Biology subjects

Schroll, A.

Publications and source records attributed to Schroll, A..

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↗

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↗

bioRxiv2019

Humans exploit robust locomotion by improving the stability of control signals

Is the control of movement less stable when we walk or run in challenging settings? One might intuitively answer affirmatively, given that adding constraints to locomotion (e.g. rough terrain, age-related impairments, etc.) imply less stable movements. We investigated how young and old humans synergistically activate muscles during locomotion, when different perturbation levels are introduced. Of these control signals, called muscle synergies, we then analyzed the stability over time. Surprisingly, we found that perturbations and older age force the central nervous system to produce more stable signals. These outcomes show that robust locomotion in challenging settings is achieved by increasing the stability of control signals, whereas easier tasks allow for more unstable control.

neuroscience↗

bioRxiv2018

Modular organization of the murine locomotor pattern in presence and absence of sensory feedback from muscle spindles

For exploiting terrestrial and aquatic locomotion, vertebrates must build their locomotor patterns based on an enormous amount of variables. The great number of muscles and joints, together with the constant need for sensory feedback information (e.g. proprioception), make the task of creating and controlling movement a problem with overabundant degrees of freedom. It is widely accepted that the central nervous system might simplify the creation and control of movement. This could happen through the generation of activation patterns, which are common to many different muscles, rather than specific to individual muscles. These activation patterns, called muscle synergies, can be extracted from electromyographic data and describe the modular organization of movement. We extracted muscle synergies from the hindlimb muscle activities of wild type and genetically modified mice, in which sensory feedback from muscle spindles is eliminated. Muscle spindle-deficient mice underwent a modification of the temporal structure (motor primitives) of muscle synergies that resulted in diminished functionality during walking. In addition, both the temporal and spatial components (motor modules) of muscle synergies were severely affected when external perturbations were introduced of when animals were immersed in water. These findings show that group Ia/II sensory feedback from muscle spindles regulates motor function in normal and perturbed walking. Moreover, when group Ib Golgi tendon organ feedback is lacking due to the reduction of gravitational load in conditions of enhanced buoyancy, the modular organization of swimming is almost completely compromised.\n\nSignificance statementLocomotion on land and in water requires the coordination of a great number of muscle activations and joint movements. Moreover, constant feedback about the position of own body parts in relation to the surrounding environment and the body itself (proprioception) is required to maintain stability and avoid failure. The theory of muscle synergies states that the central nervous system might control muscles in orchestrated groups (synergies) rather than individually. We used this concept on genetically modified mice, lacking one of the two classes of proprioceptors. Our results provide evidence that proprioceptive feedback is required by the central nervous system to accurately tune the modular organization of locomotion.

neuroscience↗