RECUMBENT VS UPRIGHT BICYCLES: OPERATIVE RANGE OF PROPULSIVE MUSCLES, 3D TRAJECTORY OF BODY CENTRE OF MASS AND LIMB MECHANICAL WORK
Creators: name: TELLI, RICCARDO
Publisher: name: Universit� degli Studi di Milano
Year: 2014

description: Introduction. Humans have always tried to move safely and faster in a variety of environment, even through the aid of passive tools that help to improve the limits imposed by the body characteristics. These means of locomotion, without supplying additional mechanical energy, are able to greatly improve the performance exploiting the use of muscular force alone. Bicycles are probably the passive tool most known and used in the world. The origin of this thesis comes from the interest to increase the knowledge about the features of a particular kind of bike: the Recumbent bicycle (RB). It is a high performance human powered vehicle where the cyclist is in a reclined position, with the back against a backrest. The peculiarity of the RB is that it allows to reach higher speeds than Normal/upright bicycles (NB), at the same metabolic power, principally due to aerodynamic advantages. Indeed, with the use of particular fairings that improve aerodynamics, these vehicles allow to exceed 130 km/h only with muscles power. The change in posture of the rider, consequent to the different characteristics and design of the bicycles, alters kinematics and energetics of cycling and could also affects muscle-tendon lengths and the operating range of the muscles length-tension curves. Despite the interest of the scientific community on the topic of cycling, some aspects still need to be investigated, especially with respect to the differences between traditional and recumbent bikes, which represent the most advanced evolution of that tool. Aim. The aim of this work is to analyze and compare the pedalling cycle on both bicycles from a biomechanical point of view. Indeed, with a comprehensive description of mechanical and metabolic consequences during cycling in both configuration, new vehicles could be designed with those technological changes that could increase the performance. Particular focus has been posed on the effect of the different position while riding the two bicycles: - on the muscle-tendon length of different muscle-tendon unit involved in cycling; - on the 3D displacement of the Body Centre of Mass (BCoM); - on the mechanical work (in particular the internal and the "additional" external mechanical work). Methods. The issues have been investigated both experimentally and trough simulations. By using 3D kinematic data and a physical simulation program we measured muscles-tendon length, 3D Body Centre of Mass (BCoM) trajectory and its symmetries and the components of the total mechanical work necessary to sustain cycling during stationary cycling, at different pedalling cadences (50, 70, 90 and 110 rpm). This approach allows to investigate the biomechanics of riding the two bicycles both through direct measurements of mechanical work and indirect estimation performed with simulation models. Results and Discussion. Joint kinematics and muscle-tendon length were analyzed with the musculoskeletal modelling software Opensim�. This analysis showed that, differently from cadence, the two bicycles caused changes in joint angles and, consequently, in muscle-tendon length. As a results in RB, when compared to NB, some muscles are slightly stretched while other are shortened, making the propulsive effectiveness impossible to be assessed. This work confirms experimentally, for the first time, that the BCoM in cycling moves along all three spatial axes, while before this study an elliptical movement in the sagittal plane was appreciated only with a 2D simulation. BCoM trajectory, confined in a 15 mm side cube, changed its orientation maintaining a similar pattern in both configurations, with advantages for RB: a smaller additional mechanical external power (on average 16.1 � 9.7 W on RB versus 20.3 � 8.8 W on NB), a greater Symmetry Index on progression axis and no differences in the internal mechanical power (ranged from 7.90 W to 65.15 W in NB and from 7.25 W to 62.16 W in RB, increasing as function of the rpm). Conclusion. Despite the human physiological characteristics have remained almost unchanged over the last millennia, performance on bicycles has increased significantly. This has been possible thanks to the work of mechanical engineers, exercise physiologists and biomechanists. In this thesis the body centre of mass trajectory and the associated additional external mechanical work while pedalling on recumbent bicycle has been studied experimentally for the first time. It is thought that the development of mechanisms reducing additional external power through a further containment of BCoM trajectory, together with additional studies on the effectiveness of propulsive muscles could be necessary to further refine design and improve performance of RB.