So the big surprise for me when I went back over the findings was not the high range-of-motion, but the ease with which that was obtained when a small-ish quantified torque (3.9Nm) was applied. No obvious resistance was noted until end-of-range-of-motion was reached – in every case tested.
The problems in obtaining accurate data in a study like this can be summed up in two words – reliability, and repeatability. In other words, is the study design robust enough that we can be confident in the results being accurate, and can the experiment be duplicated to obtain the same results?
The statistics said yes, to both counts.
Of course, for the main write-up there was hypotheses-testing and so forth, all very necessary to enable the researcher (and examining body) to have confidence in the results. Nowhere near as interesting, however, as finding that this much movement at the ankle is normal.
64 degrees – the average motion obtained when 3.9 Nm of torque was applied to 100 normal subjects.
The statistics say that this was normal. But statistics can be misleading, of course. Here were some of the measures taken to ensure that, as far as possible, the results obtained were a true reflection of available movement at the ankle.
- Empiricism. Not science, but a good place to start. I worked with feet from 1968, and witnessed many times how much movement was available at the ankle.
- The low-tech rig (see heading pic) was carefully designed to hold the leg securely so that only movement at the ankle was recorded. It can be duplicated in any university workshop at minimal cost.
- The same torque (3.9Nm) was applied to every subject. The same rig was used for every subject. The same tester obtained results for each subject.
- A highly time-consuming 100 subjects were tested, thus ensuring a good-sized sample for the number-crunching.
- A good age-range of subjects (18 – 49) were tested.
- Circadian variation (natural biological variation which can affect joint stiffness) was taken into account.
- A previous study by Peter Ball and Garth Johnson (1996), also applying a known torque to 100 subjects, came up with a slightly lower range-of-motion (although still higher than previously published). Why was it lower? Because they applied force around an axis which inhibited some of the motion. Usefully, they did show that ankle joint stiffness increases with age.
With this much available movement it seems clear that we have not changed or adapted for life on a hard, flat surface. The research confirms, scientifically, what many people already suspected (ask anyone who mobilises or manipulates ankles for a living). The healthy human foot is an effective, adaptable tool which allows us to stand, walk and run on most surfaces capable of holding our weight. In other words, we are not limited to supporting and ambulating on hard, horizontal surfaces. It is highly unlikely that we ever have been.
And finally, you may be interested to learn that only two rigorous, scientific studies have ever been undertaken, anywhere, to find the range-of-motion of inversion and eversion at the ankle joint – the Ball and Johnson study mentioned above, and this one.
The Paper describing the experimentation and results will be published in the UK in Podiatry Review in the Autumn of 2018 and the Spring of 2019.