Biology subjects

Bobbert, M. F.

Publications and source records attributed to Bobbert, M. F..

3 recordsLinked to original sources

bioRxiv2026

The impact of ankle immobility on sprint cycling performance: Implications for para-cycling classification

PurposeThe para-cycling classification system aims to minimize the impact of impairments on competition outcomes with the help of scientific evidence. This study investigated the impact of unilateral and bilateral ankle immobility on cycling performance, quantified by the maximal average mechanical power output (AMPO) over one revolution relative to that without ankle immobility. MethodsTen well-trained non-disabled cyclists performed all-out 6-second sprints on a cycle ergometer at 120 rpm under three conditions: without ankle foot orthoses (AFOs), with 1 AFO and with 2 AFOs immobilizing the ankle joint(s). Mechanical power output, pedal forces, cycling kinematics and surface-electromyography were measured. Maximal AMPO; ankle, knee and hip joint AMPO; and the amount of muscle excitation were calculated. ResultsWith 1 AFO and 2 AFOs, respectively, maximal AMPO was 96% (p<0.05) and 91% (p<0.001) of that without AFOs (1188 W). The decrease in maximal AMPO with ankle immobilization was less than the decrease in ankle joint AMPO (126 W decrease with 2 AFOs; p<0.001), due to an increase in hip joint AMPO (69 W increase with 2 AFOs; p<0.05). The amount of muscle excitation was not significantly different across conditions. ConclusionsThese findings provide a first quantitative and mechanistic indication of the impact of ankle immobility on cycling performance, which may offer valuable evidence to support the development of an evidence-based para-cycling classification system.

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↗