Philippe Vaslin

Upper limb joint dynamics during manual wheelchair propulsion

BACKGROUND Inverse dynamic methods have been widely used to estimate joint loads during manual wheelchair propulsion. However, the interpretation of 3D net joint moments and powers is not always straightforward. It has been suggested to use joint coordinate systems (expression of joint moment on anatomical axes) and the 3D angle between joint moment and angular velocity vectors (propulsion, resistance or stabilization joint configuration) for a better understanding of joint dynamics. METHODS Nine spinal cord injured subjects equipped with reflective markers propelled in a wheelchair with an instrumented wheel. Inverse dynamic results were interpreted using joint coordinate systems, 3D joint power and the 3D angle between the joint moment and joint angular velocity vectors at the three upper limb joints. The 3D angle was used to determine if the joints were predominantly driven (angle close to 0 or 180 degrees) or stabilized (angle close to 90 degrees ). FINDINGS The wrist and elbow joints are mainly in a stabilization configuration (angle close to 90 degrees ) with a combination of extension and ulnar deviation moments and an adduction moment respectively. The shoulder is in a propulsion configuration, but close to stabilization (angle hardly below 60 degrees ) with a combination of flexion and internal rotation moments. INTERPRETATION Stabilization configuration at the joints could partly explain the low mechanical efficiency of manual wheelchair propulsion and could give insight about injury risk at the wrist, elbow and shoulder joints.

Assessment of Field Rolling Resistance of Manual Wheelchairs

This article proposes a simple and convenient method for assessing the subject-specific rolling resistance acting on a manual wheelchair, which could be used during the provision of clinical service. This method, based on a simple mathematical equation, is sensitive to both the total mass and its fore-aft distribution, which changes with the subject, wheelchair properties, and adjustments. The rolling resistance properties of three types of front casters and four types of rear wheels were determined for two indoor surfaces commonly encountered by wheelchair users (a hard smooth surface and carpet) from measurements of a three-dimensional accelerometer during field deceleration tests performed with artificial load. The average results provided by these experiments were then used as input data to assess the rolling resistance from the mathematical equation with an acceptable accuracy on hard smooth and carpet surfaces (standard errors of the estimates were 4.4 and 3.9 N, respectively). Thus, this method can be confidently used by clinicians to help users make trade-offs between front and rear wheel types and sizes when choosing and adjusting their manual wheelchair.

Two-dimensional kinematic and dynamic analysis of a karate straight punch.

The mechanical effect of punches performed in martial arts or boxing sports has been studied on different ways: the impact force was either directly measured with sensors fixed on rigid frames [5, 6] or indirectly estimated from the mechanical features of materials broken during strike tests [2, 3]. A few authors developed experimental devices for measuring this force in actual fighting conditions [1] or on a punching bag [4]. Among the studies that analyzed the kinematics of the striking segments [2, 3, 5], only one [2] related kinematic and dynamic data through the linear momentum. According to this approach, a straight punch struck by a karateka (1.68 m, 68 kg, 3rd dan black belt) on a training instrument traditionally used in karate (makiwara) was analyzed in two dimensions. The peak force was two to three times lower than the maximum values (4000 to 6000 N) reported in previous studies [1, 5, 6], which could be explained by the makiwara flexibility. The large difference between the variation of the karatekas linear momentum and the linear impulse of the target-block pointed out the limitation of a 2-D analysis of this movement, which cannot take into account the angular momenta of the trunk and the upper limbs around the vertical axis.

A method for the field assessment of rolling resistance properties of manual wheelchairs

This article presents an examination and validation of a method to measure the field deceleration of a manual wheelchair (MWC) and to calculate the rolling resistances properties of the front and rear wheels. This method was based on the measurements of the MWC deceleration for various load settings from a 3D accelerometer. A mechanical model of MWC deceleration was developed which allowed computing the rolling resistance factors of front and rear wheels on a tested surface. Four deceleration sets were conducted on two paths on the same ground to test the repeatability. Two other deceleration sets were conducted using different load settings to compute the rolling resistance parameters (RPs). The theoretical decelerations of three load settings were computed and compared with the measured decelerations. The results showed good repeatability (variations of measures represented 6–11% of the nominal values) and no statistical difference between the path results. The rolling RPs were computed and their confidence intervals were assessed. For the last three sets, no significant difference was found between the theoretical and measured decelerations. This method can determine the specific rolling resistance properties of the wheels of a MWC, and be employed to establish a catalogue of the rolling resistance properties of wheels on various surfaces.

ASSESSING “POWER INPUT” OF THE MANUAL WHEELCHAIR USER DURING REAL LIFE AMBULATION

Assessing the mechanical power produced by the user of a manual wheelchair (MWC) during daily ambulation is an important issue because it highlights the users difficulties to move in his environment. Currently, this power is assessed by the power of the handrim propelling torque (PP) measured with one (or two) instrumented wheel(s) mounted on a fixed ergometer [Veeger, 1991] or on a MWC. Although this method takes into account the obvious propulsive actions of the user on both handrims (HR), it neglects the power of the user’s actions on the seat. This paper aims at presenting a new method taking into account all the user’s mechanical actions to assess the net power (PI) put by the user in the MWC system during actual ambulation on any floor using an instrumented MWC.

Dynamic calibration of a wheelchair six-component wheel dynamometer rolling on the floor

Propelling a manual wheelchair (MWC) is a strenuous form of locomotion for upper limbs and numerous pains and injuries have been diagnosed at shoulder, elbow and wrist joints. So, biomechanics research aims at decreasing stress sustained by MWC users. Measurements of forces and torques applied on handrims by the user are useful for investigating joint dynamics and kinetics. In this scope, several laboratories and manufacturers have designed various six-component wheel dynamometers (WD) [1,2,3,4,5]. However, a WD is not a simple sixcomponent force-plate, since it turns during measurements. Hence, sensors offsets evolved along with WD angular position and eventually with angular velocity: taking these parameters into account requires a dynamic calibration [4,5]. The rare dynamic calibrations described in the literature were performed with the WD vertically hung by wheel hub, implicitly assuming that signals measured when the WD freely rotates around its axle were the same as those recorded when it is rolling on the floor, while a user is sitting on the MWC. This study aims at verifying this assumption.

Respective contributions of the subject and the wheelchair to the total kinetic energy of manual wheelchair locomotion

The purpose of this study was to validate a 3D dynamic virtual model for lifting tasks against a validated link segment model (LSM). A face validation study was conducted by collecting x, y, z coordinate data and using them in both virtual and LSM models. An upper body virtual model was needed to calculate the 3D torques about human joints for use in simulated lifting styles and to estimate the effect of external mechanical devices on human body. Firstly, the model had to be validated to be sure it provided accurate estimates of 3D moments in comparison to a previously validated LSM. Three synchronised Fastrak units with nine sensors were used to record data from one male subject who completed dynamic box lifting under 27 different load conditions (box weights (3), lifting techniques (3) and rotations (3)). The external moments about three axes of L4/L5 were compared for both models. A pressure switch on the box was used to denote the start and end of the lift. An excellent agreement [image omitted] was found between the two models for dynamic lifting tasks, especially for larger moments in flexion and extension. This virtual model was considered valid for use in a complete simulation of the upper body skeletal system. This biomechanical virtual model of the musculoskeletal system can be used by researchers and practitioners to give a better tool to study the causes of LBP and the effect of intervention strategies, by permitting the researcher to see and control a virtual subjects motions.

Damping characteristics of nine samples of French boxing gloves

Boxers’ safety is a priority of the French Federation of Savate, French Boxing and Associated Disciplines (FFSBFDA), and concerns as well the boxer who receives as the boxer who executes the strikes during a fight, because it has been shown that the joint forces produced by the impacts during intensive training on a punching bag are a potential source of joint injuries (Girodet et al. 2008). For that purpose, the FFSBFDA wished to evaluate the mechanical characteristics of different French boxing gloves. As no specific standard exists for this kind of equipment, the impact test described in the norm NF 13277-2 for martial arts individual safety devices was used (Norme 2005). This norm prescribes an incident kinetic energy of only 3 J, whereas the energies measured during actual strike conditions with FFSBFDA boxers can reach much higher values (Girodet et al. 2009). Impact tests were thus performed with three incident kinetic energies (3, 10, 20 J), in order to remain within the measurement limits of the testing bench.

Drag force mechanical power during a propulsion cycle on a manual wheelchair

In this case, Fb is measured by a “drag-test” where the subject is sitting upright on the wheelchair (van der Woude et al. 1986), and Vw is approximated by the average treadmill or roller velocity. Some authors, however, have shown that both wheelchair speed (Coutts 1990, Moss et al. 2005, de Saint Rémy 2005) and braking force (de Saint Rémy 2005, Sauret et al. 2006) were not constant along the propulsion cycle. These latter results let suppose that mechanical power of wheelchair propulsion should not be constant during the cycle. That hypothesis has been investigated and three calculation methods of drag force mechanical power have been compared in this study.

Computing wheelchair drag force from the system's total weight value and distribution

A 3-D surface equation was used to estimate changes of the resultant braking forces (F b ) during real life conditions of manual wheelchair locomotion from the weight of the system (W) and its relative fore-and-aft distribution (D) on the front castors due to the subject movement.