Franck Quaine

Influence of steep gradient supporting walls in rock climbing: biomechanical analysis

This study analyses the reaction forces and variations of rock climbing in vertical and overhanging positions. Subjects voluntarily released their right foot and regained equilibrium. In the overhanging position the quadrupedal state was characterised by a significant involvement of the arms to prevent fall. Moreover, the horizontal forces applied to the holds were less important, which suggests that equilibrium was easier to maintain than in the vertical position. The tripedal state was characterised by less extensive contralateral supporting force transfer on the remaining holds in the overhanging position, which reinforces safety.

Effect of simulated rock climbing finger postures on force sharing among the fingers

OBJECTIVEnTo study the forces applied by each finger in different joint postures simulating rock climbing gripping postures.nnnDESIGNnSubjects in sitting posture applied fingertip forces perpendicular to horizontal force sensors in three different finger postures.nnnBACKGROUNDnData provided by the literature indicate that middle and ring finger are commonly injured. However, no quantitative assessment of the forces applied by each finger related to the joint postures has been made.nnnMETHODSnSix elite rock climbers performed finger flexion in a single-finger task and a four-finger task. The tests were conducted in an extended posture, a curved posture (the joints belonging to the finger were flexed) and an intermediate posture (the joints were flexed, except the distal one which was fully extended). Each fingertip force was expressed in absolute value and in percentage of the maximal force capacity of the finger.nnnRESULTSnThe greater force was applied by the middle finger (20.8 N), whatever the posture. The relative involvement amounted to 105% for the ring finger in the curved posture.nnnCONCLUSIONSnThe great force applied by the middle finger and the great relative involvement of the ring finger in the curved posture seem to be the main factors of injuries of these fingers.nnnRELEVANCEnThe analysis of force sharing among the fingers during different joint postures mimicking rock climbing is essential to a better understanding of finger injuries.

Effect of a leg movement on the organisation of the forces at the holds in a climbing position 3-D kinetic analysis

Abstract This paper describes three-dimensional force data collected during postural shifts performed by individuals simulating rock climbing skills. Starting from a quadrupedal vertical posture, six expert climbers had to release their right footholds and maintain the posture for a few seconds. The analysis of the vertical and the horizontal forces (lateral and antero-posterior forces) applied on the holds was performed before, during and after the onset of the voluntary movement. The results show that the vertical and the horizontal force changes were initiated in synchrony at the same hold. Furthermore, the changes in the forces occurred before the release of the leg. Therefore, they were not a response to, but preparatory for postural change. The force variations were characterized by loadings of the vertical forces and by loadings and unloadings of the horizontal forces. This type of force variation on the holds and their timings seemed necessary to create the dynamic conditions for the onset of the voluntary movement and to counteract the perturbations due to this movement, which balanced the climber on the wall.

Mechanical effect of additional supports in a rocking on heels movement

This study examined the influence of the addition of handles on postural adjustments associated to a rocking on heels movement. Upper and lower limb muscle EMG activities were recorded and the forces applied to the handles and beneath the feet were measured. Without handles, the anticipatory activation of the Gastrocnemius Medialis displaced the COP forwards, enabling the backward shift of the CG required to rock back on heels. This anticipatory postural activity disappeared with handles and was substituted by an EMG activity on the upper limbs. This activity engendered a forward and downward push on the handles, which largely contributed to create the dynamic conditions required to perform the movement.

Musculo-tendinous stiffness of head-neck segment in the sagittal plane: An optimization approach for modeling the cervical spine as a single-joint system

Despite the multi-linked architecture of the cervical spine, all previous studies that have made estimations of mechanical properties of the neck have considered the head-neck segment as a rigid link, with a fixed center of rotation at C7. The aim of this study was to consider the head-neck segment as a changeable geometry system for locating the resultant center of rotation and for calculating the musculo-tendinous stiffness by the quick-release method. Head kinematics during quick-releases was analyzed by recording the trajectory of surface markers. With an optimization procedure, the position of the resultant center of rotation of the head-neck segment was estimated. Thereafter, the angular displacement and acceleration of the head, together with the isometric torque developed by the cervical muscles were used to calculate the segments stiffness. The results showed a consistent center of rotation and a significant increase of the musculo-tendinous stiffness with increasing torque.

The role of anticipatory postural adjustments in a rocking on heels movement.

We studied the anticipatory postural adjustments (APAs) associated with a voluntary rocking on heels movement performed in a self-paced manner. Ground reaction forces and the EMG activity of the leg muscles were recorded. Such a movement shifted the centre of gravity (CG) backwards, due to APAs on the lower limbs. It is generally assumed that APAs only generate corrections in the opposite direction to the perturbation due to the focal movement. However, our study shows that APAs, by creating the initial backward oriented impulse, displace the CG backwards and generate the dynamic conditions required to move.

Influence of Cervical Muscle Fatigue on Musculo-Tendinous Stiffness of the Head-Neck Segment during Cervical Flexion.

Aim The aim of this study is to determine if the fatigue of cervical muscles has a significant influence on the head-neck segment musculo-tendinous stiffness. Methods Ten men (aged 21.2 ± 1.9 years) performed four quick-release trials of flexion at 30 and 50% MVC before and after the induction of muscular fatigue on cervical flexors. Electromyographic activity was recorded on the sternocleidomastoids (SCM) and spinal erectors (SE), bilaterally. Musculo-tendinous stiffness was calculated through the quick-release method adapted to the head-neck segment. Results We noticed a significant linear increase of the head-neck segment musculo-tendinous stiffness with the increase of exertion level both before (P < 0.0001) and after the fatigue procedure (P < 0.0001). However, this linear relationship was not different before and after the fatigue procedure. EMG analysis revealed a significant increase of the root mean square for the right SCM (P = 0.0002), the left SCM (P < 0.0001), the right SE (P < 0.0001), and the left SE (P < 0.0001) and a significant decrease of the median power frequency only for the right (P = 0.0006) and the left (P = 0.0003) SCM with muscular fatigue. Discussion We did not find significant changes in the head-neck segment musculo-tendinous stiffness with fatigue of cervical muscles. We found a significant increase in EMG activity in the SCM and the SE after the induction of fatigue of the SCM. Our findings suggest that with fatigue of cervical flexors, neck muscle activity is modulated in order to maintain the musculo-tendinous stiffness at a steady state.

In vivo Neck Musculo-Tendinous Stiffness in Response to Quick-Releases

This study was designed to assess musculo-tendinous stiffness of the head-neck segment in response to quick-release in flexion and extension. Musculo-tendinous stiffness of the neck was calculated using analysis of head kinematics with optimization procedure during the first 30 ms after the acceleration peak following the release at different exertion levels (20 % to 70 % MVC). Results showed a linear relationship between torque and musculo-tendinsous stiffness for flexion (R = 0.82, P < 0.5) and extension (R = 0.69, P < 0.05). Resultas shows also an increase of moment of inertia with torque. Correlation between stiffness and torque indicates that quick-release perturbations applied to the head associated with optimization procedure to assess head kinematics provide an attractive approach to investigate head-neck musculo-tendinous stiffness. In addition, changes noticed on head-neck moment of inertia shows that mechanical properties evaluated in this study could be altered by modifications of geometry of the corporal segment induced by exertion level.