Biomechanical Analysis of Sports Performance

ESS2003 Kinesiology and Biomechanics II

Laboratory Session 3

Biomechanical Analysis of Sports Performance

Dr Sharon Dixon

Purpose

To provide students with practical experience of analysing a sports skills using video data.

Aims

1.  To use kinematic data to compare kicking performance with the right and left foot.

2.  To identify the contribution of different anatomical joints to performance of a tennis serve.

Comparison of Right and Left Footed Kicking

1. Accessing the video file in Hu-m-an.

- Double click the ‘Hu-m-an’ icon on desktop

- File – ‘load trial’.

In ‘Directories/Path’ double click left mouse button on:

‘[-e-]’- progr~1 – studio~1 – captur~1

The video files will be displayed in the left hand box.

Double-click the left mouse button on Left1s~1.avi

2.  View the video sequence

In VIDEO-MODEL CONTROL window

-  play the video sequence

-  slow video playback speed by reducing ‘Speed’ to ‘1’

-  experiment with using the video controls

3.  Select model for digitising

-  Edit – Trial Set Up

Under ‘List of Trial Set Up Titles’ - Select ‘5 Pt. Lower Limb & Ball’

-  Load – Yes – Exit

4.  Select frames for digitising

In VIDEO-MODEL CONTROL window

-  use single frame forwards and backwards to identify the frame where movement begins

-  enter this frame number as the ‘Start’ frame at the top of the window.

-  Utilities – Set New Trial Subsequence (Yes)

5.  Set scaling and digitise the kicking sequence

-  Options – Digitise

DIGITISE window will be active

-  Use single frame forwards and backwards to identify a frame where both ends of the metre rule (on the back wall) are clearly visible.

-  select ‘Scale’

-  Click ‘OK’,

-  Click ‘OK’,

-  under Real Length input 1.0

-  under Length Units select ‘metres’

-  digitise (click with left mouse button) the ends of the metre rule

-  select ‘Apply New Scale’

-  Return to frame 0

-  using the left mouse button, select body landmarks as specified in the DIGITISE window

Ø  hip, knee, ankle, heel, ball of foot, ball

-  click left mouse button to advance to the next frame

-  if an error is made, click ‘re-digitise this frame’ to redigitise the whole frame

Each member of the group should take turns digitising.

When all frames have been digitised, close the DIGITISE window by clicking ‘exit’.

6.  View the model

Using VIDEO-MODEL CONTROL window

-  play the sequence to view the video and the model simultaneously

-  select (tick) +Model

-  view the sequence again

7.  Marking ball contact frame

Edit – Trial Setup

Under ‘Subject – Trial Data’ click ‘Build/Edit’

Add

Name the point as ‘ball strike’

Enter the frame number for ball strike (as identified from the video).

Tick the Activate box.

Exit

Exit Trial Setup

8.  Calculate segmental angles during kick

Calculate - Absolute angles

Select Thigh (wrt the Hip)

Ø  Calculate

Calculate Absolute Angles

Select Shank (wrt the Knee)

Ø  Calculate

Draw a stick figure showing the thigh and shank angles as defined in your model:

Figure 1 – Lower extremity segmental angles.

9.  Calculate Angular Velocities

Calculate – Velocity

Thigh (wrt the Hip) velocity – Calculate

Calculate – Velocity

Shank (wrt the Knee) velocity – Calculate

In GRAPH DATA CONTROL window

Select Thigh (wrt the Hip) velocity

Select Shank (wrt the Knee) velocity

Graph the angular velocities in Figure 2 and identify the peak angular velocity values (Table 1).

Remember that the velocities for the left foot kick will be reversed, i.e. the positive values are negative and negative values are positive.

Figure 2 – Thigh and shank angular velocities during kicking.

Include a vertical line in Figure 2 to indicate the point of ball contact.

Complete Table 1.

Table 1 – Maximum segmental angular velocities in kicking

Peak angular velocity

/

Timing

Velocity (degrees/s) /

Velocity

(radians/s) /

Number of frames prior to ball contact

Thigh (left)
Shank (left)
Thigh (right)
Shank (right)

10.  Calculate linear velocities

Calculate – Velocity

Ball – Resultant Speed – Calculate

Calculate – Velocity

Hip – X Velocity – Calculate

Calculate – Velocity

Knee – X Velocity – Calculate

Calculate – Velocity

Ankle – X Velocity – Calculate

Complete Table 2.

Table 2 – Maximum linear velocities during kicking.

Point / Left foot* / Right foot
Linear velocity (m/s) / Timing (frames prior to contact) / Linear velocity (m/s) / Timing (frames prior to contact)

Ball

Hip
Knee
Ankle

*When calculating these values for the left foot kick select the maximum negative values (the lowest points on the graph) but ignore the sign ( – ).

11.  Graph of linear velocities

Graph the linear velocities and complete Figure 3 for the ball, hip, knee and ankle.

Figure 3 – Linear velocities for the ball, hip, knee and ankle.

Repeat the above procedures for the kick with either Right1~1.avi or Right2~1.avi (use the same number as you did for the left leg digitisation and complete Table 1 and Table 2.

Questions

1.  Describe qualitatively the segmental contributions to a maximal soccer kick.

2.  How do the ball speeds compare for the left and right-footed kicks?

3.  What are the main differences in kinematics (linear and angular velocities) between the right and left kicks?

4.  Suggest reasons for any observed differences between the right and left.

5.  How does the data for the subject you analysed compare with that published in the literature?

Kinematic Analysis of a Tennis Serve

1. Accessing the video file in Hu-m-an.

- Double click the ‘Hu-m-an’ icon on desktop

- File – ‘load trial’.

In ‘Directories/Path’ double click left mouse button on:

‘[-e-]’- progr~1 – studio~1 – captur~1

The video files will be displayed in the left hand box. Double-click the left mouse button on ‘tennis.avi’.

2.  View the video sequence

In VIDEO-MODEL CONTROL window

-  play the video sequence

-  slow video playback speed by reducing ‘Speed’ to ‘1’

-  experiment with using the video controls

3.  Select model for digitising

-  Edit – Trial Set Up

Under ‘List of Trial Set Up Titles’ - Select ‘11 Pt. Symmetric’

-  Load – Yes – Exit

4.  Select frames for digitising

In VIDEO-MODEL CONTROL window

-  use single frame forwards and backwards to identify the frame where movement ends

-  enter this frame number as the ‘End’ frame at the top of the window.

-  Utilities – Set New Trial Subsequence (Yes)

5.  Digitise the serve sequence

-  Options – Digitise

DIGITISE window will be active

Digitise the right side of the body.

-  using the left mouse button, select body landmarks as specified in the DIGITISE window

Ø  head, wrist, elbow, shoulder, hip, knee, ankle, toe, tip of toe, ball, heel

-  click left mouse button to advance to the next frame

-  if an error is made, click ‘re-digitise this frame’ to redigitise the whole frame

Each member of the group should take turns digitising.

When all frames have been digitised, close the DIGITISE window.

6.  View the model

Using VIDEO-MODEL CONTROL window

-  play the sequence to view the video and the model simultaneously

-  select (tick) +Model

-  view the sequence again

7.  Marking ball contact frame

Edit – Trial Setup

Subject – Trial Data

Add

Name the point as ‘ball strike’

Enter the frame number for ball strike (as identified from the video).

Tick the Activate box.

Exit

Exit Trial Setup

8.  Calculate joint angles during serve

Calculate - Relative angles

Select Hip angle

Ø  Calculate

In GRAPH DATA CONTROL window

Select Hip angle

Calculate Relative Angles

Select Knee angle

Ø  Calculate

In GRAPH DATA CONTROL window

Click ‘Clear/Reset’

Select ‘Knee angle’

Calculate Relative Angles

Select Shoulder angle

Ø  Calculate

In GRAPH DATA CONTROL window

Click ‘Clear/Reset’

Select ‘Shoulder angle’

Calculate Relative Angles

Select Elbow angle

Ø  Calculate

In GRAPH DATA CONTROL window

Click ‘Clear/Reset’

Select ‘Elbow angle’

Identify the peak flexion angles during the serve by clicking on the appropriate points of the graph. Identify the time of peak flexion angle relative to the point of ball contact. Input results in Table 3.

*Peak flexion angles for the HIP, SHOULDER, and KNEE can be calculated by selecting the maximum point on the graph and taking it away from 360° (360° - q).

ELBOW peak flexion is the nearest point on the graph to 0°.

Table 3 – Maximum joint flexion and timing during tennis serve

Angle (degrees) / Timing
(frames prior to ball contact)
Hip
Knee
Ankle

Draw a stick figure showing the joint angles as defined in your model:

Figure 4 – Lower extremity joint angles in the tennis serve

9.  Calculate Angular Velocities

Calculate – Velocity

Hip angle – Calculate

Graph the angular velocity and identify the peak angular velocity.

When does this occur relative to ball contact?

Repeat for the knee, shoulder and elbow angular velocities, and complete Table 4.

*Maximum joint angular velocities are the minimum points on the graph during the 10 frames preceeding ball contact. These negative values are positive.

Table 4 – Maximum joint angular velocities in tennis serve.

Maximum angular velocity

Velocity (degrees/s) / Velocity
(radians/s) /

Timing (frames prior to ball contact)

Hip
Knee
Shoulder
Elbow

Questions

1.  In what order do the maximum flexion angles occur?

2.  In what order do the peak angular velocities occur?

3.  Compare what you found in the tennis serve with your findings in the soccer kick. Identify similarities and differences, and their significance.

4.  What difficulties were there in digitising the tennis serve sequence? Suggest how these may be overcome.

Additional Reading

Lees, A. and Nolan, L. (1998). The biomechanics of soccer: A review. Journal of Sports Sciences 16, 211-234.

Dorge, H.C., Bull Andersen, T., Sorensen, H. and Simonsen, E.B. (2002). Biomechanical differences in soccer kicking with the preferred and non-preferred leg. Journal of Sports Sciences 20, 293-299.

McLean, B.D. and Tumilty, D. McA. (1993). Left-right asymmetry in two types of soccer kick. British Journal of Sports Medicine 27, 260-262.

Elliott, B.C., Marshall, R.N. and Noffal, G.J. (1995). Contributions to upper limb segment rotations during the power serve in tennis. Journal of Applied Biomechanics 11, 433-442.

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