In the wake of last week's column, I received some comments and questions that I thought would be worth exploring in a follow-up. That's what I'll focus on this week.

First – you might want to take a quick peek at last week's column and the comments it generated. My responses to the various questions and comments are below:

• Endless hours of abdominal work will firm and tone the muscles beneath the skin and layer of fat. But if you want to see those firm, toned muscles, you have to lose fat under the skin that rests on top of the abs. Fitness models and competitors will tell you that the most difficult part of getting ready for a contest or photo shoot is the several weeks of strict dieting required to get to the level of leanness needed for the event (3-8 percent for men; 7-12 percent for women). I'm in the same general condition year-round. At 45, my body fat was about 9 percent in the summer, and I had a six pack for the first time in my life.

• P90X is an aggressive, intense, but a sound and balanced program, using rapidly increasing levels of challenge and a structured, fairly strict diet to accomplish impressive results. Like any fitness program based on good exercise and nutrition science, the degree of success you'll enjoy directly correlates with your level of sustained commitment. The caveats are that this level of intensity is not for everyone, pre-existing conditions and injuries can be major obstacles and it is very demanding and may be too demanding for most. But the principles upon which it's based, the Biggest Loser program and military boot camp, are solid.
• Understanding good nutrition and exercise principles is not difficult. The practice can be very challenging. There's no doubt that a structured eating plan and regularly scheduled workouts play a huge role in ensuring the best chance of success. Those measures also promote personal discipline–a key element in long-term consistency of healthy eating and working out. So the effects of structure, regularity and commitment are physiological and psychological.
• When you have integrated these habits into your life and realized both performance and aesthetic benefits, it's likely that you also have begun to include in your identity the concept of yourself as a healthy, fit person. This is the tipping point for most lifetime exercisers and healthful eaters. It's a great place to live, and something we all deserve to experience.

Note – see some of my holiday fitness and nutrition recommendations in this column.

Have a happy, healthy, holiday season!