Whole muscle length-tension relationships are accurately modeled as scaled sarcomeres in rabbit hindlimb muscles

Abstract

An a priori model of the whole active muscle length-tension relationship was constructed utilizing only myofilament length and serial sarcomere number for rabbit tibialis anterior (TA), extensor digitorum longus (EDL), and extensor digitorum II (EDII) muscles. Passive tension was modeled with a two-element Hill-type model. Experimental length-tension relations were then measured for each of these muscles and compared to predictions. The model was able to accurately capture the active -tension characteristics of experimentally-measured data for all muscles (ICC=0.88±0.03). Despite their varied architecture, no differences in predicted versus experimental correlations were observed among muscles. In addition, the model demonstrated that excursion, quantified by fullwidth-at-half-maximum (FWHM) of the active length-tension relationship, scaled linearly (slope=0.68) with normalized muscle fiber length. Experimental and theoretical FWHM values agreed well with an intraclass correlation coefficient of 0.99 (p < 0.001). In contrast to active tension, the passive tension model deviated from experimentally-measured values and thus, was not an accurate predictor of passive tension (ICC=0.70±0.07). These data demonstrate that modeling muscle as a scaled sarcomere provides accurate active functional predictions for rabbit TA, EDL, and EDII muscles and call into question the need for more complex modeling assumptions often proposed.

On the ascent: the soleus operating length is conserved to the ascending limb of the force-length curve across gait mechanics in humans

“…Our results show that the length at which passive SOL forces begin to develop correspond closely to the predicted L 0 , corroborating both standard models (Zajac, 1989) and previous experimental data (Azizi and Roberts, 2010;Winters et al, 2011), and provides further confidence in our estimates of subject-specific F-L data. The close association between the length at the initiation of passive force and L 0 may provide a convenient and less experimentally intensive approach to establishing subject-specific muscle properties for both experimental and computer simulation studies of human muscle function.…”

“…In addition, we have shown that experimental normalized maximal isometric F-L data from the SOL approximate the theoretical whole muscle and sarcomere (based on human filament lengths) F-L curves (Fig.4). The match between experimental F-L data of the human SOL and the theoretical F-L curve is not substantially different from that recently reported for rabbit muscle using in situ muscle preparations (Winters et al, 2011). The region of the F-L curve occupied by the SOL also closely matches the prediction using a recent musculoskeletal model (Arnold et al, 2010) of the muscle undergoing maximal isometric contractions across the same range of ankle angles as those measured in this study.…”

Comparison of human gastrocnemius forces predicted by Hill-type muscle models and estimated from ultrasound images

“…l 0,f was determined to be the length of the fascicle at tendon slack length. This passive force-length curve is similar to that provided by Millard and co-workers (2013) and is based on a combination of experimental data from chemically skinned human gastrocnemius fibres (Gollapudi and Lin, 2009) and rabbit whole muscles (Winters et al, 2011). The normalized force-velocity curve (Fig.…”

Force–length relation of skeletal muscles: from sarcomeres to myofibril

“…Despite reasonably good fitting of the scaled sarcomere F-L relation with experimental data of fibres and muscles (see, e.g. Gollapudi and Lin 2009;Winters et al 2011), given complexity of sarcomere mechanics in striated muscles (Pollack 1983;Rassier 2017), precise association of the sarcomere F-L relation with that of muscles requires rigourous theoretical studies.…”