Markus: With shin splints, we are talking about a painful periosteum inflammation originating from the foot flexing musculature at the front edge of the shin bone.
During trail running in particular and especially in ultras and multi-day stage races, we come across this overload phenomenon quite frequently. Such races demand a high increase in volume due to their long distances and as such cannot truly be trained in that capacity. In addition, there is the constant change in running technique from the climbs and descents. Due to the increased heel placement on downhills, the muscles that lift the foot and toes must absorb extreme forces in order to control the plantar flexion of the foot. This can irritate the shin bone periosteum with insufficient adaptation. Flat-splayed foot can in face exaggerate this effect because it already overloads the front shinbone muscle (tibialis anterior).
In order to reduce pain, there should be a break from running of one to two weeks, which should include ice applications, electrotherapy and, as needed, medications to fight inflammation. As long as only the musculature demonstrates an overload response and no inflammation of the periosteum can be shown, then methods to relax the muscle as well as kinesio taping can lead to the desired result so as to avert the need to quit, particularly in multi-day stage races.
Long term, of course, the underlying causes should be investigated. That for example can mean training of the arch of the foot with the potential of acquiring an orthotic, downhill technique training to improve the shift of the center of mass downhill, and strength and coordination exercises to rebalance muscle imbalances between the front and back of the thigh muscles.
How can this injury be proactively prevented?
Ultraruns in the mountains and also on the flats are something only experienced runners should take on. Indeed, the high increase in volume demanded by such runs, hold a high risk for training overload syndromes such as shin splints. Even with ideal physical preconditions regarding anatomy, strength balances and coordination abilities, a gradual increase in running distances is extremely essential. This allows tendinous muscle attachments along the edge of the shin as well as of course in other parts of the body to adapt to the loads demanded.
Depending on the runner, one could also forgo raised heels in footwear. These can in fact exaggerate the effect of an overload on the shin muscles due to the increased forward tilt of the upper subtalar joint they produce. In particular flatter footwear have been proved in this matter to prevent shin splints.