I'm impressed. Due to recurrent SI Joint issues which PT didn't resolve I had my movement tested. Mobility and stability were good but core stability was downfall. As a result planks are part of my workout. They consist of 3 sets of 3 reps for a total of 3 min. Each rep is 15 sec. When I started 2 weeks ago I could barely hold the 15 sec. The killer ones though are the diagonal planks. I'm holding off on those because I don't have the strength yet to raise one leg, let alone an arm and leg. My directions specifically tell me what to avoid which indicate a loss of form.

An amazing benefit of gaining core stability is how it has impacted my skiing. I feel like I'm wearing a corset, I'm able to "brace" my middle, which results in better movement, especially at speed or in bumps.

I had a discussion with my PT about how trainers disregard good form while training clients. It may not show up immediately but somewhere down the road it will and the clients end up having to visit a person like him. Poor form is the biggest complaint of the bloggers on the Strength and Conditioning pages that I read. Even poor form on the bicycle can lead to issues.

Sounds like your friend watches "the Biggest Loser" to much and needs to get realistic about training.