Jean-Marc Drouet

Changes of Pedaling Technique and Muscle Coordination during an Exhaustive Exercise

PURPOSE Alterations of the mechanical patterns during an exhaustive pedaling exercise have been previously shown. We designed the present study to test the hypothesis that these alterations in the biomechanics of pedaling, which occur during exhaustive exercise, are linked to changes in the activity patterns of lower limb muscles. METHODS Ten well-trained cyclists were tested during a limited time to exhaustion, performing 80% of maximal power tolerated. Pedal force components were measured continuously using instrumented pedals and were synchronized with surface EMG signals measured in 10 lower limb muscles. RESULTS The results confirmed most of the alterations of the mechanical patterns previously described in the literature. The magnitude of the root mean squared of the EMG during the complete cycle (RMScycle) for tibialis anterior and gastrocnemius medialis decreased significantly (P < 0.05) from 85% and 75% of Tlim, respectively. A higher RMScycle was obtained for gluteus maximus (P < 0.01) and biceps femoris (P < 0.05) from 75% of Tlim. The k values that resulted from the cross-correlation technique indicated that the activities of six muscles (gastrocnemius medialis, gastrocnemius lateralis, tibialis anterior, vastus lateralis, vastus medialis, and rectus femoris) were shifted forward in the cycle at the end of the exercise. CONCLUSIONS The large increases in activity for gluteus maximus and biceps femoris, which are in accordance with the increase in force production during the propulsive phase, could be considered as instinctive coordination strategies that compensate for potential fatigue and loss of force of the knee extensors (i.e., vastus lateralis and vastus medialis) by a higher moment of the hip extensors.

Automatic mesh generation and transformation for topology optimization methods

This paper presents automatic tools aimed at the generation and adaptation of unstructured tetrahedral meshes in the context of composite or heterogeneous geometry. These tools are primarily intended for applications in the domain of topology optimization methods but the approach introduced presents great potential in a wider context. Indeed, various fields of application can be foreseen for which meshing heterogeneous geometry is required, such as finite element simulations (in the case of heterogeneous materials and assemblies, for example), animation and visualization (medical imaging, for example). Using B-Rep concepts as well as specific adaptations of advancing front mesh generation algorithms, the mesh generation approach presented guarantees, in a simple and natural way, mesh continuity and conformity across interior boundaries when trying to mesh a composite domain. When applied in the context of topology optimization methods, this approach guarantees that design and non-design sub-domains are meshed so that finite elements are tagged as design and non-design elements and so that continuity and conformity are guaranteed at the interface between design and non-design sub-domains. The paper also presents how mesh transformation and mesh smoothing tools can be successfully used when trying to derive a functional shape from raw topology optimization results.

A Laboratory Excitation Technique to Test Road Bike Vibration Transmission

This paper describes a technique designed to measure the in-situ acceleration signals that will be used to drive a road simulator in the study of road bike vibration transmission in a laboratory setting. To measure the signals, a bike mounted by a cyclist and towed by a motor vehicle is used. A road simulator using actuators driven by a digital signal is described. The impulse response of the bike used to measure road data is convoluted with the road acceleration in order to obtain the required actuator signal. The reproduction capacity of the simulator is evaluated by comparing the frequency content as well as the time statistical parameters of the acceleration signal measurement with road to the acceleration obtained on the simulator. On a granular road with a broadband excitation spectrum, the vertical excitation obtained with the simulator adequately mimics the measured road acceleration. This technique can be used to compare vibration transmission characteristics among different road bikes.

Towards the Integration of Topology Optimization into the CAD Process

This paper presents a contribution to the automation and integration of topology optimization methods (TOM) with CAD, in the context of the design of statically loaded mechanical structures and parts. Starting from an initial CAD model with relevant engineering data, the goal is automatically generating an optimized CAD model with respect to engineering objectives and constrains. Though many optimization methods are now available, their complete and efficient integration into the design process faces several problems. After introducing the basic steps involved in the whole process and identifying the challenges inherent to this integration, this paper presents our contribution in addressing these challenges. The paper is focused on the specification of design and non-design sub-domains, on automatic mesh generation problems induced and on the adaptation of TO concepts in the context of 3D unstructured meshes. TO itself is adapted from a SIMP scheme, which is an arbitrary choice as any other optimization m...

Technique to Measure the Dynamic Behavior of Road Bike Wheels

In the quest to improve comfort in road cycling, a primary concern of the bike manufacturing industry is the vibration generated by the road and transmitted to the cyclist’s hands and buttocks. The bike wheels are considered to be one of the major components contributing to the bike’s vibration isolation. In this paper, we describe a technique that uses the measurement of a blocked force at the hub. A road simulator was used to impose a controlled white noise vertical displacement under the tire. Measurements were taken of the force under the tire and the blocked force at the wheel hub. Six different wheels were tested. When the force was applied at different locations on the wheel, some of the wheels showed important spatial variations of the blocked force. The results show that this technique is successful in differentiating and ranking the wheels. Each wheel was also characterized by its radial static stiffness. Preliminary results show that there is poor correlation R 2 = 0.41 between radial static stiffness and the blocked force at the dynamic hub.

Automatic 3D Mesh Generation of Multiple Domains for Topology Optimization Methods

This paper presents an automatic approach to generate unstructured tetrahedral meshes in the context of composite or heterogeneous geometry. Using B-Rep concepts and specific adaptations of advancing front mesh generation algorithms, this approach guarantees, in a simple and natural way, mesh continuity and conformity across the interior boundaries of a composite domain. This method presents a great potential in various fields of application such as finite element simulations (in the case of heterogeneous materials and assemblies for example), animation and visualization (medical imaging for example). After a description of the approach and its context, the paper presents a potential application in the specific domain of topology optimization.

Excitation techniques for testing bike vibration transmission in the laboratory

Vibrations generated by road surface defects are a significant source of discomfort for cyclists. This paper presents two very different laboratory techniques for studying road bike vibration. The first technique uses a treadmill with a modified belt surface. The second technique is based on the use of a road simulator that was developed specifically to generate displacement excitation under the wheels of the bike. Broadband excitation generated by coarse pavement surface is also evaluated in this study. The objective of this paper is to evaluate and compare the relative merits of these two approaches. For the purposes of evaluation, we have described a technique to obtain a realistic measurement of input in real road conditions. Our results demonstrate that the road simulator succeeds in producing adequate displacement profiles in the vertical axis resulting in a vibration frequency spectrum that closely resembles the measurements in real road conditions. Limitations in current actuator capacity prevent to reproduce very coarse road conditions. Finally, more work is needed to develop an appropriate belt surface that can generate sufficient energy excitation above the 25 Hz range.

Influence of Test Conditions on Comfort Ranking of Road Bicycle Wheels

In the past few years, the dynamic comfort of bicycles has become a hot topic in the cycling industry. To improve comfort, a wide variety of dynamic tests is used to characterize and compare bikes. Because these tests usually involve a cyclist, and since the tires have a non-linear effect on the system, test protocols are expected to have an impact on the dynamic characteristics and bicycle ranking. With the objective of establishing good practices when comparing wheel comfort, this paper presents the influence of several test parameters on the vibrations induced to the cyclist at the hands and buttocks. The influence of two excitation surfaces on bicycle dynamics is studied: a flat excitation surface and an irregular surface that locally deforms the tire. The type of excitation, such as white noise, impacts and typical road excitation, are also investigated. Results with regard to the effect of the cyclist’s mass are also presented. The conclusion of this study shows that even if those parameters have a significant influence on the vibration levels transmitted to the cyclist, they do not affect the transmissibility ranking of two wheelsets. It should be noted however that the changes observed in the cyclist’s posture and position on the bicycle can affect wheelset ranking. Great care is therefore advised in controlling the cyclist’s posture and attitude on the bicycle during the tests.

Using Substructuring to Predict the Human Hand Influence on a Mechanical Structure

Substructuring methods have been widely used on mechanical structures to study and improve the dynamic behavior of complex assemblies by analyzing the behavior of each substructure separately. Substructuring methods can potentially be used to create a functional link between the dynamic behavior of the human body and mechanical structures in order to enhance the interactions between the body and these same structures. Keeping in mind that significant amounts of vibrations are transmitted to the body from contact with vibrating structures – human-structure coupling interactions could be used as a way to study components of comfort during vibration exposure, and even with the goal of preventing injuries caused by transmitted vibration.

Effect of Structural Damping on Vibrations Transmitted to Road Cyclists

Improving ride quality is a paramount concern for road cyclists who are subjected to road induced vibrations during long rides. It has been hypothesized that adding structural damping to the bicycle can decrease the vibration levels transmitted to the cyclist. The human body is most sensitive to vibrations in the frequency range of 0–60 Hz, and the amount of damping added by the cyclist when riding the bicycle is very large. This could potentially reduce the net benefit of small improvements provided by structural damping. This paper reveals the effects of structural damping modifications on the modal parameters of a bicycle frame and on the amount of vibrations transmitted to the cyclist due to road surface excitation. A bicycle frame originally designed with damping gel inserts was tested in three different configurations: (1) with its damping gel inserts, (2) with its damping gel inserts and additional damping material wrapped around the frame’s tubing and (3) without its damping gel inserts. Three different metrics were used to assess the damping material effect on vibrations transmitted to the cyclist at the hands and buttocks: acceleration, transmitted force and power absorbed by the cyclist. This paper shows that in all configurations and measurements, added damping did not reduce the vibrations transmitted to the cyclist.