Effect of workload, upper body posture, and saddle set-back on full body angular joint kinematics, muscle activity, and lower limb haemodynamics

Abstract

'Cycling is one of the toughest sports and one of the most complex to analyse in scientific terms.' - Mr Hein Verbruggen,P residentU nion Cycliste International 1991-2005. Despite extensive research into sagittal plane lower limb cycling kinematics there is little scientific literature available investigating the three-dimensional joint kinematics of the cyclist, and especially so regarding the kinematics of the pelvis, trunk, and arms, and how these are affected by workload, upper body posture, and saddle setback. This Thesis developed a comprehensive full-body three dimensional kinematic model and then
determined the effects of workload, Upper Body Posture, and Saddle Setback on the leg, trunk, and arm kinematics of the cyclist. Competitive cycling has an extremely high aerobic component, and yet ironically there have been few studies investigating how workload or riding position affect lower limb blood flow haemodynamics. By using Near-Infrared Spectroscopy a cycling specific technique was developed to enable tissue oxygenation status of the lower limbs to be determined during cycling, which was then used to assess the effects of workload, trunk and hip angle, and saddle set-back on lower limb blood flow haemodynamics. It is unclear to what extent saddle setback affects lower limb and trunk muscle activity and cycling performance, and yet the sub-disciplines of cycling use markedly different bicycle set-ups. By using a custom cycle ergometer developed by the author this Thesis systematically assessed the effects of saddle setback on muscle recruitment and activation magnitude. When investigating the effects of bicycle set-up on cycling performance it is important to consider all the physiological and biomechanical determinants of success in unison, and how they inter-relate. To date there are no studies that have comprehensively studied the kinematic, haemodynamic, electromyographic, and
associated crank kinetics simultaneously. As such this Thesis developed a methodology to evaluate the effects of changing workload, upper body posture, and saddle setback on fullbody three-dimensionalk inematics, lower limb blood flow haemodynamicsl,e g and trunk electromyography, and crank torque profiles, in order to arrive at the optimum riding
position and highlight the compromises required when aiming to maximise cycling performance.
The effects of workload were assessed by undertaking a 25W. min" graded maximal exercise test to exhaustion. In order to assess the kinematic, haemodynamic, and electromyographic effects of altering riding position a custom independently adjustable cycle ergometer was developed to permit precise accurate adjustment of the four main macro settings (saddle height and setback, and saddle to handlebar reach and drop) while maintaining the spatial coordinates of the other parameters. Three Upper Body Postures (Hoods,D rops and a Time Trial position), and six SaddleS etbacksw ere used (100,50, and Omm behind the bottom bracket, and 50,100, and 150mm in front of the bottom bracket).
For all three studies three-dimensional full body kinematics were recorded using a stereophotogrammetricin fra-red motion capture system. Leg and trunk muscle activity were recorded using an 8-lead surface electromyographic system, and tissue oxygenation levels were recorded using Near Infrared Spectroscopy on the Vastus Lateralis. Corresponding crank torque profiles were measured simultaneously using a crank dynamometer.
Increasesi n workload produced progressived ecreasesin Oxyhaemoglobina nd pedalling smoothnessin dex, and continual increasesin total haemoglobinc ontenta nd muscle activity in the majority of muscle groups, but produced little change in full-body kinematics until 80% maximal aerobic power was surpassedC. hanging from the Hoods to the Drops and into a Time Trial position had little effect on lower and upper limb kinematics, but produced significant increases in all lower limb muscle activity except the gluteus maximus, as well as considerable reductions in tissue oxygenation status, and resulted in cyclists pedalling with greater peak torque values. Moving the saddle forwards significantly affected joint kinematics, muscle activity, tissue oxygenation status, and the crank torques profiles. A saddle positioned with the nose directly over the bottom bracket minimised angular rotations of the ankle, knee, hip, and trunk as well as global muscle activation.
Tissue oxygenation status was also significantly higher using this setting, suggesting that although an aerodynamic cycling position must take priority, setting the saddle with the nose directly over the bottom bracket and maintaining the operating range of motion at the hip and knee appears to maximise cycling performance, and that the spinal kinematics appear to act as a torque-induced engine by means of increases in axial rotation magnitude in the lumbar, mid-thoracic and thoracic spinal segments.