DOI: 10.5061/dryad.3tx95x6nh
title: Evidence for multi-scale power amplification in skeletal muscle

description: Many animals use a combination of skeletal muscle and elastic structures
 to amplify power output for fast motions. Among vertebrates, tendons in
 series with skeletal muscle are often implicated as the primary
 power-amplifying spring, but muscles contain elastic structures at all
 levels of organization, from the muscle tendon to the extracellular matrix
 to elastic proteins within sarcomeres. The present study used ex vivo
 muscle preparations in combination with high-speed video to quantify power
 output, as the product of force and velocity, at several levels of muscle
 organization to determine where power amplification occurs. Dynamic ramp
 shortening contractions in isolated frog flexor digitorum superficialis
 brevis were compared with isotonic power output to identify power
 amplification within muscle fibers, the muscle belly, free tendon and
 elements external to the muscle tendon. Energy accounting revealed that
 artifacts from compliant structures outside of the muscle–tendon unit
 contributed significant peak instantaneous power. This compliance included
 deflection of clamped bone that stored and released energy contributing
 195.22±33.19 W kg−1 (mean±s.e.m.) to the peak power output. In addition,
 we found that power detected from within the muscle fascicles for dynamic
 shortening ramps was 338.78 ±16.03 W kg−1, or nearly twice the maximum
 isotonic power output of 195.23±8.82 W kg−1. Measurements of muscle belly
 and muscle–tendon unit also demonstrated significant power amplification.
 These data suggest that intramuscular tissues, as well as bone, have the
 capacity to store and release energy to amplify whole-muscle
 power output.
description: # Dissecting muscle power output: Evidence of multi-scale power
 amplification in skeletal muscle
 [https://doi.org/10.5061/dryad.3tx95x6nh](https://doi.org/10.5061/dryad.3tx95x6nh) Corresponding Author: Jarrod Petersen, Brown University, jarrod\_petersen@brown.edu Principal Investigator: Thomas Roberts, Brown University, thomas\_roberts@brown.edu ## Overview & General Information **Data Types** The raw data included starts with six different individual identifiers 001-006 (n=6) and can be broken down into three different types of files: 1. [XXX\_MotorData\_AllTrials.csv] 2. [XXX\_TrackedData\_FVXX.csv] 3. [XXX\_TrackedData\_RampX.csv] For each of these file types, "X" represents a character that will vary based on the individual and trial (as listed below) while the base name of each file type is listed above and detailed here: Type 1 data are raw data obtained from a PowerLab data acquisition system that receives a digital signal from an Aurora Scientific 10N muscle servomotor. The motor converts an analog signal into digital force and length output waves. Type 2 and 3 data are both user-generated data from tracking two-dimensional points from a high-speed video recording in XMALab. Multiple variables along the muscle were tracked for each data type including "fiber\_x\_top" and "muscle\_y\_bottom." Type 2 data have fewer variables and are from video tracked from isotonic contractions where the servomotor holds a constant preset force value and the muscle then shortens or lengthens rather than producing force exceeding this value. Type 3 data are for dynamic shortening ramp contractions where the motor shortens (thus, allowing the muscle to shorten) based on predefined ramp signals that correspond with time. **Trial Nomenclature** Following the base names, the file names (and variable names in Type 1 data) have specific nomenclature that represents which trial they are a part of. There are two main types of trials: 1. "FVXX" 2. "RAMPX" For both of these trial types, "X" represents a number that references the parameters in that trial. These trial names are also present in the variables names for Type 1 data. "FVXX" trials correspond to "Force-Velocity" contractions, or isotonic contractions as mentioned above. The number following the "FV" corresponds to the percent of the maximum force value that the servomotor regulates. For example, "FV10" corresponds to a trail of a "Force-Velocity" contraction, or the isotonic contraction, that is \~10% of the maximum force value. These numbers range from 10-80, however, there is a variable in Type 1 data (as detailed below) that uses 100, or 100% of the maximum force value, resulting in an isometric contraction where there is no shortening. "RampX" trials correspond dynamic shortening ramp contractions where the number, ranging from 1-4, corresponds to a specific shortening velocity of the muscle servomotor, and therefore, the muscle: * '1' = 60mm/s * '2' = 90mm/s * '3' = 120mm/s * '4' = 160mm/s For example, Ramp4 corresponds to the fourth "Ramp" contraction, or the fastest of the four dynamic shortening ramps at 160mm/s. **NULL Data** For "XXX\_TrackedData\_XXXX" files of FV20 and Ramp1-4 trials, there are "null" data in cells prior to and following the relevant contraction period for most muscle, mtu, and bone coordinate variables. The start of each trial and the end of each trial are not relevant to the experiment, and are often periods where data is being acquired but equipment voltages are not changing. This means that many values may appear to be similar or even the same during this waiting period. Null values acted to speed up the consuming process of marker tracking during data analysis, so data was not collected for these variables. Other variables may have all of these values present reflecting a different subjective decision during analysis, likely where time was not a constraint. ## Data-specific Information for Type 1 [XXX\_MotorData\_AllTrials.csv] Number of variables: 22 Number of rows: 1003 Sampling rate: 1000 Hz Units: "Fmotor\_XXX" variables are all in Newtons, "Lmotor\_XXX" variables are all in millimeters Note - Data acquisition measured the first datapoint (row 1) at time 0 **Variable List:** * "Fmotor\_XXX" - Force detected from the motor where "XXX" corresponds to the name of each trial (ex. Fmotor\_FV10 corresponds to the "Force-Velocity" contraction, or the isotonic contraction, that is \~10% of the maximum force value). * "Lmotor\_XXX" - Length detected from the motor where "XXX" corresponds to the name of each trial (ex. Lmotor\_Ramp1 corresponds to the first "Ramp" contraction, or the slowest of the four dynamic shortening ramps at 60mm/s). * "Fmotor\_FV100" & "Lmotor\_FV100" - These force and length signals are also detected from the motor, but are distinct in that their naming convention (FV100) does not appear in other files. This is because they are isometric contractions where, rather than force being held constant, length is held constant and these trials are used to determine maximum muscle force. Since length is held constant, the muscle-tendon unit cannot shorten and no videos were analyzed in Type 2 or 3 data files. There is one "Fmotor\_FV100" and one "Lmotor\_FV100" variable per individual. ## Data-specific Information for Type 2 [XXX\_TrackedData\_FVXX.csv] Number of variables: 10 Number of rows: 501 Sampling rate: 500 fps (frames per second) Units: Millimeters Note - Data acquisition measured the first datapoint (row 1) at time 0 **Variable List:** * "fiber\_x\_top" - The x-coordinate of a two-dimensional point located at a marker at the top of the muscle fascicle for an individual (mm) * "fiber\_y\_top" - The y-coordinate of a two-dimensional point located at a marker at the top of the muscle fascicle for an individual (mm) * "fiber\_x\_bottom" - The x-coordinate of a two-dimensional point located at a marker at the bottom of the muscle fascicle for an individual (mm) * "fiber\_y\_bottom" - The y-coordinate of a two-dimensional point located at a marker at the bottom of the muscle fascicle for an individual (mm) * "muscle\_x\_top" - The x-coordinate of a two-dimensional point located at a marker at the top of the muscle belly for an individual (mm) * "muscle\_y\_top" - The y-coordinate of a two-dimensional point located at a marker at the top of the muscle belly for an individual (mm) * "muscle\_x\_bottom" - The x-coordinate of a two-dimensional point located at a marker at the bottom of the muscle belly for an individual (mm) * "muscle\_y\_bottom" - The y-coordinate of a two-dimensional point located at a marker at the bottom of the muscle belly for an individual (mm) * "Corrected\_Lf" - The length of the muscle fascicle throughout the trial calculated from the x and y coordinates of the muscle fascicle variables and corrected with a factor obtained from measuring the length of the real muscle fascicle vs. the length between muscle fascicle markers (mm) * "Corrected\_Lm" - The length of the muscle belly throughout the trial calculated from the x and y coordinates of the muscle belly variables and corrected with a factor obtained from measuring the length of the real muscle belly vs. the length between muscle belly markers (mm) ## Data-specific Information for Type 3 [XXX\_TrackedData\_RampX.csv] Number of variables: 16 Number of rows: 501 Sampling rate: 500 fps (frames per second) Units: Millimeters Note - Data acquisition measured the first datapoint (row 1) at time 0 Note - Blank values are present where there was negligible movement, thus, no need for marker tracking **Variable List:** * "fiber\_x\_top" - The x-coordinate of a two-dimensional point located at a marker at the top of the muscle fascicle for an individual (mm) * "fiber\_y\_top" - The y-coordinate of a two-dimensional point located at a marker at the top of the muscle fascicle for an individual (mm) * "fiber\_x\_bottom" - The x-coordinate of a two-dimensional point located at a marker at the bottom of the muscle fascicle for an individual (mm) * "fiber\_y\_bottom" - The y-coordinate of a two-dimensional point located at a marker at the bottom of the muscle fascicle for an individual (mm) * "muscle\_x\_top" - The x-coordinate of a two-dimensional point located at a marker at the top of the muscle belly for an individual (mm) * "muscle\_y\_top" - The y-coordinate of a two-dimensional point located at a marker at the top of the muscle belly for an individual (mm) * "muscle\_x\_bottom" - The x-coordinate of a two-dimensional point located at a marker at the bottom of the muscle belly for an individual (mm) * "muscle\_y\_bottom" - The y-coordinate of a two-dimensional point located at a marker at the bottom of the muscle belly for an individual (mm) * "mtu\_x\_top" - The x-coordinate of a two-dimensional point located at a marker at the top of the muscle-tendon-unit for an individual (mm) * "mtu\_y\_top" - The y-coordinate of a two-dimensional point located at a marker at the top of the muscle-tendon-unit for an individual (mm) * "mtu\_x\_bottom" - The x-coordinate of a two-dimensional point located at a marker at the bottom of the muscle-tendon-unit for an individual (mm) * "mtu\_y\_bottom" - The y-coordinate of a two-dimensional point located at a marker at the bottom of the muscle-tendon-unit for an individual (mm) * "Corrected\_Lf" - The length of the muscle fascicle throughout the trial calculated from the x and y coordinates of the muscle fascicle variables and corrected with a factor obtained from measuring the length of the real muscle fascicle vs. the length between muscle fascicle markers (mm) * "Corrected\_Lm" - The length of the muscle belly throughout the trial calculated from the x and y coordinates of the muscle belly variables and corrected with a factor obtained from measuring the length of the real muscle belly vs. the length between muscle belly markers (mm) * "Corrected\_Lmtu" - The length of the muscle-tendon-unit throughout the trial calculated from the x and y coordinates of the muscle-tendon-unit variables and corrected with a factor obtained from measuring the length of the real muscle-tendon-unit vs. the length between muscle-tendon-unit markers (mm) * "Corrected\_Lbone" - The y-coordinate of the marker on the distal bone for an individual. This variable is not corrected with a scaling value like the other variables that start with "corrected..." are, it simply represents the point distance of the bone in millimeters (mm)