Interval Runs
Sprinting is one of the most powerful and natural movement patterns which synergistically builds strength in the foot, lower leg, upper leg and hips whilst also providing a great cardiovascular workout. Mark or eyeball a start and finish position and sprint from one to the other. Either walk back to the start position and repeat or rest where you are and sprint back when ready. Complete for the desired number of rounds. The further you travel (and the faster you go) the harder this exercise becomes. Importantly if you are just getting back into sprinting use no more than 80% speed and start with shorter distances.
(Last but not least running up a hill, slope or gradient simultaneously increases the strength demands, intensity levels and safety of sprinting. Highly recommended if possible!)