One of the main attributes to improving physical fitness is endurance. This involves increasing low to medium intensity activities gradually over a longer period of time. This depends of course one an individual's own fitness levels and goal.
Client Example 'Client A' could not run any distance at all, but their goal was to complete a 10k event. We started off with a gentle jog of 10 minutes followed by a walk of 3 minutes. We then gradually increased the distance of the jog and reduced the walk time to 2 minutes, until they felt able to increase both the length and speed of the jog. After 6 weeks they are now running 6.5 km in 35 minutes and we are aiming to enter our first 10km event together in one month's time.