Biology subjects

Ramdani, S.

Publications and source records attributed to Ramdani, S..

3 recordsLinked to original sources

bioRxiv2026

From linear to nonlinear gait measures: validity of a multi-view markerless motion capture system

Markerless motion capture offers a practical alternative to marker-based optoelectronic systems, yet validation studies have focused almost exclusively on linear gait measures. Nonlinear measures of gait dynamics, sensitive to the fine temporal structure of locomotor signals, remain unvalidated in markerless systems. This study assessed the concurrent validity of a three-camera markerless system against a 15-camera optoelectronic system across four treadmill speeds in 22 healthy adults. Inter-system agreement was evaluated for spatiotemporal parameters (mean, variability, detrended fluctuation analysis [DFA] scaling exponents) and for joint angle and trunk acceleration time series (maximum Lyapunov exponents, sample entropy, Attractor Complexity Index [ACI]). Temporal measures reached near-perfect agreement, and spatial measures showed good to excellent agreement with small speed-dependent positive biases. Sagittal-plane joint kinematic waveforms were compared using statistical parametric mapping, with root-mean-square error (RMSE) reported for significant intervals. Agreement was best at the hip, with knee and ankle showing comparable, higher error (RMSE: 1.2-3.0{degrees} hip, 3.7-5.5{degrees} knee and 3.8-5.1{degrees} ankle). ACI demonstrated moderate to good agreement across all joints and good agreement across trunk acceleration directions. Most DFA scaling exponents for step-based series supported group-level comparisons: both measures are usable for markerless assessment of gait's nonlinear dynamics. Maximum Lyapunov exponents and sample entropy showed lower absolute agreement: at the hip and knee, they preserved inter-individual ranking and remained usable for within-system group comparisons, but agreement collapsed at the ankle and for trunk sample entropy, indicating these measures still need refinement. These findings define a tiered, measure-specific scope for markerless gait analysis, extending validation beyond spatiotemporal parameters.

bioengineering↗

bioRxiv2026

Broadband gamma-band EEG changes during magnetophosphene perception induced by 20 Hz magnetic field stimulation

ObjectiveMagnetophosphenes are visual percepts induced by extremely low-frequency magnetic fields (ELF-MF; <300 Hz), yet the EEG expression of suprathreshold magnetophosphene-inducing stimulation remains poorly characterized and is not reliably captured by classical low-frequency markers. We tested whether suprathreshold 20 Hz tAMS is accompanied by broadband high-frequency EEG changes rather than focal oscillatory effects. ApproachEEG was recorded in N=13 healthy volunteers during 20 Hz sinusoidal magnetic-field exposure delivered using transcranial alternating magnetic stimulation (tAMS) in a global-head configuration. Three conditions were analyzed: no exposure (0 mT), subthreshold (5 mT), and suprathreshold (50 mT). Gamma-band activity (30-80 Hz) was quantified using complementary spectral approaches, including aperiodic-adjusted gamma power. Main resultsPerception reports sharply dissociated the three conditions, with frequent perception at 50 mT only. Suprathreshold stimulation was associated with spatially distributed increases in gamma-band activity over frontal and occipito-parietal electrodes. These effects persisted after aperiodic correction using two independent parameterization methods and did not exhibit a consistent narrowband peak, indicating broadband high-frequency changes. No focal power change over primary occipital electrodes remained significant after Bonferroni correction. SignificanceSuprathreshold magnetophosphene-inducing stimulation is not reliably captured by focal low-frequency EEG markers but is accompanied by distributed broadband high-frequency activity. Because stimulation intensity and perceptual reports were strongly coupled, these effects should be interpreted as EEG correlates of a suprathreshold stimulation-perception state rather than as isolated markers of perception.

neuroscience↗

bioRxiv2025

Challenging the loss of complexity theory: insights from the neuromuscular system in chronic obstructive pulmonary disease

BackgroundAccording to the "loss of complexity" theory, aging and disease are expected to reduce complexity of physiological outputs, thereby limiting the systems adaptability. However, it remains unclear whether this concept applies to the neuromuscular system in people with chronic obstructive pulmonary disease (pwCOPD). This study aimed to challenge the loss of complexity hypothesis by assessing the regularity, as well as the steadiness and the accuracy, of force production during submaximal isometric contractions in pwCOPD compared to healthy individuals. MethodsSeventeen pwCOPD and seventeen age- and sex-matched healthy participants performed submaximal isometric contractions of the knee extensors at six target forces, ranging from 10 to 60% of their maximal voluntary contraction (MVC). Regularity of force signals was assessed using sample entropy (SampEn) and percentage of determinism (DET) from the recurrence quantification analysis. Steadiness and accuracy were quantified using the coefficient of variation (CV) and the root-mean-square error (RMSE), respectively. ResultsPwCOPD exhibited 26.5% lower MVC than healthy individuals. Despite this muscular weakness, no significant main effect of group or interaction effect (group x contraction intensity) was observed for SampEn, DET, CV and RMSE, suggesting a preserved force control in pwCOPD at all assessed force levels. ConclusionOur results indicate that the loss of complexity theory may not apply in moderate COPD, at least for the neuromuscular system. These findings suggest that neuromuscular alteration associated with COPD may not be sufficient to impair the complexity of force output, questioning the universality of the loss of complexity theory.

physiology↗