Biology subjects

Raiteri, B. J.

Publications and source records attributed to Raiteri, B. J..

11 recordsLinked to original sources

bioRxiv2026

3D ultrasound fascicle tractography for objective muscle architecture analysis.

Muscle architecture shapes muscle function and changes with age, growth, training and disease, yet quantifying three-dimensional (3D) muscle architecture in vivo remains challenging. We introduce a hybrid fascicle tractography approach for freehand 3D ultrasound data that accurately reconstructs 3D muscle fascicles with respect to an objective, anatomically relevant coordinate system defined by the muscle's central aponeurosis. The hybrid approach combines Hessian-based fascicle detection with wavelet-based refinement to generate volumetric fascicle orientations. In a synthetic dataset with known ground truth, fascicle orientations and lengths were estimated with errors of [≤]2{degrees} and ~1.5%, respectively. In vivo, the approach detected physiologically plausible fascicle lengthening in the human tibialis anterior following a passive plantar flexion rotation, whereas diffusion tensor imaging of the same muscle did not. The proposed method enables anatomically relevant, objective and non-invasive quantification of 3D muscle architecture in vivo, providing a practical framework for applications in clinical and applied muscle physiology.

bioengineering↗

bioRxiv2026

Stretch versus shortening contractions subsequently decrease versus increase neural drive to the human tibialis anterior

EMG-based muscle force predictions are often inaccurate following active muscle stretch or shortening because of residual force enhancement (rFE) or depression (rFD), respectively, which can alter the neural drive to a muscle. However, the extent of neural drive modulation due to rFE or rFD remains unknown, making it difficult to correct EMG-based force predictions. Therefore, seventeen participants performed dorsiflexion contractions at 20 and 40% of maximum voluntary torque (MVT) in three conditions: stretch-hold, shortening-hold, and fixed-end reference (REF) conditions. The ankle dorsiflexion torques and angles were matched using dynamometry to the REF condition over a 10-s steady state following a 1-s 25{degrees} stretch or shortening, during which we recorded and decomposed tibialis anterior individual motor unit action potentials from high-density surface EMG recordings to gain insights into neural drive. Normalized EMG amplitudes were 2% lower following stretch and 1 or 3% higher following shortening relative to REF at 20 versus 40% MVT (p[≤].008), respectively. Discharge rates (DRs) from 19 matched motor units per person on average obtained via DEMUSE and MUedit were similar (p=.871). Following stretch and shortening, DRs were [~]1 Hz lower (p[≤].004) and 0 (p=.966) to 1 Hz higher relative to REF (p=.003), respectively. More unique motor units were also detected following shortening versus REF and in REF versus following stretch. These findings indicate that to account for rFE or rFD, neural drive is respectively decreased or increased via reduced or additional motor unit recruitment and DR modulation, with a contraction-intensity specific discharge rate modulation following active shortening.

physiology↗

bioRxiv2025

A passive upper-limb exoskeleton effectively reduces shoulder muscle activity over a large shoulder workspace

Industrial upper-limb exoskeletons are used to offload the upper limb during overhead tasks with the aim of preventing musculoskeletal disorders to the shoulder. Although numerous studies showed reduced shoulder muscle activity during upper-limb exoskeleton use for overhead postures, it remains unknown whether and how upper-limb exoskeletons provide support over a large shoulder workspace beyond overhead work. Therefore, this study evaluated the Ottobock Paexo Shoulder over a large shoulder workspace from overhead to hip height with shoulder abduction and adduction. Upper body kinematics, muscle activity, and subjective user feedback were obtained by three-dimensional motion capture, bipolar surface EMG and questionnaires, respectively, and captured while participants performed static and dynamic work tasks with an electric screwdriver. Participants completed these tasks while 1) not wearing the exoskeleton, 2) wearing a disengaged exoskeleton, with 3) moderate exoskeleton support, and with 4) high exoskeleton support. Exoskeleton support reduced deltoid muscle activity (-9 to -24s%, p[≤].001) in postures with an abducted shoulder or extended elbow, including non-overhead postures. Exoskeleton support modestly decreased shoulder flexion (-3 to -5{degrees}, p[≤].001) and increased shoulder abduction (2 to 5{degrees}, p[≤].032), but the movement patterns during the dynamic task were unaffected. Additionally, exoskeleton-related effects increased with increasing support, but the subjective perception of change also increased, and perceived comfort decreased. Our results indicate that the tested exoskeleton provides support beyond overhead work and that there is a trade-off between exoskeleton support and subjective perception. Accordingly, further optimization of user-exoskeleton interaction is warranted for long-term prevention of musculoskeletal disorders in overhead workers.

physiology↗

bioRxiv2024

Fascicle stretch during partial muscle deactivation does not enhance the human tibialis anterior's subsequent neuromechanical output

We were interested in whether stretching the muscle via elastic tissue recoil during partial muscle deactivation could trigger stretch-induced mechanisms that subsequently enhance the muscles steady-state neuromechanical output. Two torque-controlled experiments were conducted to test this aim. In Experiment 1, fifteen participants performed fixed-end dorsiflexion contractions to a moderate or high-then-moderate level with torque-drop rates of 0, 10, 20, 40, or 80% MVC{middle dot}s-1 from 60-40% MVC, while net ankle joint torque, tibialis anterior (TA) muscle activity level, and TA ultrasound images were recorded. The same measurements were performed in Experiment 2, which tested twelve different participants who performed fixed-end contractions to three reference levels or to a higher-then-lower level (with torque-drop amplitudes of 85-45, 85-30, and 85-15% MVC at 20% MVC{middle dot}s-1). Increased fascicle shortening amplitudes (Experiment 1: 1-2 mm, p[≤].049; Experiment 2: 5-10 mm, p<.001) to initially higher joint torques and different fascicle stretch rates (0.6 to 4.3 mm{middle dot}s-1, p[≤].041) and amplitudes (4-9 mm; p[≤].001) did not significantly affect TAs subsequent muscle activity level relative to the reference contractions at similar joint torques (0-1% MVC, p[≥].659 and p[≥].626). However, the torque steadiness relative to the reference conditions was significantly reduced after the 85-15% MVC (p=.036) and 85-30% MVC (p=.036) torque drops. Consequently, the history of force production affected the control of muscle force more than TAs steady-state neuromuscular output. These findings indicate that assessing fascicle kinematics concurrently with motor unit behavior during fixed-end contractions with large torque drops might provide unique insights into the neuromechanical contributors to impaired torque control. NEW & NOTEWORTHYThe history of force production affected the subsequent control of dorsiflexion torque more than tibialis anteriors (TAs) neuromuscular output following larger amounts of fascicle stretch during fixed-end contractions. Larger fascicle stretches also reduced the median frequency of TAs EMG signal, which tentatively indicates that the voluntary control of muscle force was altered in the steady state. Together, these findings indicate that voluntary force control might be impaired by stretch-induced and/or activity-level-dependent mechanisms during fixed-end contractions.

physiology↗

bioRxiv2024

The stretch-shortening cycle effect is not associated with cortical or spinal excitability modulations

It is unclear whether cortical and spinal excitability modulations contribute to enhanced SSC performance. Therefore, this study investigated cortical and spinal excitability modulations during and following shortening of stretch-shortening cycle (SSC) contractions compared with pure shortening (SHO) contractions. Participants (N = 18) performed submaximal voluntary plantar flexion contractions while prone on the dynamometer bench. The right foot was strapped onto the dynamometers footplate attachment and the resultant ankle joint torque and crank arm angle were recorded. Cortical and spinal excitability modulations of the soleus muscle were analyzed by eliciting compound muscle actional potentials via electrical nerve stimulation, cervicomedullary motor-evoked potentials (CMEPs) via electrical stimulation of the spinal cord, and motor-evoked potentials (MEPs) via magnetic stimulation of the motor cortex. Mean torque following stretch was significantly increased by 7{+/-}3% (p=0.029) compared with the fixed-end reference (REF) contraction and mean torque during shortening of SSC compared with SHO was significantly increased by 12{+/-}24% (p=0.046). Mean steady-state torque was significantly lower by 13{+/-}3% (p=0.006) and 9{+/-}12% (p=0.011) following SSC compared with REF and SHO, respectively. Mean steady-state torque was not significantly lower following SHO compared with REF (7{+/-}8%, p=0.456). CMEPs and MEPs were also not significantly different during shortening of SSC compared with SHO (p[≥]0.885) or during the steady state of SSC, SHO, and REF (p[≥]0.727). Therefore, our results indicate that SSC performance was not associated with cortical or spinal excitability modulations during or after shortening, but rather driven by mechanical mechanisms triggered during active stretch. Key pointsO_LIA stretch-shortening cycle (SSC) effect of 12% was observed during EMG-matched submaximal voluntary contractions of the human plantar flexors C_LIO_LIThe SSC effect was neither associated with cortical or spinal excitability modulations nor with stretch-reflex activity C_LIO_LIThe SSC effect was likely driven by mechanical mechanisms related to active muscle stretch, which have long-lasting effects during shortening C_LIO_LIResidual force depression following SSC was not attenuated by the long-lasting mechanical mechanisms triggered during active muscle stretch C_LIO_LISteady-state torques were lower following shortening of SSCs versus pure shortening and fixed-end contractions at the same final ankle joint angle, but the torque differences were not correlated with cortical or spinal excitability modulations C_LI

neuroscience↗

bioRxiv2024

UltraTimTrack: a Kalman-filter-based algorithm to track muscle fascicles in ultrasound image sequences

BackgroundBrightness-mode (B-mode) ultrasound is a valuable tool to non-invasively image skeletal muscle architectural changes during movement, but automatically estimating architectural features such as fascicle length remains a major challenge. Existing fascicle tracking algorithms either require time-consuming drift corrections or yield noisy estimates that require post-processing. We therefore aimed to develop an algorithm that tracks fascicles without drift and noise across a range of experimental conditions and image acquisition settings. MethodsWe applied a Kalman filter to combine fascicle length and fascicle angle estimates from existing and openly available UltraTrack and TimTrack algorithms into a hybrid algorithm called UltraTimTrack. We applied the hybrid algorithm to ultrasound image sequences collected from the human medial gastrocnemius of healthy individuals (N=8, 4 women), who performed cyclical submaximal plantar flexion contractions or remained at rest during passive ankle joint rotations at given frequencies and amplitudes whilst seated in a dynamometer chair. We quantified the algorithms tracking accuracy, noise, and drift as the respective mean, cycle-to-cycle, and accumulated between-contraction variability in fascicle length and fascicle angle. We expected UltraTimTracks estimates to be less noisy and to drift less across experimental conditions and image acquisition settings, compared with estimates from its parent algorithms. ResultsThe proposed algorithm had low-noise estimates like UltraTrack and was drift-free like TimTrack across the broad range of conditions we tested. Estimated fascicle length and fascicle angle deviations accumulated to 2.1 {+/-} 1.3 mm (mean {+/-} s.d.) and 0.8 {+/-} 0.7 deg, respectively, over 120 cyclical contractions. Average cycle-to-cycle variability was 1.4 {+/-} 0.4 mm and 0.6 {+/-} 0.3 deg, respectively. In comparison, UltraTrack had similar cycle-to-cycle variability (1.1 {+/-} 0.3 mm, 0.5 {+/-} 0.1 deg) but greater cumulative deviation (67.0 {+/-} 59.3 mm, 9.3 {+/-} 8.6 deg), whereas TimTrack had similar cumulative deviation (1.9 {+/-} 2.2 mm, 0.9 {+/-} 1.0 deg) but greater variability (3.5 {+/-} 1.0 mm, 1.4 {+/-} 0.5 deg). UltraTimTrack was significantly less affected by experimental conditions and image acquisition settings than its parent algorithms. It also performed well on a previously published image sequence from the human tibialis anterior, yielding a smaller root-mean-square deviation from manual tracking (fascicle length: 2.7 mm, fascicle angle: 0.7 deg) than a recently proposed hybrid algorithm (fascicle length: 4.5 mm, fascicle angle: 0.8 deg) and a machine-learning (DL_Track) algorithm (fascicle length: 8.2 mm, fascicle angle: 4.8 deg). ConclusionWe developed a Kalman-filter-based method to improve fascicle tracking from B-mode ultrasound image sequences. The proposed algorithm provides low-noise, drift-free estimates of muscle architectural changes that may better inform muscle function interpretations.

physiology↗

bioRxiv2023

Eccentric exercise is not equal to eccentric contraction

Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series elasticity. Therefore, this study investigated the impact of changing the activation timing and level (i.e., pre-activation) on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were employed to assess muscle fascicle kinematics and muscle activity levels, respectively. While joint kinematics were similar for MTU-stretch-hold contractions, increasing pre-activation increased fascicle shortening and stretch amplitudes (9.9 - 23.2 mm, p [≤] 0.015). This led to increasing positive and negative fascicle work with increasing pre-activation. Despite significantly different fascicle kinematics, similar peak fascicle forces during stretch occurred at similar fascicle lengths and joint angles regardless of pre-activation. Similarly, residual force enhancement (rFE) following MTU stretch was not significantly affected (6.5-7.6 %, p = 0.559) by pre-activation, but rFE was strongly correlated with peak fascicle force during stretch (rrm = 0.62, p = 0.003). These findings highlight that apparent eccentric exercise causes shortening-stretch contractions at the fascicle level rather than isolated eccentric contractions. The constant rFE despite different fascicle kinematics and kinetics suggests that a passive element was engaged at a common muscle length among conditions (e.g., optimal fascicle length). Although it remains unclear whether different fascicle mechanics trigger different adaptations to eccentric exercise, this study emphasizes the need to consider MTU series elasticity to better understand the mechanical drivers of adaptation to exercise. New & NoteworthyApparent eccentric exercises do not result in isolated eccentric contractions, but shortening-stretch contractions at the fascicle level. The amount of fascicle shortening and stretch depend on the pre-activation during the exercise and cannot be estimated from the muscle-tendon unit or joint kinematics. As different fascicle mechanics might trigger different adaptations to eccentric exercise, muscle-tendon unit series elasticity and muscle pre-activation need to be considered when eccentric exercise protocols and designed and evaluated.

physiology↗

bioRxiv2023

Residual force depression is not related to positive muscle fascicle work during submaximal voluntary dorsiflexion contractions in humans

Residual force depression (rFD) following active muscle shortening is commonly assumed to strongly and linearly increase with increasing muscle work, but this has not been systematically tested during voluntary contractions in humans. Using dynamometry, we compared steady-state ankle joint torques (N=16) following tibialis anterior (TA) muscle-tendon unit (MTU) lengthening and shortening to the torque during submaximal voluntary fixed-end dorsiflexion reference contractions (REF) at a matched MTU length and EMG amplitude. B-mode ultrasound revealed that TA fascicle shortening amplitudes were significantly reduced (p<0.001) during MTU lengthening with no preload over small (LENsmall) and medium (LENmedium) amplitudes, respectively, relative to REF. MTU lengthening with a preload over a large (LENlargeP) amplitude significantly (p<0.001) increased fascicle shortening relative to REF, as well as stretch amplitudes relative to LENsmall and LENmedium (p[≤]0.001), but the significant (p[≤]0.028) steady-state fascicle force enhancement relative to REF was similar to LENsmall and LENmedium (3-5%). MTU shortening with and without a preload over small (SHOsmallP/SHOsmall) and large (SHOlargeP/SHOlarge) amplitudes significantly (p<0.001) increased positive fascicle and MTU work relative to REF, but significant (p[≤]0.006) rFD was observed in SHOsmallP and SHOlargeP (7-10%) only. rFD was linearly related to positive MTU work (rrm(47)=0.48, p<0.001), but not positive fascicle work (rrm(47)=0.16, p=0.277). Our findings indicate that MTU lengthening without substantial fascicle stretch enhances steady-state force output, which might be due to less shortening-induced rFD. Our findings also indicate that different amounts of positive fascicle and MTU work induce similar rFD, which cautions against using work to predict rFD during submaximal voluntary contractions.

physiology↗

bioRxiv2022

Residual force enhancement within the human quadriceps is greatest during submaximal stretch-hold contractions at a very long muscle length

Little is known about how muscle length affects residual force enhancement (rFE) in humans. We therefore investigated rFE at short, long, and very long muscle lengths within the human quadriceps and patellar tendon (PT) using conventional dynamometry with motion capture (rFETQ) and a new, non-invasive shear-wave tensiometry technique (rFEWS). Eleven healthy male participants performed submaximal (50% max.) EMG-matched fixed-end reference and stretch-hold contractions across these muscle lengths while muscle fascicle length changes of the vastus lateralis (VL) were captured using B-mode ultrasound. We found significant rFETQ at long (7{+/-}5%) and very long (12{+/-}8%) but not short (2{+/-}5%) muscle lengths, whereas rFEWS was only significant at the very long (38{+/-}27%), but not short (8{+/-}12%) or long (6{+/-}10%) muscle lengths. We also found significant relationships between VL fascicle length and rFETQ (r=0.63, p=.001) and rFEWS (r=0.52, p=.017), but relationships were not significant between VL fascicle stretch amplitude and rFETQ (r=0.33, p=.126) or rFEWS (r=0.29, p=.201). PT shear-wave speed-angle relationships did not agree with estimated quadriceps muscle force-angle relationships, which indicates that estimating PT loads from shear-wave tensiometry might be inaccurate. We conclude that increasing muscle length rather than stretch amplitude contributes more to rFE during submaximal voluntary contractions of the human quadriceps.

physiology↗

bioRxiv2020

Corticospinal drive does not contribute to increased torque production in the presence of residual force enhancement

Following active muscle stretch, muscle force is enhanced, which is known as residual force enhancement (rFE). As earlier studies found apparent corticospinal excitability modulations in the presence of rFE, this study aimed to test whether corticospinal excitability modulations contribute to rFE. Fourteen participants performed submaximal plantar flexion stretch-hold and fixed-end contractions at 30% of their maximal voluntary soleus muscle activity in a dynamometer. During the steady state of the contractions, participants either received subthreshold or suprathreshold transcranial magnetic stimulation (TMS) of their motor cortex, while triceps surae muscle responses to stimulation were obtained via electromyography (EMG), and net ankle joint torque was recorded. B-mode ultrasound imaging was used to confirm muscle fascicle stretch during stretch-hold contractions in a subset of participants. Following stretch of the plantar flexors, an average rFE of 7% and 11% was observed for contractions with subthreshold and suprathreshold TMS, respectively. 41-46 ms following subthreshold TMS, triceps surae muscle activity was suppressed by 19-25%, but suppression was not significantly different between stretch-hold and fixed-end contractions. Similarly, the reduction in plantar flexion torque following subthreshold TMS was not significantly different between contraction conditions. Motor evoked potentials, silent periods and superimposed twitches following suprathreshold TMS were also not significantly different between contraction conditions. As TMS of the motor cortex did not result in any differences between stretch-hold and fixed-end contractions, we conclude that rFE is not linked to changes in corticospinal excitability, making rFE a muscle mechanical property rather than a combined neuro-muscular property.

neuroscience↗

bioRxiv2019

Triceps surae torque-length relationships relevant for walking activity levels with and without an ankle exoskeleton

AbstractAnkle exoskeletons have been developed to assist walking by offloading the plantar flexors work requirements, which reduces muscle activity level. However, reduced muscle activity alters plantar flexor muscle-tendon unit dynamics in a way that is poorly understood. We therefore evaluated torque-fascicle length properties of the soleus and lateral gastrocnemius during voluntary contractions at simulated activity levels typical during late stance with and without an ankle exoskeleton. Soleus activity levels (100, 30, and 22% maximal voluntary activity) were produced by participants via visual electromyography feedback at ankle angles ranging from -10{degrees} plantar flexion to 35{degrees} dorsiflexion. Using dynamometry and ultrasound imaging, torque-fascicle length data of the soleus and lateral gastrocnemius were produced. The results indicate that muscle activity reductions observed with an exoskeleton shift the torque-angle and torque-fascicle length curves to more dorsiflexed ankle angles and longer fascicle lengths where no descending limb is physiologically possible. This shift is in line with previous simulations that predicted a similar increase in the operating fascicle range when wearing an exoskeleton. These data suggest that a small reduction in muscle activity causes changes to torque-fascicle length properties, which has implications for the design and testing of future ankle exoskeletons for assisted walking.\n\nSignificance StatementAssistive lower-limb exoskeletons reduce the metabolic cost of walking by reducing the positive work requirements of the plantar flexor muscles. However, if the exoskeleton reduces plantar flexor muscle activity too much, then the metabolic benefit is lost. The biological reasons for this are unclear and hinder further exoskeleton development. This research study is the first to directly evaluate if a reduction in plantar flexor muscle activity similar to that caused by wearing an exoskeleton affects muscle function. We found that reduced muscle activity changes the torque-length properties of two plantar flexors, which could explain why reducing muscle activity too much can increase metabolic cost.

physiology↗