Is it permissible to combine the Maghrib and Isha prayers due to exercising for an hour or more, knowing that Maghrib prayer time begins at 5:20 and Isha at 6:50, and the training starts at 6:0?

The fundamental principle is that every obligatory prayer must be performed within its prescribed time, and it is not permissible to combine two prayers except for a legitimate Shar'i (Islamic legal) excuse. Practicing sports is not among these excuses. Therefore, you have committed a grave error by combining the prayers, and you must repent and not return to such an act.