I finally ended up simplifying the whole task and starting from the very beginning. I had two data sets of two athletes with the same training attributes (data columns). The earlier matlab script did some sort of pretraining with the one dataset and some sort of main training and cross validation with the second dataset. Remember, I am still trying to reproduce the results from the paper (which were generated with Data Engine) using MatLab.

I now merged these two datasets into one with 42 examples (still not many, though) and modified the script to do simple cross validation with one dataset. It’s therefore more generic and can be applied to different data as well. The results look as follows:
Still not perfect, the average error is way too high and I will have to experiment with different parameters.

modified script