European Journal of Applied Physiology最新文献

We investigated whether caffeine ingestion reverses the deleterious effect of sleep restriction on high-intensity exercise (HIE) performance, and its impact on ventilatory, blood acidosis, and neuromuscular fatigue. Nine physically active men (29 ± 6 years, 176 ± 5 cm, 80.4 ± 7.4 kg) completed a session of HIE under: (1) habitual sleep plus placebo ingestion (HSP); (2) sleep restriction plus placebo ingestion (SRP); and (3) sleep restriction plus 5 mg.kg^-1 of caffeine ingestion (SRC). Ventilatory responses were continually monitored, while blood H⁺, plasma lactate, maximal voluntary isometric contraction (MVIC), voluntary activation (VA), and quadriceps potentiated doublet-twitch force (PT) were assessed at pre-capsule ingestion, after completing 70% of the HIE, and at task failure. Time to task failure was shorter (p < 0.001) in SRP (6.23 ± 2.11 min) than in HSP (7.68 ± 2.92 min) and SRC (7.83 ± 3.19 min), without differences between HSP and SRC (p = 0.96). Sleep restriction reduced minute ventilation (~6%) and tidal volume (~7%) and increased respiratory frequency (~5%) near to the end of HIE (p < 0.05); caffeine ingestion, however, reverted these effects of sleep restriction. Blood H⁺ was higher (~34%) and plasma lactate lower (~21%) at post-exercise in SRP than in HSP and SRC (p < 0.05), but similar between HSP and SRC (p > 0.05). The VA decreased (p < 0.05) from pre- to post-exercise in SRP (4 ± 5%), but not in HSP and SRC (p > 0.05). The MVIC and PT decreased similarly from pre- to post-exercise in all conditions (p < 0.05). Caffeine ingestion reverses the impairment of sleep restriction on HIE performance, likely by restoring normal ventilatory pattern and preventing sleep restriction-induced exacerbated acidosis and central fatigue.

This manuscript comprehensively examines current approaches for analyzing neural commands through high-density surface electromyography (HDsEMG) recordings and associated decomposition algorithms, discussing their applicability across multiple research settings. We present a detailed overview of EMG-derived analyses, including the extraction of motoneuron discharge properties, coherence analysis, estimation of persistent inward currents, and evaluation of motoneuron input-output gain. These approaches are discussed in the context of their physiological significance and are supported by robust statistical frameworks to ensure analytical rigour. Although some of these techniques are also applicable to intramuscular EMG, the present review focuses explicitly on advanced methodologies developed for high-spatial-resolution surface EMG. We summarize key analytical strategies for the interpretation of EMG data, integrating recent methodological advancements with established practices in HDsEMG decomposition and analysis. The aim of this review is to serve as a comprehensive and accessible resource for researchers in applied physiology investigating neuromuscular function. By highlighting both the physiological relevance and methodological precision of HDsEMG-derived techniques, we outline current best practices to support the accurate and meaningful interpretation of neural signals in human motor control research.

Exposure to high-altitude reduces oxygen availability, leading to hypoxemia. To combat this physiological stressor, the body initiates a cascade of short- and long-term compensatory responses (i.e., high-altitude acclimatization). Some notable adaptations include rapid increases in ventilation, heightened sympathetic neural activity, and reductions in plasma volume during early acclimatization, followed by increases in hemoglobin mass and concentration. Despite these physiological responses, many of the ~ 40 million people who travel to high altitude regions (i.e., > 2500 m) each year, suffer from acute mountain sickness (AMS), which is often paired with reductions in overall sleep quality. Acetazolamide (ACZ), the most prescribed high-altitude pharmacological intervention, alleviates AMS symptoms by inducing a renal metabolic acidosis, which increases basal ventilation and improves oxygenation. However, the unpleasant side effects of ACZ for some individuals and the lack of 100% efficacy underscores the need for alternative and potentially more effective treatments for AMS. Exogenous ketone monoester (KME) supplementation raises circulating ketone body levels and has been demonstrated to increase resting ventilation at both sea-level and high-altitude. Similar to ACZ, the mechanism(s) responsible for KME-stimulated hyperventilation are thought to be primarily linked to a hallmark acidosis response, leading to increases in blood oxygen saturation similar to ACZ at high altitude. Additionally, there is preliminary evidence that KME may improve sleep architecture and efficiency at high altitude, which are known to exacerbate the development of AMS. This perspective outlines key physiological mechanisms, identifies current knowledge gaps, and proposes future directions for exploring the potential impact of KME in mitigating AMS.

This study aimed to assess the effects of three flat running surfaces (i.e. athletic track, road, and gravel) on the critical power (CP) parameters and running patterns of highly trained trail runners. Within a two-week timeframe, thirteen male and seven female trail runners underwent three testing sessions to evaluate CP and the work over CP (W'). Each session comprised two time trials of 9 and 3 minutes, separated by a 30-min rest, in which a Stryd running power meter was used to collect the data. The CP and W' were subsequently determined using the inverse of time linear CP model. There were no significant differences in CP across the different surfaces (F_(2,38)= 1.4; p = 0.253). However, significant differences were found in W' (F_(2,38)= 3.8; p = 0.032). Specifically, athletes displayed a higher W' on the track compared to gravel (1.8 [0.2 to 3.4] kJ, p = 0.026), and higher, though non-significant, W' on the road compared to gravel (0.9 [-0.7 to 2.5] kJ, p = 0.478). Regarding the running patterns, the athletes displayed lower duty factor on the track compared to gravel (-1.1 [-2.2 to -0.1] %; p = 0.030) as well as on the road compared to gravel (-1.1 [-2.0 to -0.1] %; p = 0.019). In conclusion, the CP remained stable across surfaces, whereas W' was reduced on gravel compared to track and road. The differences in W' were accompanied by significant changes in the athletes' running patterns. Specifically, athletes exhibited a lower duty factor on the track and road compared to gravel, resulting in a more aerial running form.

Purpose: To examine whether the interaction between exercise intensity and sleep duration/quality is associated with heart rate variability (HRV).

Methods: A sample of 391 adults (M_age = 57 years) from the Midlife in the United States Biomarker study 2004-2009 provided sleep actigraphy, electrocardiogram (ECG) HRV measurements, completed the Pittsburgh Sleep Quality Index (PSQI), and answered questions on exercise habits. Participants were grouped as short (< 6 h) or non-short sleepers (≥ 6 h), poor (> 5 PSQI global score), or good sleepers (< 6 PSQI global score), and exercise was divided into vigorous (VPA) and moderate (MPA) intensities. Based on CDC guidelines, VPA was classified into adequate (≥ 75 min/week) and inadequate (< 75 min/week) groups. For MPA, adequate (≥ 150 min/week) and inadequate (< 150 min/week) groups. Linear models, adjusted for sociodemographic and health-related covariates, examined the interaction between sleep duration/quality and exercise on HRV.

Results: Inadequate VPA was associated with lower HRV, HF-HRV (B = - 0.25, SE = 0.09, p = 0.007), and RMSSD (B = - 0.15, SE = 0.05, p = 0.0009). MPA showed no significant main associations with HRV. Sleep duration/quality did not show direct associations with HRV; however, interactions were found with sleep duration. Among short sleepers, inadequate VPA was associated with lower HF-HRV (B = - 0.62, SE = 0.25, p = 0.01) and inadequate MPA was associated with lower RMSSD (B = - 0.26, SE = 0.10, p = 0.01) compared to adequate exercise. Among non-short sleepers, there were no significant differences in HRV between exercise groups.

Conclusion: These findings suggest that short sleep and inadequate exercise may interact to lower HRV.

The incidence of metabolic syndrome (MetS) is rising rapidly, particularly among older adults, and is associated with comorbidities that impair respiratory and immune functions. Physical exercise has proven effective in mitigating the adverse effects of both aging and MetS. However, evidence on the impact of high-intensity resistance training (HIRT) on the respiratory and immune systems in older adults with MetS remains limited. This study aimed to evaluate the effects of HIRT on respiratory function, skeletal muscle strength, and immune modulation in older adults with MetS, highlighting its potential as a complementary therapeutic approach. A total of 43 older adults with MetS were enrolled and divided into two groups: a HIRT intervention group (n = 23; mean age 66.71 ± 4.98 years) and a non-exercising control group (n = 20; mean age 66.91 ± 5.26 years). The HIRT protocol involved twice-weekly sessions (10 total) over 5 weeks, performed at 80-90% of one-repetition maximum. Results showed that HIRT significantly improved lung mechanics (R5Hz, R20Hz, Z5Hz, X5Hz), peripheral muscle strength, and both maximal expiratory and inspiratory pressures. Furthermore, HIRT increased anti-inflammatory and anti-fibrotic cytokines in sputum (klotho, IL-10, adiponectin) and serum (klotho, relaxin-1, relaxin-3, IL-10), while reducing pro-inflammatory cytokines in sputum (IL-6, TNF-α) and serum (IL-1ra, IL-6, TNF-α, leptin). A decrease in total leukocyte, neutrophil, lymphocyte, and monocyte counts was also observed. In conclusion, HIRT effectively mitigates the effects of MetS on respiratory, muscular, and immune functions in older adults and may be recommended as a complementary strategy for managing MetS in this population.

Purpose: This study aims to assess the impact of HR-matched exercises under varying hypoxic stress levels on exercise and post-exercise autonomic and cardiovascular responses.

Methods: Twelve moderately aerobically trained healthy men (mean age: 23 ± 2 years, height: 179 ± 8 cm, weight: 71.2 ± 9.9 kg, BMI: 22.2 ± 2.2 kg/m², VO₂max: 53.1 ± 4.2 mL/min/kg) completed an interval exercise session at 75% of their normoxic maximum heart rate (75%HRmax) under three hypoxic conditions: FiO₂ = 16.2% (2000 m a.s.l; H16), FiO₂ = 14.3% (3000 m a.s.l; H14), and FiO₂ = 12.6% (4000 m a.s.l; H12). Each session included 5 min of seated rest, a 5-min sub-maximal load warm-up, and five 5-min work intervals with 1-min passive recovery periods.

Results: During hypoxic exercise, RMSSD decreased significantly following the first bout coinciding with an increase in heart rate. The RMSSD increase during 60-s recovery intervals was significantly lower after the 4th and 5th bouts compared to the 1st and 2nd bouts (p < 0.05). At 15 min post-exercise, mean RR, systolic blood pressure and stroke volume decreased. No changes were observed in cardiac output or baroreflex sensitivity. At 60 min post-exercise, SDNN, RMSSD, mean arterial pressure and diastolic blood pressure increased significantly compared to 15 min post-exercise. No condition or interaction differences were found.

Conclusion: Despite the decreased oxygen saturation with increased hypoxia levels, HR-matched interval exercise induced similar cardiac and autonomic responses across all hypoxic conditions. Baseline cardiac autonomic function and hemodynamics recovered within 60 min with no impact of hypoxia on baroreflex sensitivity.

Maximal lactate accumulation rate ( $\dot{\text{c}}$ La_max) has recently gained increased attention in exercise science as a parameter characterising the maximum power of glycolytic metabolism. Since a lot of sports put high demands on both oxidative as well as substrate-level phosphorylation, $\dot{\text{c}}$ La_max may be a promising augmentation to metabolic profiling in athletes. However, scientific examinations still demonstrate inconsistencies in terms of terminology, procedures, calculations and application that highlight the need for an extensive literature review. This review aims to summarise the current evidence of $\dot{\text{c}}$ La_max and provide recommendations for future research and application in practice. Findings of N = 60 accepted peer-review Journal articles in English language were extracted to highlight the origin, development, terminology, procedures, reliability, specificity, applicability and adaptability of $\dot{\text{c}}$ La_max. It provides a critical view of this field of research to assist international colleagues who might not yet be familiar with $\dot{\text{c}}$ La_max. It is evident that $\dot{\text{c}}$ La_max has spread across the globe and is already applied in various sports like (hand-)cycling, running, swimming, rowing, kayaking and paratriathlon. Sport-specific all-out sprint tests lasting 10-12 s and measurements of post-exercise lactate concentration every minute for 10 min are recommended to determine $\dot{\text{c}}$ La_max that demonstrates a high reliability and specificity. Whereas $\dot{\text{c}}$ La_max is associated with sprint performance and strength parameters, its utility to predict/simulate individual performances ≥ 1 min is still inconclusive. Future studies need to validate $\dot{\text{c}}$ La_max by means of enzyme activity and/or muscle fiber typology, focus on female athletes (currently 25%) and assess its adaptability to certain training regimes.

Purpose: Assessing the validity of maximum oxygen uptake (V̇O₂_max) estimates provided by a commercially available smartwatch (Garmin Forerunner 245, Garmin Ltd., Olathe, USA) compared to laboratory-based respiratory gas analysis in moderately-to-highly trained athletes.

Methods: Thirty-five endurance athletes (Tier 2-3 athletes, 24 males, 11 females; age: 25.1 ± 3.5 years; V̇O₂_max: 60.1 ± 8.2 ml·min⁻¹·kg⁻¹) completed a treadmill ramp test with respiratory gas analysis to determine criterion V̇O₂_max. Additionally, each athlete performed two submaximal 15-min outdoor runs at > 70% of maximum heart rate, during which the smartwatch estimated V̇O₂_max. Athletes were stratified into moderately trained (V̇O₂_max ≤ 59.8 ml·min⁻¹·kg⁻¹) and highly trained (V̇O₂_max > 59.8 ml·min⁻¹·kg⁻¹) subgroups.

Results: Across all athletes, the smartwatch underestimated V̇O₂_max [mean differences: - 4.73 ml·min⁻¹·kg⁻¹ (run 1), -4.05 ml·min⁻¹·kg⁻¹ (run 2)]. Intraclass correlation coefficients (ICC) indicated moderate agreement between smartwatch and laboratory values (run 1: ICC = 0.71 [95% CI: 0.03-0.90]; run 2: ICC = 0.75 [95% CI: 0.17-0.91]), with mean absolute percentage errors (MAPE) of 7.9% and 7.2%. Subgroup analyses revealed better accuracy of smartwatch estimated V̇O₂_max in moderately trained group (MAPE: 4.1-2.8%; ICC: 0.63-0.66 [95% CI: 0.09-0.87]), whereas in highly trained athletes, the smartwatch underestimated V̇O₂_max by 6.3 ml·min⁻¹·kg⁻¹ (MAPE: 10.4-9.4%; ICC: 0.34-0.41 [95% CI: - 0.11-0.75]).

Conclusion: Smartwatch-derived V̇O₂_max estimates are valid in moderately trained athletes but less valid in highly trained individuals. While smartwatches are useful for general monitoring, caution is warranted in their interpretation, particularly in highly trained individuals. Laboratory-based gas analysis remains the preferred method when precision is required.

The present study aimed to investigate which of two commonly performed running interval sessions elicited the greatest magnitude of and time spent with elevated muscle deoxygenation in trained middle-distance runners. Thirteen trained middle-distance runners (22.4 ± 3.2 y; 63.1 ± 10.9 kg; n = 9 males) participated in the study. Subjects completed a field-based incremental running test and two interval sessions. The interval sessions comprised a 6 × 1 km and a 15 × 400 m interval session, both with 1 min passive recovery periods. Both sessions were implemented with the aim of achieving the maximal sustainable pace for each repetition, while mean speed, heart rate, RPE, blood lactate concentration and muscle deoxygenation responses were monitored. Mean speed during the interval repetitions was significantly higher during the 400 m intervals (~ 5.63 ± 0.35 m·s^-1 vs ~ 5.30 ± 0.28 m·s^-1; p < 0.001). Both the peak magnitude of muscle deoxygenation (absolute difference ± CI 3.42 ± 2.23%; p = 0.006) and the time spent with values > 60% peak muscle deoxygenation (83.5 ± 66.4 s; p = 0.02) were significantly greater during the 400 m intervals, while the time spent with a heart rate > 90% peak heart rate was significantly longer during the 1 km interval session (570 ± 143, p < 0.001). Despite this, there was no difference in RPE, blood lactate concentration or peak heart rate between sessions. These findings suggest that 1 km intervals may preferentially target central physiologic responses while 400 m intervals may elicit greater peripheral physiological responses in trained middle-distance runners.