## 1 Introduction  
Posture is defined as \"the position of the body in space and the spatial relationship between the skeletal segments, the aim of which is to maintain balance, both in static and dynamic conditions, to which neurophysiological, biomechanical, psycho-emotional and relational factors contribute, also linked to the evolution of the species\" [1]. It is defined as correct when the \"deformation is coherent with gravity\", that is, when it activates anti-gravity functions with less energy expenditure both during walking and in standing position [1]. The human body functions like a system capable of self-regulation, self-adaptation and self-programming. Based on the information received instant by instant from the external and internal environment, it constantly tries to better maintain a system of perfect homeostasis by means of feed-forward (cortical, subcortical and, once acquired, cerebellar areas) and feedback (subcortical areas) control systems [2; 3]. Posture is therefore the result of complex interactions between environmental stimuli and mechanisms that integrate visual, otovestibular, proprioceptive and exteroceptive afferents [4; 5]. Any force acting on this system will entail an attitude of compensation with reprogramming of postural system and balance [6]. These compensations, if repeated over time, can be structuralized by the central nervous system, first as functional mnemonic posture mechanisms and subsequently at peripheral level, as real anatomical anomalies [7; 8]. This phenomenon, called the motor engram, represents the set of motor experiences memorized by the individual as programming activating the feed-forward system responsible for direct neuro-motor activation. The more a motor action is repeated over time the more it is strengthened, like a neuro-associative conditioning [9].  
Sports actions also include motor actions. In particular, different types of sports with repeated stresses on the spine, presenting themselves as motor engrams, can determine not only benefits deriving from muscle training, but also negative influences on the body, which affect postural structure [10; 11].  
In fact, in subjects who practice these sports at professional level, repeated stresses can lead to postural adaptations of the spine, both functional adaptive and dysfunctional [12].  
Rasterstereography is an optical measurement system that provides a reliable method for three-dimensional analysis of the back and reconstruction of spinal deformities without radiation exposure [13; 14]. This system allows a three-dimensional reconstruction of spinal posture and pelvic position starting from the analysis of the posterior surface during orthostasis. [15; 16].  
This radiation-free system provides information that correlates well, on the sagittal plane, with radiographic data and that can be used over time to perform postural analysis and evaluate the effects of therapies [17]. This technique could be used to noninvasively assess the postural characteristics of athletes.  
The purpose of the observational study was to study various postural variables involved in postural adaptations of athletes practicing symmetric and asymmetric load sports at professional level. Postural variables related to primary injury prevention were also investigated with respect to a sample of sedentary subjects.