COST OF TRANSPORT, LOWER LIMBS ASIMMETRY AND THE DYNAMICS OF RUNNING.

The main topic of my PhD project regards the effects of the human symmetry on energetic and locomotion. The concept of symmetry, applied in many and different fields, from arts to physical sciences, has been always related to beauty, balance and equilibrium. Most individuals, animals and humans as well, are characterized by an almost complete morphological bilateral symmetry, and the deviation from it caused by environmental stresses, developmental instability and genetic problems, is called Fluctuating Asymmetry (FA). In numerous studies regarding FA, it has been demonstrated that this index is related to several different features, like sexual selection, body mass, running performance in humans and in racehorses. Similarly, symmetry plays a key role in the maintenance and design of our vehicles. They are periodically inspected, to guarantee a wheel balance/alignment and homogeneous tyre wearing. In this way the fuel consumption can be reduced. The main aim of this project has its origin from the comparison between mechanical vehicles and the human body. In human locomotion the skeletal muscles (the motor), and the limb lever system (the machine), interact together, in order to produce the movements of the whole body system. We assume that an anatomical or structural symmetry of the human body could have effects on the dynamic asymmetry during locomotion and also could be related to some metabolic energy saving. Several authors studied symmetry in locomotion with different methodological approaches in human, but also in animals. Different symmetry indices were found in order to classify subjects in different categories, or for pattern identification and pathologies diagnosis, but the relationships between symmetry and the Cost of Transport were poorly investigated. Gait symmetry has been defined as a perfect agreement between the actions of the lower limbs and general this assumption was adopted to simplify data collection and analysis of the lower limbs. Gait asymmetry instead, does not appear to be the consequence of abnormality, but rather reflects natural functional differences between the lower extremities. In the present study, we tried to validate our hypothesis, investigating anatomical and, dynamical symmetries, and the cost of transport in 19 different aged and trained male runners, in order to find out significant relationships between these parameters. Subjects were divided in three categories: Occasional Runners (OR), Skilled Runners (SR) and Top Runners (TR), depending of their training/performance level. Differently from others studies, we compare two different kinds of symmetries: the dynamic symmetry during running at different velocities (i.e. spatial differences, in Body Center of Mass (BCOM) trajectory, between two step), and the anatomical symmetry of the human lower limbs. A Magnetic Resonance (MR) protocol was applied for each subject, to evaluate the anatomical symmetry of three different anatomical districts Pelvis district (PD), Upper-Leg district (UD) and Lower-Leg district (LD). All the recorded images were analyzed with a custom, ad hoc program that can identify the MR images and calculate a cross correlation index, between right lower limb and left lower limb. This anatomical symmetry index can assume values from -1 to 1 and it is bigger the more the subject’s limbs are symmetrical. Level running at incremental velocities on a treadmill was performed in order to record kinematic functional symmetries. The human body was modelled as a series of linked, rigid segments with twenty reflective markers and their positions were captured by an optoelectronic system in order to evaluate trajectory of the BCOM. The coordinate describing this position were successively used to evaluate the main aspects of the gaits and the individual characteristics of movements, a sort of “locomotion signature” capable to reflect any significant change in the motion pattern. The time course of each of the 3 BCOM coordinates was fit by a Fourier Series and three single anatomical indices (one for each direction) were calculated. To evaluate running economy, heart rate (HR) and oxygen consumption (VO2) were measured continuously during level running/kinematic registration. The hypothesis we assumed, arising from to the world of the motor vehicles, found some answers with the results obtained in this work. The human body and the mechanical vehicle seem to have some similarity regarding the structure stability. In the human body, a high level of dynamical symmetry, during running locomotion is accompanied by structural/anatomical symmetry, but, differently from the motor vehicles, the energetic consumption doesn’t change with the level of anatomical and dynamic symmetry. Furthermore, training seems to be an important element in the stability and in the dynamical symmetry of running, even if no relationship was found between training level and Cost of transport. Also we found significant negative correlations between anatomical/structural symmetry and subject age. According to the literature asymmetry increase with the age of the subjects. We can conclude that our body can be biased by asymmetrical anatomical structures of the lower limb in the dynamical symmetry of the BCOM displacement, but without changing the energetic cost of running. Maybe some physiological adaptations of the human machine can compensate for small imperfections in the mechanics of our legged system, with no influence on the metabolic cost of transport, while larger anatomical imperfection, like length legs discrepancy or a body mass not uniformly distributed, or also prosthesis and support for pathological situations, could have a significant effect on the energetic cost of transport. This work brings new developments in the study of symmetry in locomotion, both for the introduced methods and for the presented result. Anyway further developments could be carried out in order to understand the already obtained results. The number of participants should increase and a longitudinal work could be carried out in order to find out differences between groups. Furthermore kinematic and energetic recording should be performed for a longer period. In this way the subjects could arise higher running velocity, and also we could observe new physiological parameters that we didn’t notice in only some minutes of registration.