Background: The effect of external lateral stabilization on medio-lateral gait stability has been investigated previously. However, existing lateral stabilization devices not only constrains lateral motions, but also transverse and frontal pelvis rotations. This study aimed to investigate the effect of external lateral stabilization with and without constrained transverse pelvis rotation on mechanical and metabolic gait features.

Methods: We undertook 2 experiments with eleven and ten young adult subjects, respectively. Kinematic, kinetic, and breath-by-breath oxygen consumption data were recorded during 3 walking conditions (normal walking (Normal), lateral stabilization with (Free) and without transverse pelvis rotation (Restricted)) and at 3 speeds (0.83, 1.25, and 1.66 m/s) for each condition. In the second experiment, we reduced the weight of the frame, and allowed for longer habituation time to the stabilized conditions.

Results: External lateral stabilization significantly reduced the amplitudes of the transverse and frontal pelvis rotations, in addition to medio-lateral, anterior-posterior, and vertical pelvis displacements, transverse thorax rotation, arm swing, step length and step width. The amplitudes of free vertical moment, anterior-posterior drift over a trial, and energy cost were not significantly influenced by external lateral stabilization. The removal of pelvic rotation restrictions by our experimental set-ups resulted in normal frontal pelvis rotation in Experiment 1 and significantly higher transverse pelvis rotation in Experiment 2, although transverse pelvis rotation still remained significantly less than in the Normal condition. Step length increased with the increased transverse pelvis rotation.

Conclusion: Existing lateral stabilization set-ups not only constrain medio-lateral motions (i.e. medio-lateral pelvis displacement), but also constrains other movements such as transverse and frontal pelvis rotations, which leads to several other gait changes such as reduced transverse thorax rotation, and arm swing. Our new setups allowed for normal frontal pelvis rotation and more transverse pelvis rotation (yet  less than normal). However, this did not result in more normal thorax rotation and arm swing. Hence, to provide medio-lateral support without constraining other gait variables, more elaborate set-ups are needed.

During Experiments 1 and 2, kinematic data was obtained from an Optotrak motion analysis system (Northern Digital Inc, Ontario, Canada), sampled at 100 samples/s. Clusters of three infrared markers were attached to the thorax (over the T₆ spinous process), the pelvis, the waist belt of the frame (see Figure 2 A. & B.), the left and right arms (over the lateral and middle part of the humerus segment) and the heels. We also obtained kinetic data from the force plates embedded in the treadmill (ForceLink b.v., Culemborg, the Netherlands), sampled at 200 samples/s in Experiment 2. During all experiments, participants wore a mask and breath-by-breath oxygen consumption was obtained using a pulmonary gas exchange system (Cosmed K4b², Cosmed, Italy).

Data and codes for Mahaki et al. 2021

How does external lateral stabilization constrain normal gait, apart from improving medio-lateral gait stability?

           A) GasData     - contains all Oxygen data plus a script to run the data.

- Subject01-Subject11               - folders with oxygen data in Experiment 1.

- Subject12-Subject22               - folders with oxygen data in Experiment 2.

• MainMohammad_EC [type of file: MATLAB code (.m)] script to analyze the oxygen data. The outcomes have been saved as ECexp1_L1,2, and 3min and ECexp2_L1,2, and 3min [type of files: MATLAB data (.mat)] for experiments 1 and 2, respectively. For example, ECexp1_L3min (.mat) includes gross metabolic rate (i.e.ECgross_L3min), net energy cost (i.e. ECnett_L3min), gross energy expenditure (i.e. EEgross_L3min), and net energy expenditure (i.e. EEnett_L3min). ECnett_L3min is related to net energy cost of walking calculated by analyzing the last 3 minutes of a 5 minutes trial. 
• EC_Stat_ECnetLast1,2, and 3min [type of files: MATLAB code (.m)] script to statistically test the main effect of Condition, the main effect of Speed, and the Interaction effect (Condition × Speed) on net energy cost of walking. The results are presented by boxplots together with individual data points for experiments 1 and 2.
• Exp1_ECnet_L1,2, and 3min [type of files: Jamovie (.omv)] files to statistically test the main effect of Condition, the main effect of Speed, and the Interaction effect (Condition × Speed) on net energy cost of walking in Experiment 1.
• Exp2_ECnet_L1,2, and 3min [type of files: Jamovie (.omv)] files to statistically test the main effect of Condition, the main effect of Speed, and the Interaction effect (Condition × Speed) on net energy cost of walking in Experiment 2.

 

           B) KinData  - contains all kinematic and kinetic data (one folder per subject)

             - Marker.xlsx     - info on which markers were placed where

             - Pointers.xlsx   - info on which pointer trials contain which virtual        markers

             - Trials.xlsx        - info on which files contain which conditions

             - Subjectxx        - folder with all the data:

- Subject01-Subject11      - folders with kinematic data in Experiment 1.

- Subject12-Subject22 - folders with kinematic and kinetic data in Experiment 2.                     

- The *.ndf files contain the kinematics (can be read with readndf.m, available in a subfolder of the VU 3d model.

- The *.grf1 and *.grf2 files contain the kinetics (can be read with matlab load function)

- The *. poa files contain the kinetics (can be read with matlab load function)

- The *.afp files contain the raw voltage data from the force plates. These can be converted to forces and moments using the function FBW_dualbelt.m,  available in a subfolder of the VU 3d model.

- The _HS.mat files contain calculated events (see script A below), and are normal matlab files.

 

           C) Software - contains all code used to get from the kinematic data to outcome variables, script were ran as:

- AMainHeelstrikes - script which calculates heelstrikes, and prompts the user to check these. Results are saved in the same folder (and under same name, but with extension HS.mat) as original data.

- BMainMohammadOutcomes - script which was used to calculate main outcomes for each subject and condition. Results of this script were stored as:

• Direct Outcomes  folder- folder includes the outcomes which were directly influenced by external lateral stabilization:

1. PelvisRot_X and PelvisRot_Z [type of files (.mat)] – include the amplitudes of frontal and transverse pelvis rotations, respectively. The statistics together with boxplots for both experiments can be checked by running the Boxplot_Stat_X_PlevisRotation and Boxplot_Stat_Z_PlevisRotation [type of files (.m)], respectively.
2. PelvisDisp_AP, PelvisDisp_Z and _ML [type of file (.mat)] – include the amplitudes of anterior-posterior, vertical and medio-lateral pelvis displacements over steps, respectively. The statistics together with boxplots for both experiments can be checked by running the Boxplot_Stat_AP_PlevisDisplacement, Boxplot_Stat_Z_PlevisDisplacement, Boxplot_Stat_ML_PlevisDisplacement [type of files (.m)], respectively.
3. PelvisDisp_AP_drift [type of file (.mat)] - include the amlitude of anterior-posterior drift over a walking trial. The statistics together with boxplots for both experiments can be checked by running the Boxplot_Stat_AP_Drift [type of file (.m)]. 

• Indirect Outcomes folder- folder includes the outcomes which were indirectly influenced by external lateral stabilization:

1. ThoraxRot_Z, [type of files (.mat)]- include the amplitude of transverse thorax rotation. The statistics together with boxplots for both experiments can be checked by running the Boxplot_Stat_Z_ThoraxRotation [type of file (.m)].

2. F_combined_range [type of files (.mat)] –includes the amplitude of FVM which was calculated as the differences between maximum and minimum time normalized FVMs per gait cycle and then the median of amplitudes over gait cycle for each trial.

3. F_combined_max, F_combined_min [type of files (.mat)] – include the maximum/minimum of vertical ground reaction moment (also referred to as ‘free vertical moment (FVM)’).  First, FVM time-normalized to 0-100% for each gait cycles. The maximum/minimum of free vertical moment was calculated as the maximum/minimum vertical ground reaction moments per gait cycle and then the median of all maximums/minimums over gait cycle for each trial.

4. F_combined_mean [type of files (.mat)] - includes the mean of FVM. First, the time-normalized FVM was rectified. Then, the median of rectified FVM was calculated.

The statistics together with the related boxplots of  F_combined_range, F_combined_max, F_combined_min, and F_combined_mean for both experiments can be checked by running Boxplot_Stat_FVM [type of file (.m)].

5. Left Arm Swing/ Right Arm Swing [type of files (.mat)] – include the amplitudes of left and right arm swing, respectively. The statistics together with the related boxplots related to the differences between left and right arm swing  in each walking speed and in each condition as well as the statistics together with boxplots related to the effect of Condition, Speed and Interaction (Condition vs Speed) on averaged arm swing can be checked by running Boxplot_Stat_Test_Arms [type of file (.m)]. 

6. StepLenght_L  and StepLenght_R [type of files (.mat)] - include the left and right step length data, respectively. The statistics together with the related boxplots related to the differences between left and right step lengt  in each walking speed and in each condition as well as the statistics together with boxplots related to the effect of Condition, Speed and Interaction (Condition vs Speed) on averaged step length can be checked by running Boxplot_Stat_Test_StepLength [type of file (.m)]. 

7. StepWidth [type of files (.mat)] - includes the step width data. The statistics together with boxplots for both experiments can be checked by running the Boxplot_Stat_SW  [type of file (.m)]. 

Note that Step length and step width were calculated as the median of the distances between anterior-posterior and medio-lateral foot placements at heel strike, respectively.

• Plots – folder includes the figures related to mean± 1sd of each time-normalized outcome per each subject and each trial.
• Statistics [Jamovie] – folder includes the .omv format files to check the statistics results for each outcome.
• Figures (.eps) - folder includes the .eps format files of included figures.
• =VU 3D model= - the somewhat under documented VU 3D model, several functions of which are being used.

 

          D) SetUpmeasurements – folder includes two subfolder entitled “Force Test” and “Friction Test” which are related to our additional experiments to provide a detailed description of the characteristics of our set-up and the forces acting in it, which can be found in the Supplementary Material.