What's your opinion of HIIT vs steady state cardio? Why would you do one over the other and what time of the day do you believe is optimal?

I'm a 14yr stage 4 testicular cancer survivor having problems making gains. My diet is clean and I make sure I get enough protein, carbs, and healthy fats(try to anyway). I have low T and cortisol issues that I have a Dr  appt for on June 16. I had half my right lung removed because the cancer had spread and my Dr wants me doing cardio for 30 mins 5 days a week. Is it at all possible to put on lean muscle while stil pushing myself as hard as I possibly can and having to do this much cardio? Any help is greatly appreciated! Thanks Marc.

How important is or how important do you feel is stretching before, during, during sets or post workout?

I want to maximize fat loss and I know Tabata is equal to a much longer amount of steady state, so I would prefer to do this style of cardio, but how many Tabata sessions are too much? Any recommendations for cardio programming?

My mom is overweight and is considered obese. She works 4 12 hour long days and 1 8 hour day and is very  exhausted  when she gets home. On the weekends she just sits on the couch and relaxes.. I try to get her to exercise even if it's to just go out for a walk. Or to have her track her food and eat a bit healthier. She wants no part of it. She realizes she's overweight and knows that she needs to change it but is to "lazy".  What can I try to do besides educate her about the importance of eating healthy and exercising ? 

I had a personal training class this past semester at school where time under tension was the main focus. My professor, a former strength and conditioning coach said that time under tension is best way to promote muscle growth. I was curious as to whether or not time under tension is as important as he and many others seem to claim.

what is your preferred exercises to train your abs? Also how  frequent should you train your abs? Lastly if your at a low body fat (sub 8%) and have a good 6 pack, do you think it's better to focus on other lagging body parts rather than spend more time on training your abs if you are pressed for time? 

What's your opinion on training muscles more than once per week? Can this be effective for bringing up lagging body parts? Do you think this can potentially lead to overtraining?

Hi Marc I am 50 years old and I have never been that active. I am overweight and I want to get in better shape so I can live a longer life and be able to do physical things humans were meant to do. I have a desk job and work 50-55 hours a week. I want to join a gym but I don't know how to workout. Or how to start... I don't want to be one of those people, who just goes to the gym and walks on the treadmill for hours. Any advice you could give me would be much appreciated