If you need to improve work capacity, try these relays with KB farmer walks.
You'll end up performing a few reps of deadlifts, tons of carries and your entire body will be worked.
Notice the extra KB's in the background.
You need several KB's for this, so simply farmer walk the bells down to a certain distance, sprint back or jog / walk depending on your fitness, grab the next heavier pair of bells, and repeat until all bells are finished.
Then, perform the same thing going back!
I have gone UP in weight on each set but you can also go down.
carrying 88 lb KB's may not be tough, but for distance, plus sprints, plus more carries, your work capacity will improve greatly!