Biology subjects

Franz, J. R.

Publications and source records attributed to Franz, J. R..

5 recordsLinked to original sources

bioRxiv2023

Reduced Achilles tendon stiffness in aging persists at matched activations and associates with higher metabolic cost of walking

The mechanisms responsible for increased walking metabolic cost among older adults are poorly understood. We recently proposed a theoretical premise by which age-related reductions in Achilles tendon stiffness (kAT) can disrupt the neuromechanics of calf muscle behavior and contribute to faster rates of oxygen consumption during walking. The purpose of this study was to objectively evaluate this premise. We quantified kAT at a range of matched activations prescribed using electromyographic biofeedback and walking metabolic cost in a group of 15 younger (age: 23{+/-}4 yrs) and 15 older adults (age: 72{+/-}5 yrs). Older adults averaged 44% less kAT than younger adults at matched triceps surae activations (p=0.046). This effect appeared to arise not only from altered tendon length-tension relations with age, but also from differences in the operating region of those length-tension relations between younger and older adults. Older adults also walked with a 17% higher net metabolic power than younger adults (p=0.017). In addition, we discovered empirical evidence that lesser kAT exacts a metabolic penalty and was positively correlated with higher net metabolic power during walking (r=-0.365, p=0.048). These results pave the way for interventions focused on restoring ankle muscle-tendon unit structural stiffness to improve walking energetics in aging.

bioengineering↗

bioRxiv2023

Simulations suggest walking with reduced propulsive force would not mitigate the energetic consequences of lower tendon stiffness

Aging elicits numerous effects that impact both musculoskeletal structure and walking function. Tendon stiffness (kT) and push-off propulsive force (FP) both impact the metabolic cost of walking and are diminished by age, yet their interaction has not been studied. We combined experimental and computational approaches to investigate whether age-related changes in function (adopting smaller FP) may be adopted to mitigate the metabolic consequences arising from changes in structure (reduced kT). We recruited 12 young adults and asked them to walk on a force-sensing treadmill while prompting them to change FP ({+/-}20% & {+/-}40% of typical) using targeted biofeedback. In models driven by experimental data from each of those conditions, we altered the kT of personalized musculoskeletal models across a physiological range (2-8% strain) and simulated individual-muscle metabolic costs for each kT and FP combination. We found that kT and FP independently affect walking metabolic cost, increasing with higher kT or as participants deviated from their typical FP. Our results show no evidence for an interaction between kT and FP in younger adults walking at fixed speeds. Individual lower body muscles showed unique effects across the kT and FP landscape. Our simulations suggest that reducing FP during walking would not mitigate the metabolic consequences of lower kT. Wearable devices and rehabilitative strategies can focus on either kT or FP to reduce age-related increases in walking metabolic cost. Author SummaryOur muscles and tendons are affected by aging. Tendon stiffness and push-off forces both impact the energy cost of walking, which in turn increases with age. We investigated whether age-related changes in function (less push-off force) may be adopted to mitigate the metabolic consequences arising from structural changes (lower tendon stiffness). Reducing push-off force during walking would not mitigate the metabolic consequences of lower tendon stiffness. Wearable devices and rehabilitative strategies can focus on either tendon stiffness or push off intensity to reduce age-related increases in walking metabolic cost.

bioengineering↗

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

Automated Analysis of Medial Gastrocnemius Muscle-Tendon Junction Displacements During Isolated Contractions and Walking Using Deep Neural Networks

Direct measurement of muscle-tendon junction (MTJ) position is important for understanding dynamic tendon behavior and muscle-tendon interaction in healthy and pathological populations. Traditionally, obtaining MTJ position during functional activities is accomplished by manually tracking the position of the MTJ in cine B-mode ultrasound images - a laborious and time-consuming process. Recent advances in deep learning have facilitated the availability of user-friendly open-source software packages for automated tracking. However, these software packages were originally intended for animal pose estimation and have not been widely tested on ultrasound images. Therefore, the purpose of this paper was to evaluate the efficacy of deep neural networks to accurately track medial gastrocnemius MTJ positions in cine B-mode ultrasound images across tasks spanning controlled loading during isolated contractions to physiological loading during treadmill walking. Cine B-mode ultrasound images of the medial gastrocnemius MTJ were collected from 15 subjects (6M/9F, 23 yr, 71.9 kg, 1.8 m) during treadmill walking at 1.25 m/s and during maximal voluntary isometric plantarflexor contractions (MVICs). Five deep neural networks were trained using 480 labeled images collected during walking, and were then used to predict MTJ position in images from novel subjects 1) during walking (novel-subject), and 2) during MVICs (novel-condition). We found an average mean absolute error of 1.26{+/-}1.30 mm and 2.61{+/-}3.31 mm in the novel-subject and novel-condition evaluations, respectively. We believe this approach to MTJ position tracking is an accessible and time-saving solution, with broad applications for many fields, such as rehabilitation or clinical diagnostics.

bioengineering↗

bioRxiv2020

Muscle Metabolic Energy Costs While Modifying Propulsive Force Generation During Walking

We pose that an age-related increase in the metabolic cost of walking arises in part from a redistribution of joint power where muscles spanning the hip compensate for insufficient ankle push-off and smaller peak propulsive forces (FP). Young adults elicit a similar redistribution when walking with smaller FP via biofeedback. We used targeted FP biofeedback and musculoskeletal models to estimate the metabolic costs of operating lower limb muscles in young adults walking across a range of FP. Our simulations support the theory of distal-to-proximal redistribution of joint power as a determinant of increased metabolic cost in older adults during walking.

bioengineering↗