Have you ever wondered how stride length and stride frequency, and associated muscular strategies change with increasing running speed? Check out this open access article by Dorn et al. (https://lnkd.in/gMb7ZbWx ) for the details. In summary, as shown in the graph, more of the speed increase at lower speeds is due to stride length, whereas high speed running is due to greater stride frequency increases.
Stride length and frequency are critical determinants of speed, so how can you train them?
Vest loading is ideal for overloading the ankle plantarflexors, soleus and gastrocnemius, improving vertical support forces and hence increasing stride length.
Limb loading such as wearing weighted shorts or calf sleeves are ideal for improving step frequency via the strengthening of the iliopsoas, gluteus maximus and hamstrings. Unloaded you will have a faster swing phase and therefore step frequency.
So identify your athletes weak links and then target strength train accordingly. If in doubt, then use both vests and shorts.