DOI: 10.5061/dryad.0p2ngf26p
title: Data from: Linking in vivo muscle dynamics to in situ force-length and force-velocity reveals that guinea fowl lateral gastrocnemius operates at shorter than optimal lengths

description: Force-length (F-L) and force-velocity (F-V) properties characterize
 skeletal muscle’s intrinsic properties under controlled conditions, and it
 is thought that these properties can inform and predict in vivo muscle
 function. Here, we map dynamic in vivo operating range and mechanical
 function during walking and running, to the measured in situ F-L and F-V
 characteristics of guinea fowl (Numida meleagris) lateral gastrocnemius
 (LG), a primary ankle extensor. We use in vivo patterns of muscle (tendon)
 force, fascicle length, and activation to test the hypothesis that muscle
 fascicles operate at optimal lengths and velocities to maximize force or
 power production during walking and running. Our findings only partly
 support our hypothesis: in vivo LG velocities are consistent with
 optimizing power during work production, and economy of force at higher
 loads. However, LG does not operate at lengths on the force plateau (±5%
 Fmax) during force production. LG length was near L0 at the time of EMG
 onset but shortened rapidly such that force development during stance
 occurred almost entirely on the ascending limb of the F-L curve, at
 shorter than optimal lengths. These data suggest that muscle fascicles
 shorten across optimal lengths in late swing, to optimize the potential
 for rapid force development near the swing-stance transition. This may
 provide resistance against unexpected perturbations that require rapid
 force development at foot contact. We also found evidence of passive force
 rise (in absence of EMG activity) in late swing, at lengths where passive
 force is zero in situ, suggesting that history dependent and viscoelastic
 effects may contribute to in vivo force development. Direct comparison of
 in vivo work loops and physiological operating ranges to traditional
 measures of F-L and F-V properties suggests the need for new approaches to
 characterize dynamic muscle properties in controlled conditions that more
 closely resemble in vivo dynamics.
description: **Data Explanation File (ReadMe)** **Data set name: Data from: “Linking in
 vivo muscle dynamics to in situ force-length and force-velocity reveals
 that guinea fowl lateral gastrocnemius operates at shorter than optimal
 lengths”.** \**Manuscript currently published in ***Journal of
 Experimental Biology * **General Information** The dataset contains two
 specific data files. One is the matlab files (.mat) that contain
 continuous in vivo recordings of muscle length, force, and activation for
 all in vivo individuals (n = 6) during walking and running on the
 treadmill. The other one (.xsls) contains summary values used to run the
 statistics of the accompanying manuscript. Below one can find detailed
 descriptions of these source data and their meaning. ***In vivo
 recordings*** Each .mat file contains the in vivo recordings of one trial
 recorded of an individual while walking (1p5 extension) or running (3p5
 extension) on the treadmill. The 1p5 refers to 1.5 mph that corresponds to
 the setting of the treadmill. This corresponds to 0.67 meters per second.
 The running speed was 3.5 miles per hour, which corresponds to 1.56 meters
 per second. Each file also contains corresponding in situ measures for
 each bird, as well as muscle weight. Detailed descriptions of these data
 can be found below. | **Field Name** | **Value** | |
 :--------------------- |
 :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Ind** | Individual number. | | **Speed\_ms** | Locomotion speed in meters per second. | | **Muscle** | The muscle of which data was recorded. For this dataset, the only muscle measured is the Lateral Gastrocnemius (LG). | | **MuscleMass\_g** | Muscle mass in grams. | | **MuscleForce\_N** | Muscle force in Newtons. Measured through a force buckle for an entire treadmill recording at 5000 Hz. | | **FascicleLength\_mm** | Fascicle length in millimeters. | | **EMGfilt** | Filtered EMG. For details on filtering, see manuscript. | | **EMGRaw** | Raw EMG recording. This data is untouched and unfiltered. | | **Time** | Time in seconds. | | **ForceFilter** | Filtering values for force buckle data. | | **CutIndex** | These indexes have been used to cut the data mid-swing to mid-swing. These timings were based on ankle joint kinematics. | | **UsedStrides** | These indexes indicate the strides that were used for further analysis. As birds did not always continue steady locomotion, unsteady strides were cut from further analysis. | | **FootOn** | Indexes that correspond with time of foot on. | | **FootOff** | Indexes that correspond with time of foot off. | | **Fmax\_N** | Maximum LG muscle force measured through 200 ms isometric contractions In situ. Note this does not account for total Gastrocnemius force (including MG).  To estimate total Gastroc force (Gtot),  multiple Fmax by the ratio of G:LG PCSA, in the “StatisticsSpreadsheet.xls” file under AnimalMeasures (see below). | | **L0\_mm** | Optimal active length in millimeters. | | **Vopt\_Lfs** | Optimal shortening velocity in fascicle lengths per second. | | **Vmax\_Lfs** | Maximal shortening velocity in fascicle lengths per second. | *Data used for statistics* This Excel file contains the values (originating from the in vivo and in situ data presented in the manuscript) that were used to run the statistical tests. To run the appropriate statistical test averages were calculated for each individual, before generating group averages. Sheet 1 contains all animal measurements. Sheet 2 contains the measures used for the statistical tests. Units for each value are reported in the Excel spreadsheet. | **Field Name** | **Value** | | :----------------------- | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Ind** | Individual number | | **Mph** | Locomotor speed in miles per hour (corresponding to treadmill settings). | | **L\_EMGon\_L0** | Muscle fascicle length (L) at time of EMG on (EMGon) in optimal lengths (L0). | | **Std\_L\_EMGon\_L0** | Standard deviation (Std) of the muscle length (L) at time of EMG on (EMGon) in optimal lengths (L0). | | **F\_EMGon\_Fmax** | Muscle force (F) at time of EMG on (EMGon) in fractional LG force (Fmax). Fractional force is calculated by dividing LG muscle force (in vivo) by maximum LG force (in situ). | | **Std\_ F\_EMGon\_Fmax** | Standard deviation (Std) of the muscle force (F) at time of EMG on (EMGon) in fractional force (Fmax). | | **F\_Ton\_Fmax** | Force (F) at time of foot on (Ton) in fractional LG force (Fmax) | | **Std\_F\_Ton\_Fmax** | Standard deviation (Std) of the force (F) at time of foot on (Ton) in fractional LG force (Fmax) | | **L\_Fpk\_L0** | Fascicle length (L) at time of peak force (Fpk) in optimal lengths (L0). | | **Std\_L\_Fpk\_L0** | Standard deviation (Std) of the fascicle length (L) at time of peak force (Fpk) in optimal lengths (L0). | | **F\_Fpk\_Fmax** | Force (F) at time of peak force (Fpk) in fractional LG force (Fmax) | | **std\_F\_Fpk\_Fmax** | Standard deviation (Std) of the force (F) at time of peak force (Fpk) in fractional LG force (Fmax) | | **L\_Frise\_L0** | Fascicle length (L) at time of force rise (Frise) in optimal lengths (L0). | | **std\_L\_Frise\_L0** | Standard deviation (Std) of the fascicle length (L) at time of force rise (Frise) in optimal lengths (L0). | | **F\_Frise\_Fmax** | Force (F) at time of force rise (Frise) in fractional LG force (Fmax) | | **std\_F\_Frise\_Fmax** | Standard deviation (Std) of the force (F) at time of force rise (Frise) in fractional LG force (Fmax) | | **L\_Ffall\_L0** | Fascicle length (L) at time of force fall (Ffall) in optimal lengths (L0). | | **std\_L\_Ffall\_L0** | Standard deviation (Std) of the fascicle length (L) at time of force fall (Ffall) in optimal lengths (L0). | | **F\_Ffall\_Fmax** | Force (F) at time of force fall (Ffall) in fractional LG force (Fmax) | | **std\_F\_Ffall\_Fmax** | Standard deviation (Std) of the force (F) at time of force fall (Ffall) in fractional LG force (Fmax) | | **V\_Fpk\_L0** | Shortening velocity (V) at time of peak force (Fpk) in optimal lengths (L0) per second. | | **std\_V\_Fpk\_L0** | Standard deviation (Std) of the shortening velocity (V) at time of peak force (Fpk) in optimal lengths (L0) per second. | | **V\_Ton\_L0** | Shortening velocity (V) at time of foot on (Ton) in optimal lengths (L0) per second. | | **std\_V\_Ton\_L0** | Standard deviation (Std) of the shortening velocity (V) at time of foot on (Ton) in optimal lengths (L0) per second. | **Changes made since previously published version: **Updated the StatisticsSpreadsheet as the one of the columns contained the raw data, not the data that went into the statistical analysis. We have clarified this in the updated readme file as well.