Question 1

At what height would most players hit the ball during the serve - give your answer in relation to their own body height?

Accepted Answer

The answer of At what height would most players hit...

Question 2

Why do you think that there has been an increase in the average height of the top 5 male tennis players in the world between 1999 and 2018?

Accepted Answer

The answer of Why do you think that there has...

Question 3

The Hanning algorithm

Accepted Answer

The Hanning algorithm is a moving average method of data smoothing, but its inflexibility limits its use for all types of biomechanical data.

Question 4

In electromyography recordings, a spike in the frequency domain around 50 or 60 Hz is likely related to

Accepted Answer

Spikes in the frequency data around 50 Hz, for countries like the United Kingdom and Australia, or 60 Hz, for countries like the United States of America, likely reflect environmental noise related to the country's AC power supply

Question 5

The 2nd order Butterworth algorithm is applied to the data twice

Accepted Answer

When applied to data, the 2nd order Butterworth algorithm introduced a temporal shift in the data. To correct for this time shift, the data is processed a second time, but in reverse.

Question 6

Given the following: x_i-1 = 1.221 X_i = 1.274 X_i+1 = 1.253 Use the Hanning algorithm to calculate the smoothed data point (y_i) to 3 decimal places.

Accepted Answer

Using the Hanning algorithm, the smoothed data point would be calculated as:
(0.25*1.221) + (0.50*1.274) + (0.25*1.253) = 1.256

Question 7

Quintic spline algorithms

Accepted Answer

The quintic spline method seeks to use a fifth-order (quintic) polynomial to sequentially fit a smoothed curve over adjacent collections of data points; repeating this process until the end of the data set is reached. Advocates for spline-based techniques suggest that they are more suited for processing kinematic data, as they better replicate the smooth nature of human movement and provide more precise results for the first and second derivatives.

Question 8

Digitisation errors may be caused by

Accepted Answer

Digitization errors commonly occur due to; i) difficulties with consistently and/or accurately identifying reference points and joint centres; or ii) limitations in the resolution of the digitising system (e.g. the size of the image relative to the actual field of view)

Question 9

Any noise in displacement data, will be exacerbated in velocity data

Accepted Answer

When displacement data includes errors (noise), these errors are increased during the differentiation process. As such, velocities derived from displacement data and accelerations derived from velocity data are less reliable for noisy displacement data.

Question 10

The Hanning algorithm offers greater flexibility than alternate methods, such as the 2nd order Butterworth algorithm

Accepted Answer

Although the Hanning algorithm is quite simple, it lacks the flexibility that is often needed to attenuate the noise that is inherent in biomechanics data.

Question 11

In your own words, describe why the 2nd and 4th order Butterworth algorithms are related

Accepted Answer

The answer of In your own words, describe why the...

Question 12

The following data represent a subject's horizontal walking velocity over a 10-metre distance, with each data point representing the average velocity over each 1-metre increment. Using the Hanning algorithm and the appropriate start and end point routines, calculate the smoothed values for the following dataset:
 $ \begin{array}{ll}\text { Data point \# } & \text { Raw Velocity }(\mathrm{m} / \mathrm{s})& \text {  Smoothed Velocity(m/s)}  \ 1 & 0.287 \ 2 & 0.792 \ 3 & 0.911 \ 4 & 1.132 \ 5 & 1.221 \ 6& 1.178 \ 7 & 1.221 \ 8& 1.252 \ 9 & 1.228 \ 10& 1.205\end{array} $

Accepted Answer

The answer of The following data represent a subject's horizontal...

Quiz 7: Measurement and Analysis Techniques