you should engage in at least 30 minutes of moderate activity each day to realize the health benefits of exercise.You would then repeat the interval cycles for 20 minutes, ultimately achieving 10 minutes of high-intensity exercise and 10 minutes of active rest. This would provide the equivalent benefit of one hour of moderate physical activity.
I have heard that it is important not to exhaust your body out. So 45 minutes to an hr. I know I have done P90x in the past and I believe that the longest exercise that they had was 1 hr and 15 minutes. The yoga may have been 1 hr and 30 minutes. I think it depends on you and your body.
The amount of exercise one can do in a day depends on many different factors.
What types of exercises,? (strength training, cardio, crossfit etc..)
What is your experience level? (training for years, new to training, etc...)
How much rest between exercises? (level of intensity?)
What are the goals? Just to build muscle or increase strength, power, endurance?
Lots of factors go into how long you should exercise to build muscle fast.
Of course Diet and nutrition are key components.
As is rest and sleep.
You could build muscle exercising only 20 minutes a day, but far more than just exercise factor into building muscle.
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