I am currently studying with ISSA to become a trainer...

I've gotten myself a potential client...he is my co-worker...and I need advice from an experienced trainer or guru of the sort.

He wants to sign up to the gym with me and I want to help him with his nutrition and exercise program.

Thing is...I'm unsure how to approach this. Being his size I don't want to get his back or joints injured.

Two things I want to do with him before we hit the gym.

1) Get him to walk 2-3 times a week for half an hour for a couple of weeks
2) Get his core in shape.

#1 is easy...but #2 is tricky for me as I've never helped anyone this big before...how do I get his core in decent shape without destroying his back or joints? And how do I proceed with stretching with a person this big?

He is in the 305-310 lbs range. He is about 6' 2".

For the first two weeks I will have him do 3 cardio sessions per week to get his heart used to exercise after which I will switch his routine to a 5-10 min light cardio warm-up followed by high rep/endurance circuit training. I will be switching his routines every 4 weeks in order to eliminate any chance of his body reaching a plateau in development. After 1 month I will get him to go to the gym 4 times a weeks and will gradually get him to get 5 times per week. I will make him a solid nutritional plan that will also help him in his goals.