They will remain unchange or experience a drop in stamina, and if they're 32 yrs old or above they might have a drop in skills.
You can choose to train them too by giving them training minutes instead of just the main trainee, just place them as backup for the position that you planned to train for the week before training update. But of course, you will get a not so good result for the main trainee if the main trainee did not receive full training minutes.
You can also have a multiple position training if you plan to train your whole team. Take a look at training minutes and number of position here or it is in the earlier post>
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