Abstract

INTRODUCTION One of the main activities developed by the human being, and which has captured the interest of movement specialists, has been the biped locomotion. The analytic study about the generation of mechanical energy is the key in the study of the human gait. This analysis shows the principle of conservation of the energy in the motor activity of locomotion. This would be related with motor control, but this has not still been established. The characteristic of mechanical energy generation over corporal segments can be an indicator of the indemnity or deterioration of musculoskeletal and neurological systems. In this study the mechanical energy generation rate was described during the beginning of gait, also establishing the differences between males and females. METHODS Nine subjects were measured, (n=9, women: 4, men: 5) with an average weight of 66.2±13.4kg who accepted to participate in this project by means of informed consent. The exclusion criteria consisted in: antecedents of neurological, muscular or skeletal pathology, surgery history in limbs or spine and people who habitually practice some sport discipline. They were placed 4 passive markers located bilaterally on the external border of the acromion process apex in the scapula and on the greater trochanter apex of the femur. With these markers, trunk segment was configured. The volunteers walked 5 times, which was located inside the volume of calibration of the motion analysis system used for the acquisition of this data (APAS System, Ariel Dynamics Inc. San Diego, USA). They realized 2 gaits of adaptation and later on 3 gaits that were registered, being executed to a comfortable velocity selected in natural form by each subject, beginning all with the same foot, which was chosen by the subject in study. For the later analysis of the data in relation to the gait cycle was considered the progression of the same extremity. During the gait analysis, the COM displacement of the trunk segment was measured during the three first steps of the limb with which the subject began the test. The first step was considered from the heel off (HO), until the heel contact (HC) of the same foot. The following two gait cycles went from the second HC through to third HC of the same limb. The first cycle was considered, for the data analysis, like a 50% of a normal cycle. Each following step corresponds to 100% of a normal gait cycle. This gave a total of 250% of a normal gait cycle. The total energy (ET) was calculated in the following manner: ET Eug ????Ek Where, Ek is kinetic energy, and Eug, the gravitational potential energy. The lineal regression was calculated between the peaks of total energy and the percentage of the gait cycle (%GC), this way the slope describe the mechanical energy generation rate. To the obtained –413– XVIIth Congress of the International Society of Electrophysiology and Kinesiology 18–21 June 2008 results they were applied a statistical non- parametric Mann-Whitney test through a statistical analysis software (Minitab, Minitab Inc. company Pennsylvania State, USA), with a significance level of 95% (????=0.05). RESULTS The studied subjects presented average slopes of 37.96±11.92 (J/%GC). The average slope for men was 41.71±14.87 (J/%GC), with a mean one of 40.33 (J/%GC). The women presented an average slope 33.28±5.63 (J/%GC) with a mean of 33.79, with a maximum of 38.78 and minimum of 26.77(J/%GC). The subjects didn't present any significant differences as for slopes differentiation between sex (p>0.05), according to Mann-Whitney test. . DISCUSSION The quantification of energy slopes and their correlation grade gives precise information about the mechanical energy generation rate. This rate can be useful to future investigations to value the energy generation in pathologies that affect the neurological system as well the musculoskeletal system. The relevance of evaluating the energy slopes during the first three steps, resides in that this gives the information of the energy change from a previous state to the beginning of gait, where the translational velocity of COM is zero, toward a state in which the displacement velocity of COM increases. In many pathologies the rate of energy generation is increased, but isn’t evaluated the fact that they vary in the increment from the steady state until later gait cycles, beyond the first three cycles. For the other hand, for the total energy system calculation -in this case, the trunk- although it was considered Ek and the Eug, Niagara Falls, Ontario, Canada it haven’t been considered the elastic potential energy neither the energy rotational component. Previous investigations have described the COM excursion in relation to the vertical axis during continuous gait cycles, giving the position changes variations and COM velocity, of body and their segments. In this research they weren’t significant variations as for sex, neither they have related slopes of many energy peaks, in spite of the fact that evidence shows an increase in the energy generation during normal gait cycles (Miller and Verstraere, 1999; Gard et al, 2004). However, this research shows an increase in energy peaks, establishing positive slopes among them. CONCLUSIONS i.-The total energy generation rates of trunk segment increased during the first three steps of gait cycle. ii.-They weren’t significant differences as for the slopes normalized in the time, between men and women. REFERENCES Miller C.A. and Verstraere M.C. (1999).Gait & Posture 9, 3: 158-166. Gard et al. (2004). Human Movement Science, 22 597-610.