The latest UK Chief Medical Officers Physical Activity Guidelines for Adults* includes the following components:
1)    Adults should be physically active every day. Any activity is better than none, and more is better still.
2)    Muscle strengthening activities should be done on at least two days of the week, but any strengthening activity is better than none.
3)    Each adult should accumulate at least 150 minutes of moderate intensity activity; or 75 minutes of vigorous intensity activity; or even shorter durations of very vigorous intensity activity; or a combination of moderate, vigorous and very vigorous intensity activity.
4)    Adults should aim to minimise the amount of time spent sedentary and should break up long periods of inactivity with at least light physical activity.
Please provide a critical overview of the evidence behind each of the components of these physical activity guidelines.  In your answer, consider evidence from epidemiology; laboratory studies of the biological mechanisms underpinning how activity affects health; and intervention trials.  Please comment on the strengths and limitations of the available evidence, and how the guidelines might change in the future.