Download Assignment #1 – Original Analysis in Human

HK 474 Advanced Biomechanics
Squat Jump Lab
Purpose:
 Familiarization with the operation of the force plate.
 Collect and analyze kinetic data generated during vertical jumping.
 Synchronize force plate data with video data.
 Apply theories to explain your findings.
 Review the literature and retrieve a few (but very relevant) articles to support your theories.
Resources:
 Force plate and necessary data collection accessories.
 Video camera and computer equipped with Dartfish software.
 Thoroughly warmed-up subject equipped with reflective markers
 HUMAN software
 Checklist for using a Digital Video Camera.doc
 Collecting Data with the Force Plate.doc
 Force plate and NetForce software manuals
General Description:
According to your well devised theoretical models, jump height is primarily determined by the vertical
impulse applied by the ground to the feet of the jumper during the upward movement of the jumper’s
center of gravity. The other determinant is the height of the jumper’s center of gravity at take-off. For
the average athlete with a moderate level of coordination, the height of the jumper’s center of gravity at
take-off will have an insignificant amount of variation from jump to jump. Theoretically, lowering the
squat depth from which an athlete jumps should increase the time of force application and therefore
impulse. This should result in a higher jump height. In order to test this theory one subject from each
group will perform three maximal squat jumps.
Jumping: Jumps will be performed from two sets of knee and hip angles [(105, 75), and (85, 55)] while
keeping the ankle angle at a constant 100 for both jumps. Dartfish (use drawing tools) should be used
in conjunction with the projector and projector screen, so that the jumper can correctly fit themselves
into the required position. It is vital that each jump used for analysis is a maximal effort jump. It is
also possible that the coordination of body segments is not optimized from each jump position. Do
your best to ensure this happens and redo trials if necessary. When filming make sure the camera zoom
doesn’t change from trial to trail. In order to work within the constraints of HUMAN’s 2D Model (see
below), all movements must occur in a plane perpendicular to the camera. Therefore, the arms will
hang vertically down from the shoulders throughout the jump. That means they should remain parallel
to gravity throughout the jumps. Trials with arm movement should be discarded. Only videos and
force plate files that will be analyzed should remain on the computers. DELETE ALL OTHER DATA
YOU COLLECT. Jumpers should warm-up thoroughly. Warm-up squat jumps should be taken from
the two depths in an attempt to simulate the data collection conditions.
Dr. Sasho MacKenzie – Advanced Biomechanics
HUMAN Analysis: In order to calculate the jumper’s center of gravity throughout the jump, you will be
using the 9 Point Symmetric model as defined in HUMAN. Please read the Help files in HUMAN to
determine exactly where to place the reflective markers. Marker movement is a big issue. Subjects
should wear tight clothing (spandex if possible) that will move very little relative to the body. A tank
top with spandex shorts would be good. Dark spandex shorts with no shirts, or an Under Armour
bodysuit would be ideal.
Logistics: Depending on the camera used you may have to convert the video files for use in HUMAN.
You may also have to split the files if 30 fps doesn’t allow you to determine the timing of segments.
Use EditV32 in the HUMAN folder and be sure to convert back to HUMAN format to reduce file size
(See Original Kinematic Analysis in HUMAN Lab). Delete all unnecessary intermeditiate files.
Hip
angle
Knee
angle
ankle
angle
Lab Report to be passed in:
When appropriate make references to the literature to support your answers.
1) Pictures showing the starting position for each jump. Include ankle knee and hip angles in each
picture. I believe this can be done in both HUMAN or DartFish. (3)
2) On a single graph, plot the vertical ground reaction force for the entire 4 second collection
period for all three jumps synchronized so that initiation of upward motion occurs at the same
time. Draw a horizontal line representing the bodyweight of the jumper. Use a 1 or 2 pt
connecting line NOT symbols for each line. (2)
3) Plot the net vertical force acting on the jumper, as well as, the cumulative net vertical impulse
for each jump for the entire 4 second collection period. Each jump should be plotted on a
separate graph. Draw one vertical line representing the initiation of upward movement and a
second vertical line representing the time at take-off. (3)
4) Were there any discrepancies in the four methods used to calculate jump height (see table
below)? Explain why these discrepancies existed. Which calculation method is most valid?
Why? (4)
5) Which squat depth resulted in the highest jump height? Was the peak force from the deep squat
jump less than the other jumps? If so, why? (2)
6) Can the reduced vertical ground reaction forces from the deep squat position be explained using
the muscle mechanics factors learned in HK 376? (4)
Dr. Sasho MacKenzie – Advanced Biomechanics
7) Plot the knee extension torque during the mid squat depth jump and compare to similar curves
or measurements available in the literature. This will first require calculation of the location of
the center of pressure. You will also need to know where the center of pressure is in relation to
the foot. For example, if you successfully calculate the CoP, it will be in relation to the origin
of the force plate. Therefore, you need to know the foot’s position in relation to the origin of
the force plate. The best way to do this is to ensure that the ankle marker for the subject is at
the origin of the force plate. The jumper must also be symmetrical on the force plate (e.g., one
foot should NOT be ahead of the other). (4)
8) Complete the following table: Note that jump time refers to the total time from initiation of
upward movement until take-off. (4)
Subject weight reading from force plate for each jump
Jump Ht. of CG from HUMAN CG data
Jump Ht. of CG from force plate impulse data
Jump Ht. of CG from force plate time in air data
Jump Ht. of CG from integrating acceleration
Ht. of CG at bottom of squat from HUMAN CG data
Ht. of Hip marker at bottom of squat
Jump time (force plate)
Average net vertical force during the jump time
Peak net vertical force and (the percentage of jump
time that it occurs).
Max hip angular velocity and (the percentage of jump
time that it occurs).
Max knee angular velocity and (the percentage of
jump time that it occurs).
Max ankle angular velocity and (the percentage of
jump time that it occurs).
Deep Squat
Eg. 685.4
Shallow Squat
Eg. 687.9
Eg. 800 N (60%)
Eg. 60 rad/s (50%)
Note: Please place two graphs on each 8 ½ by 11 sheet of paper. Each graph should have time on the X
axis.
Total =
26
Dr. Sasho MacKenzie – Advanced Biomechanics