A study on the biomechanical efficiency of different cycling positions

It is well known that several are the "biomechanical" parameters (e.g. the pedalling frequency, the crank-arm length, the saddle height, the seat tube angle, etc only to name a few) that could affect cycling performance. Even if the optimal values and the sensitivity of each parameter would differ whether the efficiency or the power output have to be maximized, the variations in the positioning of the athlete are found to be, in either case, of particular importance. The biomechanical analysis of bicycle pedalling through experimental devices designed to evaluate the muscular efficiency of the lower limbs is an important asset in sport medicine. In this field, one of the main effort is focused to improve athlete’s performance through special positions that may influence the muscular coordination and the pedalling technique [1] [2].. For these reasons, in the last decades many researches has been carried out in sport medicine making use of both mechanical and medical techniques. The biomechanical analysis of pedalling requires a theoretical model together with a proper experimental device, suitably equipped to detect the parameters involved by the model in order to obtain a fully determined activity monitoring [3]. Then by a mathematical model of the two human body structures, the skeleton and the muscular apparatus, the kinematics and dynamics of the system of lower limbs and crank can be obtained. The medical techniques mainly consist of estimating the muscle metabolism based on measurements of heart rate, lactate production, oxygen uptake and determination of the ventilatory threshold [4] while mechanical-engineering devices are developed to detect the kinematical and dynamical parameters [5]. In order to study the improvement in the cycling performance due to variations in the position, a systematic series of tests on an actuated and instrumented bicycle prototype were performed in this research. In particular the relationship between the mechanical and the physiological parameters are taken into account with particular concern to the maximal O2 consumption (Vo2max) and the lactate production registered with different values of the seat tube angle (STA) and the frame geometry. Ten semi-professional road male cyclist volunteers participated in the experiments. In the first step the tests were performed in two different sessions (separated at the most by one week) at approximately the same hour of the day. The special prototype adopted allows to detect the external mechanical power, the pedalling frequency, the force exerted on each pedal in three main directions, the angle of oscillation of each pedal during revolution and the forces exerted on the saddle and the handlebar. By “link-segment modeling” and considering the kinematical parameters, by means of an inverse dynamic procedure it is possible to calculate the internal actions and in particular the moments acting on each link segment with free-body diagram method. The bidimensional five-bar linkage model has been previously and successfully applied in many researches [6]. The athletes were equipped with a portable system (Cosmed quark b2) to measure pulmonary ventilation (VE, [lmin-1]), HR [bpm], carbon dioxide output (VCO2, [lmin-1]) and oxygen uptake (VO2; [lmin-1]) on time basis. In the first session, performed with the ergometer in a configuration reproducing the position of each subject usual bicycle frame, the athletes were monitored passing from a resting state reproducing their natural metabolic rate and gradually increasing the external mechanical power by 50 W every 5 min. The subjects were requested to maintain the 90 rpm pedalling cadence at each load rate. In this way the anaerobic threshold with V-slope method was determined for each subject and the power rate for the second session was determined. In the second experimental session the subjects were requested to repeat the test with the fixed power and pedalling rate while the STA was changed from 70° to 75° with an interval of 1 degree every 5 min. The tests performed with a rigid protocol shows an interesting relationship between the trend of the coefficient of variation of O2 consumption (respiratory dynamics) and the forces measured on saddle and handlebar. The stabilization of the respiratory dynamics registered for a particular position could be considered as a first step of O2 consumption physiologic adaptation. On the basis of this results a second step was carried out to analyze the long term adaptation concerning other metabolic parameters i.e. lactate involved in the process. A professional road male cyclist performed the same two previous experimental sessions, with the same accurate protocol, and then was requested to train for 8 weeks with a frame bicycle that reproduced the equilibrium force position between the horizontal component of the force on the saddle and on the handlebar registered with the prototype ergometer. The test seems to confirm the presence of a stabilization of the respiratory dynamics in case of equilibrium between the force on saddle and handlebar for a particular position and suggests the possibility to identify an optimization of the O2 consumption.