Sports Rehabilitation. Study on Counter Movement Jump Performance in a Force Platform.

Vertical jumping ability is an essential motor skill in many sporting, athletic and daily activities. It is common in many sports to perform loaded or unloaded jump series for better performance and explosive strength. This is the reason why many studies have analyzed the vertical jump from a physical point of view to establish the factors that have to be improved to increase jump height and minimize possible injury following higher jumps (Ortega, Rodriguez, & Rosa, 2010). Examination and the development of vertical jumping strength and skill have become an integral part of sports rehabilitation, especially among explosive sporting athletes. Jumping is usually preceded by a counter movement, which can be described as an initial bend of the hip and knee during which the body’s center of mass drops somewhat before being propelled vertically up off the ground with the extension of hip and knee(Harman, Rosenstein, Frykman, & Resenstein, 1990). According to (Harman et al., 1990), the countermovement jump uses the principle of Stretch-Shortening Cycle, which describes the use of elastic energy produced due to eccentric muscle stretching (during bending movement), is stored which is released or used during the subsequent concentric muscle contraction (during extension and take off).

The aim of this study was to understand and analyze different kinematics and kinetics of vertical jump motion performed on a force platform which may help to enhance sports rehabilitation. Many computer software has been developed that can produce curves of velocity and displacement of the jumper’s center of mass by numerical integration of the force–time record from a force platform. An effective relationship between the forces acting on a body and the resulting acceleration, velocity, and displacement of the body can be achieved and illustrated by the examination of these curves(Linthorne, 2001).

The biomechanical analysis of vertical jump performance has become the essential field of study in many sporting events such as soccer, basketball, and tennis etc. for the better performances, to ensure maximum safety during the events, and improve sports rehabilitation. For example, the vertical GRF on the body during landing can be a determinant of injury, especially if the jumps are made very often and GRF are high (McNair, Prapavessis, & Callender, 2000). Impact forces may contribute to optimal skeletal health (Fuchs, Bauer, & Snow, 2001). So, in order to understand the fact that why some athletes perform better vertical jump without any injury while many perform relatively lower jump heights and also faces with the injuries, it is necessary to assess and study both their muscle strength capabilities and jump techniques (Vanezis & Lees, 2005).

Therefore, the purpose of this study is to assess and understand the factors such as joint angles, moments and powers, muscle performances and ground reaction forces that play a key role in jump performance.

Methods and Procedures

The participant was a male (26 year’s age) with a body weight of 69.7 kg and the height of 168 cm. The supervisor briefed about the test, equipment used and safety majors of the test.

This study on countermovement jump performance on force plate was done in HPL lab. Of Massey University, Palmerston North to assess joint angles, moments and powers and ground reaction forces during a countermovement jump performance by the participant. Personal data was collected in Sports Biomechanics practical Lab. Class.

 Equipment

A force plate, Bertec Force Plate (Colombus, OH) was positioned firmly on the floor and was connected to a computer system with Bioware Software (Kistler, Detroit). Ground reaction forces were collected at the same time as the video was taken with a Casio Exilim Ex-F1 digital camera. Halogen Lights were used to provide adequate light to capture video clearly with marked positions in the body by using Casio Exilim Ex-F1 Digital camera.  The force plate and video were synchronized and digitized by using Max Traq software. Matlab software was used to kinetic and kinematic analysis of data and calculations for the results.

Procedure

To begin the study, first of all, 11 positions were marked on the body which will be digitized after the test for data analysis and results. The 11 positions were marked clearly in circular forms by using marker pen in following points;Vertex- the uppermost point on the head, Shoulder- greater tuberosity of the humerus, Elbow- lateral epicondyle of the humerus, Wrist- midpoint between the radial and the ulnar styloid process, Finger- metacarpophalangeal joint of the middle finger, Pelvis- superior iliac spine, Hip- greater trochanter of the femur, Knee- lateral epicondyle of the femur, Ankle- lateral malleolus, Heel- midpoint of the calcaneus, Toe- metatarsophalangeal joint of little toe. 

The subject first gets on the force plate and the initial force exerted on the plate was measured. The subject comes down to the plate and then gets on the plate again to perform the countermovement vertical jump while the video was captured. The reference frame to digitize was set as .66m and the points were digitized up to 601 frames starting from 0 to 900 frames. All the points along with left force plate and right force plate points as points 12 and 13 were digitized in each frame either by using manual tracking or automatic tracking method in Max Traq software.

Movement analysis and data presentation 

Data analysis was started from the start of a movement to take off, which included counter movement for the preparation of the jump.  This was followed by push-off and take-off phases before the jumper forcefully lifts his body off the ground to gain maximum jump height. Finally, data were analyzed for the time in the air, followed by landing and recovery phases (see appendix 1. fig. 1 for stick pictures of different phases in countermovement jump).

Kinematic analysis procedure

The three-dimensional motion data were analyzed in 13 marked points by using the Matlab software. These data were projected on the sagittal plane in order to compute segment orientations and joint flexion angles. These data were smoothed by using Fourier analysis method, which was then used to calculate joint angles, velocity, and accelerations and the segmental center of mass locations. Also, the X and Y locations of the whole body center of mass were calculated assuming the symmetry between the right and left sides of the body by using the formula as (X_cm=∑m_ix_i/∑m_i)_.

Kinetic analysis procedure

Ground reaction force files were loaded in the Matlab. Segments accelerations joint moments, contact forces and joint power were calculated by using standard procedures and equations (see appendix 2 for the equations and details of symbols). GRFs were presented in X, Y and Z directions as forward-back, sideways and vertical reaction forces respectively. Extension joint angles were presented as positive while flexion as negative. Similarly, joint power generation with concentric muscle contraction was presented as positive, while joint power absorption with eccentric muscle contraction was presented as negative. Total jump height was calculated from the vertical ground reaction force data as (velocity=Impulse/Mass), where the impulse is the integration of force and time interval over which the force acts.

Results

The total height of the jump performed was 0.2446 m with the impulse and velocity of 152.8503 and 2.1908m/sec respectively.

( I will update this post with a complete report, graphs, and detail data analysis soon. Thank you.)

Reference

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