Substantiating Appropriate Motion Capture Techniques for the Assessment of Nordic Walking Gait and Posture in Older Adults

This study was performed in accordance with the guidelines of the Research Ethics Board of the University of Ottawa.

1. Screening Procedure

1. Provide side show presentations to local area walking groups and post recruitment posters at community centers and public facilities in order to recruit a group of active, community-dwelling older adults.
2. Upon initial visit, first greet the participants, introduce them to the laboratory, and provide them time to change into appropriate attire (i.e. shorts, t-shirt, and running shoes). Once ready, provide each participant with an in-depth study description, obtain written informed consent, and screen each individual for study eligibility using various questionnaires.
   NOTE: Inclusion criteria includes: 55-80 years of age, novice to Nordic walking (NW), no neurological conditions, no cognitive impairments, no cardiac conditions, no previous injury or surgery affecting gait and upper extremity movement, and the ability to walk unaided.
   1. Have the participant complete a General Health and Physical Activity Questionnaire and the Physical Activity Readiness Questionnaire (PAR-Q) in order to confirm age, activity level, any existing neurological conditions, and briefly assess cardiac health.
   2. Next, have them complete a self-reported postural stability and falls questionnaire (adapted from Ashburn et al.¹⁰) to determine fall prevalence, if applicable. Lastly, complete the Montreal Cognitive Assessment (MOCA) with each subject in order to control for mild cognitive impairment¹¹, constituting a minimum score of 26 out of 30.

2. Pole Set-up and Nordic Walking Instruction

1. Provide each participant with a set of poles, and instruct them on how to adjust the poles to an optimal length relative to their height. Ensure that the adjustment corresponds to approximately 65% of the individual's body height.
   1. Provide each participant with the following instructions regarding pole adjustment. Ask the participants to stand tall, have the participants place the pole tip in front of the toes, instruct the participants to place the elbow and forearm next to the body, and ask the participants to lengthen the poles so the elbow forms an approximate 90° angle next to the body. Finally, securely tighten the poles and angle the boot tips backwards.
2. Instruct the participant the following 4 basic steps in order to minimize the amount of information to process and ensure a thorough understanding of technique¹². Allot approximately 30 min for instruction and subsequent practice of the technique.
   NOTE: Nordic walking instructions are to be given by a certified Nordic pole walking instructor.
   1. Before securing the wrist straps, instruct the participant to place their poles behind the lower back and stand tall. Ask the participants to stand with their chest tall and the shoulders relaxed.
      NOTE: Explain to the participant that this is done to gain an understanding of the required upright body posture for Nordic walking.
   2. Have each participant secure the wrist straps, place the pole tips behind them, and relax their arms at their sides. While keeping their hands open (i.e. not grasping handles), instruct the subject to begin walking with minimal arm swing for approximately 100 m.
      NOTE: At this stage, the poles are simply trailing behind the participant.
   3. While still keeping the hands open and dragging the poles behind them, instruct the participant to begin walking faster. Ask the participants to visualize bringing their hand up as if they are about to shake someone's hand.
      NOTE: At this phase, explain that the goal is to promote the natural reciprocal and rhythmic actions of the arms and legs during gait.
   4. Finally, as the arm swings forward, have the participant gently grasp the handle and apply a force against the ground. With each arm swing, instruct the individual to slightly lift the poles off the ground and firmly plant them with each subsequent stride.
      NOTE: At this stage, explain that the applied force aids in progression of gait and provides resistance to the upper body musculature.

3. Data Collection and Testing Protocol

1. Using a standard tape measure, weight scale, and caliper, take the participant's anthropometric measurements, including height, weight, inter-ASIS distance, left and right leg lengths, knee widths, ankle widths, shoulder offsets, elbow widths, wrist widths, and hand thicknesses.
   1. Using a tape measure, measure each leg length as the distance from the anterior-superior iliac spine (ASIS) to the center of the medial malleolus as well as the distance between the left and right ASIS (i.e. inter-ASIS distance).
      1. Next, measure the widths of each joint using a caliper by finding the distance between the bony prominences (e.g. condyles) of each joint. Lastly, measure the height and weight of the participant using a standard tape measure and scale, respectively.
2. In order to assess gait patterns (e.g. spatial-temporal measures) and postural alignment over a long period of time, use an accelerometry system for data collection during the 6 Minute Walk Test (6MWT), which is a valid and appropriate test in the assessment of older adult physical endurance¹³.
   1. For the accelerometry system, ensure that it is comprised of at least 6 sensors, each with accelerometers and gyroscopes incorporated into them in order to measure both the acceleration (g) and angular velocity (deg/sec) of each specific body segment.
      1. Prior to placement on the participant, ensure that all sensors are securely docked to the system's docking station in order to synchronize them and calibrate the system, and ultimately relay precise data measurements¹⁴.
   2. Attach the sensors using adjustable hook and loop straps, secure the sensors to the wrists, ankles, lumbar spine (L5) and trunk and collect at a sampling rate of a minimum of 100 Hz.
      1. When placing the sensors, ensure that they are oriented according to the system guidelines. Position the ankle sensors anteriorly. Position the wrist sensors posteriorly (when in anatomical position). Position the trunk sensor atop the sternum, and position the L5 sensor directly at the L5 vertebrae.
         NOTE: Kinematic data is wirelessly transmitted from these sensors to an access point, which is used to precisely time the transmission of the synchronized data.
   3. Fit the participant with the 6 sensors and ask them to perform two trials of the 6MWT, one with poles and one without. Randomly assign these two trials to control for order effect.
   4. Instruct the participant to walk back and forth along a 25 m walkway at a self-selected speed for the 6MWT, for both with and without poles. At this time, be sure to click 'Start' to begin data collection with the accelerometry system.
      NOTE: During pole trials, provide further instruction to the participant to implement their poling instruction.
3. Finally, assess short duration gait events using a 3-dimensional motion capture system collecting at a minimum of 100 Hz, with two force plates embedded in the pathway. Synchronize the force platforms with the motion capture system, ensure that the force platforms are zeroed to prevent noise in the data, and ensure that they are collecting at a sufficient sampling rate, for example 1,000 Hz.
   1. Synchronize the force plates to the motion capture system by first connecting them to the computer via the wires provided from the company. Second, directly within the motion capture system software, it is imperative to 'add' the force plates to the capture volume by entering the dimensions, sensitivities, sampling rates, and any other required information for the system.
   2. Ensure that the force plates have been 'zeroed'. Do this in two steps: 1) right click on each force plate within the software and select 'Zero force plate' and 2) press the 'zero' button that is directly on the data acquisition box of the force plates.
      NOTE: Ensure that the motion capture system collects real-time information from both the left and right legs from foot strikes on each force platform and allows for spatial-temporal, kinematic, and kinetic analysis.
4. Complete a dynamic calibration of the system (aimed at defining the capture volume that is to be used during data collection). To do this, wave a 3-marker wand in a controlled manner through the capture space. Then perform a static calibration of the system to set the global coordinate system (i.e. reference point of 0, 0, 0 (x, y, z) by placing a 4-marker L-frame at that specified reference point and select 'Set Volume' within the computer software.
   NOTE: The dynamic calibration later assists in the reconstruction of the 3-dimensional position of 39 reflective markers used for this model.
   1. Fit the participant with the 39 reflective markers, attaching them using double-sided tape and placing them on specific anatomical landmarks including: second metatarsals, lateral malleoli, calcanei, left and right mid-shank, lateral femoral condyles, left and right mid-thigh, ASIS, PSIS, T10, C7, right back, clavicle, sternum, acromion processes, left and right mid-humerus, lateral epicondyles, left and right mid-forearm, medial and lateral wrists, second metacarpals, anterior-lateral head, and posterior-lateral head.
   2. Instruct the participant to then perform 6 trials of a 5 m walk through the systems capture volume, three with poles and three without. Randomly assign these trials to control for order effect and provide the same instruction as per the 6MWT.

4. Data and Statistical Analysis¹⁴

1. During analysis of the 6MWT, remove all turns during the trial in order to account for strictly steady state walking After removing the turns, use the system software to extract the spatial-temporal measures, trunk range of motion (ROM) in all places, and trunk velocities in all planes.
   NOTE: This is done automatically during this protocol through algorithms used by the system itself¹⁴. The steps to extract the necessary dependent variables within this system are listed below.
   1. Using the accelerometry system software, first click on 'Monitor Data', select the appropriate time stamped trials that have been collected, right click on the trials, and select 'Convert to CSV'. After doing this, open the CSV file and ensure that data from all 6 sensors has been exported for further analysis.
   2. Next, select the trial again and click 'Export to PDF'. Observe the system generate a PDF report with a number of variables. From here, extract variables that are desired for the study, in this case, spatial-temporal and kinematic measures.
2. For 3-dimensional motion capture, filter all trials using a fourth-order zero lag Butterworth filter for analog devices with a cut-off frequency of 10 Hz as well as a Woltring filter for the marker trajectories with a 15 mm MSE predicted value. To do this, attach the 'Butterworth and Woltring' filtering options to the operations pipeline within the system software, select the aforementioned cut-off frequencies and MSE values, and click 'Run'.
   1. Add an 'Export to ASCII file' operation to the operations pipeline within the system and select 'Run'. Save the newly exported ASCII (spreadsheet) worksheet to the computer.
   2. Open the exported ASCII files and within each file, locate the power outputs and moments of force (i.e. kinetics) for each of the lower extremity joints, including the ankle, knee, and hip.
      NOTE: Using the minimum and maximum functions within the worksheet, calculate the upper and lower peaks corresponding to the different phases of a single gait cycle (e.g. A1, K1, H1, etc.) as outlined by Winter¹⁴.
   3. Next, extract the spatial-temporal measures using the specific system software, which in this instance, is automatically calculated through system algorithms and from anthropometric measurements. To extract the specific variables, first import the desired trial into the system software, select 'Events', and click on the desired variable to obtain the variable average from each trial.
3. Lastly, using the ASCII files, locate the trajectories for the C7 marker as well as the sacral/pelvic markers. Using these trajectories, calculate postural alignment as the differential between these markers and trajectories in both the medial-lateral and anterior-posterior directions.
4. Open statistical software and import the specific trial. First, using Shapiro-Wilks test for normality, ensure whether data is normally distributed.
   1. To compare with and without poles, use paired t-tests when data is normally distributed and Wilcoxon Signed Rank Tests when skewed. Use Holm-Sidak multiple pairwise comparison procedures when necessary. Significance level is set at p <0.05.