The Variable Resistance Protocol
Why Terrain is Not Scenery—It’s Your Most Accurate Training Tool
Most athletes treat terrain as something they must survive.
The road runner avoids hills to keep splits consistent. The trail runner slogs through climbs just to reach the finish line. Both view elevation change as an obstacle—something that disrupts their training plan rather than defines it.
After 25 years of coaching endurance athletes, I’ve learned that this perspective costs you adaptations you desperately need.
Here’s what changes when you shift the paradigm.
Terrain as Equipment
A strength coach doesn’t randomly select weights. They manipulate load to elicit specific adaptations. Three sets of five reps at 85% builds something different than five sets of ten at 65%.
The endurance coach who understands this principle applies the same logic to terrain.
Gravity is the weight. Grade is the rep range. Pace is the intensity.
When you change the angle of the surface beneath your feet, you fundamentally alter the physiological demand. Not by making it “harder” in some vague sense—by changing which energy systems activate, which muscle actions dominate, which structural tissues absorb load.
This isn’t motivational language. This is biomechanics.
The Physics of the Vector
Every surface you run on creates a force vector through your body. Understanding these vectors allows you to prescribe terrain the way a physician prescribes medication—with specific dosage, timing, and purpose.
The Uphill Vector: Concentric Force Production
When you incline the surface, two things happen simultaneously.
First, you reduce impact forces. There’s less vertical distance to fall with each footstrike. Your joints thank you.
Second, you drastically increase propulsive force requirements. Your muscles must overcome gravity with every stride. No elastic recoil. No bounce. Pure muscular metabolic work.
This is weightlifting for the cardiovascular system.
Your heart rate climbs not because you’re “working harder” in some abstract way, but because your working muscles demand more oxygen to maintain ATP production against gravitational resistance. You’re forcing your oxidative system to support high-force muscular contractions.
The adaptation this creates: You build the capacity to sustain high cardiac output while maintaining power. This is precisely what the road runner needs to build speed without the hamstring risk of track sprints. This is exactly what the ultrarunner needs for technical climbing.
The Downhill Vector: Eccentric Durability
Gravity pulls you downward faster than your legs want to turn over. Your muscles must lengthen under load to brake your momentum.
This is chassis construction.
Eccentric loading triggers the release of mechanogrowth factors—proteins that signal your body to strengthen tendons and reinforce collagen structures. Done correctly, this makes you more durable. Done carelessly, this is where injury happens.
The key variable is volume. Eccentric muscle actions create significantly more structural microdamage than concentric actions. Your quads can handle far less downhill volume before reaching failure than they can uphill volume.
This is potent medicine. Dose it like medicine.
For the master's athlete, especially, eccentric work is non-negotiable. Your cardiovascular system remains robust into your 50s and beyond. Your structural system—cartilage, tendons, fascial networks—does not. You must deliberately build eccentric strength to preserve joint integrity while maintaining performance.
The Flat Vector: Velocity and Economy
Remove the vertical component entirely, and you isolate pure running economy. The goal becomes minimizing energy cost per meter traveled.
This is neural patterning. Learning to relax at speed, finding the cadence and stride length that allows your elastic tissues to store and return energy with maximum efficiency.
Flat running is where you teach your body the rhythm of pace. But it’s not where you build the engine or reinforce the chassis. Those adaptations require the other two vectors.
Strategic Application
Understanding the physics is useless without implementation protocols. Here’s how you deploy terrain strategically based on your training objective.
Strategy A: The Governor
Purpose: Force low-intensity aerobic work.
The problem most athletes face isn’t going too easy on easy days. It’s the chronic drift into Zone 3—that grey zone where you’re working too hard to build aerobic capacity but not hard enough to create meaningful adaptation.
Steep terrain solves this mechanically.
It’s nearly impossible to run fast up a 15% grade. Your body cannot generate enough power to push your heart rate into Zone 4 while maintaining a running gait. You naturally downshift to a hike.
For the road runner: Use a treadmill at 15% incline for walking recovery sessions. You get blood flow through the legs without impact stress. Your heart rate stays conversational. Your joints recover while your muscles work.
For the trail runner: The hiking anchor. If you cannot breathe through your nose, you hike. The terrain dictates the gait, not your ego.
This is the terrain acting as your discipline coach.
Strategy B: The Dynamometer
Purpose: Develop maximum power without impact.
Short, maximum-effort bursts against gravity recruit high-threshold motor units—your fastest muscle fibers. These are the fibers that provide acceleration, reactive strength, and the “snap” that separates efficient runners from plodders.
The advantage of hill sprints over flat sprints: You get identical neural recruitment with dramatically reduced impact forces. Your foot contacts the ground at a slower velocity. Your joints don’t pay the same price.
For the road runner: Ten-second hill sprints. Eight to twelve repeats. Full recovery between efforts. This preserves fast-twitch capacity in aging legs without the injury risk of track work.
For the trail runner: Technical climbing intervals. Power over roots and rocks. This builds the specific neuromuscular patterns you need for race day.
Run these once weekly during the base phase. Every other week during the build phase. During taper, keep the intensity but cut the reps by 50% to maintain neural pathways without accumulating fatigue.
Strategy C: The Shuttle
Purpose: Teach lactate clearance under fatigue.
Your body produces lactate during high-intensity work. This is normal. The adaptation we want is teaching your system to clear that lactate efficiently while continuing to exercise.
Rolling terrain creates this stimulus naturally.
Uphill: Lactate production spikes as you push against gravity. Your working muscles produce more lactate than your cardiovascular system can immediately clear.
Downhill: Lactate clearance. Your legs continue to move while operating at a lower intensity. Your system learns to process accumulated metabolites without stopping.
For the road runner: Rolling tempo runs. Don’t hold even power. Spike the climbs at threshold effort. Float the descents at Zone 2. This is far more specific to racing than steady-state tempo work on flat ground.
For the trail runner: This is the specific demand of the sport. You must learn to recover while running downhill, not while stopping at aid stations.
The 40+ Advantage
As we age, our cardiovascular system remains remarkably resilient. Your maximum heart rate declines slowly—roughly one beat per year after age 30. But your heart’s stroke volume, your mitochondrial density, your lactate threshold—these respond to training across your lifespan.
Your structural system does not age as gracefully.
Cartilage thins. Tendons lose elasticity. Intervertebral discs compress. The cumulative impact of thousands of footstrikes begins to matter in ways it didn’t at 25.
This is why shifting training emphasis toward uphill vectors becomes increasingly valuable with age.
Flat running is high repetition, moderate impact. Ten thousand footstrikes in a 10-mile run, each one sending force through your joints.
Uphill running is high metabolic load, low impact. You can achieve the cardiovascular stimulus of a 5:00 mile pace at the biomechanical stress of a 10:00 mile pace.
You maintain the V8 engine inside a chassis that needs protection.
The prescription: Shift 30% of your intensity work to uphill vectors. You preserve cardiac output capacity while reducing cumulative structural load. This allows you to continue training at high volume without accumulating the microdamage that leads to chronic injury.
This is not a compromise. This is an intelligent adaptation based on biological reality.
The Method
Don’t just run the route. Use the route.
Before every training session, analyze the elevation profile. This takes 30 seconds. Open your GPS watch or training platform. Look at the terrain you’ll encounter.
Then assign a purpose to each section.
Flat sections: Economy work. Find your rhythm. Stay relaxed.
Moderate climbs (4-8%): Aerobic power. Push these at threshold on hard days. Hike these on easy days.
Steep climbs (10%+): The weight room. Never run these on easy days. Either power over them during workouts or hike them deliberately.
Technical descents: Eccentric conditioning. These cost more than they feel like they cost. Respect the structural load.
Smooth descents: Free speed. Let gravity work. Stay light on your feet.
The mistake most athletes make is treating terrain as random variation—something that happens to them. The durable athlete treats terrain as a training tool—something they deploy strategically based on the adaptation they’re chasing.
Gravity is the most honest coach you will ever hire. It never lies about your fitness. Use it.
Your Turn: The Terrain Audit
Pull up your last month of training data. Calculate what percentage of your mileage occurred on each terrain type:
Flat: ____%
Uphill: ____%
Downhill: ____%
Now compare that to your race goals. If you’re training for a mountainous ultra on flat roads, you’re not preparing—you’re just logging miles.
The terrain distribution in your training should mirror that of your goal event. If it doesn’t, you’re building general fitness instead of specific capability.
Adjust accordingly.
