INVESTIGATING THE METABOLIC PROFILE OF RUN-UP RACES AND THE MECHANICS OF WOBBLING VISCERAL MASS IN VERTICAL JUMPS.

This Thesis is organized in two parts based on two different investigations about human motion: the metabolic and mechanical analysis of ‘skyscraper running’, and the estimation of the visceral mass displacement in vertical jumps. Skyscraper running is a novel sport activity, in which the athletes run on emergency stairs of the tallest building of the world, during the ‘run up’ races of the world championship circuit. In PART I of this Thesis, this topic has been analysed in terms of mechanical and metabolic requirements, both at general and individual level. Skyscraper runners’metabolic profile, has been inferred from the total mechanical power estimated in 36 world records (48-421 m tall buildings), ranked by gender and age range. Individual athlete’s performance (n=13) has been experimentally investigated during the Pirelli Vertical Sprint, with data loggers for altitude and heart rate. At a general level, a non-linear regression of Wilkie’s model relating maximal mechanical power to event duration, revealed the gender and age differences in term of maximum aerobic power and anaerobic energy resources particularly needed at the beginning of the race. The total mechanical power was found to be partitioned among: the fraction devolved to raise the body centre of mass: W˙ STA.EXT = 80.4 ± 2.9%, the need to accelerate the limbs with respect to the body: W˙ STA.INT = 4.5 ± 2.1%, and running in turns between flights of stairs: W˙ TUR =15.1 ± 2.0%. At the individual level, experiments revealed that these athletes show a metabolic profile similar to middle-distance runners. Furthermore, best skyscraper runners keep constant vertical speed and heart rate throughout the race, while others suddenly decelerate, negatively affecting the race performance. In PART II of this Thesis another interesting study has been discussed: the mechanics of visceral mass motion in vertical jumps. This internal mass motion could occur in all the locomotion paradigms, and also in all the movements characterized by a high centre of mass vertical displacement. Moreover, visceral mass shows significant couplings with the respiratory system, as has been discussed in the past in famous studies on quadruped locomotion. Here viscera motion has been analyzed in a simple and well know motor task as the vertical jump, focusing on the effect of respiratory and muscle contractions strategies to limit its displacement, and to improve trunk-pelvis segment stiffness. A validated method for the estimation of visceral mass displacement has been applied during jump sequences with two different techniques: six subjects before and after a specific training period, executed the natural jump and the “controlled” jump sessions. In that method, the simultaneous measurement of ground reaction forces and spatial coordinates allow the estimation of the relative movement between the ‘invisible’ abdomen content and the ‘container’, i.e. the rest of the body as described by the position of external markers. The results show a significantly higher (p < 0.05 – paired t-test) mean of visceral mass displacement (Total = 0.087 ± s.d. 0.021 m) of all the subjects, in normal jumps, compared to the mean of visceral mass displacement (Total = 0.070 ± s.d. 0.027 m) in controlled jumps. An analysis of variance (ANOVA 2-ways) shows a significant effect of jump technique but also of subject and jump-subject interaction, confirming an elevated variability between the subjects. A intraclass-correlation exhibit a significant pattern (ICC= 0.791; p = 0.017) and in 5 of 6 subjects, there is a higher mean nominal value of VMD in normal jumps. Also pectorals and low abdominal fat displacements has been measured, showing mean values (weighted by a scaling factor) of 4.5×10-4 m and 8.9×10-4 m in normal jumps, and 4.5×10-4 m and 9.6×10-4 m in controlled jumps respectively. A quantitative and qualitative analysis on visceral mass displacement curve has been completed for both the jumping techniques: a comparison with the ‘periodic’ curve of body centre of mass show a constant delay (‘phase shift’) with a mean value of 18.1 ± s.d. 5.73 ms during the aerial phase and 18.8 ± s.d. 9.8 ms in the landing phase. Finally a preliminary estimation of the internal mass vibration parameters has been showed: the mean values and s.d. of the stiffness in normal and controlled jumps are k1= 18.2 ± 13.5 KN/m and k2= 17.9 ± 12.1 KN/m respectively, while the damping constant mean values and s.d. are c1 300.3 ± 170.7 N/(m/s) is and c2 is 287.3 ± 129.8 N/(m/s). For the first time, a method for the estimation of visceral mass displacement, useful in biomechanics and in locomotion-respiratory coupling investigations, has been used in an applied condition. The effects of the “controlled” jumping techniques using respiration and muscles contraction strategies to limit viscera displacement has been demonstrated. The displacement of visceral mass and the body frame have been quantified and compared, and a preliminary estimation of vibration parameter of the internal system has been showed. We foresee an increasing interest in sports biomechanics to improve athletes jumping performance, as well as in the energetics and biomechanics of locomotion.