These things always seem to arrive in groups and this time the issue I’ve seen most of recently is mobility related. In order to run efficiently and correctly, you need to be able to get over the top of your big toe. If the joint is locked up that can’t happen and the body has to compensate.
The centre of pressure can start to make excursions in order to bypass the joint. This lateral movement then requires a late and steep forefoot pronation to get the big toe down on the ground for toe off. This is driven by the peroneals and hip adductors. Sometimes this will result in peroneal and adductor tightness and it also compounds the stiffness in the hallux joint. As flexor hallucis longus (FHL) will have to work even harder to stabilise the late lateral movement. The other compensation, rather than the lateral shift that can be made is an increase in workload for the hip flexors that have to work to pick the leg up and over the stiffened joint again resulting in a less than efficient running stride.
By spending time rolling the fascia with a focus on the FHL tendon and stretching the joint it is possible to get a much cleaner and more efficient toe off. If the joint is arthritic or structurally rigid maybe because of a bunion then an orthotic can provide the answer.
As with all these things there is an opposite end to the spectrum. If the big toe joint is hypermobile, the toes simply move out of the way as soon as any load goes near them and propulsion is reduced. In these cases, tension needs to be brought back into the foot through intrinsic work or an orthotic.
This is the last point of contact with the ground and if it doesn’t function in the correct way, we lose a lot of our stored energy. Over the course of the marathon and the training leading up to it, that adds up to a lot of wasted energy.