It means that exercising for a longer duration at low intensity will produce the same improvement as exercising for less time at higher intensity, if the total number of calories expended is the same or similar. Improvement is achieved if the exercise is intermittent or continuous. So, exercising once for 30 minutes or 3 times for 10 minutes produces roughly the same benefit. One should exercise three days a week to maximize improvement. Students who exercise more than 5 days per week have no improved fitness for the added extra days of exercise.
Cross training is best to target the various major muscle groups.
High impact activities are not wise for beginners because of injury risk. Because muscle strength declines as one ages, it is important to perform some resistance training in addition to the aerobic exercise for a healthy lifestyle. Strength training that uses lighter weight and a greater number of repetitions builds endurance while those featuring heavier weights and fewer repetitions build strength. For most students who are not interested in bodybuilding, the strength gains achieved by performing additional sets or lifting heavier weights are not appreciable. Additionally, a heavier weight imposes a greater risk of injury.