Arterial Stiffness Intercostal Muscle Oxygenation and Aerobic-Anaerobic Capacity in Elite American Football Players

American football has become an increasingly popular sport in Türkiye, and one of the key determinants of success in this discipline is the development of strong aerobic and anaerobic exercise capacities. Previous research has examined arterial stiffness in various athletic populations, including endurance athletes, wrestlers, badminton players, volleyball players, and soccer players. These studies highlight the importance of detailed cardiovascular and hemodynamic evaluation to identify potential risk groups and to better understand sport-specific physiological adaptations. In sports requiring prolonged physical effort, maximal oxygen uptake is a major determinant of performance, underscoring the need to assess this parameter in elite athletic populations. Although a limited number of studies have investigated aerobic and anaerobic exercise capacities in American football athletes, no research to date has evaluated arterial stiffness or intercostal muscle oxygenation in this group. The present study aims to investigate arterial stiffness, intercostal muscle oxygenation, aerobic and anaerobic exercise capacity, and upper-extremity endurance in elite American football players compared with sedentary individuals. A cross-sectional study design will be used. Elite male athletes from the Gazi University American Football Team who volunteer to participate will be included, and their results will be compared with age- and sex-matched sedentary individuals. A total of 15 elite male athletes and 15 sedentary participants aged 18-30 years will be enrolled. All participants will undergo standardized assessments of arterial stiffness, intercostal muscle oxygenation, aerobic and anaerobic capacity, and upper-extremity endurance. Normality of variables will be assessed using visual inspection and the Kolmogorov-Smirnov and Shapiro-Wilk tests. Descriptive statistics will be reported as means, standard deviations, and 95% confidence intervals for normally distributed variables, and medians with interquartile ranges (25th-75th percentiles) for non-normally distributed variables. Frequencies and percentages will be used for categorical data. Between-group comparisons will be conducted using the independent samples t-test for normally distributed variables and the Mann-Whitney U test for non-normally distributed variables. Categorical variables will be analyzed using the chi-square test. A p-value of \<0.05 will be considered statistically significant.

American football is a sport that demands strength, speed, courage, teamwork, and tactical intelligence, and is played with three units-offense, defense, and special teams-over four quarters of 15 minutes each. Beyond technical and tactical training, aerobic and anaerobic power, speed, endurance, body composition, flexibility, coordination, and motor skills are fundamental contributors to performance. From a mechanical perspective, American football is classified as a moderate-dynamic, moderate-static sport, while metabolically it is predominantly anaerobic. Regular physical training plays a critical role in both the prevention and management of cardiovascular disease. Arterial stiffness is an established biomarker of vascular health and an independent determinant of cardiovascular risk. Although the term refers broadly to reduced elasticity, increased rigidity, or diminished distensibility of the arterial wall, all reflect impaired vascular compliance. Progressive arterial stiffening fosters a vicious cycle: rising aortic pressure accelerates vascular damage, promotes left ventricular hypertrophy, increases myocardial oxygen demand, and disrupts diastolic function. Research examining aortic impedance suggests that age-related increases in arterial stiffness occur more slowly in individuals who engage in lifelong regular exercise, although changes that emerge later in life may be irreversible. Acute aerobic exercise has been shown to transiently improve arterial compliance, with increases of up to 30-40%, returning to baseline approximately one hour after exercise due to enhanced vasodilation. Studies evaluating athletes' brachial and central blood pressure and pulse wave velocity indicate that high-performance sport does not adversely affect arterial stiffness, and proposed reference values may support more detailed cardiovascular and hemodynamic assessment in elite athletic populations. Notably, no studies have specifically examined arterial stiffness in elite American football players. Based on existing evidence, it is anticipated that these athletes will exhibit lower arterial stiffness than sedentary individuals, suggesting reduced cardiovascular risk-a finding that may help identify at-risk groups more accurately. Assessment of muscle oxygen metabolism in athletes is also crucial. During high-intensity competition, increased ventilatory demand can reduce blood flow to locomotor muscles, contributing to exercise intolerance and premature fatigue. Intercostal muscle oxygenation has been shown to be closely associated with peak oxygen uptake in athletes. As ventilation increases, the metabolic cost of breathing and oxygen consumption rise, elevating the respiratory muscles' oxygen requirements. The ability to adequately deliver oxygen to these muscles is therefore functionally important and merits investigation. However, no studies to date have evaluated intercostal muscle oxygenation in American football players. Although several studies have explored physical and physiological characteristics across various sports, research specifically examining athletes engaged in American football-particularly in Türkiye, where the sport is expanding at the university level-remains limited. In prolonged athletic activity, maximal oxygen uptake (VO₂max) is a critical determinant of performance, reflecting the capacity to transport oxygen from inspired air to skeletal muscle mitochondria. At exercise intensities beyond the point at which cardiac output plateaus, the respiratory system must work disproportionately harder to maintain oxygen delivery to active tissues. VO₂max fundamentally represents the oxidative capacity of skeletal muscle mitochondria; higher values support the ability to sustain exercise for longer durations under stable physiological conditions. Aerobic capacity therefore depends on the integrated function of pulmonary, cardiovascular, hematologic, and muscular oxidative systems. Anaerobic performance also plays a key role in sports requiring high-intensity, short-duration exertion. Energy for such activities is provided primarily through phosphagen and glycolytic pathways, which generate ATP rapidly but in limited quantities, whereas aerobic metabolism produces ATP at a slower rate but with virtually unlimited capacity. The phosphagen system supports explosive movements lasting up to approximately 15 seconds; activities lasting 15-30 seconds rely on both phosphagen and glycolytic pathways; and efforts of around 30 seconds depend almost entirely on glycolysis. Anaerobic performance varies according to individual and environmental factors, but regular training enhances these systems significantly. Athletes with higher anaerobic capacities typically exhibit greater fast-twitch muscle fiber content, larger muscle cross-sectional area, and superior muscle strength-factors that contribute to essential performance attributes such as sprinting and explosive lower-limb force. Despite the central role of these physiological determinants, no research has examined arterial stiffness in elite American football players, and studies evaluating intercostal muscle oxygenation as well as aerobic and anaerobic capacities in this population are scarce. Therefore, the present study aims to evaluate arterial stiffness, intercostal muscle oxygenation, and aerobic and anaerobic exercise capacity in elite American football players and to compare these outcomes with those of sedentary individuals.