Impact of Creatine Monohydrate Supplementation on Breath-Hold Exercise Performance on a Bicycle Ergometer

Creatine is well known for its role in enhancing adenosine triphosphate (ATP) regeneration and therefore aiding in short high-intensity activities, improving work capacity and power output of skeletal muscle, and delaying the onset of muscle fatigue. However, research on creatine supplementation in endurance sports has yielded inconsistent results. Some studies in this field showed improved endurance performance, while others failed to demonstrate it, or even showed decrements in it. This variability may stem from different supplementation protocols or the wide range of protocols used for measuring performance. Additionally, the increase in body mass resulting from creatine's osmotic properties may negatively impact performance in weight-bearing sports. Another factor may be muscle fiber composition, as individuals who respond best to creatine supplementation typically have a higher proportion of type II muscle fibers, whereas endurance athletes usually predominantly possess type I fibers.

Breath-hold diving is the practice of diving underwater on a single breath. Sport disciplines in breath-hold diving can be divided into three categories: static breath-hold, depth disciplines and dynamic disciplines. Static breath-hold focus on holding the breath for the longest possible time, depth disciplines focus on reaching the greatest possible depth underwater, while dynamic disciplines focus on covering the greatest possible distance underwater on a single breath. These disciplines test diver's oxygen (O2) management, metabolic byproducts tolerance, movement efficiency and energy conservation. Some of the limitations in breath-hold diving include tolerance to fatigue-inducing metabolic byproducts, the buildup of carbon dioxide (CO2) and O2 availability. As dive time and the muscular activity increase, O2 levels decrease, and reliance on anaerobic metabolic pathway intensifies, leading to the accumulation of metabolic byproducts such as lactate. Therefore, divers, among other things, train to optimize O2 utilization, to delay metabolic acidosis onset, and to enhance tolerance to elevated levels of metabolic byproducts.

Although breath-hold diving may not be considered a high-intensity sport in terms of heart rate and movement speed, it involves a unique performance pattern that includes limited availability of O2 and triggers a shift to anaerobic metabolism. This shift is sustained over extended periods, requiring significant effort and endurance to maintain performance. It is important to highlight that no form of exercise is purely anaerobic or aerobic, and that all energy systems contribute to ATP re-synthesis. However, their contribution depends on the nature of the activity. So, even though the phosphocreatine system may not dominate when it comes to endurance sports, it can still buffer energy demands and therefore prevent early onset of fatigue. Therefore, the energy produced by creatine phosphate (CP) is used for ATP yield as long as possible and it was shown that even though contribution of CP is reduced between 100 and 200 meters of running sprint, the CP stores are depleted only at the end of 400 meters.

As breath-hold diving requires efficient O2 utilization and as body relies predominantly on anaerobic metabolism that leads to metabolic acidosis, efficient ATP production, O2 utilization and CO2 production are crucial. Creatine supplementation may offer benefits by providing efficient energy production and delaying the onset of metabolic acidosis. In addition, creatine has an ability to buffer acidity by accepting and neutralizing excess hydrogen ions that accumulate in the muscles as a byproduct of anaerobic metabolism.

Lactate threshold (LT) is defined as the point of the exercise intensity at which lactate begins to accumulate in the blood at a faster rate than it can be cleared. A higher LT allows athletes to sustain higher speeds or higher power outputs before the onset of fatigue. Breath-hold divers could also benefit from a higher LT because of the delayed buildup of anaerobic metabolism byproducts. In various strength-endurance test protocols, creatine supplementation was suggested to increase LT, by improving ATP regeneration and increasing muscle buffering capacity, as well as to improve performance measured by total work (TW), time to exhaustion (TTE) and power output. Still, some studies failed to show improved endurance performance and increased LT.