Physiologia, Volume 5, Issue 2 (June 2025) – 6 articles

Background/Objectives: Creatine monohydrate (CRE) is a popular nutritional supplement that increases lean/muscle mass accretion. Although data regarding CRE and its effects on muscle protein synthesis are mixed, we hypothesized that CRE may potentiate/extend the anabolic response to essential amino acids given that CRE acts as a high-energy phosphate buffer to potentially amplify anabolic signaling. Therefore, we used an in vitro model to determine whether CRE synergistically enhances myotube protein synthesis and the anabolic signaling responses to EAA-rich whey protein (WP). Methods: C₂C₁₂ murine myotubes were treated with control media containing PBS (CTL), WP serum (5 mg/mL), CRE (10 mM), or WP + CRE. Myotubes were collected following 1, 4, and 24 h treatments (n = 6 replicates per treatment and time point) and assayed for relative creatine levels, myotube protein synthesis levels, and phosphorylation markers. Results: Cellular creatine levels were greater in CRE and WP + CRE versus CTL and WP at all treatment time points (p < 0.05). The protein synthesis levels with 4 hr treatments with WP and WP + CRE were greater compared to the CTL (p = 0.036 and p < 0.001, respectively), and 24 h levels were greater with WP versus other treatments (p < 0.05). p-p70S6K (Ser389) and p-rpS6 (Ser235/236) were greater with WP at 1 h compared to all other treatments (p < 0.05). No effects across time points were observed for p-mTOR (Ser2448), p-4E-BP1 (Thr37/46), or p-AMPKα (Thr172). Conclusions: WP increases protein synthesis and anabolic signaling with no additive effect from CRE. However, given that myotubes were not stressed nor stimulated to contract, such models are needed with the current treatment schematic to examine potential interactions. Full article

Introduction: Oral rehydration reduces thirst sensation (TS), which may negatively affect autonomic function, measured by heart-rate variability (HRV). However, it is unclear if this effect is independent of hydration changes. This study examines whether TS influences autonomic function between intravenous and oral rehydration. Methods: Twelve males (mean ± SD; age, 29 ± 12 years; 74.7 ± 7.9 kg; 179.4 ± 7.0 cm; VO2_max, 49.8± 6.6 mL·kg⁻¹·min⁻¹) cycled at 55% VO_2max for 90 min followed by a 12 km time trial. Two experimental conditions were performed in a counterbalanced, randomized order; (a) the high thirst (HT) group were infused 25 mL of isotonic saline every 5 min via an intravenous tube, and (b) the low thirst (LT) group ingested 25 mL of water every 5 min. TS and heart rate were collected every 5 min. HRV was assessed pre exercise, post steady-state exercise, and post time trial. HRV parameters included time domain, frequency domain, and non-linear measures analyzed by two-way repeated measures ANOVA. Results: There was a significant time x condition for the root mean square of successive RR interval differences (RMSSD_log), high-frequency (HF) power, and SD1 (p < 0.05). In LT, RMSSD_log decreased from Pre to Mid (3.71 ± 0.61 ms to 2.53 ± 1.15 ms, p < 0.01) and Pre to Post (2.18 ± 0.90 ms, p < 0.01) but stabilized from Mid to Post (p = 0.39). High-frequency (HF) power in HT was maintained from Pre (3.7 ± 0.6 nu) to Mid (3.4 ± 0.8 nu, p = 0.21) but decreased from Pre to Post (2.5 ± 0.7 nu, p < 0.01) and Mid to Post (p < 0.01). LT decreased in HF power from Pre (3.7 ± 0.5 nu) to Mid (3.0 ± 0.8 nu, p < 0.01) and Pre to Post (3.0 ± 0.7 nu, p < 0.01); Mid and Post was maintained (p = 0.99). SD1, decreased in HT (Pre: 3.4 ± 0.4 ms, Mid: 2.0 ± 1.1 ms, Post: 1.1 ± 0.5 ms; all comparisons p < 0.05). In LT, SD1 decreased from Pre (3.4 ± 0.6 ms) to Mid (2.18 ± 1.15 ms, p < 0.01) and Pre to Post (1.83 ± 0.90 ms, p < 0.01), but stabilized Mid to Post (p = 0.39). Conclusion: Satiating thirst through oral rehydration increases parasympathetic activity post exercise, reducing stress and increasing recovery between exercise bouts. These findings have implications for optimizing rehydration strategies in sports and occupational settings. Full article

Background/Objectives: Studies of the effects of anchor schemes (perceived intensity vs. relative intensity) on muscular performance have reported mixed findings. Therefore, the present study examined the effects of different anchor schemes on time-to-task failure (TTF), muscular performance, neuromuscular responses, and potentiated twitch torque (PTT). Methods: On separate days, 15 men (age = 21.5 ± 2.3 yrs) performed forearm flexion maximal voluntary isometric contractions (MVICs) before and after sustained tasks anchored to a rating of perceived exertion of 6 (RPEFT) and with the torque at RPE = 6 (TRQFT). Electromyographic amplitude (EMG AMP) and mean power frequency (EMG MPF) were recorded from the biceps brachii (BB). Supramaximal stimuli were delivered to the motor nerve of the BB following the MVICs to quantify the PTT. Repeated measures ANOVAs assessed the mean differences between anchor schemes for MVIC, neuromuscular, and PTT responses. Paired t-tests compared the magnitude of percent changes for the dependent variables. Results: The TTF for the RPEFT was longer (p < 0.001) than the TRQFT, but the MVIC decreased similarly (12.7 ± 9.5% vs. 20.3 ± 7.9%, p = 0.054). Electromyographic AMP did not change (p = 0.288), while EMG MPF decreased (15.7 ± 10.2%, p < 0.011) for the TRQFT only. Mean decreases in PTT were comparable for both tasks (p < 0.003), although the percent change was greater for the TRQFT (49.6 ± 16.1%, p < 0.001). Conclusions: The differences in TTF, but similar decreases in MVIC suggested that participants reached a sensory tolerance limit. Based on EMG MPF and PTT, the TRQFT caused greater peripheral perturbations to contractile function than the RPEFT. Full article

Background: Extensive data exists on external load during training and competition, but a significant gap remains in understanding internal physiological load, particularly in protocols conducted in ecological settings. Given the scarcity of studies on the on-field cardiorespiratory profiles of national-level athletes, especially in Argentine soccer, this study aimed to identify the on-field cardiorespiratory fitness profile of ten highly trained youth field soccer players (13.6 ± 1.3 years old) from both the first league of the Argentine Football Association and members of the national team in their age group category in the current year. Methods: Each athlete performed an on-field cardiorespiratory exercise test (20-m Shuttle Run Test, 20-m SRT) with the COSMED K5 wearable metabolic system (COSMED, Rome, Italy) in dynamic micro-mixing chamber mode. The 20-m Shuttle Run Test involves running back and forth between two lines set 20 m apart, following the pace set by an audio signal. The test starts at a running velocity of 8.5 km·h⁻¹ and increases by 0.5 km·h⁻¹ each min. Results: Mean velocity at maximal oxygen uptake (v$\dot{\mathrm{V}}$O_2max) was 12.3 ± 0.7 km·h⁻¹. The maximal oxygen uptake ($\dot{\mathrm{V}}$O_2max) on-field was 67.1 ± 5.3 mL·kg⁻¹·min⁻¹. The $\dot{\mathrm{V}}$O₂ at the first and second ventilatory thresholds (VT1 and VT2) were identified at 67.0 ± 3.0% $\dot{\mathrm{V}}$O_2max (44.9 ± 3.3 mL·kg⁻¹·min⁻¹) and 84.7 ± 3.7% $\dot{\mathrm{V}}$O_2max (56.8 ± 3.8 mL·kg⁻¹·min⁻¹), respectively. Conclusions: This is a scarce on-field gas exchange assessment, conducted in an ecological context using a portable analyzer with highly trained national-level youth soccer players from the Argentine youth national team, which underlines their cardiorespiratory fitness, showcases their high-performance potential, offers valuable insights into a selective group of players, and provides a reference for larger-scale research on elite youth soccer and the long-term development of aerobic power and capacity. Full article

Background/Objectives: Neurodegenerative diseases represent a growing global health challenge with limited therapeutic options. Physical exercise has emerged as a promising non-pharmacological intervention with potential neuroprotective effects. This narrative review examines the mechanisms through which exercise induces neuroplasticity and their implications for neurodegenerative disease prevention. Methods: We synthesized evidence from molecular, animal, and human studies on exercise-induced neuroplasticity and neurodegenerative disease prevention through a comprehensive literature review. Results: Exercise enhances neuroplasticity through multiple pathways: (1) neurotrophic signaling (BDNF, IGF-1, VEGF), (2) neuroendocrine regulation, (3) epigenetic modifications, and (4) metabolic pathway optimization. These molecular changes support structural adaptations including hippocampal neurogenesis, enhanced synaptic plasticity, improved cerebrovascular function, and optimized brain network connectivity. Exercise directly impacts pathological features of neurodegenerative diseases by reducing protein aggregation, attenuating excitotoxicity and oxidative stress, and enhancing mitochondrial function. Clinical evidence consistently demonstrates associations between physical activity and reduced neurodegenerative risk, with intervention studies supporting causal benefits on cognitive function and brain structure. Conclusions: Exercise represents a multi-target intervention addressing several pathological mechanisms simultaneously across various neurodegenerative conditions. Its accessibility, minimal side effects, and multiple health benefits position it as a promising preventive strategy. Future research should focus on understanding individual response variability, developing sensitive biomarkers, and creating personalized exercise prescriptions for optimal neuroprotection. Full article

Background: The aim of this systematic review was to collect, appraise, and synthesize the available information related to the cardiovascular and metabolic demands of commonly performed firefighting tasks while wearing personal protective equipment (PPE) inclusive of self-contained breathing apparatus (SCBA). Methods: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, academic databases (PubMed, Embase, and SPORTDiscus databases) were searched for relevant records which were subjected to dedicated eligibility criteria with included articles quality appraised using the Critical Appraisal Skills Programme (CASP) checklist. Results: Of an initial 1463 identified records, 20 studies with a mean CASP of 8.26/11 informed the review. A myriad of varying field tests have been employed to determine physical preparedness and assess the metabolic demand of firefighting. Conclusions: The volume of evidence suggests that PPE and SCBA must be incorporated when assessing the demands of firefighting as they clearly increase the metabolic cost of combined simulated firefighting tasks. Although real-world scenarios are made up of a combination of individual firefighting tasks, there remains a clear need to determine the metabolic cost of isolated firefighting tasks such as forcible entry, hose drag, victim rescue, ladder raise, and stair climbing with and without PPE and SCBA. The quantification of the metabolic demand of these tasks may assist tactical trainers when designing simulated scenarios and training programs for firefighters. Full article