European Journal of Applied Physiology最新文献

Introduction: Cerebrovascular reactivity (CVR) describes the vasculature's response to vasoactive stimuli, where prior investigations relied solely on mean data, rather than exploring cardiac cycle differences.

Methods: Seventy-one participants (46 females and 25 males) from two locations underwent TCD measurements within the middle or posterior cerebral arteries (MCA, PCA). Females were tested in the early-follicular phase. The hypercapnia response was assessed using a rebreathing protocol (93% oxygen and 7% carbon dioxide) or dynamic end-tidal forcing as a cerebral blood velocity (CBv) change from 40 to 55-Torr. The hypocapnia response was quantified using a hyperventilation protocol as a CBv change from 40 to 25-Torr. Absolute and relative CVR slopes were compared across cardiac cycle phases, vessels, and biological sexes using analysis of covariance with Tukey post-hoc comparisons.

Results: No differences were found between hypercapnia methods used (p > 0.050). Absolute hypercapnic slopes were highest in systole (p < 0.001), with no cardiac cycle differences for absolute hypocapnia (p > 0.050). Relative slopes were largest in diastole and smallest in systole for both hypercapnia and hypocapnia (p < 0.001). Females exhibited greater absolute CVR responses (p < 0.050), while only the relative systolic hypercapnic response was different between sexes (p = 0.001). Absolute differences were present between the MCA and PCA (p < 0.001), which vanished when normalizing data to baseline values (p > 0.050).

Conclusion: Cardiac cycle variations impact CVR responses, with females displaying greater absolute CVR in some cardiac phases during the follicular window. These findings are likely due to sex differences in endothelial receptors/signalling pathways. Future CVR studies should employ assessments across the cardiac cycle.

This study investigated the effect of caffeinated chewing gum (GUM_CAF) on muscle fatigue (isometric vs. dynamic) after severe-intensity cycling bouts. Fifteen trained male cyclists participated in four visits. Each visit involved two severe-intensity cycling bouts (Δ₁ and Δ₂) lasting 6 min, separated by a 5-min recovery period. Muscle fatigue was assessed by isometric maximal voluntary knee extension contraction (IMVC) with twitch interpolation technique and dynamically by 7 s all-out cycling sprints. Assessments were performed before GUM_CAF (Pre-GUM) and after the cycling bouts (Post-Exercise). GUM_CAF and placebo gum (GUM_PLA) were administered in a randomized double-blind procedure with participants receiving each gum type (GUM_CAF and GUM_PLA) during two separate visits. The results showed no significant interaction between gum types and time for the isometric and dynamic measurements (p > 0.05). The percentage change in performance from Pre-GUM to Post-Exercise showed no significant difference between GUM_CAF and GUM_PLA for either the dynamic-derived T_MAX (~ -17.8% and -15.1%, respectively; p = 0.551) or isometric IMVC (~ -12.3% and -17.7%, respectively; p = 0.091) measurements. Moderate to large correlations (r = 0.31-0.51) were found between changes in sprint maximal torque and maximal power output measurements and isometric force, for both gum conditions. GUM_CAF was not effective in attenuating muscle force decline triggered by severe-intensity cycling exercises, as measured by both isometric and dynamic methods. The correlations between IMVC and cycling maximal torque and power output suggest caution when interpreting isometric force as a direct measure of fatigue during dynamic cycling exercises.

Recovery methods, such as thermal interventions, have been developed to promote optimal recovery and maximize long-term training adaptations. However, the beneficial effects of these recovery strategies remain a source of controversy. This narrative review aims to provide a detailed understanding of how cold and heat interventions impact long-term training adaptations. Emphasis is placed on skeletal muscle adaptations, particularly the involvement of signaling pathways regulating protein turnover, ribosome and mitochondrial biogenesis, as well as the critical role of satellite cells in promoting myofiber regeneration following atrophy. The current literature suggests that cold interventions can blunt molecular adaptations (e.g., protein synthesis and satellite cell activation) and oxi-inflammatory responses after resistance exercise, resulting in diminished exercise-induced hypertrophy and lower gains in isometric strength during training protocols. Conversely, heat interventions appear promising for mitigating skeletal muscle degradation during immobilization and atrophy. Indeed, heat treatments (e.g., passive interventions such as sauna-bathing or diathermy) can enhance protein turnover and improve the maintenance of muscle mass in atrophic conditions, although their effects on uninjured skeletal muscles in both humans and rodents remain controversial. Nonetheless, heat treatment may serve as an important tool for attenuating atrophy and preserving mitochondrial function in immobilized or injured athletes. Finally, the potential interplay between exercise, thermal interventions and epigenetics is discussed. Future studies must be encouraged to clarify how repeated thermal interventions (heat and cold) affect long-term exercise training adaptations and to determine the optimal modalities (i.e., method of application, temperature, duration, relative humidity, and timing).

Background: Although brief skin cooling (BSC) is widely used in sports medicine and rehabilitation for its positive effects on motor performance, the mechanism underlying this motor facilitation effect remains unclear.

Objectives: To explore the hypothesis that BSC enhances muscle force generation, with cold-induced sympathetic activation leading to heightened muscle spindle sensitivity, thereby contributing to this effect.

Methods: The study involved two experiments. Experiment 1 included 14 healthy volunteers. Participants submerged their hand in ice water for 3 min. Sympathetic activity was measured via heart rate (HR), muscle force generation was assessed through plantar flexor strength during maximum voluntary contraction (MVC), and cortical contribution to force generation via the volitional wave (V-wave) with and without the cold pressor test (CPT). Experiment-2 involved 11 healthy volunteers and focused on muscle spindle sensitivity and Ia synapse efficacy, assessed using soleus T-reflex and H-reflex recordings before, during, and after CPT.

Results: Experiment 1 showed significant increases in HR (7.8%), MVC force (14.1%), and V-wave amplitude (93.4%) during CPT compared to pre-CPT values (p = 0.001, p = 0.03, and p = 0.001, respectively). In Experiment-2, hand skin temperature significantly decreased during CPT and remained lower than pre-CPT after 15 min (p < 0.001). While H-reflex and background EMG amplitudes remained unchanged, T-reflex amplitude (113.7%) increased significantly during CPT and returned to pre-CPT values immediately afterward (p < 0.001). A strong correlation was also observed between HR and T-reflex amplitude (r = 0.916, p = 0.001).

Conclusion: BSC enhances muscle spindle sensitivity via the sympathetic nervous system, promoting more significant muscle force generation. The method used in this study can be safely applied in clinical practice.

Purpose: Training zones are generally assessed by gas-exchange thresholds (GET). Several mathematical analyses of heart rate variability (HRV) are proposed for indirect GET determination. Our study aimed to investigate the accordance of the detrend fluctuation analysis (DFA α1) for determining GET with first (VT1) and second ventilatory (VT2) thresholds in well-trained subjects.

Methods: Eighteen female and 38 male sub-elite cyclists performed a maximal incremental cycling test of 2-min stage duration with continuous gas exchange and HR measurements. Power output (PO), Oxygen uptake ( $\dot{\text{V}}$ O₂) and HR at VT1 and VT2 were compared with DFA α1 0.75 (HRVT1) and 0.50 (HRVT2). Agreements between PO, $\dot{\text{V}}$ O₂ and HR values were analyzed using Bland-Altman analysis.

Results: Large limits of agreement between VT1 and HRVT1 were observed for measures of $\dot{\text{V}}$ O₂ expressed in mL.min^-1.kg^-1 [- 21.3; + 14.1], HR [ 39.2; + 26.9] bpm and PO [- 118; + 83] watts. Indeed, agreements were also low between VT2 and HRVT2 for measures of $\dot{\text{V}}$ O₂ [- 26.7; + 4.3] mL.min^-1.kg^-1, HR [- 45.5; + 10.6] bpm and PO [- 157; + 35] watts. Our results also showed a sex effect: women obtained worst predictions based on DFA α1 than men for HR (p = 0.014), PO (p = 0.044) at VT1 and ${\dot{\text{V}}\text{O}}_2$ (p = 0.045), HR (p = 0.003) and PO (p = 0.004) at VT2.

Conclusion: There was unsatisfactory agreement between the GET and DFA α1 methods for VT1 and VT2 determination in both sex well-trained cyclists. Trial registration number 2233534 on 2024/03/05 retrospectively registered.

Purpose: Whether stretch exercise improves muscle anisotropy in relation to intramuscular adipose tissue (IntraMAT) is unclear. This study aimed to compare the diffusion tensor imaging (DTI) parameters of the quadriceps before and after stretching and to investigate correlations between the magnitudes of changes and IntraMAT ratios.

Methods: Twenty young males were included. Single axial DTI and T1-weighted imaging of the right mid-thigh region were conducted before and after rest and stretching. Individual quadriceps were segmented, λ_1-3 and fractional anisotropy (FA) were measured using DTI, and the IntraMAT ratios were measured using T1-weighted imaging. To test an intervention-by-time interaction effect, two-way repeated-measures analysis of variance was conducted. The correlation coefficients between the changing λ_1-3 and FA magnitude by stretching and the IntaMAT ratio were assessed.

Results: There was a significant interventions-by-time interaction effect in the λ_1-3 and FA in the vastus medialis (VM). After stretching, in the VM, the λ_1-3 values significantly decreased (mean difference, 0.07 mm²∙s^-1∙10^-3 for λ_1-3), and the FA significantly increased (mean difference, 0.021). Furthermore, the decreasing λ₂ and λ₃ in the VM were significantly inversely correlated with the IntraMAT ratio (r = - 0.50 for both), and the increasing FA magnitude was significantly positively correlated with the IntraMAT ratio (r = 0.45).

Conclusion: Stretching the quadriceps acutely decreased λ_1-3 and increased FA in the VM, and the magnitude of the λ₂, λ₃, and FA changes were correlated with the IntraMAT ratio. Stretching the quadriceps could improve VM function, particularly in overweight and obese people.

Sleep deprivation has been associated with impaired thermoregulatory function. However, whether these impairments translate to changes in whole-body heat exchange during exercise-heat stress remains unknown. Therefore, following either a night of normal sleep or 24 h of sleep deprivation, 10 young men (mean (SD): 23 (3) years) completed three 30-min bouts of semi-recumbent cycling at increasing fixed rates of metabolic heat production (150, 200, 250 W/m²), each separated by a 15-min rest in dry heat (40 °C, ~ 13% relative humidity). Rates (W/m²) of whole-body total heat exchange (dry + evaporative) were measured continuously and expressed as peak responses [mean of the final 5-min of exercise at the highest metabolic heat production (250 W/m²)]. Body heat storage was quantified as the temporal summation of heat production and loss. Core temperature, indexed by rectal temperature, was measured continuously. Relative to normal sleep, sleep deprivation did not modify whole-body heat exchange (evaporative (-6 [-18, 5] W/m²; P = 0.245), or dry (7 [-5, 19] W/m²; P = 0.209; sleep deprivation-normal sleep mean difference [95%CIs]) and therefore total heat loss (1 [-14, 15] W/m²; P = 0.917). There were no differences in either the change in body heat storage (-9 [-67, 49] kJ; P = 0.732) or change in core temperature (0.1 [-0.1, 0.3] °C; P = 0.186) between conditions. Overall, we showed that 24-h sleep deprivation did not influence whole-body dry or evaporative heat exchange, resulting in no differences in total whole-body heat exchange or body heat storage in young adults during exercise under hot-dry conditions.