DOI: 10.5061/dryad.mgqnk996q
title: Data from: Does the unusual phenomenon of sustained force circumvent the speed-endurance trade off in the jaw muscle of the southern alligator lizard (Elgaria multicarinata)?

description: The jaw muscles of the southern alligator lizard, Elgaria multicarinata,
 are used in prolonged mate-holding behavior, and also to catch fast prey.
 In both males and females, these muscles exhibit an unusual type of high
 endurance known as sustained force in which contractile force does not
 return to baseline between subsequent contractions. This phenomenon is
 assumed to facilitate the prolonged mate-holding observed in this species.
 Skeletal muscle is often subject to a speed-endurance trade off. Here we
 determine the isometric twitch, tetanic, and isotonic force-velocity
 properties of the jaw muscles at ~24°C as metrics of contractile speed and
 compare these properties to a more typical thigh locomotory muscle, to
 determine whether endurance by sustained force allows for circumvention of
 the speed-endurance trade-off. The specialized jaw muscle is generally
 slower than the more typical thigh muscle; time to peak twitch force,
 twitch 90% relaxation time (p&lt;0.01), and tetanic 90% and 50%
 relaxation times (p&lt;0.001) are significantly longer, and
 force-velocity properties are significantly slower (p&lt;0.001), in
 the jaw than the thigh muscle. However, there seem to be greater effects
 on relaxation rates and shortening velocity that on force rise times;
 there was no effect of muscle on time to peak, or 50% of tetanic force.
 Hence, the jaw muscle of the southern alligator lizard does not seem to
 circumvent the speed-endurance trade-off. However, the maintenance of
 force rise times despite slow relaxation, potentially enabled by the
 presence of hybrid fibers, may allow this muscle to meet the functional
 demand of prey capture.
description: # A comparison of the force-velocity properties of the jaw muscle of the
 southern alligator lizard (*Elgaria multicarinata*) used in long-lasting
 mating behaviors to a more typical thigh muscle.
 [https://doi.org/10.5061/dryad.mgqnk996q](https://doi.org/10.5061/dryad.mgqnk996q) The data file Nguyenetal_DryadData_2024.xlsx consists of Excel sheets (BodySize&MuscleDimensions, IsometricProperties, RepresentativeTwitchFigure1A, RepresentativeTetanicFigure1B, BoxpotFigure1C) of data points of figures in the manuscript for the isometric properties (e.g., twitch and tetanic contraction times, stress values, and physiological cross-sectional area, CSA) and the corresponding boxplots (TPT: time to peak tension; TP90: time to 90% of peak tension; RT50: time to 50% relaxation, measured from peak to 50% relaxation; RT90: time to 90% relaxation, measured from peak to 90% relaxation), force velocities individual data points and curve fits, and power curves individual data points and curve fits. The result of this data suggests that the jaw muscle is slower than the limb muscle of the southern alligator lizards. Additionally, information on the individuals identification numbers, sex, body mass, muscle fiber length, and muscle mass data. Supplemental figure of mixed-effects modeling done in R in pdf format. The FV data were modeled with a mixed effects model using a gamma distribution and a log-link function with a 95% confidence interval. Our study contains multiple measurements per individual thus a mixed model analysis was necessary. Relative velocity was the dependent variable as it was measured at different set forces, and the independent variables were relative force and muscle type (fixed effects) and individual (random effect). There is a significant effect of muscle type (*i.e.*, jaw vs. thigh) on velocity, with the jaw muscle being slower than the thigh. However, while there was an effect of muscle type on shortening velocity, it does not appear as though there is an effect on the shape of the force-velocity relationship as there is no significant interactive effect of force and muscle type on velocity. This is reflected in the very similar power ratios for the two muscle types.