Running well requires the ability to stabilise, absorb and produce force on one limb. Adding in single leg exercises that accentuate the eccentric component can be very beneficial for the runner. The first half of stance phase involves the absorption of force, as the muscles of the lower limb - predominantly the quadriceps - absorb the ground reaction force and stop the centre of mass from falling to the ground with gravity. This job is harder than it seems, and the stronger the quadriceps, calf and gluteals are eccentrically, the better the lower limb can resist deformation under the large loads of a running stride. Here are a few examples of single leg strength exercises one could utilise to improve this ability.