Javelin throwing in the winter is not fun when the temperature approaches zero degrees. That is way javelin throwers move indoors for training. The problem with training indoors it that there is no room to throw a javelin 80 meters, so a different type of training is used. The javelin fitted with a rubber tip is thrown into a net. This way, the technique can still be practiced without the javelin’s flight. Unfortunately, the flight of the javelin can tell a lot about how well the javelin is thrown. Without that feedback, it is hard to know if an improvement in technique also results in a better throw. This project aims the fill that gap and provides performance feedback to the javelin thrower and the coach. Javelin throwing context First, the javelin throwing context is analyzed. The most critical parameters for measuring the performance of an athlete are the release velocity, release angle, and angle of attack. These parameters need to be measured with an accuracy of 0,25 m/s for the velocity and 1,5 degrees for both angles to give a realistic indication for the performance of the throw. The feel of the javelin is also crucial. It should hold the same as a standard javelin and should behave the same way when moving it around. Sports data collection The most used data collection now in day to day training is video recording, which can be played back in slow motion to dissect the technique of the athlete. As mentioned before, this does not tell everything about the performance of the throw. Several 3D tracking technologies are explored to find the best way the tracking the velocity and angles of the javelin. The best option seems to be a combined system of an inertial measurement unit inside the javelin with video tracking as an external reference system. The video can also be used to playback the recording of the throw. This way, the link between the technique and the performance of the throw becomes more apparent. Development For both the inertial measurement unit and the video tracking a proof of concept prototype is developed. The systems are combined to use the strengths of one system to fill in the weakness of the other. In this case, the video tracking can compensate for the drift of an inertial measurement unit, and the inertial measurement unit can reduce the noise in the video tracking data. Product A product name PRODON in build around the two tracking systems. It has active trackers front and back for the video tracking system to pick up. The inertial measurement unit is built into the back in a protective casing. The PRODON uses an app to communicate the collected performance data to the athlete and coaches. Combined with a video of throw, this can be a meaningful addition to indoor javelin training. Evaluation The accuracy of the prototype is tested in the situation where the javelin is thrown perpendicular to the camera. The velocity error calculated from this test is 0,02 m/s. The angle error tested came out to be 0,5 degree. Although these measurements fall below the set requirements, they are tested in a controlled 2D environment. Further testing in real conditions is needed to say for sure that this technology can provide accurate data.