Just a quick post Mike, I haven't read the paper yet. I think that spring-mass and inverted-pendulum are effectively the same model. That is, the inverted-pendulum model is just and example of the spring-mass model with a very, very high Kleg. In other words, the spring-mass model considers the leg to be relatively more compliant than the inverted-pendulum model, but theoretically if we plotted GRF's and energetics for every Kleg from infinitely compliant to infinitely stiff, would we not see a gradual transition from those observed with the spring-mass model towards those observed with the inverted-pendulum model as leg stiffness increased toward infinity??
Now, until I've read the paper, I have no idea why they modelled running as a stiff-legged gait.
I agree about the stiff spring-mass model in walking from our discussions last year. Perhaps the paper will shed some light on the matter of why a stiff spring-mass model was used.
Right Ive had a read and the authors state their main aim.
So I see what they say but I still don´t get why the knee was removed, In my way of thinking the flexion -extension moment at the knee would effect the cushioning at the ground foot interface ?