Biology subjects

Kistemaker, D. A.

Publications and source records attributed to Kistemaker, D. A..

4 recordsLinked to original sources

bioRxiv2025

Accuracy of experimentally estimated muscle properties: Evaluation and improvement using a newly developed toolbox

The mechanical behaviour of a muscle-tendon complex depends on properties such as the force-length relationships, the force-velocity relationship, and the excitation dynamics. Quick-release and step-ramp experiments are commonly used to estimate these properties. The accuracy of these methods is unclear, as the actual values of these properties are unknown in experiments on real muscle. We conducted a modelling study using a Hill-type muscle-tendon complex model with literature-derived parameter values and simulated quick-release, step-ramp, and isometric experiments. From the simulated experiments, we assessed how accurately the models parameter values could be retrieved. Using a method traditionally used in literature, the series elastic element stiffness was underestimated by ~35%, due to the incorrect assumption that muscle fibres do not shorten during quick releases. Consequently, this yielded an overestimation of the excitation dynamics activation time constants of ~20%. We developed an improved method that accounted for muscle fibre length shortening during quick releases. Using our improved method, all parameter values closely matched their actual values. A sensitivity analysis showed that the most critical parameters were robust to perturbations in experimental data. Lastly, we compared Hill-type MTC model predictions against in situ data from three rat m. gastrocnemius medialis muscles. Predictions based on parameters from the improved method showed closer agreement than those based on the traditional method -- both for quick-release, step-ramp, and isometric experiments, as well as for independent stretch-shortening cycles. In conclusion, the improved method enables more accurate estimates of muscle-tendon complex properties, addressing limitations of the traditionally used method.

physiology↗

bioRxiv2025

Maximising average mechanical power output during stretch-shortening cycles of rat medial gastrocnemius muscle

The average mechanical power output (AMPO) during a stretch-shortening cycle produced by a muscle depends on muscle length and stimulation over time. While the effects of cycle frequency and muscle length excursion on AMPO are well-known, several questions remain about the effects of muscle length and stimulation over time on the maximal attainable AMPO. For example, which precise muscle length and stimulation over time yield maximal AMPO? In situ experiments are inherently limited to a finite set of muscle length and stimulation over time. To overcome this limitation, we combined in situ experiments on rat m. gastrocnemius medialis with Hill-type muscle modelling. We first performed dedicated trials to estimate the muscle-tendon-complex (MTC) properties of each rat. Subsequently, we performed various stretch-shortening cycles with substantial differences in cycle frequency, shortening-to-lengthening time ratio and MTC length excursion. Model-predicted AMPO correlated nearly perfect with experimentally measured AMPO (r2 > 0.98). This justified further exploration using the Hill-type MTC model. Using the Hill-type MTC model, we predicted that AMPO peaks at a cycle frequency of 3.5 Hz, with a shortening-to-lengthening time ratio of 6:1 and an MTC length excursion of 8 mm. Notably, cycle frequency and MTC length excursion showed a strong interaction: increasing one necessitated a decrease in the other to maximise AMPO. By contrast, the optimal shortening-to-lengthening time ratio remained remarkably constant across all tested combinations of cycle frequency and MTC length excursion. This shows that muscles should spend substantially more time shortening than lengthening to maximise AMPO.

physiology↗

bioRxiv2025

Mechanical efficiency during sub-maximal cycling is underestimated because negative muscular power is ignored

The in vivo mechanical efficiency of muscles has often been estimated during sub-maximal cycling. In this approach, it has implicitly been assumed that the average amount of positive mechanical muscle power equals the average mechanical power output, i.e., that no power is dissipated by muscles. Here, we investigated the validity of this assumption using an optimal control musculoskeletal model. We identified optimal muscle stimulation patterns for 4 cadences (60, 80, 100 and 120RPM) and 5 levels of average mechanical power output (50, 100, 150, 200 and 250W). We found that the amount of negative mechanical muscular power was substantial, with the average across all conditions being -84,6W (56,4%). The amount of negative mechanical muscular power was found to increase with increasing cadence and was independent of the average mechanical power output. To investigate the effect of negative muscular power on in vivo estimates of the muscular efficiency, we used our simulation results to correct gross efficiencies measured during sub-maximal cycling. The resulting increases in the gross efficiency were substantial, with the average increasing from 16.9% to 27.5%. These results suggest that current estimates of the muscular efficiency during sub-maximal cycling underestimate the true muscular efficiency.

physiology↗

bioRxiv2025

Simultaneous stabilizing feedback control of linear and angular momentum in human walking

Stabilizing bipedal gait is mechanically challenging. To analyze how gait is stabilized, previous studies have focused on the control of the body center of mass (CoM). These studies often linked deviations in linear momentum of the CoM to subsequent shifts in position of the center of pressure (CoP), or of the foot, relative to the COM, and interpreted these as stabilizing responses to correct linear CoM momentum. Mechanically, however, CoP shifts do not cause changes of linear CoM momentum, whereas they do cause changes in whole-body angular momentum. We hypothesized that experimentally observed correlations between CoP to CoM distance and horizontal ground reaction forces are related to the need to control both linear and whole-body angular momentum. We show that, in human walking, linear and angular momentum follow quasi-periodic functions with similar periodicity and phase. Combining the equations of linear and rotational motion for a system of linked rigid segments shows that, in this case, the horizontal distance between CoP and CoM should be correlated to horizontal force in the corresponding direction. This suggests that linear and angular momentum are simultaneously controlled and may explain the success of preceding studies that correlated CoM states to CoP or foot locations. Regression models fitted to experimental data of participants walking at normal and slow speeds showed that deviations in horizontal ground reaction forces and in moments of the ground reaction force about the sagittal and transverse axes could be predicted from deviations in the preceding linear and angular momentum respectively. Our analyses support that linear and angular momentum are indeed controlled simultaneously in human walking.

biophysics↗