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.
 Or, High Speed camera and computer equipped with MaxTraq 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. You will test this theory.
Jumping: Squat jumps will be performed from two depths. The first jump will be from a preferred
depth; the depth the participant feels they can jump the highest from. The second jump will be from a
much deeper (~15 cm lower based on the vertical position of the center of mass. 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. For example, the arms must not move in-and-out of the plane during the
jump. Ensure reflective markers are not occluded for significant portion of the jump. 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.
HUMAN Analysis: In order to calculate the jumper’s center of gravity throughout the jump, you will be
using the 9 or 12 Point Symmetric model as defined in HUMAN. Please read the Help files in
Dr. Sasho MacKenzie – Advanced Biomechanics
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 intermediate files.
OR
You can digitize in Maxtraq. Upsample the data to the same frequency as the force plate. Import both
the Trial Coordinate data and Force Plate data into HUMAN and allow you to do all the complex
calculations.
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 both 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)
Dr. Sasho MacKenzie – Advanced Biomechanics
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)
7) Plot the ball, ankle, knee, and hip torques during the preferred 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 or toe
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 =
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Dr. Sasho MacKenzie – Advanced Biomechanics