In order to complete a biomechanical assessment of the Back In Form techniques, several methods of data collection were used to evaluate the subject who performed the tasks. These methods include motion capture using the Fastrak electromagnetic system, video capture and analysis, and electromyography (EMG) capture.
The Fastrak electromagnetic motion tracking system was used for the motion capture of this assessment. This system captures 6 degrees of freedom in real time by tracking the position and orientation of small sensors as they move relative to the receptor. Each marker contains an electromagnetic source that is detected by this receptor and the signals are then processed by the system’s electronics unit. From this, the position and orientation values are computed for each of the markers and are stored in Excel spreadsheets. For these analyses, five markers were placed at the center of gravity of caregiver’s segments to provide a three-dimensional representation of the upper body. The segments on which they were placed were the hand, the forearm, the upper arm, the thorax (T8) and the pelvis (L5/S1). The data collected from the motion capture was used to compute the joint angles. By analyzing the behaviour of the joint angles during the motion, the segment kinematics of the upper body segments can be determined and compared to the other data collection methods. Observations can be made on the symmetry of the joint angles for both the right and left sides and also the time at which the joint angles are changing.
Electromyography was used to record the electrical activity of the muscles used during the tasks. For these analyse, surface electrodes were used to detect the electrical potential generated by the muscle cells. This method of data collection is useful for biomechanical assessments in that it provides information about the level of muscle activity during the entire motion indicates the initiation of muscle activation and can be used to detect fatigue occurring throughout the motion. The muscle activity in the upper body of the caregiver was recorded in order to assess the specific muscles that were being used to perform the tasks. To obtain the most accurate signal, the electrodes were placed on the midline of the muscle belly to avoid the innervation zones and myotendinous junctions which affect the EMG signal. Focussing on the upper body, the electrodes were placed on the anterior and posterior deltoids, upper trapezius, bicep, tricep, T8 and L4 erector spinae and the latissimus dorsi. It should also be noted that the EMG was only recorded on the right side of the caregiver.
For a more accurate representation of the muscle activity, the EMG RMS voltage signals were normalized using maximum voluntary contraction (MVC) data that was collected from the caregiver. The maximum value from the data set for each muscle was determined in order to convert the EMG RMS voltage to %MVC over time. By representing the muscle activity during the motion as a percentage of the maximum voluntary contraction, the data can be generalized and show a more realistic interpretation of how hard the caregiver is working. For the evaluation of these signals, from 0% to 30% was considered low muscle activity, 30% to 70% was medium muscle activity and above 70% was considered to be high muscle activity. The EMG signals are also useful when determining when there is co-contraction of specific muscles and can indicate whether the muscles are being used to stabilize the movement or if they are engaging in placing the segment in a non-neutral position to complete the movement.
Video Capture and Analysis
In addition to motion capture and EMG, video capture was used to record and analyze the Back In Form techniques. A video recorder was set up at an angle to best capture the motion of the caregiver. A video file was created for each trial and for each technique and was started and stopped as accurately as possible in conjunction with the motion capture and EMG data collection. Video representation of the techniques is a useful way to visually examine how the technique is performed and to interpret the different phases of the movement. Using 3D Match, a program that evaluates upper body postures and the loading and forces in the shoulder and spine the video files for each technique were analyzed. In order to accurately interpret these parameters, the height, weight, gender and age of the subject being analyzed is input into the system. The total weight of the load being handled, in this case the weight of the patient is also entered for accurate calculations of loading and forces. In this program, the video is examined frame by frame, where for each frame the posture of each body segment is selected based on the position of the caregiver. Also, for each frame, the mass of the load being handled on both the right and left side is entered in the x, y and/or z direction based on the actions being performed with the load such as push, pull or lift.
Once the video analysis was completed in 3D Match, the posture and loading information is processed in the program and the data is output to a spreadsheet in Excel. From this data, the percent of the time spent in awkward postures for the trunk, shoulder and neck can be extracted. The values are categorized in extension, neutral, mild or severe postures.