Tendon compliance and preload must be considered when determining the in vivo force–velocity relationship from the torque–angular velocity relation

Abstract

In vivo, the force–velocity relation (F–v–r) is typically derived from the torque–angular velocity relation (T–ω–r), which is subject to two factors that may influence resulting measurements: tendon compliance and preload prior to contraction. The in vivo plantar flexors’ T–ω–r was determined during preloaded maximum voluntary shortening contractions at 0–200°/s. Additionally, we used a two factor block simulation study design to independently analyze the effects of preload and tendon compliance on the resulting T–ω–r. Therefore, we replicated the in vivo experiment using a Hill-type muscle model of the gastrocnemius medialis. The simulation results matched a key pattern observed in our recorded in vivo experimental data: during preloaded contractions, torque output of the muscle was increased when compared with non-preloaded contractions from literature. This effect increased with increasing contraction velocity and can be explained by a rapidly recoiling tendon, allowing the contractile element to contract more slowly, thus developing higher forces compared with non-preloaded contractions. Our simulation results also indicate that a more compliant tendon results in increased ankle joint torques. The simulation and the experimental data clearly show that the deduction of the in vivo F–v–r from the T–ω–r is compromised due to the two factors preloading and tendon compliance.

Eccentric exercise ≠ eccentric contraction

“…This is likely to be because MTU elasticity was at its highest among the conditions at MTU-stretch onset, and MTU elasticity took time to decrease as muscle activity and force rose during MTU stretch. Consequently, fascicle length changes depend on MTU series elasticity and muscle activity level as we showed, as well as MTU stretch velocity, similar to muscle-tendon interactions during pre-activated shortening contractions (59). The increased PL along with the observed differences in fascicle kinematics led to both greater joint work and muscle fascicle work, which partly supports our second hypothesis.…”

A 6-week randomized-controlled field study: effect of isokinetic eccentric resistance training on strength, flexibility and muscle structure of the shoulder external rotators in male junior handball players

“…Eccentric training can be interpreted a beneficial form of prevention training due to the rightward shifts in the eccentric torque-angle relationship ( Blazevich et al, 2007 ). This supports the capability of energy absorption and energy transfer to concentric actions ( Mörl et al, 2016 ; Köhler et al, 2022 ; Holzer et al, 2023 ; Köhler and Witt, 2023 ).…”

Determination of muscle shape deformations of the tibialis anterior during dynamic contractions using 3D ultrasound

“…Therefore, in order to ensure more controlled conditions in terms of movement direction and velocity, future studies should include a fixture of the leg which enables only plantarflexion and dorsiflexion movements. The fixation of the leg and the kinematic control of a reproducible cyclic joint movement may be realized by using an isokinetic measurement system, such as an ISOMED ( Holzer et al, 2023 ). Through the possibility of more controlled measurements with less movement artifacts, the deformation gradient of the muscle may be computed.…”