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

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 E..., , , **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 set...