Original episode & show notes | Raw transcript
This document provides a comprehensive breakdown of the core concepts discussed in the Empirical Cycling podcast episode on pacing and programming endurance. It is designed for an educated audience seeking a detailed understanding of the science and application of modern endurance training philosophy.
The central theme of the discussion is that endurance adaptations are not tied to a specific “zone” or intensity but are rather the result of a trade-off between the intensity of work and the duration for which it is performed.
The podcast references a review paper that analyzed numerous studies on endurance training. The key findings were:
Adaptation vs. Intensity: When looking at a marker for mitochondrial density (citrate synthase), there was no clear correlation between the intensity of training and the magnitude of adaptation. High-intensity, sprint, and lower-intensity endurance training all produced similar levels of this marker.
Adaptation vs. Total Work: The strongest correlation was found between adaptation and the total volume of work, defined as Duration x Intensity. This implies that a longer ride at a lower intensity can produce a similar adaptive signal to a shorter, more intense workout.
The reason various intensities yield similar adaptations is that they all trigger the same master signaling pathways for aerobic adaptation.
The Master Switch: The hosts identify PGC-1 alpha (along with PGC-1 beta and PRC) as a primary “bottleneck” or master regulator for creating new mitochondria and improving aerobic capacity.
Intensity Agnostic: This signaling cascade is activated by various stressors, including the metabolic stress from high-intensity work and the calcium signaling from prolonged muscle contraction in lower-intensity work.
A Suite of Genes: Activating PGC-1 alpha doesn’t just turn on one specific adaptation (e.g., fat burning). It initiates a broad genetic program that improves the entire aerobic system: more mitochondria, more Krebs cycle enzymes, more lactate transporters (MCTs), etc.
The Substrate Myth: A crucial takeaway is that the signal for adaptation is not dependent on the substrate being used (fat vs. carbohydrates vs. lactate). The idea that you must “burn fat to get better at burning fat” is an oversimplification. The underlying cellular stress and signaling are what matter.
If all intensities drive adaptation, the primary programming variable becomes managing the cost of that adaptation. The hosts break this cost into two concepts: the “Fatigue Burden” and the “Energy Burden.” The main tool to manage this is the Rate of Perceived Exertion (RPE).
The podcast strongly advocates for using RPE as the primary guide for endurance rides, over heart rate or power.
Subjectivity is a Feature: RPE is inherently individual. An elite athlete’s “4 out of 10” effort might be a high power output but feels sustainable, while a less experienced athlete’s “4 out of 10” will be a lower power output. This self-regulation is key.
The RPE Decoupling Point (LT1): The most critical concept for pacing is an RPE threshold, analogous to the first lactate threshold (LT1). This is the point where a very small increase in power causes a disproportionately large jump in RPE (e.g., from a “2/10” conversational pace to a “5/10” focused effort). The vast majority of endurance riding should be done below this RPE threshold.
Passing the “Talk Test”: A practical way to gauge this is the ability to hold a full conversation or, as the hosts suggest, be on a Zoom call where nobody could tell you are exercising.
This refers to the acute and residual muscular and nervous system fatigue from a workout.
Non-Linear Cost: Once you ride above that RPE threshold (LT1), the fatigue burden increases non-linearly. The adaptive benefit may only increase slightly, but the recovery cost skyrockets.
Protecting Quality: The primary goal of easy endurance rides is to accumulate volume with a minimal fatigue burden. This ensures you arrive at your key high-intensity workouts fresh enough to perform them at the highest possible quality, which is essential for progression.
This refers to the sheer caloric cost of training, which becomes the primary limiter at very high volumes.
The Caloric Deficit: On very long rides (e.g., 6+ hours), it is nearly impossible to consume enough fuel to stay energetically neutral, even with aggressive fueling (100-120g carbs/hour). An 8-hour ride can create an energy expenditure of 6,000-8,000 kilojoules (calories).
Prolonged Recovery: It can take 2-5 days to fully restock muscle glycogen after such a massive effort. This is not just muscular fatigue; it’s a systemic energy crisis that the body must resolve before it can positively adapt.
Food Max: This burden explains why elite athletes doing 20-30 hour weeks must keep their endurance intensity very low. They are limited by their ability to eat and digest enough food to recover.
The training philosophy is built around prioritizing 1-3 “quality” high-intensity sessions per week and using endurance volume to support them without compromising recovery. How this is balanced depends on the athlete’s total available training time.
Context is Key: The reason for low volume matters. An athlete limited by a high-stress job has a different recovery profile than one who simply has less free time.
Intensity Leeway: Because the total Fatigue and Energy Burdens are lower, there is more room for endurance rides to be paced at a slightly higher RPE (i.e., closer to, but still generally below, LT1).
Hard Day Frequency: Can often support 2-3, or in rare cases even 4, high-quality hard days per week, as the intervening days are short and recovery is more manageable.
Intervals on Long Rides: It is highly effective to add interval work (e.g., FTP efforts) to the longest ride of the week to maximize time efficiency.
Pacing Becomes Critical: This is where riding endurance “too hard” (e.g., consistently at 70-75% of FTP) becomes highly detrimental. It will cap the volume an athlete can handle and compromise recovery.
Hard Day Frequency: Typically decreases to 2-3 hard days per week. The increased volume is a significant stressor in itself. The focus shifts toward accumulating more total work.
Intensity is Strictly Controlled: Endurance rides must be at a very low RPE (well below LT1, often 40-60% of FTP).
Hard Day Frequency: The number of dedicated interval days drops significantly, often to only 1-2 per week.
Volume is the Driver: The primary driver of adaptation becomes the massive accumulation of low-intensity volume. The goal is to stimulate adaptation while managing the enormous Energy Burden.
Can you overtrain on volume? Yes, but it’s almost always a function of the intensity being too high for that volume. Overtraining from purely low-RPE volume is rare and typically requires an extreme energy deficit.
Does volume hurt sprinters? No. Fatigue from poorly paced volume hurts sprinting. A high volume of low-RPE riding, combined with specific, fresh sprint work, improves a sprinter’s endurance and repeatability without blunting top-end speed.
Are coffee stops bad? No. They do not ruin adaptations. Stopping to refuel is beneficial. The only minor risk is a temporary “bonk” upon restarting if a large carb load triggers an insulin response while resting.
Is fasted training useful? No. The podcast unequivocally rejects it for endurance athletes. The theoretical benefits are based on flawed premises (e.g., that fat burning is the signal for adaptation). The practical costs—lower quality work, impaired recovery, increased stress—far outweigh any potential marginal gain. It is always better to be fully fueled.
What about cadence? Don’t overthink it. Ride at a self-selected, comfortable cadence. Forcing a specific cadence (high or low) typically increases metabolic cost for no added benefit.