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The functional importance of human foot muscles for bipedal locomotion
Dominic James Farris, Luke A. Kelly, Andrew G. Cresswell, Glen A. Lichtwark
Proceedings of the National Academy of Sciences Jan 2019, 116 (5) 1645-1650; DOI: 10.1073/pnas.1812820116

With regard to the paper mentioned above ,what happened to the toes during the controlled loading experiment after the block ? (See below )
Just as some of the intrinsic foot muscles span the longitudinal arch of the foot ,so do the tendons of the larger extrinsic toe flexor muscles .

Experiment 1: Controlled Loading.

Compression of the LA was measured by changes in the Cal-Met angle formed between the calcaneus and metatarsal segments (illustrated in Fig. 1A). Peak vertical ground reaction force (vGRF) during loading cycles was varied between 0.5 and 2.5 body weights and produced proportional changes in the Cal-Met angle (Fig. 2C). There was a significant effect of the nerve block on LA deformation, with the changes in Cal-Met angle being greater for equivalent peak forces in the nerve block condition, although only by modest magnitudes (<1° difference in group means; Fig. 2C).

 

With regard to Farris et al, above , why would the extrinsic toe flexors ( FHL , FDL ) not take on additional load when the intrinsics are anaesthetized ?

What one might look for with regard to experiment 1 is relatively straight toes with load and no block ,and a collapsing of the lesser toes into a hammer like configuration with load and block .

 

In the paper under discussion , the authors address the possibility of the extrinsic toe flexors ( extrinsics generally in fact ) stepping in to replace the force lost with the anaesthetization of the intrinsics but discount this on the grounds of muscle morphology .

It should be note however , that recent EMG studies have shown that toe curling activities are not primarily about intrinsic activation but must therefore be powered by the extrinsic toe flexors . This demonstrates that the extrinsics can easily apply arch supporting forces beyond the simple isometric .

Also a question . If the quadratus plantae ,which applies force through the tendons of the flexor digitorum longus ,can be thought of as an arch supporting muscle ,then why not the flexor digitorum longus itself .
As indicated by toe curling activities ,it certainly seems to have the range .

 

Below are are couple of photographs from a Sydney University project based around strengthening the foot .
In photograph b you an see the toe flexors are firing , including an input from the intrinsics or the toes would be curling .

Now in photo b you can see the ball of the foot lifting off the floor ,but here a question .

In earlier work ,researchers showed that loading the foot causes it to flatten and that electrical stimulation of the intrinsics can counter this flattening by shortening the foot and raising the MLA . But how much of this measurable arch lift is produced not by foot shortening but by the met heads being lifted a little , or at least put under less compression ,by the plantarflexing toes ?
During early stance should the MLA be viewed as extending from the heel to the met heads or from the heel all the way to the tip of the toe ?
A jointed arch .