Photocell and reflector units
Tripods or stands
Connection leads. (5 and 30m)
Set up Jumping timing system
Jon’s results
The graph shows an increase in speed over the first 10m then his acceleration starts to decrease but is speed (velocity) is still increasing. This happens til he has reached is maximum velocity.
The chart shows 4 out of the 5 values that the heavy the body mass the greater the mechanical power. In terms of acceleration and body mass it shows that lighter the body mass quicker the acceleration. The first value is lower but this result could be affected by gender differences hence female participant.
Discussion
The set up of the newtest powertimer is fairly basic and easy to use. There is a manual provided to assist in the set up. The power timer provides simple options on what to measure, and data is easy to collect and record. It is able to show a number of subject’s results within the memory capacity. The photocells work from a beam that goes to a reflector located directly opposite and is reflected back.
“Al though photocells are used frequently to estimate running speed, little information exists on the accuracy of the system.” (Yeadon et al,1998)
The method that Newtest powertimer uses to determine jump height is:
Equation = the calculation of distance in one direction.
The problem with the system is that it assumes that the subject is at there top height but there only half way though there jump. It assumes the jumping is upward not forward motion. (Flight time) The start position, centre mass and finishing position are different the system does not take this into account.
Specific measurements errors could be present when using the photocell gates.
- Sprinting over a short distance, not covering enough distance to again true acceleration.
- Safety of wires tacking to the floor
- Distance measured not enough room e.g. to close to walls.
- The time interval where the subject actually starts from
- Distances of the photocells not exactly 10m could be bigger or smaller
- The height of the photocell could increase the measurement error this due to the reflector being too low or too high. “This is when the legs or head breaking the beam earlier then the torso would have done. This would effectively reduce the split time and exaggerate the athletes speed between consecutive gates.” (UK athletics)
Issues concerning the jump timing system, that the calculation used for jump height does not work in terms of landing and jumping technique.
Yeadon 1998 suggested in his journal; Measuring running speed using photocells. That using a double beam system would solve the problem of certain parts of the body breaking the beam. This would work in terms of having two photocells instead of one so that it would reduce the possibility of triggering the system with the arm or leg. It would increase the possibility of selecting the instant that the torso breaks the beam. The other method used was to use a measurement system that had accuracy. This system was used to measure running speed using film and video analysis together with a linked model of the human body (Hay and Miller, 1985; Mero and Komi, 1985; Hay et al,1986; Hamilton,1993)
References
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Graham-Smith,P,(2002) How to use your speed timing lights, UK Athletics, Available online at URL:
- Hay,J.G. and Miller, J.A (1985). Techniques used in transistion from approach to takeoff in the long jump. International journal of sport biomechanics, 174-184.
- Hay,J.G. Miller, J.A and Canterna, R.W (1986). The techniques of elite male long jumpers. Journal of sport biomechanics, 19, 855-866.
- Newtest Powertimers-homepage,(2004),Available online at ULR:http://www.newtest.com
- Yeadon, M.R, Kato, T and Kerwin, D.G, (1999), Measuring running speed using photocells, journal of sports sciences, 1999, 17, 249-257
The chart shows that the correlation for the drop jump is lower compared to the static jump. This is the points on the chart show that there is one subject that does not have the quickest acceleration over 10m but as a higher mechanical power out put. Also the subject who had the quickest acceleration was had a lower power out put. In terms of static jump there was a more positive correlation. This was static jump did not produce more power output then drop jump. This was not in one of the subjects results.
