Great to hear from you and thanks again for attending the MPWorkshop at Training Peaks last November.
Specificity is king when it comes to training any sport. HOWEVER…. keep the following in mind.
1) Running and Hiking with a pack share a great deal of similarities. Running gains will transfer to rucking better than rucking gains will transfer to running. This is due to the impact or eccentric loading that comes with running.
2) Rucking involves a more muscle mass so it will result in a greater HR response for the same speed. If you are impact averse (ie can’t run) then rucking can get your HR up at relatively low speeds. Rucking will have a positive training effect on all the postural support muscles of the core and shoulders.
3) We generally like to establish basic aerobic capacity through unweighted running or hiking BEFORE adding extra weight and especially when doing our weighted uphill ME workouts. We’ve had good results with this progression. It sounds like you’ve got a solid background in this type of training so this may not apply to you.