Abstract:It is well known that, in spite of its crucial role in the posture, locomotion and voluntary movements, trunk has received less consideration from researchers than upper and lower limbs. On the other hand, rehabilitative interventions of patients with upper motoneuron syndrome have always been focused firstly on treatment and recovery of trunk's posture during standing, sitting and walking.Trunk is a complex anatomical structure and it is composed by a large variety of bones, articulations, ligaments and muscles. From a functional point of view, trunk muscles have been subdivided into two systems: a local system which ensures stability and a global system which enables movements. Muscles of these two systems work by eccentric and concentric contractions, according to the functional needs.Surprisingly, in the literature are reported only a few studies regarding the trunk muscle activations during walking. These studies investigated the electromyographic activation patterns in different experimental conditions as walking on a walkway, over a treadmill at different velocities, in water or in deep-water. Furthermore, data analysis was differently performed by analyzing the qualitative and quantitative features of timing and amplitude of electromyographic recordings for each muscle or by other more sophisticated methods as cluster analysis or principal components analysis. Finally, some variability has been observed in the normal population also including sex differences. The aim of this review is to show the state of art of this topic, in normal subjects.