Advances in Sport Physiology, Nutrition, and Metabolism

1. Introduction

The fields of sport physiology, nutrition, and metabolism are advancing at an unprecedented pace, driven by growing interest in understanding the biological mechanisms that govern human responses to physical exercise and training [1,2]. Human physical performance and physiological adaptation to exercise are no longer interpreted through a single physiological lens [3,4]. Rather, they represent complex phenomena resulting from the interaction of numerous intrinsic and extrinsic determinants [5,6].

Consequently, research in sport and exercise science aims to understand physiological responses to exercise [7], metabolic adaptations to training [8], and the role of nutritional strategies in supporting performance and recovery in physically active and athletic populations [9].

Despite the rapid expansion of research in sports science [10], important questions remain regarding the physiological and metabolic responses to different exercise stimuli, the mechanisms underlying training-induced adaptations [11], and the role of nutritional strategies in supporting recovery [12] and metabolic regulation [13]. In addition, evidence regarding exercise-based interventions in specific populations and sport-specific nutritional considerations remains comparatively limited [14,15]. Addressing these questions is essential for advancing both the biological understanding of exercise responses and their practical application in physically active and athletic populations.

Under this context, the Special Issue “Advances in Sport Physiology, Nutrition, and Metabolism” brings together seven original research articles and one review. These contributions address physiological responses to exercise, metabolic adaptations to training, and nutritional strategies, reflecting the breadth and contemporary focus of research in sport physiology, nutrition, and metabolism. The main findings of the included contributions are summarized in the following section.

2. Overview of Published Articles

The articles published in this Special Issue address several important questions in sport physiology, training adaptation, and nutrition.

Two studies in this Special Issue (contributions 2 and 6) examined post-activation performance enhancement (PAPE) using isometric conditioning activity (ICA) protocols and addressed methodological uncertainties in their experimental design. The article by Latocha et al. (contribution 2) investigated the role of inter-set rest intervals during ICA in 15 resistance-trained males, a factor that remains insufficiently examined due to substantial variability in protocol parameters such as contraction duration, joint angle, and contraction distribution in previous studies. By comparing rest intervals of 1, 2, and 3 min while keeping the total contraction time constant, they aimed to isolate the influence of recovery duration between ICA sets on subsequent countermovement jump (CMJ) performance. The findings indicate that neither ICA nor the rest interval length significantly influenced CMJ height or relative peak power, suggesting limited effectiveness of the tested ICA protocols in resistance-trained individuals.

In contrast, Jarosz et al. (contribution 6) focused on another key parameter of ICA protocols, the total contraction volume, in a cohort of 14 highly trained male volleyball players. Specifically, the authors compared the effects of a single short ICA set (9 s) with a higher-volume protocol consisting of three sets (27 s in total) on CMJ performance. The results show that the higher-volume protocol significantly improved jump height and relative peak power within the first minutes following the conditioning activity.

Together, two studies (contributions 2 and 6) address an important methodological gap in the literature regarding the design of isometric conditioning activity (ICA) protocols to induce PAPE. While contribution 2 examined whether varying inter-set rest intervals (1–3 min) influence performance outcomes when total contraction time is held constant, contribution 6 directly compared different ICA volumes (9 s vs. 27 s total contraction duration). By isolating these key protocol variables across distinct trained populations, the studies help clarify how recovery structure and contraction volume independently affect the effectiveness of ICA-based warm-up strategies.

Extending the investigation of acute exercise responses (contributions 2 and 6), Skotniczny et al. (contribution 4) examined the immediate effects of maximal aerobic effort on the mechanical properties of the muscle–tendon unit. The authors investigated acute, tissue- and side-specific changes in viscoelastic properties following a progressive treadmill test to determine maximal oxygen uptake (VO₂max) in 21 high-level male soccer players. Measurements of tone, stiffness, elasticity, relaxation time, and creep were obtained before and immediately after the test using handheld myotonometry. Although muscle and tendon stiffness are known to influence athletic performance, fatigue, and injury risk, the immediate viscoelastic responses of muscle–tendon tissues to maximal aerobic exercise remain poorly understood and have rarely been systematically investigated in elite soccer players. The results reveal heterogeneous, side-dependent alterations in viscoelastic parameters across the muscles and tendons examined, with notable changes in the rectus femoris (RF) and Achilles tendon. Moreover, baseline viscoelastic properties of the RF were moderately associated with VO₂max, suggesting that tissue mechanical characteristics may serve as potential indicators of aerobic readiness.

Beyond studies examining acute responses to exercise (contributions 2, 4, and 6), three contributions in this Special Issue investigated the effects of structured training interventions implemented over longer periods (contributions 1, 3, and 8). These studies address distinct gaps in the literature concerning the design and physiological consequences of exercise training programs. Specifically, they examine (i) the effects of an integrated multicomponent training approach in elite rugby sevens athletes, (ii) the impact of plyometric training on anaerobic performance and biomechanical muscle properties in football players, and (iii) the effects of low-volume resistance training on biochemical markers related to muscle health, metabolic profile, and oxidative stress in older adults with cognitive impairment.

Marius et al. (contribution 1) evaluated the effects of a 12-week integrated training program in elite rugby sevens athletes, including both female and male players (n = 24; 12 women and 12 men). The intervention consisted of 12 training micro-cycles combining strength, speed, aerobic capacity, and rugby-specific exercises within an integrated training framework. Pre- and post-intervention assessments included sprint performance, jumping ability, resting metabolic rate, and cardiopulmonary exercise testing. The results show significant improvements in several performance variables, including sprint and jump performance, together with favorable changes in selected physiological responses to exercise. Sex-specific differences in adaptations were observed: females showed greater improvements in aerobic capacity and jumping performance, while males demonstrated larger gains in explosive power and longer sprint distances. These findings highlight the potential value of integrated training approaches that simultaneously target multiple components of physical performance in rugby players.

A complementary perspective on training adaptations was provided by Matuszczyk et al. (contribution 8), who investigated the effects of a 10-week plyometric training program in football players. Twenty male athletes were randomly assigned to an experimental group (n = 10), which performed additional plyometric training twice per week, or a control group (n = 10) that maintained regular football training. The study assessed sprint performance (5 m and 30 m), reactive strength index, and biomechanical properties of the RF and vastus lateralis muscles. The experimental group demonstrated significant improvements in sprint performance and reactive strength index (RSI) following the intervention. However, no significant group-level changes were observed in muscle tension, stiffness, or elasticity. Instead, correlation analyses indicated that baseline elasticity of the vastus lateralis, and changes in the elasticity of the rectus femoris were associated with improvements in 5 m sprint performance. These findings suggest that plyometric training can enhance short-distance sprint performance and RSI, while individual biomechanical characteristics of muscle tissue may modulate training adaptations.

While the previous studies focused on athletic populations (contributions 1 and 8), Lopes et al. (contribution 3) explored the effects of exercise in a clinical population of older adults with cognitive impairment. In this study, 28 institutionalized older adults were assigned to a low-volume resistance training group (n = 15; 6 women and 9 men) or a control group (n = 13; 9 women and 4 men). The intervention consisted of an eight-week resistance training program performed twice per week using a single-set protocol. The authors examined biochemical markers related to muscle damage, liver function, lipid profile, glycemic control, and oxidative stress. Although no significant between-group differences were observed in any biomarker at baseline or post-test, the intervention group showed increases in serum lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase activities, all of which remained within physiological ranges, suggesting an acute-phase response rather than tissue damage. Additionally, within the intervention group, high-density lipoprotein cholesterol increased, and the atherogenic index decreased. These results suggest that low-volume resistance training may induce modest changes in selected biochemical markers and represent a feasible exercise strategy for older adults with cognitive impairment.

Together, these studies (contributions 1, 3, and 8) demonstrate that structured training programs, including integrated conditioning, plyometric training, and resistance exercise, can induce measurable physiological adaptations across diverse populations. Such programs may also contribute to improvements in physical performance or health-related outcomes. In addition to studies examining acute responses and structured training interventions, other contributions in this Special Issue explore the role of nutritional strategies in supporting exercise performance and recovery. Under this context, Drviš et al. (contribution 7) examined nutritional recommendations for breath-hold divers, a population exposed to unique physiological stressors, including prolonged apnea, hypoxia, and hypercapnia. The authors highlight that, despite the extreme physiological demands of breath-hold diving, sport-specific nutritional frameworks remain largely underdeveloped. To address this gap, the review synthesizes the available literature. It proposes tailored nutritional strategies for different breath-hold diving disciplines, highlighting Mediterranean and alkaline dietary patterns as potentially useful approaches to support recovery, performance, and long-term health in freedivers.

Beyond physiological and nutritional considerations, the accurate monitoring of performance and injury risk remains a central challenge in applied sport science. Addressing this aspect, Michailidis et al. (contribution 5) investigated the relationship between asymmetries detected through a commonly used field-based test—the single-leg countermovement jump—and those identified using laboratory-based isokinetic strength assessments in 63 elite male youth football players. Given that inter-limb asymmetries have been associated with both injury risk and reduced performance, the study explored whether practical jump-based screening tools could serve as proxies for more complex strength measurements. The findings indicate only limited relationships between the two assessment methods, suggesting that simple field tests cannot fully replace laboratory-based evaluations and that a combination of approaches may be necessary for comprehensive monitoring of lower-limb asymmetry in football players.

3. Conclusions

The studies included in this Special Issue highlight several interconnected directions in contemporary sport physiology, training adaptation, and applied sport science research. Two primary research axes emerge across the contributions. The first concerns acute physiological responses to exercise and conditioning stimuli (contributions 2, 4, and 6), including the methodological optimization of isometric conditioning activity protocols to induce post-activation performance enhancement and the investigation of the immediate mechanical responses of muscle–tendon tissues to maximal aerobic effort. The second axis focuses on longer-term training interventions and their physiological consequences across both athletic and clinical populations (contributions 1, 3, and 8).

In addition to these primary research axes, this Special Issue also includes two complementary topics. One contribution (7) addresses sport-specific nutritional considerations in breath-hold divers, highlighting the limited availability of dedicated dietary frameworks for this unique discipline. Another study (5) focuses on performance monitoring in football players, examining the relationship between asymmetries detected using field-based jump tests and those identified through laboratory-based isokinetic strength assessments.

Research examining acute responses to exercise indicates that specific protocol characteristics influence the outcomes of conditioning strategies. In particular, studies investigating isometric conditioning protocols show that manipulating parameters such as rest intervals or contraction volume does not necessarily yield consistent improvements in countermovement jump performance. However, certain configurations—such as higher total contraction volume—may produce short-term increases in jump height and relative peak power in trained individuals. At the same time, investigations of maximal aerobic exercise demonstrate that exhaustive treadmill running can induce heterogeneous, tissue-specific alterations in the viscoelastic properties of muscles and tendons in high-level soccer players, suggesting that acute exercise responses may vary across different muscle–tendon structures.

Studies addressing longer-term training interventions further show that structured exercise programs can lead to measurable physiological and performance-related changes across different populations. An integrated multicomponent training approach was shown to improve several performance and physiological parameters in elite rugby sevens athletes, including sprint ability, jumping performance, and indicators of cardiovascular efficiency. Similarly, a 10-week plyometric training program improved sprint performance and RSI in football players, although no significant group-level changes were observed in biomechanical muscle properties. In a clinical context, low-volume resistance training performed over eight weeks produced modest but potentially beneficial changes in selected metabolic markers in older adults with cognitive impairment, while enzyme changes remained within physiological ranges and were suggestive of an acute-phase response rather than tissue damage.

Complementary contributions also emphasize the importance of supporting factors in applied sport science research. A review focusing on breath-hold diving highlights the current lack of dedicated nutritional recommendations for freedivers and proposes dietary strategies based on Mediterranean and alkaline dietary patterns. In addition, research on lower-limb asymmetry in youth football players shows that asymmetry indices derived from jump tests cannot replace those obtained through isokinetic strength assessments, indicating that a combination of testing approaches may be necessary for a more comprehensive evaluation of lower-limb asymmetry in football players.

Building on the directions highlighted by the studies in this Special Issue, subsequent work should further refine conditioning protocols and clarify the mechanisms underlying performance enhancement and fatigue responses, particularly in the context of acute exercise (contributions 2, 4, and 6). This encompasses systematic exploration of key methodological parameters of isometric conditioning activity—such as contraction intensity, joint angle, contraction duration, and recovery structure—and the integration of objective indicators of neuromuscular function and fatigue. Additionally, research into the viscoelastic responses of muscle–tendon structures to intense exercise should assess how training and recovery shape longer-term adaptations and determine whether targeted interventions affect performance readiness or injury risk.

Regarding longer-term training interventions (contributions 1, 3, and 8), future research should examine the effectiveness of structured training programs across diverse populations and contexts. Longitudinal studies are needed to better understand training adaptations over extended periods, including the role of integrated training strategies, plyometric interventions, and resistance training protocols. Particular attention should be paid to individual variability in training responses, the influence of athlete characteristics, and the optimization of exercise interventions in both athletic and clinical populations.

Complementary areas (contributions 5 and 7) underscore the significance of broader performance support systems. Ongoing inquiry into sport-specific nutritional strategies for disciplines with unique physiological demands (e.g., breath-hold diving) remains important, as does the advancement of diagnostic methods for monitoring performance and injury risk. Integrating field- and laboratory-based assessments to evaluate lower-limb asymmetry and function will strengthen these efforts.

Looking forward, multidisciplinary approaches that bridge physiology, nutrition, biomechanics, and performance analysis are likely to yield the most comprehensive insights. While the studies in this Special Issue address a range of topics, most focus on individual domains.

Unifying these perspectives within integrated research frameworks will better capture the multifactorial nature of athletic performance and adaptation [16], paving the way for a deeper understanding of exercise mechanisms, training effects, and recovery processes.