Special Issue “Physiological Effects of Sports on the Cardiopulmonary System”

1. Introduction

Regular physical activity and structured sports training induce a wide range of adaptations in the cardiopulmonary system, from central adaptations in cardiac structure [1] and function to peripheral adaptations in oxygen transport and utilization [2]. These adaptations underpin performance improvements across most sports disciplines and are modulated by the type, intensity, and environment of training (e.g., altitude, heat), as well as by the use of ergogenic aids. Understanding how these physiological changes occur, over what time frame, and how they translate into performance outcomes remains a central question in sports science and sports medicine.

This Special Issue, “Physiological Effects of Sports on the Cardiopulmonary System”, was launched with the aim of gathering original research, systematic reviews, and meta-analyses addressing the short-, medium-, and long-term physiological adaptations of the cardiopulmonary system to different training methods, environmental conditions, and ergogenic strategies. The contributions collected in this Special Issue address this aim from complementary perspectives: hematological and pharmacological determinants of endurance performance, structural cardiac remodeling in elite athletes, and the biomechanical and neuromuscular consequences of footwear technology and physiological fatigue on sport-specific performance. Together, they illustrate the breadth of approaches currently used to understand and monitor cardiopulmonary adaptation to sport.

2. Hematological and Pharmacological Determinants of Endurance Performance

Two contributions in this Special Issue examined how blood-related variables affect endurance-related performance in trained and elite athletes.

Alberdi-Garciandia and Santos-Concejero (Contribution 1) conducted a systematic review analyzing the hematological, physiological, and performance effects of recombinant human erythropoietin (rHuEPO) administration in well-trained endurance athletes. Based on ten studies of predominantly high methodological quality (average PEDro score of 7.2), the authors reported that rHuEPO consistently increases total hemoglobin mass and concentration, and hematocrit, together with maximal and peak oxygen uptake, regardless of the total dose administered. Maximal performance-related parameters, such as maximal and peak power output, also tended to improve, although evidence regarding submaximal performance parameters—arguably more relevant to real competition scenarios in cyclic endurance sports—remained inconclusive. This review reinforces the well-established link between oxygen-carrying capacity and aerobic performance, while highlighting the persistent challenge that anti-doping authorities face in detecting microdosing strategies that may preserve ergogenic effects while minimizing hematological fluctuations.

Complementing this pharmacological perspective, Ashikaga et al. (Contribution 2) explored a naturally occurring hematological marker—reticulocyte count—as an indicator of short-term red blood cell turnover in 105 elite Italian athletes engaged in endurance or mixed disciplines. Interestingly, reticulocyte count was negatively, rather than positively, associated with peak oxygen uptake and anaerobic threshold, remaining an independent predictor of both variables after adjusting for age, sex, hemoglobin concentration, stroke volume, and peak heart rate. These findings suggest that the transient decline in red blood cell function associated with exercise-induced accelerated erythrocyte turnover may temporarily impair oxygen transport capacity, adding a novel, non-invasive marker to the toolbox available for monitoring athletes’ hematological status and possibly informing training-load decisions prior to key competitions.

Taken together, these two studies underscore that both externally administered and endogenously regulated changes in red blood cell dynamics can meaningfully influence cardiopulmonary performance, and that hematological monitoring—whether for anti-doping or training-management purposes—remains an area requiring further methodological refinement.

3. Structural and Functional Cardiac Adaptation to Training

Sport-induced structural cardiac remodeling, commonly referred to as “athlete’s heart”, was addressed by Zamodics et al. (Contribution 3) in a cross-sectional study of 161 elite youth and adult water polo players. Using bioelectrical impedance body composition analysis alongside resting echocardiography, the authors found that skeletal muscle mass and fat-free mass were more strongly and consistently associated with cardiac chamber dimensions and wall thickness than conventional anthropometric indices such as height or body surface area. These associations were observed for both ventricles as well as atrial dimensions, confirming that cardiovascular adaptation parallels the increase in metabolically active tissue induced by high-volume mixed aerobic–anaerobic training. Based on these findings, the authors developed a freely accessible online calculator providing sex-, age-, and body-composition-adjusted percentile values for basic echocardiographic parameters, offering clinicians a practical tool to help distinguish physiological “athlete’s heart” adaptations from early signs of cardiac pathology, an area in which age- and sex-specific reference values have so far been notably scarce, particularly for mixed sports and youth populations.

4. Biomechanical and Neuromuscular Determinants of Performance Under Physiological Load

The remaining two contributions examined how training-related equipment and physiological fatigue interact with biomechanical and neuromuscular performance.

Alda-Blanco et al. (Contribution 4) investigated the influence of advanced footwear technology (AFT) spikes—differing in the presence of a curved carbon fiber plate—on running performance, energy cost, and perceptual variables across track and grass surfaces in trained runners. Spikes combining a polyether block amide (PEBA) midsole with a carbon fiber plate improved self-perceived 3000 m pace performance on both surfaces and were consistently perceived as more comfortable and effective, although there were no differences in energy cost and heart rate regardless of spike condition, illustrating how surface compliance interacts with footwear design to influence the cardiopulmonary and metabolic demand of running.

Finally, Bilić et al. (Contribution 5) used a wearable inertial measurement unit system to examine how physiological fatigue—induced through repeated serve blocks interspersed with change-of-direction drills—affects the kinetic chain and performance of the tennis serve in professional players. As heart rate rose progressively across serve blocks, several kinematics were significantly altered, most notably a progressive decline in jump height and changes in wrist velocity, which were associated with reductions in serve speed and accuracy in the final blocks. These results provide a clear, sport-specific example of how cardiovascular fatigue translates into measurable losses of biomechanical efficiency and technical performance, with direct implications for training prescription and match-play strategy.

5. Future Research

Building on the findings of this Special Issue, several avenues for future research can be identified. First, the effects of rHuEPO and other ergogenic strategies on submaximal performance parameters—arguably more representative of real competitive demands in endurance sports—warrant further dedicated investigation, together with the development of more sensitive detection methods for microdosing regimens. Second, the negative association between reticulocyte count and aerobic performance indicators should be explored longitudinally and in relation to training load and competition scheduling to determine whether monitoring this marker can meaningfully inform training decisions. Third, further research is needed to extend sex-, age-, and sport-specific reference values for cardiac structural adaptation beyond water polo, incorporating other mixed and endurance disciplines, larger female samples, and complementary imaging techniques such as cardiac magnetic resonance. Fourth, the interaction between footwear technology and surface compliance deserves further exploration across a wider range of running speeds, distances, and athlete profiles, including female runners, who were not represented in the present study. Finally, future studies on fatigue-induced changes in sport-specific technical performance should employ larger and more heterogeneous samples—including athletes of different competitive levels—to improve the generalizability of kinematic findings such as those reported for the tennis serve.