From Jillian Michaels:
“You may have heard the U.S. Surgeon General’s recommendation of at least 150 minutes of moderate physical activity each week (and that breaks down to just 30 minutes of physical activity five days a week). What’s important to understand is that this is intended for people who want to maintain the most basic level of fitness — but not for people who want to lose weight. But if you want to drop those pounds, you’re going to have to be prepared for a bit more work.
I much prefer the World Health Organization’s recommendation of 60 minutes at a time as a starting point for my clients — an hour is ideal to get the most out of your workout and see significant results. Your 60-minute workout sessions should always include a 5-minute warm-up, followed by 50 minutes of your primary cardio or strength-training exercises, followed by at least 5 minutes of cooling down and stretching.
Of course, putting in more time will get you more results — but there’s a limit. Excessive intense physical activity releases stress hormones, such as cortisol, into the body. This can actually inhibit weight loss, causing your body to react by storing fat and retaining water out of self-protection. So, to reach your goal, I recommend limiting intense exercise to no more than two hours a session.”