Finger flexor and extensor muscles load sharing: Effect of the climbing grip technique

Rock climbing requires significant fingertip flexion force generated using two well identified classical gripping techniques: the crimp and slope grips. Although these grips are biomechanically relevant, few methods allow for precise evaluation of individual agonist and antagonist muscle contributions. This study aimed to use Shear Wave Elastography (SWE) to compare flexor digitorum profundus (FDP), flexor digitorum superficialis (FDS), and extensor digitorum communis (EDC) muscle contraction between crimp and slope grips during submaximal isometric flexion fingertip force exertion. Additionally, the repeatability of SWE measurements was assessed. Forty-six experienced climbers performed isometric ramp contractions in both grip types. The shear modulus was quantified using SWE and synchronised with fingertip force data from a custom-built ergometer. Repeatability analysis showed moderate to excellent reliability (ICC: 0.62-0.83) despite notable intra-individual variability (SEM: 10-23 kPa), likely arising from probe positioning conditions. These findings support the reliability of SWE for assessing functional muscle mechanics, although caution is warranted in interpreting shear modulus differences. FDP displayed greater shear modulus in slope grip, while the FDS was stiffer in crimp grip, reflecting grip-dependent muscle recruitment. In slope grip, early and substantial force production by the FDP appears essential for stabilising the distal interphalangeal (DIP) joint and generating flexion force at the fingertip. In the crimp grip, the FDS contributes more significantly to force production, likely due to its advantageous moment arm at the proximal interphalangeal (PIP) joint. Finally, EDC shear modulus increased with fingertip force in both grips, indicating co-contraction. This effect was more pronounced in slope grip, likely reflecting a greater stabilisation demand when passive joint constraints are reduced.