Biology subjects

Maas, H.

Publications and source records attributed to Maas, H..

7 recordsLinked to original sources

bioRxiv2026

The Limited Range of Motion of the Knee Does Not Fully Explain the Altered Neural Control of Plantar Flexors During Gait in Non-Neurological Knee Flexion Contracture

Knee flexion contracture (KFC) may occur in the late stages of arthropathies, including osteoarthritis and haemophilic arthropathy. The impact of KFC on neuromuscular control remains unclear, particularly for the affected ankle plantar flexors. Surface electromyography (EMG) is widely used to assess muscle activation patterns, whereas intermuscular (EMG-EMG) coherence provides insight into common neural input. In this study we compared the neural control of ankle plantar flexors during gait between individuals with haemophilia and KFC (chronic; n = 8), and healthy individuals without (control; n = 15) and with an artificial constraint (artificial; n = 15). Bipolar EMG from plantar flexors was recorded during 30-m overground walking (1 m/s). Intermuscular coherence was estimated at 8-60 Hz during the stance phase and significance was determined using a permutation method. The chronic group showed greater knee flexion than controls (24-29 deg vs 2-20 deg), higher EMG amplitude at foot contact, and increased intermuscular coherence in the alpha (8-12 Hz) and beta (12-30 Hz) bands at mid-stance. Despite comparable sagittal knee kinematics between constrained conditions (chronic: 24-29 deg; artificial: 20-32 deg), early-stance EMG amplitude and mid-stance beta-band intermuscular coherence were higher in the chronic group across plantar-flexor pairs. Increased plantar-flexor activation in the chronic group suggests higher neural drive, while higher intermuscular coherence reflects greater common input to the plantar flexors. These findings indicate that limited ROM alone does not explain the altered neural control of plantar flexors, suggesting neural adaptations associated with non-neurological chronic KFC.

neuroscience↗

bioRxiv2026

Effects of lumbar disc injury and nociception on trunk motor control during rat locomotion

Intervertebral disc (IVD) injury is a major cause of low-back pain and can lead to structural deficits and mechanical instability. When the IVD is compromised, neuromuscular compensation by paraspinal muscles, such as the multifidus (MF) and longissimus (ML), is critical for maintaining spine stability. However, it is unknown how IVD injury and its interaction with nociception affect neuromuscular control. This study assessed the effects of IVD injury and additional muscle-derived nociception on trunk motor control during locomotion in a rat model. IVD injury was induced via needle puncture at L4/L5. One week later, hypertonic saline was injected into the lumbar MF to induce nociception. Trunk and pelvic kinematics, bilateral EMG activity of MF and ML were recorded during treadmill locomotion at baseline, one week after IVD injury, and immediately following hypertonic saline injection. Trunk and pelvic kinematics and bilateral muscle activation patterns remained largely consistent across conditions. No significant changes were found in stride duration, pelvic, lumbar and spine angle changes, variability, or movement asymmetry. MF activation was bilaterally synchronized, whereas ML showed left-right alternating activation patterns. Following IVD injury, right MF mean activation and EMG variability increased significantly compared to baseline. When muscle-derived nociception was added in the unstable spine (IVD injury) condition, left MF minimum amplitude was significantly reduced, and instability-related increases in right MF mean activation and variability were attenuated, but not fully reversed. These findings suggest that IVD injury, alone or in combination with muscle-derived nociception, elicits localized neuromuscular adaptations without disrupting the global locomotor patterns.

neuroscience↗

bioRxiv2026

Mechanical and morphological effects of intervertebral disc injury: a systematic review of in vivo animal studies

Intervertebral disc degeneration (IVDD) compromises disc structures and mechanics, yet systematic evaluations of the mechanical responses and their relationship to morphological changes in preclinical models remain limited. This systematic review and meta-analysis synthesized mechanical and morphological alterations following experimental disc injury in in vivo animal models. Searches of MEDLINE, EMBASE and Web of Science databases were conducted in accordance with PRISMA guidelines. Study quality and risk of bias were assessed using modified CAMARADES and SYRCLE tools. Twenty-eight studies were included. Pooled analyses showed significant reductions in stiffness, Youngs modulus, and disc height, and significant increases in range of motion and degeneration grade, indicating both mechanical and structural deterioration. Youngs modulus appeared to be the most sensitive marker of functional degeneration. By contrast, creep and other viscoelastic responses showed non-significant changes. High heterogeneity was evident across studies, reflecting variability in injury models, species, timepoints, and testing methods. Evidence of publication bias was detected in several domains, and moderate methodological quality was noted with overall insufficient blinding and lack of sample size calculations. In vivo animal models of IVDD demonstrate robust and consistent mechanical and morphological degeneration after injury. Youngs modulus is a sensitive mechanical indicator, supporting its use in future preclinical research. Standardization of outcome definitions, methodology, and reporting is essential to improve comparability and enhance translation of preclinical findings to clinical research.

bioengineering↗

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

An in vivo rat lumbar spine instability model induced by intervertebral disc injury

Intervertebral disc (IVD) degeneration is a potential contributor to low-back pain. While experimental IVD injury models have demonstrated IVD structural changes, the early mechanical consequences remain unclear. This study aimed to establish a rat model of lumbar spine instability via IVD injury and assess back musculature adaptations to IVD injury. Thirty-one adult male Wistar rats were assigned to three groups: IVD knife stab lesion (knife), IVD needle puncture (needle), and sham surgery control (control). In the knife and needle groups, L4/L5 IVDs were injured at 14 weeks of age. One-two weeks post-intervention, lumbar multifidus (MF) and medial longissimus (ML) muscles were excised, L4-L5 spinal segments were harvested for mechanical testing, and IVDs were collected for histology. The needle group exhibited lower peak stiffness, peak moment, and hysteresis than controls in flexion, with no difference in lateral bending. IVD height and area did not differ between groups, but the needle group had a smaller nucleus relative to annulus area compared to controls. Morphological changes were observed in both injury groups. The needle group showed higher normalized ML mass, while normalized MF mass was unchanged. In conclusion, a rat model of lumbar spine instability was successfully established via IVD needle injury.

bioengineering↗

bioRxiv2022

PDGFRα+ fibroblasts are a major site of cytomegalovirus replication in vivo and genome maintenance during latency

To date, no herpesvirus has been shown to latently persist in fibroblastic cells. Here, we demonstrate that mouse CMV (MCMV), a {beta}-herpesvirus, persists for the long term and across organs in PDGFR+ fibroblastic cells, with similar or higher genome loads than in the previously known sites of MCMV latency. Whereas MCMV gene transcription in PDGFR+ fibroblastic cells was almost completely silenced at 5 months post-infection, these cells gave rise to reactivated virus ex vivo, arguing that they supported latent MCMV infection. Notably, PDGFR+ fibroblastic cells also supported productive virus replication during primary MCMV infection. Mechanistically, Stat1-deficiency resulted in increased lytic but abolished latent infection of fibroblastic cells in vivo. In sum, fibroblastic cells have a dual role as a site of lytic MCMV replication and a reservoir of latent MCMV in vivo and Stat1 is critically involved in the regulation of MCMV latency.

microbiology↗

bioRxiv2020

The underlying mechanisms of improved balance aftershort- and long-term training in older adults

Training improves balance control in older adults, but the time course and neural mechanisms underlying these improvements are unclear. We studied balance robustness and performance, H-reflex gains, paired reflex depression, and co-contraction duration in ankle muscles after one and ten training sessions in 22 older adults (+65yrs). Mediolateral balance robustness, time to balance loss in unipedal standing on a platform with decreasing rotational stiffness, improved (33%) after one session, with no further improvement after ten sessions. Balance performance, absolute mediolateral center of mass velocity, improved (18.75%) after one session in perturbed unipedal standing and (18.18%) after ten sessions in unperturbed unipedal standing. Co-contraction duration of soleus/tibialis anterior increased (16%) after ten sessions. H-reflex gain and paired reflex depression excitability did not change. H-reflex gains were lower, and soleus/tibialis anterior co-contraction duration was higher in participants with more robust balance after ten sessions, and co-contraction duration was higher in participants with better balance performance at several time-points. Changes in robustness and performance were uncorrelated with changes in co-contraction duration, H-reflex gain, or paired reflex depression. In older adults, balance robustness improved over a single session, while performance improved gradually over multiple sessions. Changes in co-contraction and excitability of ankle muscles were not exclusive causes of improved balance. HighlightsO_LIBalance robustness and balance performance in perturbed unipedal standing was improved after one balance training session, with no further improvement after ten sessions. C_LIO_LIBalance performance in unperturbed unipedal standing was improved after ten sessions C_LIO_LIH-reflex and paired reflex depression did not change after training in unipedal or bipedal standing. C_LIO_LICo-contraction duration of antagonistic ankle muscles increased after ten sessions in perturbed and unperturbed unipedal standing. C_LIO_LIChanges in co-contraction duration and excitability of ankle muscles were not exclusive causes of improved balance. C_LI

neuroscience↗