Differences in static and dynamic bike fit with 3d motion capture
Journal Title: Journal of Science and Cycling - Year 2014, Vol 3, Issue 2
Abstract
Background: Bicycle fitting is the adjustment of bicycle configuration to suit rider requirements through appropriate placement of contact points; pedals, saddle and handlebars (Burke 1994: Clin Sports Med, 13(1), 1-14). Traditional fitting uses static assessment of parameters such as knee angle through the bottom of the pedal stroke and saddle setback measured by knee over pedal horizontal separation (KOPS) (Holmes et al., 1994: Clinics in Sports Medicine 13(1), 187). Dynamic fitting is now increasingly popular through video analysis or 3d motion capture. However no comparison has been made of differences between static and dynamic measurement or assessment reported of the reliability of motion capture for bicycle fitting. Purpose: To investigate the repeatability of key bike fitting kinematic parameters and differences between static and dynamic conditions. Methods: 15 subjects performed repeated motion capture trials over three sessions in both static and dynamic conditions. Markers were applied to anatomical landmarks and kinematics collected using a Vicon 3d motion capture system. Results: Typical intra-session errors for angular parameters ranged from 1.7° (4.2°) for dynamic (static) knee flexion to 4.2° (4.9°) for ankle plantarflexion. Typical error for KOPS was 6.6 mm (12 mm). Significant (p<0.001) differences between static and dynamic conditions were observed for all parameters. Knee flexion was 5.4° greater in dynamic conditions (95% CI 3.5°, 7.4°). Corresponding dynamic ankle plantarflexion was 7.8° greater (5.9°, 9.6°) and hip flexion 5.1° greater (3.8°, 6.5°). KOPS was 7.7 mm further forward in dynamic conditions (3.3, 12.1) and dynamic ankle plantarflexion at KOPS was 3.6° greater (1.8°, 5.4°). Discussion: Typical errors showed moderate repeatability indicating the system was fit for purpose but these errors require consideration in the fitting process. Differences between static and dynamic parameters appear to originate at the ankle, with a tendency for riders to drop their heels when stationary. Conclusion: Common guidance to fit to a knee angle between 25-35° should be adjusted to 30-40° for dynamic measurement.
Authors and Affiliations
M Corbett| Institute of Sport and Exercise Science, University of Worcester, United Kingdom, J Bevins| Institute of Sport and Exercise Science, University of Worcester, United Kingdom
Validity of using functional threshold power and intermittent power to predict cross-country mountain bike race outcome
Validity of using functional threshold power and intermittent power to predict cross-country mountain bike race outcome. Purpose: Field tests are important for athletes and sport practitioners as they offer valuable in...
The effects of forward rotation of posture on heavy intensity cycling: Implications of UCI rule 1.3.013
UCI rule 1.3.013 limits the forward displacement of the nose of the saddle to 5cm rearward of the centre of the bottom-bracket. This study tests the effects of contravening this rule on 4km laboratory time trials and hig...
Differences in visual information-seeking behavior between expert and novice time-trial cyclists
Introduction: Pacing can be defined as an ability to distribute available energy resources during the race (Hettinga et al., 2006). It’s a determinant of athletic performance, affected by an interaction between previous...
Modelling of cycling power data and its application for anti-doping
Since the introduction of the Athlete Biological Passport (ABP), research studies have suggested that there is risk of false-positive results due to a variety of factors that act to compromise its sensitivity to detect u...
Physiological characteristics of competitive Brazilian cyclists
The national cycling calendar in Brazil is extensive with numerous regional and state competitions on a weekly basis. Furthermore, several teams now compete in national, continental and international races throughout the...