Biology subjects

Franz, J. R.

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

3 recordsLinked to original sources

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↗