /how/ you attach springs to your legs which seems to be the primary contribution of the paper. The two naive options - referred to as "in series and in parallel" - don't see the same results as their proposal (which they discuss at some length in the intro). Their proposal is more about making the "springs on your legs" idea as effective as possible by using a hip attachment to adjust the loading/unloading cycle. By loading the spring with your leg while it's in the air you can improve the overall energy throughput of your gait. Other "springs on your feet" concepts (mentioned throughout the comments section) use a loading/unloading cycle that's 180 degrees out of phase with this (leg on the ground is doing the loading). Snark is kind of the enemy of critical thought