The study took place at the University of Michigan-Dearborn, in the IAVS (Biomechanical) laboratory. Subjects used an 8-foot walkway as a path to perform the activities on which the force plates were installed and was located in the middle of twelve optical tracking cameras which were mounted on adjustable tripods as shown in the Figure 12. The field of view of the Optitrack system was not able to monitor the full space of study instead the cameras focused on the wooden walkway with force plates where each of the trails took place which made data collection optimal. The field of view was limited and allowed a limited space to collect data.
Figure 12: Camera Setup
All the cameras were located high above the ground and would not interrupt the study space (Figure 12). The cameras were connected to a main computer which powered and received the data. Both the Optitrack system and APDM system were calibrated and configured before the study to ensure accurate collection of data for each subject. Both the Optitrack and APDM systems were set up to record data and activities performed by the subjects simultaneously.
Subject
id Age Height(m) Weight(kg)
1 22 1.67 53.5 2 39 1.58 67.13 3 25 1.57 44 4 23 1.52 80 5 23 1.90 108.86 6 20 1.72 63.5 7 20 1.90 81.64 8 22 1.79 84.82
23 3.3.1 Optitrack Motive Calibration
After starting the motive software and warming up the cameras for five minutes, all the grayscale image of cameras was checked (Figure 13). It was made sure that there was no reflective material in the focused space or the subject was wearing anything reflective, if so it was covered with gaffer tape.
Figure 13: Masking the cameras free of any reflective material
After completing the above procedure, the camera calibration was done using the wanding option using the calibration wand. The wanding was done until all the cameras were covered as shown in Figure 14 and the results were calculated and applied to the particular subject’s take.
Figure 14: Calibration using the wand to cover whole space
After this, the next step was to set the ground plane using the L-frame. In the lab, the force plate was considered to be the ground since the activities would take place on it (Figure 15).
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The force plates were positioned in two different ways on the walkway as shown in the Figure 16 (a) and (b) for a jump and a run activity respectively.
Figure 16: Force plate position on walkway for (a) Jump trial (b) Run trial
Reflective markers were secured onto each subject using the “Lower body Rizzoli” protocol. The lower body Rizzoli skeleton has thirty-two markers specified. An extra sixteen markers were placed on the body for better tracking of the segments while creating a rigid body. The markers were placed on key bony locations, such as the joints by manually palpating the subject and the extra sixteen markers were placed in the form of a square cluster on the lateral side of both the thighs above the opal sensors and four on the gastrocnemius (lower back part of shank) just below knee for both the legs. Table 7 below lists all the marker labels that are required to be placed in the lower section of body.
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Table 7: Marker Labels
Waist Right leg Left leg Right foot Left foot
§ RASIS § RTH § LTH § RLM § LLM
§ LASIS § RLE § LLE § RMM § LMM
§ LGT § RHF § LHF § RCA § LCA
§ RGT § RME § LME § RFM § LFM
§ RTT § LTT § RDP § LDP
§ RSK § LSK § RVM § LVM
§ RSM § LSM
Figure 17 shows all the key bony points of the lower limb for where the reflective markers have to be placed.
Figure 17: Biomechanics Gait Marker Set for Lower Limb [30]
The description of all the thirty two Rizzoli lower body protocol to be placed on the body at various locations has been explained briefly in the Table 8.
Table 8: Marker Descriptions
Body Segment Marker Label Anatomical Location Description of Location
Waist
RASIS Right Anterior superior
iliac spine On the top of the anterior iliac spine. LASIS Left Anterior superior
iliac spine RPSIS Right Posterior superior
iliac spine locations where the spine On top of the bony joins the pelvis. LPSIS Left Posterior iliac spine
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Right Upper Leg
RGT Right great trochanter Right most lateral prominence of the greater
trochanter external surface.
RTH Right thigh Lower 1/3 of the lateral
surface of right thigh. RLE Right lateral epicondyle Most lateral prominence
of the lateral femoral epicondyle. RME Right medial epicondyle Right medial prominence
of the medial femoral epicondyle.
Left Upper Leg
LGT Left great trochanter Left most lateral prominence of the greater
trochanter external surface.
LTH Left thigh Lower 1/3 of the lateral
surface of left thigh. LLE Left lateral epicondyle Most lateral prominence
of the lateral femoral epicondyle. LME Left medial epicondyle Left medial prominence
of the medial femoral epicondyle.
Right Lower Leg
RHF Right proximal tip of the head of the fibula
RTT Right most anterior
border of the tibial tuberosity
RSK Right shin of the knee Near the midline of the shin below the right knee. RMM Right medial malleolus On the distal apex of the
medial malleolus of right knee.
Left Lower Leg
LHF Left proximal tip of the head of the fibula LTT Left most anterior border
of the tibial tuberosity
LSK Left shin of the knee Near the midline of the shin below the left knee. LMM Left medial malleolus On the distal apex of the medial malleolus of left
knee,
Right Foot
RCA Right calcaneus Upper ridge of the
calcaneus posterior surface. RVM Right fifth metatarsal
head On the fifth toe of the right foot RFM Right first metatarsal head Dorsal of the first foot
head
RDP1 Right distal phalanx Near the end of big toe, distal end of right
phalanges RSM Right second metatarsal
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Left foot
LCA Left calcaneous Upper ridge of the
calcaneus posterior surface.
LVM Left fifth metatarsal head On the fifth toe of the left foot
LFM Left first metatarsal head Dorsal of the first foot head
LDP1 Left distal phalanx Near the end of big toe, distal end of right
phalanges LSM Left second metatarsal
head Dorsal of the second foot head.
3.3.2 APDM Moveo Calibration
Figure 18: APDM setup
The APDM system was also configured before recording any data of the subjects. The hardware setup was done using the Moveo Explorer software on the computer. If any error occurred, the sensors would not be configured which was indicated by the software. After completing the configuration of the sensors, a test subject was added on the Mobility system software by filling in the required fields. The type of test form used for this study was “free form” as the activities (jump and run) which we performed were not listed in the software. The opal sensors were placed at particular locations specified by the software for the lower limb protocol (Figure 19).
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Table 9 below gives a detailed description about how the APDM opal sensors were to be placed on the subject’s body. In this study we only used the lower leg and upper leg sensors avoiding the foot and lumbar one. Upper and lower leg sensors were fixed to the subjects using co-flex bands at the required positions specified in the table.
Table 9: Sensor Location Description [6]
Body part Anatomical Description Common Description Orientation Lower Leg Just medial to the anterior
surface of the tibia, high enough for the strap to wrap just above the widest part of the gastrocnemius
Just inside the front of the shin, on the flat surface of the bone, high enough for the strap to wrap just above the widest part of the calf muscle.
Connector pointed straight down towards the floor
Upper leg Lateral side of thigh, on top of the iliotibial band,~4inches above the knee
Side of thigh, midline, between muscular tissue, one hand’s width above the knee
Connector pointed straight down towards the floor