# UTMB Champions Use Polarized Training to Build Race-Winning Fatigue Resistance
Scott Johnston, coach to Ultra-Trail du Mont-Blanc winners Tom Evans and Ruth Croft, credits polarized training for developing the fatigue resistance that separates elite ultramarathoners from the rest.
Polarized training concentrates effort into two distinct intensity zones while minimizing moderate-intensity work. Athletes spend roughly 80 percent of training time at low intensity, building aerobic base and recovery capacity, then dedicate 15 to 20 percent to high-intensity intervals or tempo efforts. The remaining 5 percent fills the gap. Johnston applies this structure to ultrarunning, where mental and physical durability over 6 to 30+ hours determines placement.
The method works because it forces the body to adapt differently at each end of the spectrum. Low-intensity runs build mitochondrial density and capillary networks in slow-twitch muscle fibers. These adaptations allow runners to sustain effort for hours without accumulating lactate. High-intensity sessions activate fast-twitch fibers and improve lactate threshold, the pace at which the body can clear metabolic byproducts faster than they accumulate. Together, these adaptations create runners who can run hard when necessary but recover metabolically during slower stretches.
Evans and Croft proved this works at the highest level. Evans won UTMB, one of the world's most demanding ultramarathons, covering 171 kilometers with 10,000 meters of elevation gain over two days. Croft, another elite ultra runner, has powered similar performances across brutal mountain terrain. Neither relied on moderate-paced grind work that leaves runners chronically fatigued and underperforming.
The contrast with traditional high-volume training is stark. Many runners historically logged 50 to 80 miles per week at "moderate" effort, hoping volume alone would deliver results. Johnston's approach requires less total mileage because quality matters more than quantity. Runners complete fewer weekly kilometers but extract greater adaptation from each session.
Polarized training also reduces injury risk compared to moderate-intensity dominated plans. The body tolerates high-intensity work twice weekly because recovery days fully repair muscle and nervous system damage. Moderate intensity, by contrast, taxes the body without providing complete recovery, creating chronic fatigue and inflammation that lead to overuse injuries.
Applying this to your own training means restructuring your week. Identify your easy pace (conversational, sustainable for 2+ hours) and establish your hard intensity (intervals near or above VO2 max, or sustained threshold efforts). Easy runs should feel genuinely easy. Hard sessions should feel genuinely hard. A typical week might look like: four easy runs of varying length, one long easy run, one high-intensity interval session, one tempo run, and one rest day.
The mental component Johnston emphasizes matters as much as physiology. Ultrarunners face doubt, pain, and fatigue that training must prepare for. By racing intervals and pushing hard intentionally twice weekly, runners develop confidence in their ability to sustain effort under stress. They prove to themselves that they can hurt and keep moving. Low-intensity base work builds the patience required to run for hours at conversational effort when racing longer events.
This framework scales from 50-kilometer races to 100-milers and beyond. The specific paces change, but the principle remains. Build an engine that runs forever at conversational speed, then build the capacity to accelerate when opportunities emerge. That combination created UTMB champions. It builds durable runners at every level.