DOI: 10.5061/dryad.1zcrjdg14
title: Soft tissue can absorb surprising amounts of energy during knee exoskeleton use

description: Soft tissue deformation at the human exoskeleton interface can deform
 under load to absorb, return, and dissipate the mechanical energy
 generated by the exoskeleton. These soft tissue effects are often not
 accounted for and may mislead researchers on the actual joint assistance
 an exoskeleton provides. We assessed the effects of soft tissue by
 quantifying the performance and energy distribution of a knee exoskeleton
 under different assistance strategies using a mechanical lower limb
 phantom. The phantom emulated knee kinematics and soft tissue deformation
 at the exoskeleton interface. We loaded the exoskeleton on the phantom
 under six different spring stiffness conditions. Motion capture marker and
 load cell data from the phantom-exoskeleton assembly allowed us to
 estimate the moments, stiffness, and energy contributions of the
 exoskeleton and physical interface to the total knee power. We found that
 soft tissue caused interface power to increase and exoskeleton power to
 decrease with increasing spring stiffness. Additionally, increases in
 exoskeleton peak moments were not proportional to the change in spring
 stiffness despite consistent phantom joint motion under all conditions.
 Our methodology improves the exoskeleton design process by estimating
 energy distribution and transfer for exoskeletons while accounting for the
 effects of soft tissue deformation before human testing.
description: # Soft tissue can absorb surprising amounts of energy during knee
 exoskeleton use [Access this dataset on
 Dryad](https://doi.org/10.5061/dryad.1zcrjdg14) This repository contains
 data pertaining to the synthetic phantom limb and exoskeleton study to
 assess the effects of soft tissue deformation on exoskeleton performance.
 We used a synthetic phantom limb to move a passive exoskeleton across 6
 different spring stiffness conditions. The springs were rated at 3.4 kN/m,
 6.1 kN/m, 9.2 kN/m, 13.6 kN/m, 18.0 kN/m, and 21.7 kN/m. We recorded
 kinematics from the exoskeleton, phantom limb, and spring with motion
 capture markers. Load cells attached to the bottom of the phantom limb
 recorded reaction forces. A load cell attached in series with the
 exoskeleton spring recorded spring force. The processed data contains
 exoskeleton/phantom kinematics (deg), work (J), and power (W) for every
 spring stiffness condition. ## Description of the data and file structure
 This repository contains two zip files: "Data S1" and
 "MATLAB Data Analysis" "MATLAB Data Analysis" contains
 a "Raw_Data" subfolder with raw experimental data titled
 "3.4 Marker", "3.4 Load Cell", "6.1 Marker",
 "6.1 Load Cell", "9.2 Marker", "9.2 Load
 Cell", "13.6 Marker", "13.6 Load Cell",
 "18.0 Marker", "18.0 Load Cell", "21.7 Load
 Cell", and "21.7 Marker". The number dictates the spring
 stiffness condition. The "Marker" data contains the X, Y (up),
 and Z positions of markers placed at the exoskeleton (thigh and shank),
 phantom (ankle, knee, and hip), and exoskeleton spring (upper and lower
 ends). Marker data was recorded at 100 Hz with units of millimeters. The
 "Load Cell" data contains raw data for three load cells attached
 to the ankle of the phantom limb recording vertical reaction forces and a
 spring load cell recording spring forces. Load cell data was recorded at
 1000 Hz with units of Volts (converted to Newtons in the MATLAB processing
 file). The "Analysis.mat" file contains the processing pipeline
 for all the raw data. It outputs processed data pertaining to the
 exoskeleton knee angle, phantom knee angle, knee moments, work, and power.
 The remaining .mat files contain functions used to process the raw data.
 The "Data S1" zip file contains Excel files with the processed
 data pertaining to the study. Each Excel file has the following format:
 Columns - gait stride ID # (1 - 126) Rows - spring stiffness (3.4, 6.1,
 9.2, 13.6, 18.0, and 21.7 kN/m) Phantom_do = phantom stance knee flexion
 (degrees) Exo_do = exoskeleton stance knee flexion (degrees) MM = knee
 moments (Nm) Phantom_KK = phantom quasi-stiffness (Nm/rad) Exo_KK =
 exoskeleton quasi-stiffness (Nm/rad) Phantom_W_net = knee net work (J)
 Phantom_W_neg = knee negative work (J) Phantom_W_pos = knee positive work
 (J) Exo_W_net = exoskeleton net work (J) Exo_W_neg = exoskeleton negative
 work (J) Exo_W_pos = exoskeleton positive work (J) Gel_W_net = interface
 net work (J) Gel_W_neg = interface negative work (J) Gel_W_pos = interface
 positive work (J) Spring_W_net = spring net work (J) Spring_W_neg = spring
 negative work (J) Spring_W_pos = spring positive work (J) Frame_W_net =
 frame net work (J) Frame_W_neg = frame negative work (J) Frame_W_pos =
 frame positive work (J) "Data S1" also contains an R file for
 statistical analysis of the processed data in the same folder. The
 statistical analysis uses the Krustal-Wallis test to assess the
 significance of the processed variables across spring conditions. ##
 Code/Software The code for data processing was written in MATLAB R2023a.
 Statistical analysis was done in R version 4.3.2