TV Guide’s summary of The Trainer, a Lifetime TV movie:
A recently divorced woman joins a gym and quickly becomes friends with Alex, a young trainer. Unfortunately, Alex is psychotic and a murderer.
Yes, that is quite unfortunate.
The official synopsis by Lifetime, also listed on IMDB, adds:
Sadly Alex is psychotic and has been murdering her trainees for years.
Very sad indeed. A slight flaw in Alex’s character.