Im sure some certification companies out there have certs specific to the needs of overweight/obese people but I dont think its necessary esp with your advanced degree. I certify personal trainers and have worked with many overweight people in the past. A couple of issues/things to think about include:
1.don't use BIA (bioelectirc impedance) to calculate body fat. It probably wont work on those over 300 lbs. all youll get is a big letter "E" (error) that you will have to explain
2. if they are very large they may have a pacemaker. Again, dont use BIA if that is the case
3. if using tape measuires to do circumference, be careful of the abdominal region. in very large people (BMI > 40) the tape may not make it around. same for the hips also.
4. they may have poor balance and low staimina. as such try intermittant exercise at first instead of steady state exercise
5. the person may be type II diabetic. if you are not sure and the client is african american, look at the skin on the back of the neck. darker skin there may be a sign of type II diabetes / metabolic syndrome.
6. circuit training (incorporating some aerobic activity into the cirucit) is probalby the safest mode of exercise for this individual. keep the weight light (ie 12-15RM) use the RPE scale to guage fatigue level.
7. if diabetic, see if you can get an idea of their Hb A1c levels. they should know this or their doctor certinaly knows this.
I hope some of this helps. let me know if you have any other questions
good luck.
Joe
my website:
www.Joe-Cannon.com