Estimation of finger muscle tendon tensions and pulley forces during specific sport-climbing grip techniques

The present work displayed the first quantitative data of forces acting on tendons and pulleys during specific sport-climbing grip techniques. A three-dimensional static biomechanical model was used to estimate finger muscle tendon and pulley forces during the "slope" and the "crimp" grip. In the slope grip the finger joints are flexed, and in the crimp grip the distal interphalangeal (DIP) joint is hyperextended while the other joints are flexed. The tendons of the flexor digitorum profundus and superficialis (FDP and FDS), the extensor digitorum communis (EDC), the ulnar and radial interosseus (UI and RI), the lumbrical muscle (LU) and two annular pulleys (A2 and A4) were considered in the model. For the crimp grip in equilibrium conditions, a passive moment for the DIP joint was taken into account in the biomechanical model. This moment was quantified by relating the FDP intramuscular electromyogram (EMG) to the DIP joint external moment. Its intensity was estimated at a quarter of the external moment. The involvement of this parameter in the moment equilibrium equation for the DIP joint is thus essential. The FDP-to-FDS tendon-force ratio was 1.75:1 in the crimp grip and 0.88:1 in the slope grip. This result showed that the FDP was the prime finger flexor in the crimp grip, whereas the tendon tensions were equally distributed between the FDP and FDS tendons in the slope grip. The forces acting on the pulleys were 36 times lower for A2 in the slope grip than in the crimp grip, while the forces acting on A4 were 4 times lower. This current work provides both an experimental procedure and a biomechanical model that allows estimation of tendon tensions and pulley forces crucial for the knowledge about finger injuries in sport climbing.

Maximal resultant four fingertip force and fatigue of the extrinsic muscles of the hand in different sport climbing finger grips

This study investigates the effect of simulated sport climbing finger grips on the resultant four fingertip force and the rate of fatigue of finger flexor muscles. Six elite sport climbers sat on a chair with the right forearm placed in a handgrip dynamometer modified so that only the fingertips applied direct force. They were asked to perform three maximal voluntary contractions (MVC). After ten minutes, they had to reach 80 % of the peak MVC intermittently with a 5 s contraction followed by 5 s of rest for 20 repetitions. Two common sport climbing finger grips were tested: the "slope" grip and the "crimp" grip. In the "crimp" grip, the distal interphalangeal joint (DIP) is hyper-extended and the proximal interphalangeal joint (PIP) is flexed from 90 degrees to 100 degrees . In the "slope" grip, DIP is flexed from 50 degrees to 70 degrees and PIP is flexed just slightly. The surface EMG of the hand extrinsic flexors and the maximal resultant four fingertip force were recorded. Results show that the maximal resultant four-fingertip force does not depend on the type of finger grips (on average 420 N, p > 0.05). EMG median frequency of finger flexor muscles and resultant four fingertip force rate decrease are similar between both sport climbing finger grips (p > 0.05). This shows that the fatigue rate is not dependent upon the sport climbing finger grips. In conclusion, the results suggest that the use of the "crimp" or the "slope" grip does not provide any benefit with respect to muscular fatigue in sport climbing.

Finger flexors fatigue in trained rock climbers and untrained sedentary subjects

The present series of experiments were conducted to access the surface EMG frequency parameters during repeated fingertip isometric contractions to determine if they can be used as a fatigue index under specific grip used in rock climbing. Electromyograms of the finger flexors and extensors were characterised in ten elite climbers and ten non-climbers. The exercise consisted in reaching 80 % of maximal isometric finger force as quickly as possible intermittently with a 5-s contraction followed by 5-s of rest until exhaustion (i. e. when the subject was unable to maintain 80 - 70 % MVC force range for the 5 s). The results clearly indicate that expert climbers performed significantly greater fingertip force than sedentary subjects (420 +/- 46 N vs. 342 +/- 56 N). This force was maintained during twelve repetitions (12.88 +/- 4.96) in sedentary subjects, whereas the climbers maintained the force during nineteen repetitions (19.33 +/- 4.84). The median frequency of both the flexor and extensor EMG power spectra decreased during fatiguing isometric contractions, but at different rates in climbers and non-climbers. In non-climbers, the results replicated previous findings, whereas in climbers the results were novel.

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

OBJECTIVE

To study the forces applied by each finger in different joint postures simulating rock climbing gripping postures.

DESIGN

Subjects in sitting posture applied fingertip forces perpendicular to horizontal force sensors in three different finger postures.

BACKGROUND

Data 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.

METHODS

Six 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.

RESULTS

The 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.

CONCLUSIONS

The 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.

RELEVANCE

The analysis of force sharing among the fingers during different joint postures mimicking rock climbing is essential to a better understanding of finger injuries.