THE SECOND WIND
Recently I ran with a six-person team on a 210-mile relay race through the Smoky Mountains of Western North Carolina – covering about 43 individual miles with many of them featuring steep climbs and descents. As excited as I was to traverse the trails with endless vistas, I knew I would find challenges that would make me question embarking on this journey. The longer the race, the more frequently I stumble upon adversity. Whether it’s the internal mental battle or physical cramps and exhaustion, or the external thunderstorms or rough terrain. Yet through the fog and fatigue, if I am able to persist long enough, I find renewal on the other side. Sometimes, when it feels like my quads and calves will not handle another step, it seems as if my legs are gifted back to me. When my brain is telling me to stop running, some force over-rules it and gives me mental strength to push forward. Where does that extra energy come from when we feel completely drained?
The second wind is an elusive experience. Imagine finding your legs again after hitting the wall at mile 20 of the marathon. Or discovering strength you didn’t know you had in a critical moment. Scientists have long-studied fatigue, but it seems that peak human performance may be discovered by tapping into a hidden Reserve Capacity – a hidden and underutilized pool of physical and mental resources that emerge when pushed to the edge. What if this Reserve Capacity can be systematically expanded through deliberate exposure to controlled adversity? We train to improve measurable outputs like strength, speed, endurance, etc. But how might we deepen this reserve of untapped resilience that seems to be a critical factor in performance under pressure? Maybe performance is not only about how high your peak is – it’s about how deep your reserves go.
The question of why we experience fatigue has been asked and answered with various theories. The traditional biological model suggests that fatigue is experienced when physical resources are drained. Glycogen depletion and lactic acid build up eventually overwhelm the system and force us to slow down or stop. But the traditional model seems to ignore the mental and emotional influences on fatigue. Recognizing this, Tim Noakes came up with a Central Governor Model to explain the role of the brain. Noakes suggests that the brain intentionally regulates exercise output to prevent catastrophic homeostatic failure, like severe muscle damage or cardiac arrest. When we red-line during a race or hard training session, fatigue is an emotional response in the brain to protect the body, not a pure reflection of physical limitation. Therefore, Noakes suggests you can negotiate with the Central Governor to a degree, especially with motivation or external stimuli like crowds and competition.
Another model is Samuel Marcora’s Psychobiological Model, in which Marcora argues that endurance performance is ultimately determined by perception of effort and not physiological failure. This is why the Rating of Perceived Exertion (RPE) scale is frequently used to gauge an athlete’s intensity using a 6-20 or 1-10 scale. Marcora’s studies show that mental fatigue alone can impair endurance performance even if the muscles are fresh. If you perform difficult cognitive tasks prior to performing a time trial on a bike or on the track, your physical performance will suffer. Due to these findings Marcora has introduced Brain Endurance Training, adding cognitive tasks to physical training sessions to promote adaptations to these perceptions of effort. The Reserve Capacity is not just physical – cognitive reserves matter too.
Reserve Capacity is a hidden pool of physical, cognitive and emotional resources that is available only when certain thresholds are crossed. This phenomenon can be seen beyond the endurance athlete space. Think of special forces candidates tapping into an entirely new mental and physical layer after being subjected to extreme fatigue and adversity, or first responders under life-threatening conditions demonstrating physical feats beyond their lab-tested VO2 max or strength measures. Or even every day people accomplish critical tasks under severe stress.
So, what are the underlying mechanisms that might explain this elusive "second wind" and the activation of our Reserve Capacity?
Metabolic Switching and Fuel Utilization: While the traditional model points to glycogen depletion, the "second wind" could be linked to the body's ability to switch fuel sources. When muscle glycogen stores run low, the body becomes more efficient at utilizing fatty acids for energy. This shift, though slower to initiate (fatty acids take approximately 10 minutes to sufficiently produce ATP, compared to about 30 seconds for muscle glycogen), can provide a sustained energy supply. In conditions like McArdle's disease, where muscle glycogen is unavailable, individuals can experience a "second wind" much earlier (6-10 minutes of light activity) as their bodies are forced to rely on fat metabolism from the outset. This highlights the adaptive capacity of our metabolic systems. But fuel sources alone are unlikely to be the only player behind unlocking hidden endurance.
Enhanced Oxygen Utilization and Lactic Acid Clearance: Heavy breathing during initial exercise helps with cooling. As the body warms up and capillaries dilate, cooling becomes more efficient through the skin, potentially reducing the need for heavy breathing and allowing for a more balanced oxygen supply. Some theories suggest the "second wind" occurs when the body finds the optimal balance of oxygen to metabolize lactic acid build-up. While lactic acid was once seen purely as a waste product leading to fatigue, it's now understood that lactate can be used as a fuel source by other muscles and the heart, especially when mitochondrial function is high. Training can enhance this lactate clearance, allowing athletes to perform at higher intensities for longer.
Neurochemical Release: The Role of Endorphins and Other Brain Chemicals: The "runner's high" is often attributed to the release of endorphins, natural opioids produced by the brain in response to stress and pain. A "second wind" might involve a similar neurochemical release, providing a natural analgesic effect and an improved mood, effectively masking the sensation of fatigue. Other neurotransmitters, like dopamine, which is associated with motivation and reward, could also play a role in overriding the brain's "stop" signals.
Mitochondrial Adaptations: Endurance training leads to significant adaptations in our cellular powerhouses – the mitochondria. These organelles are responsible for aerobic energy production. Zone 2 training, for example, is specifically designed to enhance mitochondrial function by increasing their number and efficiency. A greater density and capacity of mitochondria means the body can more effectively use both fat and lactate as fuel, leading to improved endurance and a deeper well of usable energy. Studies have shown that improved mitochondrial function can increase fat combustion and lactate clearance, both crucial for sustained performance.
Plasma Volume and Red Blood Cell Volume Expansion: Endurance training can lead to an increase in plasma volume and, over time, red blood cell volume. For instance, endurance athletes can exhibit up to 40% increments in red blood cell volume compared to sedentary individuals. This increased blood volume and red blood cell count enhance the body's ability to deliver oxygen to working muscles, directly impacting aerobic capacity and potentially contributing to a feeling of renewed energy when the system is optimized.
Psychological Resilience and Self-Efficacy: Beyond the physiological, the mental aspect of Reserve Capacity is critical. The belief in one's ability to continue, even when faced with discomfort, can be a powerful driver. Success in overcoming previous challenges can build self-efficacy, making it easier to push through future adversity. The "second wind" could be a manifestation of this psychological resilience, a shift in mindset that allows the athlete to access previously perceived limitations. This is where deliberate exposure to controlled adversity in training can be so impactful – it's not just physical adaptation, but a strengthening of the mental fortitude required to tap into those deeper reserves.
This concept of Reserve Capacity suggest that our perceived limits are often not our true limits. By understanding the intricate interplay of metabolic, neurological, and psychological factors, we can potentially unlock more of our inherent potential. This isn't about pushing ourselves to the point of collapse, but rather intelligently training our bodies and minds to access and expand these hidden reserves, ultimately redefining what we thought was possible.
