Biology subjects

Beck, O. N.

Publications and source records attributed to Beck, O. N..

9 recordsLinked to original sources

bioRxiv2026

Limb Lengthening Induces Substantial Muscle Remodeling in Humans

To correct lower limb length discrepancies, orthopedic surgeons often perform limb lengthening procedures. These procedures involve directly lengthening a primary bone (e.g., femur), which also stretches the muscles and tendons spanning the elongation site. Limb lengthening procedures improve lower-limb length symmetry, often at the expense of chronic joint-level decrements. For example, knee joint range of motion and strength does not always return to pre-surgery values following femur lengthening. These joint-level decrements governed by altered muscle force-length characteristics, but it is unestablished how human muscles remodel during surgical limb lengthening. Here, we characterized bilateral human vastus lateralis fascicle force-length profiles following femur lengthening. At 2.2 {+/-} 1.7 years (Avg {+/-} SE) post-initial surgery, the lengthened limb's vastus lateralis fascicles were longer, effectively stiffer, and weaker than the contralateral limb. The lengthened limb's vastus lateralis fascicles were 38 mm longer (Avg) than that of the contralateral limb, even though the lengthened limb's femur was only 31 mm longer (Avg). The onset of vastus lateralis fascicle passive force production began at 22% shorter (Avg) operating lengths in lengthened versus contralateral limb muscles. Additionally, vastus lateralis peak active force production was 34% less (Avg) in the lengthened versus contralateral limbs, and in-series quadriceps tendon stiffness was not stiffer in lengthened limbs. These data suggest that active muscle tissues lengthen more than passive muscle tissues following limb lengthening, effectively creating stiffer muscles. Years after limb lengthening, patient muscles exhibit numerous differences in their force-length properties versus that of natural growth, likely contributing to impaired joint-function.

bioengineering↗

bioRxiv2026

More isn't always better: Too much exoskeleton torque can disrupt balance

Wearable exoskeletons are a promising tool for augmenting balance and reducing fall risk. Recent work suggests that active ankle exoskeletons need to act faster than the human to improve reactive balance control. However, the magnitude of exoskeleton torque that is best for improving reactive balance remains unknown. Drawing from the optimal torque for minimizing metabolic expenditure, we hypothesized that reactive balance would improve with increased exoskeleton torque. Participants wearing bilateral ankle exoskeletons were instructed to maintain standing balance during 15cm backward support-surface perturbations. Three exoskeleton plantarflexion torque conditions were tested: NO (Off), LOW (15Nm), or HIGH (30Nm). LOW torque improved balance performance compared to NO torque (p<0.001), with a 7{+/-}3% decrease in peak center of mass (CoM) displacement. Although HIGH torque caused a 9{+/-}11% decrease in peak CoM displacement compared to NO torque (p=0.12), it was not significant due to high intersubject variability. Whereas LOW torque decreased peak CoM displacement in all (range: -0.2 to -1.6cm), HIGH torque only decreased it in some (range = 1.2 to -2.6cm). The change in CoM displacement from LOW to HIGH torque was associated with balance ability, quantified by the narrowing beam test (R2=0.29, p=0.06), while this relationship didnt meet conventional statistical significance, likely due to the small sample size, it suggests that higher levels of exoskeleton torque may hinder balance performance in individuals with better balance ability. Taken together, more exoskeleton torque is not always better for balance, highlighting a potential need to personalize exoskeleton torque for balance augmentation.

bioengineering↗

bioRxiv2025

Functional Electrical Stimulation of the Soleus Redistributes Lower-Limb Joint Work Distally in Young and Older Adults

Older adults walk with reduced ankle and greater hip mechanical output compared to young adults. This "distal-to-proximal redistribution" likely contributes to the greater metabolic energy expenditure during walking in older versus young adults. Due to the inverse relationship between ankle and hip use, functional electrical stimulation (FES) of the ankle extensors may increase ankle mechanical work and indirectly decrease hip mechanical work. Although FES increases stimulated muscle metabolism, bilateral soleus stimulation may restore more youthful walking kinetics without a detectable change in whole-body metabolism because ankle extension requires less metabolic energy than hip extension. Ten young adults and 10 older adults walked on a treadmill at 1.25 m/s with and without FES bilaterally applied over the respective legs soleus when the anterior-posterior ground reaction force exceeded 10% body weight. FES use altered walking mechanics and metabolic power similarly across age groups (all FES condition and age-group interactions p[≥]0.214). Across age groups, FES increased ankle mechanical power (p=0.041) and redistributed mechanical work production to occur relatively more at the ankle and less at the hip (p=0.010). The lower-limb joint redistribution ratio of older adults walking with FES was not different to that of young adults during baseline (p=0.785). Moreover, walking with FES increased metabolic power by 2% (p=0.037). FES attenuated older adult distal-to-proximal redistribution and modestly increased whole-body metabolic rate. FES applied to soleus muscles during the late stance of walking affects users similarly across the lifespan, indicating that FES interventions ought to consider a persons functional needs, regardless of age.

physiology↗

bioRxiv2024

Co-existence of ST-Segment Depression and Exaggerated Blood Pressure Response in Older Runners

Exercise stress tests are typically performed on symptomatic patients and those at elevated risks of ischemic heart disease. In more recent years, these tests are increasingly recommended for masters athletes who regularly perform exercise training. In the sample of apparently healthy physically active older adults who were recruited for a research study to evaluate exercise economy, we found the coexistence of ST-segment depression and exaggerated BP response in older runners. These findings are consistent with the notion that the screening and assessment of cardiovascular risks should be extended to masters athletes who vigorously train regularly and are seemingly healthy.

physiology↗

bioRxiv2024

Center of mass states render multi-joint torques throughout standing balance recovery

Successful reactive balance control requires coordinated modulation of hip, knee, and ankle torques. Stabilizing joint torques arise from feedforward neural signals that modulate the musculoskeletal systems intrinsic mechanical properties, namely muscle short-range stiffness, and neural feedback pathways that activate muscles in response to sensory input. Although feedforward and feedback pathways are known to modulate the torque at each joint, the role of each pathway to the balance-correcting response across joints is poorly understood. Since the feedforward and feedback torque responses act at different delays following perturbations to balance, we modified the sensorimotor response model (SRM), previously used to analyze the muscle activation response to perturbations, to consist of parallel feedback loops with different delays. Each loop within the model is driven by the same information, center of mass (CoM) kinematics, but each loop has an independent delay. We evaluated if a parallel loop SRM could decompose the reactive torques into the feedforward and feedback contributions during balance-correcting responses to backward support surface translations at four magnitudes. The SRM accurately reconstructed reactive joint torques at the hip, knee, and ankle, across all perturbation magnitudes (R2>0.84 & VAF>0.83). Moreover, the hip and knee exhibited feedforward and feedback components, while the ankle only exhibited feedback components. The lack of a feedforward component at the ankle may occur because the compliance of the Achilles tendon attenuates muscle short-range stiffness. Our model may provide a framework for evaluating changes in the feedforward and feedback contributions to balance that occur due to aging, injury, or disease. NEWS AND NOTEWORTHYReactive balance control requires coordination of neurally-mediated feedforward and feedback pathways to generate stabilizing joint torques at the hip, knee, and ankle. Using a sensorimotor response model, we decomposed reactive joint torques into feedforward and feedback contributions based on delays relative to center of mass kinematics. Responses across joints were driven by the same signals, but contributions from feedforward versus feedback pathways differed, likely due to differences in musculotendon properties between proximal and distal muscles.

bioengineering↗

bioRxiv2022

Evaluating the "cost of generating force" hypothesis across frequency in human running and hopping

The volume of active muscle and duration of extensor muscle force well-explain the associated metabolic energy expenditure across body mass and speed during level-ground running and hopping. However, if these parameters fundamentally drive metabolic energy expenditure, then they should pertain to multiple modes of locomotion and provide a simple framework for relating biomechanics to metabolic energy expenditure in bouncing gaits. Therefore, we evaluated the ability of the cost of generating force hypothesis to link biomechanics and metabolic energy expenditure during human running and hopping across step frequencies. We asked participants to run and hop at 0%, {+/-}8% and {+/-}15% of preferred step frequency. We calculated changes in active muscle volume, force duration, and metabolic energy expenditure. Overall, as step frequency increased, active muscle volume decreased due to postural changes via effective mechanical advantage (EMA) or duty factor. Accounting for changes in EMA and muscle volume better related to metabolic energy expenditure during running and hopping at different step frequencies than assuming a constant EMA and muscle volume. Thus, to ultimately develop muscle mechanics models that can explain metabolic energy expenditure across different modes of locomotion, we suggest more precise measures of muscle force production that include the effects of EMA.

physiology↗

bioRxiv2021

Relatively Shorter Muscle Lengths Increase the Metabolic Rate of Cyclic Force Production

During animal locomotion, force-producing leg muscles are almost exclusively responsible for the whole-bodys metabolic energy expenditure. Animals can change the length of these leg muscles by altering body posture (e.g., joint angles), kinetics (e.g., body weight), or the structural properties of their biological tissues (e.g., tendon stiffness). Currently, it is uncertain whether relative muscle fascicle operating length has a measurable effect on the metabolic energy expenditure of cyclic locomotion-like contractions. To address this uncertainty, we measured the metabolic energy expenditure of human participants as they cyclically produce two distinct ankle moments at three separate ankle angles (90{degrees}, 105{degrees}, 120{degrees}) on a fixed-position dynamometer exclusively using their soleus. Overall, increasing participant ankle angle from 90{degrees} to 120{degrees} (more plantar flexion) reduced minimum soleus fascicle length by 17% (both moment levels, p<0.001) and increased metabolic energy expenditure by an average of 208% (both p<0.001). Across both moment levels, the increased metabolic energy expenditure was not driven by greater fascicle positive mechanical work (higher moment level, p=0.591), fascicle force rate (both p[≥]0.235), or active muscle volume (both p[≥]0.122); but it was correlated with average relative soleus fascicle length (r=-179, p=0.002) and activation (r=0.51, p<0.001). Therefore, the metabolic energy expended during locomotion can likely be reduced by lengthening active muscles that operate on the ascending-limb of their force-length relationship.

physiology↗

bioRxiv2020

Adding carbon fiber to shoe soles does not improve running economy: a muscle-level explanation

In an attempt to improve their distance-running performance, many athletes race with carbon fiber plates embedded in their shoe soles. Accordingly, we sought to establish whether, and if so how, adding carbon fiber plates to shoes soles reduces athlete aerobic energy expenditure during running (improves running economy). We tested 15 athletes during running at 3.5 m/s in four footwear conditions that varied in shoe sole carbon fiber plate bending stiffness. For each condition, we quantified athlete aerobic energy expenditure and performed biomechanics analyses, which included the use of ultrasound imaging to examine soleus muscle dynamics in vivo. Overall, increased footwear bending stiffness lengthened ground contact time (p=0.048), but did not affect ankle (p[≥]0.060), knee (p[≥]0.128), or hip (p[≥]0.076) joint angles or moments. Additionally, increased footwear bending stiffness did not affect muscle activity (all seven measured leg muscles (p[≥]0.146)), stride averaged active soleus volume, (p=0.068) or aerobic power (p=0.458) during running. Hence, footwear bending stiffness does not appear to alter the volume of aerobic energy consuming muscle in the soleus, or any other leg muscle, during running. Therefore, adding carbon fiber plates to shoe soles slightly alters whole-body and calf muscle biomechanics but does not improve running economy.

bioengineering↗

bioRxiv2020

Ultrasound imaging links soleus muscle neuromechanics and energetics during human walking with elastic ankle exoskeletons

Unpowered exoskeletons with springs in parallel to human plantar flexor muscle-tendons can reduce the metabolic cost of walking. We used ultrasound imaging to look under the skin and measure how exoskeleton stiffness alters soleus muscle contractile dynamics and shapes the users metabolic rate during walking. Eleven participants (4F, 7M; age: 27.7 {+/-} 3.3 years) walked on a treadmill at 1.25 m s-1 and 0% grade with elastic ankle exoskeletons (rotational stiffness: 0-250 Nm rad-1) in one training and two testing days. Metabolic savings were maximized (4.2%) at a stiffness of 50 Nm rad-1. As exoskeleton stiffness increased, the soleus muscle operated at longer lengths and improved economy (force/activation) during early stance, but this benefit was offset by faster shortening velocity and poorer economy in late stance. Changes in soleus activation rate correlated with changes in users metabolic rate (p = 0.038, R2 = 0.44), highlighting a crucial link between muscle neuromechanics and exoskeleton performance; perhaps informing future muscle-in-the loop exoskeleton controllers designed to steer contractile dynamics toward more economical force production.

bioengineering↗