PEP 294: Web-Based Labs

Lab #5: Time Analysis

Before you start this lab, first read the general instructions for the PEP 294 web-based labs.

Procedures: Swimming Race Analysis (10 pts.)

Videotaping athletic events allows coaches and biomechanists to quantitatively evaluate the performance of an individual. Time analysis involves the use of video cameras linked to the start of the race in order to synchronize time intervals.

It is possible to determine the average velocity (v) of an athlete by dividing the distance covered by the amount of time necessary to travel the distance:

   [1]

where d = distance, and = elapsed time. Further, average velocity is also a function of cycle length (CL) and cycle rate (CR):

    [2]

Equations 1 and 2 are commonly used in the time analysis to compute the average velocities and the average cycle lengths in sports such as track events & swimming. Based on these calculations, coaches and athletes may review the performance to understand what may be deficiencies and/ or proficiencies during the performance. The purpose of this lab is to perform a time analysis based on the data obtained from an international swimming competition.

Figure 1 below shows a diagram that describes the camera arrangement utilized in order to capture the swimmers for a 100 meter sprint. The Start interval is measured from 0 meters to 10 meters (10 m). The Clean Swim I interval is measured from 10 m to 42.5 m (32.5 m). This is the interval in which the stroke rate (SR) is measured by identifying the time interval that the athlete’s arm enters the water and begins the stroke cycle. The time interval is stopped when the same hand enters the water for the second cycle. This information has been calculated for you in the lab. The Turn interval is from 42.5 m to 57.5 m (15 m). The Clean Swim II interval is measured from 57.5 to 92.5 m (35 m). Once again, this interval is used to calculate the SR of the swimmer. The Finish interval, or Sprint, is from 92.5 m to 100 m (7.5 m).

The following data were taken from the male 18+ age group in 100m freestyle during the 10^th Asia-Pacific Age-Group Swimming Championships held in 1996.

The above times are the absolute times as recorded from the cameras. A device called 'time code generator' was used to insert the time codes in the video images. The time codes were read off from video and converted to seconds.

Stage 1: Interval Times

In order to put these times in terms of the interval time, we need to subtract the times. For example, to determine the time spent in Clean Swim I:

Interval Time (CS I)  =  Time at 42.5 m - Time at 10.0 m

                             =   20.82 s - 3.64 s  =  17.18 s

Thus the total time spent in Clean Swim I is 17.18 s. Calculate the remaining interval times for the swimmers in Table 2 below using the time data given in Table 1. The first place finisher has been done for you.

Stage 2: Average Velocities

Once we have calculated the interval times between each point, we can compute the average velocity (v) of the swimmer through each time interval:

   [3]

The length of CS I is 32.5 m (Table 3), so the average velocity of LI (HKG) will be:

Compute the average velocities of all the intervals in Table 3.

Stage 3: Average Stroke Lengths

From Equation 2, velocity is also a function of stroke length and stroke rate. Since we can compute the average velocity of the athlete and we can determine the SR from the camera and time intervals, we can calculate the stroke length of the athlete:

   [4]

Stroke rates (SRs) were measured during the Clean Swim intervals by marking the time when the arm begins and ends two stroke cycles. Thus, the SR is only valid during the Clean Swim portion of the swim. For our purposes, the SR were calculated and given in Table 4. Note in the table that the velocities are in m/s but SRs are in 1/min rather than in 1/s.

Compute the Stroke Lengths (SL) of each athlete during the Clean Swim intervals (Table 4) using Equation 4. For example, the SL of LI (HKG) in Clean Swim I is then:

Note in the above computation that 60 was multiplied to convert the unit of the SR from 1/min to 1/s.

Stage 4: Data Analysis

By comparing the times, average velocities, stroke lengths, and stroke rates during the athletic event, coaches and researchers can review athletic performance, and evaluate the differences (deficiencies & proficiencies) between athletes. Quantitative assessment of athletic performance, such as that above, can lead to a greater understanding of the physical demands necessary during competition.

Based on the data obtained, answer to the following questions.

Questions (15 pts)

1. The most important factor in swimming is the ability to swim fast. In this regard, compare the swimmers' Clean Swim velocities. Which swimmers had higher swim velocities than others? Include a chart that summarizes the CS velocities of the swimmers.

2. Often times in swimming, the swimmer who wins does not always have the greatest velocity throughout the entire race. Two competing swimmers may have the exact same velocity throughout the Clean Swim intervals, yet one swimmer may be slower during the Start or Turn. Using Table 3, compare the average velocities of the swimmers in the Start interval and the Turn interval. Which swimmers had higher Start and/or Turn velocities? Include a chart that summarizes the Start & Turn velocities of the swimmers.

3. Look at the changes in the swimmers' velocities throughout the race. What happens to the swimmers' velocities as they swam through the intervals? Include a chart that summarizes the velocity changes throughout the race.

4. Compare the Start & Turn velocities with the immediately following Clean Swim velocities? What is the practical implications of this result?

5. Compare the SRs and SLs of the swimmers between Clean Swim I and Clean Swim II. What happened to the SR and SL as the swimmer moved from Clean Swim I to Clean Swim II? Include graphs that summarize the SRs and the SLs in CS I & II.

Tips: Use a spreadsheet program to draw the graphs. Insert the graphs into your answers. Pay attention to the axis labels, units, and the legends.