They also claim that working out 6 days a week makes it habit, which makes it a part of who you are and becomes as ordinary as brushing your teeth or showering every day. You eat and sleep each day, and feel better when you do so appropriately, so it makes sense that you feel more energized and healthier when you also workout regularly. In fact, most people notice other areas in their life improving as well, like positive attitude and healthier skin, when they exercise consistently. They say that people that don't workout consistently are less likely to see progress and then are less likely to stick to working out at all.
Of course, you need to take into consideration your fitness level when determining how often to exercise each week and also what you'd like to achieve. If you are a beginner, most experts recommend 20 minutes three times a week, which can be broken up into ten minute sessions throughout the day or all at once. And of course, any exercise is better than no exercise.
Beginners are likely to need more recovery time than seasoned athletes too. Answer Fitness says:
"As a general rule of thumb, a good training frequency for someone who is new to the gym, or returning after a lengthy break, is three resistance workouts a week lasting between 45 and 60 minutes. This will allow you to work each major muscle group with at least one exercise and give yourself 48 hours for recovery between workouts."
As for the US government, when asked the question, they released a report called Dietary Guidelines for Americans which said:
"To help manage body weight and prevent gradual, unhealthy body weight gain in adulthood: Engage in approximately 60 minutes of moderate to vigorous-intensity activity on most days of the week while not exceeding caloric intake requirements."
We Be Fit's website goes on to explain that you should consider cardio workouts four to six times a week between 20 and 60 minutes each session for optimum fat loss. Exceeding an hour of this can be harmful to your body though, as it begins to eat muscle that is used to fuel your body. To maintain muscle mass, they recommend resistance/strength training three days a week for about 30 - 60 minutes.
Those recommendations are similar for people of ages up to even 70 and 80 years old.
The recommendations for how often to exercise each week may vary, but what all the websites have in common is that you should start out slowly, so as not to injure yourself, pace yourself, start with lighter weights, shorter sessions, and gradually work your way up. They all also recommend on day of rest minimum each week. You will burn yourself out if you never give your body a chance to rest, especially when engaging in vigorous workouts. I think my personal rule of thumb is always to listen to your body. Each body is different and you know when you are pushing too hard or when you aren't pushing enough. So listen to your body, lace up your shoes, and get sweaty!!