Zone-based treadmill conditioning on Technogym Skillruns: five heart-rate zones, from easy aerobic running through threshold work to full max-effort intervals.
Zone 2 easy jog to warm up and hold steady state. Zones 3 and 4 for threshold work: a genuinely hard pace, held. Zone 5 for HIIT at max effort. Then parachute sprints for power measured in watts, and sled pushes for raw horizontal strength.
Zone 4 is a percentage of your capacity, so the same call from the coach means a different speed on every treadmill in the room. Training the full range, rather than living in one middle gear, builds the aerobic base and the top end together. The coach calls the zone. You find the speed that gets you there.