Adaptation of the human calcaneus to variations of impact forces during running

Objective. The influence of varied forces under the heel induced by changes in midsole hardness on adaptations of the human calcaneus during running training was investigated. Design. A longitudinal study was conducted over a period of 20 weeks with subjects training for 50 km per week on average. Background. The skeletal systemsʹ metabolism acts highly dynamic, governed by mechanical factors. The amount of running training has been shown to increase the bone mineral density in the calcaneus. Mechanical factors have not been controlled in former investigations. Methods. Bone quality parameters were determined before and after the training by use of an ultrasound system and quantitative MRI while the mechanics of foot-ground contact were controlled. The total group of 26 subjects was divided into three subgroups based upon different magnitude of forces under the heel inside the shoe. Results. The biomechanical testing demonstrate no relationship between midsole hardness and external or in-shoe impacts. Bone parameters showed specific differences for all groups which are pronounced in runners with intermediate impacts. Conclusions. The observed variations reflect metabolic changes in bone marrow which appear to be effected by the impact magnitude and cannot be characterised as negative.