Biology subjects

Mersmann, F.

Publications and source records attributed to Mersmann, F..

4 recordsLinked to original sources

bioRxiv2023

Speed-specific optimal contractile conditions of the human soleus muscle from slow to maximum running speed

The soleus is the main muscle for propulsion during human running but its operating behavior across the spectrum of physiological running speed is currently unknown. This study investigated experimentally the soleus muscle activation patterns and contractile conditions for force generation, power production and efficient work production (i.e. force-length potential, force-velocity potential, power-velocity potential and enthalpy efficiency) at seven running speeds (3.0 m/s to individual maximum). During submaximal running (3.0 to 6.0 m/s), the soleus fascicles shortened close to optimal length and at a velocity close to the efficiency-maximum, two contractile conditions for economical work production. At higher running speeds (7.0 m/s to maximum), the soleus muscle fascicles still operated near optimum length, yet the fascicle shortening velocity increased and shifted towards the optimum for mechanical power production with a simultaneous increase in muscle activation, providing evidence for three cumulative mechanisms to enhance mechanical power production. Using the experimentally-determined force-length-velocity potentials and muscle activation as inputs in a Hill-type muscle model, a reduction in maximum soleus muscle force at speeds [≥]7.0 m/s and a continuous increase in maximum mechanical power with speed was predicted. The reduction in soleus maximum force was associated with a reduced force-velocity potential. The increase in maximum power was explained by an enhancement of muscle activation and contractile conditions until 7.0 m/s, yet at the maximal running speed mainly by increased muscle activation. Summary statementThe study provides experimental evidence that the human soleus muscle favors contractile conditions for economical work production during submaximal running and for enhancing mechanical power production during maximal running speed.

physiology↗

bioRxiv2022

Contractile work and biarticular mechanisms of the triceps surae muscles facilitate net ankle mechanical work at high walking speeds

Increasing walking speed is accompanied by an enhancement of the mechanical power and work performed at the ankle joint despite the decrease of the intrinsic muscle force potential. We measured Achilles tendon (AT) elongation and, based on an experimentally determined AT-force-elongation relationship; we quantified AT-force as a proxy of the triceps surae muscle force at four walking speeds (slow 0.7 m.s-1, preferred 1.4 m.s-1, transition 2.0 m.s-1 and maximum 2.6{+/-}0.3 m.s-1). Further, we investigated the mechanical power and work of the triceps surae muscles at the ankle joint (TSA) and the mechanical power and work of the biarticular gastrocnemii at the ankle and knee joint. We found a ~21% decrease of maximum AT-force at the two higher speeds compared to the preferred; however, the net TSA-work increased as a function of walking speed. An earlier plantarflexion accompanied by increased activation of the triceps surae muscles and a knee-to-ankle energy transfer via the biarticular gastrocnemii enhanced the net TSA-mechanical work by 1.7 and 2.4-fold in the transition and maximum walking speeds, respectively. Our findings provide first time evidence for different mechanistic participation of the monoarticular soleus muscle and the biarticular gastrocnemii for the speed-related enhancement of net TSA-work.

bioengineering↗

bioRxiv2021

Muscle-specific economy of force generation and efficiency of work production during human running

Human running features a spring-like interaction of body and ground, enabled by elastic tendons that store mechanical energy and facilitate muscle operating conditions to minimize the metabolic cost. By experimentally assessing the operating conditions of two important muscles for running, the soleus and vastus lateralis, we investigated physiological mechanisms of muscle energy production and muscle force generation. Results showed that the soleus continuously shortened throughout the stance phase, operating as energy generator under conditions that were found to be optimal for work production: high force-length potential and enthalpy efficiency. The vastus lateralis promoted tendon energy storage and contracted nearly isometrically close to optimal length, resulting in a high force-length-velocity potential beneficial for economical force generation. The favorable operating conditions of both muscles were a result of an effective length and velocity-decoupling of fascicles and muscle-tendon unit mostly due to tendon compliance and, in the soleus, marginally by fascicle rotation.

biophysics↗

bioRxiv2020

Quantifying mechanical loading and elastic strain energy of the human Achilles tendon during walking and running

The purpose of the current study was to assess Achilles tendon (AT) mechanical loading and strain energy during locomotion using a new in vivo approach for measuring AT length that considers the AT curve-path shape. Eleven participants walked at 1.4 m/s and ran at 2.5 m/s and 3.5 m/s on a treadmill. AT length, defined as the distance between its origin at the gastrocnemius medialis myotendinous junction (MTJ) and the calcaneal insertion, was determined experimentally by integrating kinematics and ultrasound analysis. Small foil markers were placed on the skin covering the AT path from the origin to the insertion, and the MTJ, tracked using ultrasonography, was projected to the reconstructed skin to account for their misalignment. Skin-to-bone displacements were assessed during a passive rotation (5 {degrees}/s) of the ankle joint and considered in the calculation of AT length. Force and strain energy of the AT during locomotion were calculated by fitting a quadratic function to the experimentally measured tendon force-length curve obtained from maximum voluntary isometric contractions. Maximum AT strain and force were affected by speed (p<0.05, ranging from 4.0 to 4.9% strain and 1.989 to 2.556 kN), yet insufficient in magnitude to be considered an effective stimulus for tendon adaptation. Further, we found a recoil of elastic strain energy at the beginning of the stance phase of running (70-77 ms after touch down) between 1.7 {+/-}0.6 and 1.9 {+/-}1.1 J, which might be functionally relevant for running efficiency. Summary statementA new accurate in vivo approach to assess Achilles tendon strain, force and strain energy during locomotion.

bioengineering↗