Comparison of JuniStat technology and laser systems for running tests


Introduction

At the first meeting, each club and federation is usually interested in the accuracy of measurements that the technology can provide. junistat. As part of the pilot launch, measurements are taken according to a certain familiar and understandable standard. Over the past six months, testing of players has been carried out to verify the validity of data on lasers by three federations and two clubs. We have gained experience in this area and want to share it. It should be noted that all validations were successful, but the results required explanation. In most cases, the first reaction was surprise because 70-80% of the results match, and the remaining 20-30% look like outliers, but in fact they are not. It is necessary to analyze the different methods of measurement and find out why the results differ.

How is jerk time measured now?

When testing players, one of two methods of measuring dash time are currently most commonly used:

  1. Using a stopwatch

  2. With a laser system

Rice.  1 Scheme of measuring the jerk time.

Rice. 1 Scheme of measuring the jerk time.

When measuring with a stopwatch, the coach measures the required distance, gives the command to start and presses the button on the stopwatch. When the athlete finishes, the coach stops the countdown. The reaction time of the athlete and coach, as well as different ways of fixing the moment of the finish, can affect the accuracy of the measurement. Someone looks at the intersection with the hand, someone with the foot, someone with the pelvis, and so on. The reaction time can give an error of up to ± 0.01-0.02 sec, and the factors for fixing the moment of the finish can give up to 0.1 sec, which is 5-10% of the total time when jerking at a distance of 10-15 meters.

To reduce the influence of the human factor and improve the measurement accuracy, laser systems are used. Special racks with laser sensors are installed at the start and finish of the running distance. In this case, the time from crossing the rack at the start to crossing the rack at the finish is fixed, and the reaction time of the athlete and coach is no longer included in the result. However, the use of laser systems can also have its own characteristics, which will be discussed below.

Experiment Method

To compare jerk times, laser sensors and JuniStat technology are used. To measure the time of passing a distance using the JuniStat application, you need to perform a number of preparatory steps. First of all, it is necessary to install cones or markers at the start and finish, similar to the start and finish gates used in laser systems. This will allow you to determine the beginning and end of the distance at which the experiment will take place.

Lasers record only the time the runner passes through the points on the distance, and JuniStat additionally collects information about reaction time, running time, speed and other parameters. With the simultaneous use of laser sensors and JuniStat, results can be obtained that can be used for further analysis and comparison of results.

Fig 2. Platform for comparing the measurement time by lasers and using JuniStat technology.

Fig 2. Platform for comparing the measurement time by lasers and using JuniStat technology.

results

The table shows the results of one of the measurements showing the time of passing the distance through lasers and obtained using JuniStat technology, carried out by independent experts.

Table 1. 15m dash time measured with lasers and JuniStat technology

Table 1. 15m dash time measured with lasers and JuniStat technology

As can be seen from the table, in some cases the results coincide with an accuracy of hundredths, and in some cases the result obtained with the help of lasers is 0.02-0.06 sec longer. Let us consider the reasons that led to the appearance of such differences in the results obtained.

Reasons for discrepancies in results

At first glance, the measurement accuracy with the help of lasers depends only on the quality of synchronization of the “gates” with each other and the response speed of the photosensor. Even not the most expensive laser systems are capable of providing an accuracy of the order of 0.001 seconds or hundredths of a percent. This is more than enough to solve the problem. However, when using lasers, a problem arises that a person is not a material point or a solid body. Lasers can be triggered by crossing the arm, head, or shoulder (Fig. 3), which can lead to measurement errors.

Rice.  3 The athlete crosses the laser with his head while tilting at the moment of the jerk, while his pelvis remains motionless.

Rice. 3 The athlete crosses the laser with his head while tilting at the moment of the jerk, while his pelvis remains motionless.

A person can cross the starting gate “with a run”, for this it is enough to step back from the starting line by 15-20 cm, etc. In contrast, the Junistat application uses video analysis, which avoids such problems.

Rice.  4 The athlete crosses the starting line with speed already gained.

Rice. 4 The athlete crosses the starting line with speed already gained.

Also, it is important to take into account that in humans, different parts of the body begin to accelerate in different ways, which differs from the mechanics of the beginning of movement in a rigid body. For example, at the moment of start, the body is tilted much more strongly than at the moment of finish. At the same time, the head starts a little earlier than the pelvis, and they finish almost simultaneously. To obtain more accurate and comparable results, it is necessary to follow the most stable point, a certain center of mass, which in humans is located in the pelvic area, in front of the sacrum. With the help of lasers, this is quite problematic.

In the process of research, we noticed that some people (about 10%) reproduce their result with an accuracy of hundredths. They move exactly the same from run to run. One of these athletes was asked to change the starting position in order to see how the starting point affects the result. Figure 5 shows the silhouette of the same person in different races with a difference in distance to the starting line at the time of the signal. The place of setting the foot, the length of the step and the speed indicators are the same to within pixels, if the start is virtually shifted to one point. When the athlete’s starting position is shifted by 15-20 cm, the laser time may differ by several hundredths (3-5%), which is considered quite significant.

Fig 5. Two races of the same athlete.

Fig 5. Two races of the same athlete.

An additional advantage of using video analysis is that it is possible to collect such metrics as speed, acceleration, reaction time and identify errors in the exercise technique, as well as unify the measurement methodology.

Figure 6. The speed of the athlete in different areas.  It can be seen that the athlete continues to accelerate to the finish line

Figure 6. The speed of the athlete in different areas. It can be seen that the athlete continues to accelerate to the finish line

Figure 7. The speed of the athlete decreases towards the end of the distance.  We need to work on the finish line.

Figure 7. The speed of the athlete decreases towards the end of the distance. We need to work on the finish line.

conclusions

In recent years, youth football has attracted more and more attention. Regular football testing of players has become the norm and an integral part of the training process. Regular data collection is carried out in all clubs, where they are aimed at player development and achievement of sports results.

As you can see from the story above, lasers can provide very accurate results, but are not always the most appropriate tool for collecting data in sports. It is necessary to follow a number of requirements for the experiment in order to realize the full potential of the laser system in terms of measurement accuracy. The influence of human factors is still great. Different trainers who use the same lasers may use different measurement techniques. Someone asks to start a little earlier, place lasers at different heights, and so on. All this also contributes to the final result. Thus, the same athlete may get different results depending on who took the measurements.

Moreover, when using lasers to measure running time, small physical differences between athletes can lead to skewed results. A shorter athlete can cross the beam with his head or shoulder, and a taller athlete with his arm or pelvis. In this case, the difference in the results can reach several hundredths of a second.

On the other hand, when using video analysis, you can see all the details of the movement and determine exactly what the deviations are. For example, you may notice that the athlete starts early from the starting line or crosses the laser beams due to body tilt. By examining such details, one can draw more accurate conclusions about the athlete’s ability and performance.

The use of video analysis in sports may be the preferred method of measurement as it is less sensitive to human error, provides a more uniform methodology and allows for more detailed analysis of the athlete’s movements and allows for all these nuances to be taken into account so that all participants are on an equal footing.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *