My experiences:
The colder the water, the higher the chance of tendonitis (if that is what it is). Diving in the winter in 6-8 C water, for one day of about 1.5 hours total dive time, I experienced extreme pain at the base of my toes and the end of the foot. I could no longer bend my toes all the way forward. This persisted, without any further monofin diving, for 2-3months. At that time it began slowly decreasing in pain and some time in the summer, I no longer sensed it. Diving in the warmer waters, it did not return, until I allowed my foot to get extremely cold again. This time not as much though and it recovered within a week.
I switched to bi-fins during cold season, with full footpockets, which extended the amount of time in the cold I could stay, before having the same symptoms. However, since the new bi-fin was more work to move than previous fins I had, my ankle began getting a similar symptom, such as the one Bevan refers to.
So from these experiences my opinion is:
- whether it is tendonitis or not, extreme cold does heighten the chance of injury to stressed joints/tissues.
- the injury can heal depending on the original damage, your body, your rest, your nutrition.
- it makes sense that if the tendons shrink/compress due to the cold, then exerting strain on them can damage them, since they will not have the characteristics that they are meant to operate under. The tissues will be inflexible and may tear/stretch abnormally.
Recommendation for Bevan in addition to the recommendations already supplied:
- simulate the ankle strain in warmer waters somehow, such as swim with stiff bi-fins at the surface to add strength and flexibility to the ankle location.
- work in dry conditions on ankle strength and do lots of stretching.
Cheers,
Tyler