Original episode & show notes | Raw transcript
For anyone who has ever started a new sport or returned to training after a long layoff, the experience of “noob gains” is both exhilarating and motivating. It’s a period of remarkably rapid improvement where performance seems to leap forward with every session. An athlete’s Functional Threshold Power (FTP) or running pace can improve dramatically in a matter of weeks. But what is happening inside the body to drive this accelerated progress?
While many assume these initial gains come from the muscles getting stronger and more efficient, the scientific evidence points to a different primary driver. This document, based on the detailed discussion in the Empirical Cycling podcast, explores the key physiological adaptations that underpin this phenomenon, revealing that the most significant initial changes happen not in the muscles, but in the blood.
To understand noob gains, we must first distinguish between two categories of physiological adaptation to endurance training:
Peripheral Adaptations: These are changes that occur directly within the skeletal muscles. They include an increase in the number and size of mitochondria (the powerhouses of the cell), a greater density of capillaries to deliver blood, and increased activity of aerobic enzymes. These adaptations enhance the muscle’s ability to use the oxygen delivered to it.
Central Adaptations: These are changes related to the body’s oxygen delivery system. This involves the heart, lungs, and blood. Key adaptations include an increase in the heart’s stroke volume (the amount of blood pumped per beat) and an increase in total blood volume.
While both types of adaptation are crucial for long-term endurance performance, research shows that central adaptations are the primary drivers of the initial, rapid increases in peak oxygen uptake (VO2 max) and FTP.
A pivotal 2015 paper by Montero et al., titled “Hematological rather than skeletal muscle adaptations contribute to the increase in peak oxygen uptake induced by moderate endurance training,” provides the core evidence for this conclusion.
Participants: The researchers took 16 previously untrained young men.
Training: They underwent a six-week supervised cycling program at a moderate intensity (around 65% of their VO2 peak).
Measurements: Before and after the training, the researchers conducted an exhaustive battery of tests, measuring both central factors (cardiac output, blood volume, plasma volume, hemoglobin) and peripheral factors (mitochondrial volume, capillary density, muscle fiber size).
The Critical Experiment: The most innovative part of the study occurred after the post-training test. Scientists performed a phlebotomy, drawing blood from the participants to remove the exact amount of blood volume they had gained during training. They were then tested a third time.
Significant Performance Gains: After six weeks, the participants’ peak power output (W peak) increased by nearly 16%, and their VO2 peak improved by 9%.
Gains Vanish with Blood Volume: When the training-induced blood volume was removed, the improvements in VO2 peak were almost completely erased, returning the participants to their pre-training baseline levels.
Muscular vs. Blood-Related Changes: While the participants saw a massive 40% increase in mitochondrial volume in their muscles, this peripheral adaptation did not have a strong statistical correlation with the increase in VO2 peak. The strongest predictors of the VO2 peak improvement were the central, hematological factors: peak cardiac output, total blood volume, plasma volume, and hemoglobin mass.
This study conclusively demonstrated that the ability to deliver more oxygenated blood—not the muscle’s enhanced ability to use it—was the overwhelming reason for the initial jump in aerobic fitness.
The mechanism by which increased blood volume boosts performance is explained by a fundamental principle of cardiac physiology: the Frank-Starling Law.
This law states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the ventricles (the “preload”). Think of the heart muscle like a rubber band: the more it is stretched by incoming blood, the more forcefully it contracts, ejecting more blood with each beat.
The sequence of events for a new trainee is as follows:
Endurance exercise signals the body to retain more fluid, expanding total blood volume, primarily through an increase in plasma (the liquid component of blood).
This larger blood volume increases the preload, filling the heart’s chambers more completely before each beat.
The increased stretch on the cardiac muscle causes a more powerful contraction.
This results in a higher stroke volume—more blood is pumped to the body with each heartbeat.
A higher stroke volume leads to a higher cardiac output (Total Blood Pumped per Minute = Stroke Volume × Heart Rate).
This enhanced cardiac output delivers significantly more oxygenated blood to the working muscles, directly increasing VO2 max and, consequently, FTP.
While blood volume is the star of the show, other parallel adaptations contribute to the overall experience of noob gains.
Learning to Suffer: A significant component is psychological. New athletes learn to tolerate the discomfort of hard efforts and gain a better sense of their physical limits, allowing them to push harder and realize their existing potential.
Neuromuscular Coordination: The body becomes more efficient at the specific movement pattern of the sport (e.g., a pedal stroke). It learns to recruit muscle fibers more effectively, reducing wasted energy and improving economy.
Endurance Improvements: The peripheral adaptations, like mitochondrial growth, are happening concurrently. While they don’t drive the initial spike in VO2 max, they are absolutely critical for improving fatigue resistance and the ability to sustain efforts for longer durations.
For New Athletes: Almost any form of consistent training, whether low-intensity or high-intensity, will trigger these powerful central adaptations. The key is consistency and allowing for adequate recovery (sleep, nutrition, stress management) so the body can build its new blood volume.
For Trained Athletes: Experienced athletes can no longer rely on this mechanism for easy gains. Their blood volume is already high, and their performance is limited more by the maximal contractile capacity of their highly trained heart and the efficiency of their muscles. Their progress depends on the slow, steady accumulation of peripheral adaptations. This is why the training that made you fast initially will not be the same training that makes you faster later in your athletic career.
In conclusion, the phenomenon of “noob gains” is a clear example of the body’s remarkable ability to adapt. It prioritizes the most effective strategy first: expanding the oxygen delivery service. By increasing blood volume, the body rapidly enhances the heart’s capacity to fuel the muscles, leading to the swift and satisfying performance improvements that hook so many on a lifetime of sport.