Journal of applied physiology最新文献

Surgical hyoid repositioning (HR) improves upper airway (UA) patency. Tracheal displacement (TD) likely influences HR outcomes, and vice versa, due to hyoid-trachea connections. This study used computational modeling to investigate the influence of TD and HR (with fixation) on UA outcomes and the impact of a lower baseline hyoid position [obstructive sleep apnea (OSA) phenotype]. A two-dimensional (2-D) finite element model of the rabbit UA simulated TD and HR (with fixation) in different directions, separately and combined. Model outcomes included UA closing pressure (Pclose), area, anteroposterior diameter (APD), and soft tissue mechanics (stress/strain). Simulations were repeated with a more caudal baseline hyoid position. Compared with baseline (TD = HR = 0 mm), TD alone reduced Pclose by -34%, increased area by 21% and APD by up to 18%. HR alone (except caudal) improved outcomes, particularly anterior-cranial HR, which decreased Pclose by -106%, increased area by 32% and APD by up to 107%. TD + HR (except caudal) enhanced these outcomes, with TD + anterior-cranial HR further decreasing Pclose (-131%) and increasing area (55%) and APD (128%). A more caudal baseline hyoid position reduced the effect of TD + anterior-cranial HR on Pclose (-43%), area (49%), and APD (115%). Combined TD and HR (except caudal) improved UA outcomes beyond either intervention applied alone. A more caudal baseline hyoid position reduced these effects. This computational model of the rabbit upper airway suggests that optimizing OSA treatment outcomes could involve considering baseline hyoid position, degree of TD, and direction/extent of HR, with potential benefits from combining HR and TD-based approaches.NEW & NOTEWORTHY Computational simulations of the rabbit upper airway suggest that combining tracheal displacement with anterior-based hyoid repositioning, with fixation, improves airway outcomes more than either approach alone. However, a lower natural hyoid position, characteristic of obstructive sleep apnea (OSA), reduces these benefits. Optimizing OSA treatment may require considering the natural hyoid position, surgical hyoid repositioning direction/magnitude, and natural tracheal displacement range. A combined tracheal displacement-hyoid repositioning strategy may further improve airway patency in select cases.

Dietary nitrate ([Formula: see text]), a source of nitric oxide (NO), enhances muscle contractility in numerous populations, but it is still unclear whether young women also benefit. The efficacy of [Formula: see text] supplementation might vary with menstrual cycle phase, due to lower endogenous NO bioavailability when estradiol (E₂) is low. Using a double-blind, placebo-controlled, crossover design, we determined the effects of acute ingestion of 200 μmol/kg of [Formula: see text] (from concentrated beetroot juice) or placebo on muscle function in 12 normally menstruating women during the early follicular (EF) and late follicular (LF) phases of their cycle. Muscle function was determined through maximal knee extensions on an isokinetic dynamometer and electrical stimulation of the quadriceps, with menstrual phase confirmed through plasma hormone measurement. E₂ concentrations were significantly lower in EF versus LF (220 ± 90 vs. 583 ± 260 pM; P < 0.001), whereas progesterone levels did not differ. Despite this, dietary [Formula: see text] had no effect on maximal muscle power or velocity during either phase. Dietary [Formula: see text] also had no effect on unpotentiated or potentiated peak twitch torque, rate of torque development (RTD), rate of relaxation (RR), or the torque frequency relationship during either phase. However, the RTD was 2%-8% greater in the LF versus EF phase, especially in the unpotentiated state (P < 0.01). The RR was also 9% slower in the LF versus EF phase (P < 0.05). Variations in E₂ during the menstrual cycle seem to subtly influence muscle contractile function. Acute [Formula: see text] supplementation, on the contrary, has no apparent effect on muscle contractility in young women.NEW & NOTEWORTHY We determined the effects of dietary [Formula: see text] on muscle contractile function during the early follicular (EF) and late follicular (LF) phases of the menstrual cycle. Although [Formula: see text] supplementation had no impact on muscle contractility, during electrically evoked twitches, the rate of torque development was greater, and the rate of relaxation was slower, in the LF phase. These findings enhance our understanding of how dietary [Formula: see text] and female sex hormones impact muscle contractile function.

Fatigue is a complex process that affects both force production and movement execution. Traditional measures, such as countermovement jump (CMJ) height, assess performance decrements but fail to capture compensatory movement adaptations. Nonlinear analysis of motor variability derived from acceleration signals provides a novel approach to monitoring fatigue by detecting subtle changes in movement execution. This study examined fatigue induced by three resistance training modalities-power, hypertrophy, and maximal strength-on motor variability during squats. Forty-four participants performed 10 squats at 70% of 1 repetition maximum (RM) before and after a training session, with follow-up assessments at 24, 48, and 72 h. Lower-back acceleration was recorded using inertial measurement units (IMUs). Acceleration variability was analyzed in terms of magnitude [standard deviation (SD)] and temporal structure [fuzzy entropy (FuEn); detrended fluctuation analysis (DFA)]. CMJ height served as a traditional marker of fatigue. Significant reductions in CMJ height were observed across the three training modalities (P < 0.05). No significant changes were found in SD for any modality (P > 0.05). FuEn increased after hypertrophy (P < 0.01; ES = 0.07) and maximal strength training (P = 0.01; ES = 0.03), but not after power training (P = 0.99). DFA decreased following hypertrophy (P = 0.02; ES = 0.03) and maximal strength sessions (P = 0.02; ES = 0.03), with no significant change after power training (P = 0.78). Nonlinear analysis of motor variability through acceleration signals provides valuable insight into fatigue-induced movement adaptations, complementing traditional metrics. This cost-effective approach offers practical applications for optimizing training and rehabilitation, particularly when high-intensity assessments are impractical.NEW & NOTEWOIRTHY Traditional fatigue assessments often overlook subtle movement adaptations. This study applies nonlinear motor variability analysis using inertial measurement units to detect fatigue-induced changes during resistance training. By using fuzzy entropy and detrended fluctuation analysis, we demonstrate how different training modalities influence movement patterns and recovery. This approach offers a cost-effective and ecologically valid tool for monitoring fatigue, optimizing training, and reducing injury risk in both athletic and clinical populations.

Lifestyle intervention is critical for young adults with early-stage hypertension. A Western diet has negative effects on kidney function and blood pressure; however, time-of-day effects are understudied. We hypothesized that consumption of a Western-style meal that is misaligned with the endogenous circadian rhythm would have adverse effects on blood pressure, kidney function, and vascular function. Ten young adults with elevated blood pressure or stage 1 hypertension (means ± SD: 26 ± 8 yr, 50% female) underwent a randomized crossover, isocaloric controlled feeding intervention. Participants were allocated to receive a Western-style meal high in sodium, sugar, and saturated fat in the morning (MMC) or the evening (EMC). Participants completed 24-h urine collection and simultaneous 24-h ambulatory blood pressure monitoring. Daytime fractional excretion of sodium was greater after MMC compared with EMC (MMC vs. EMC: 0.84 ± 0.28 vs. 0.35 ± 0.13%, P = 0.008). However, nighttime sodium excretion was not elevated after EMC (0.48 ± 0.24 vs. 0.39 ± 0.30%, P = 0.314), suggestive of overnight sodium retention. There were increased systolic (126 ± 6 vs. 121 ± 6 mmHg, P = 0.028), diastolic (80 ± 4 vs. 77 ± 6.4 mmHg, P = 0.028), and mean arterial (95 ± 5 vs. 91 ± 6 mmHg, P = 0.028) blood pressures during waking hours of MMC. Following consumption of the EMC, nocturnal blood pressure elevation was mitigated, presumably through protective sodium storage mechanisms (systolic pressure dipping: 15 ± 5 vs. 12 ± 5%, P = 0.249). Resting systolic blood pressure was increased the morning following EMC (119 ± 8 vs.121.8 ± 9 mmHg, P = 0.018). The findings suggest that in young adults with early-stage hypertension, a misaligned Western-style meal consumed late at night results in extended sodium retention and nocturnal blood pressure control was uncoupled from renal-mediated mechanisms.NEW & NOTEWORTHY Using a controlled feeding intervention, we investigated the time-of-day impact of Western-style meal consumption on acute blood pressure and renal responses in young adults with early-stage hypertension. Our pilot results translate preclinical work demonstrating that endogenous diurnal kidney function does not acutely respond to food as a time cue. Therefore, timing of a high sodium meal that was misaligned with the endogenous kidney function rhythm extended sodium retention, and blood pressure regulation was potentially uncoupled from renal-mediated mechanisms.

Understanding the dynamic interaction between the cardiovascular and cerebrovascular systems during exercise is essential to evaluate the mechanisms supporting brain perfusion. This study examined age- and sex-specific differences in cardiovascular and cerebrovascular dynamic response and used systems modeling to assess physiological coupling during moderate-intensity exercise. We recruited adults to complete a single session of moderate-intensity exercise on a recumbent stepper. Middle cerebral artery blood velocity (MCAv), mean arterial pressure (MAP), heart rate (HR), and end-tidal CO₂ ([Formula: see text]) were continuously recorded. In 164 participants, we analyzed the dynamic responses to exercise using mono-exponential modeling and functional data analysis. Granger causality within a subject-specific vector autoregression framework evaluated directional influence among physiological signals. Advancing age was associated with an attenuated dynamic response for MCAv, [Formula: see text], and HR while MAP was elevated. Older adults exhibited significantly smaller MCAv amplitude and slower time constants than young and middle-aged groups. Although sex did not influence overall MCAv, MAP, or HR kinetics, men had significantly higher [Formula: see text] throughout exercise. Granger causality analysis revealed bidirectional coupling among MCAv, HR, MAP, and [Formula: see text]. Prior [Formula: see text] levels significantly predicted MCAv, while MAP had both short- and long-lag predictive effects on MCAv. MCAv also influenced subsequent changes in MAP and [Formula: see text], indicating feedback regulation. [Formula: see text] emerged as a dominant driver of MCAv, though systemic interactions reflect an integrated physiological network with multicomponent feedback loops. This study advances understanding of cerebrovascular regulation and highlights the utility of systems modeling during exercise.NEW & NOTEWORTHY This study demonstrates strong age effects and minimal sex effects on cerebrovascular and cardiovascular responses to moderate-intensity exercise. Using Granger causality modeling, we confirmed [Formula: see text] as a dominant driver of MCAv and revealed bidirectional feedback among systemic and cerebrovascular variables. These findings highlight the value of systems modeling for uncovering dynamic physiological interactions during exercise and provide new insight into how cerebrovascular regulation changes across the adult lifespan.

Obstructive sleep apnea is an independent risk factor for stroke, potentially due to intermittent hypoxia (IH)-induced impairment of cerebral autoregulation. Human cerebral autoregulation during sleep is poorly characterized, and whether IH exposure during sleep alters cerebral autoregulation during sleep is unknown. In a secondary, exploratory analysis of previously collected cerebral blood flow (transcranial Doppler ultrasound measurement of peak blood velocity through the middle cerebral artery; [Formula: see text]), mean arterial pressure (MAP; finger photoplethysmography), and end-tidal partial pressure of CO₂ ([Formula: see text]) data, dynamic cerebral autoregulation (dCA) was quantified using transfer function analysis gain, phase, and coherence in healthy males (n = 10; age: 26 ± 6 yr; body mass index: 24.5 ± 1.7 kg/m²; MAP: 87.5 ± 8.0 mmHg) during wakefulness and during nonrapid eye movement (NREM) sleep in normoxia or accompanied by IH. Compared with wakefulness, [Formula: see text] variability was lower during both sleep in normoxia and sleep accompanied by IH in the very low frequency (0.02-0.07 Hz) and low frequency (LF: 0.07-0.2 Hz) ranges (both comparisons, P ≤ 0.02) with MAP variability being lower in the LF range (P = 0.045); gain, phase, and coherence were similar between wakefulness and sleep (all comparisons, P ≥ 0.062). dCA measures during normoxic and IH-sleep were similar (all comparisons, P ≥ 0.09). Moreover, dCA gain and phase, and multiple and partial coherences during IH-sleep were not different between acute (<1 h) and prolonged (∼2 h) exposure (all comparisons, P ≥ 0.055) even though [Formula: see text] was lower following prolonged IH exposure (P = 0.002). These findings indicate dCA is effective during stage 2/3 NREM sleep and is not impacted by ∼2 h of sleep accompanied by IH.NEW & NOTEWORTHY This study found that dynamic cerebral autoregulation (dCA) is not different between wakefulness and stages 2/3 nonrapid eye movement (NREM) sleep in young healthy males and that ∼2 h of intermittent hypoxia exposure during sleep mimicking that experienced by patients with moderate-to-severe obstructive sleep apnea does not alter NREM stage 2/3 sleep dCA. This maintained dCA during sleep may result from the reduced cerebral blood flow and blood pressure variability observed during sleep.

Postexercise muscle oxygen consumption (mV̇o₂) rate may contribute to understanding responses to and recovery from exercise. To measure postexercise mV̇o₂ of the vastus lateralis (VL) muscle after various exercise intensities using near-infrared spectroscopy (NIRS). Twenty healthy individuals, 18-35 yr old, participated in two testing sessions. An NIRS device was placed on the belly of the VL to measure differences in oxygenated and deoxygenated hemoglobin (Hb_diff). Electrodes were placed proximally and distally to the NIRS device, and a cuff capable of rapid inflation was placed on the upper leg. mV̇o₂ at rest was assessed as the slope of the Hb_diff signal (% s^-1) during 3 × 30-s cuff inflations at 300 mmHg. Neuromuscular electrical stimulation (NMES) was applied for 30 s, and mV̇o₂ was assessed 5 min later. Participants performed maximal and submaximal (60% V̇o_2peak) cycling tests 1 wk apart, and mV̇o₂ was assessed 15 min later. Desaturation slopes (% s^-1) were calculated in Hb_diff signals to measure mV̇o₂. On average, mV̇o₂ 5 min post-NMES was 1.8-fold higher compared with resting (P < 0.001). mV̇o₂ was 4.2-fold and 2.7-fold higher 15 min after maximal and submaximal cycling, respectively, compared with resting (both P < 0.001). Blood lactate was elevated 10 min after maximal (10 ± 3 mmol/L) and submaximal (4 ± 3 mmol/L) cycling (both P < 0.001). Muscle metabolism remained highly elevated 15 min after cycling exercise. NIRS-based mV̇o₂ may have value as an indicator of postexercise muscle metabolism.NEW & NOTEWORTHY We found that the muscle oxygen consumption rate 15 min after cycling exercise remained three- to fourfold higher than at rest. Higher-intensity exercise resulted in higher postexercise muscle oxygen consumption despite having the same total work during exercise. The detected elevations in muscle metabolism 15 min postexercise are comparable with those observed during light to moderate intensity exercise. Monitoring postexercise muscle metabolism may have practical applications for training and rehabilitation.

This study investigated the effect of running in a hot environment compared with a temperate environment on exogenous carbohydrate oxidation, while maintaining a state of euhydration. Ten trained runners (24 ± 6 yr; 72.7 ± 8.3 kg; V̇o_2peak: 63 ± 6 mL/kg/min) completed two trials [100 min of steady state running at ∼65% V̇o_2peak in either a temperate (19°C; TEMP) or a hot environment (34°C; HOT)]. Water was provided every 20 min to replace ∼90% of body mass losses (TEMP: 0.8 ± 0.2 L; HOT: 1.7 ± 0.4 L). In each trial, participants consumed 60 g/h (bolus every 20 min) of a 35% dextrose solution enriched with [U-¹³C] glucose (145 ± 2 δ‰ vs. PDB). Expired breath (analyzed for ¹³C:¹²C) and blood samples were collected every 20 min during exercise. Average (40-100 min) and peak exogenous carbohydrate oxidation rates were 20% (HOT: 0.43 ± 0.09 vs. TEMP: 0.54 ± 0.12 g/min; P = 0.006) and 18% (HOT: 0.67 ± 0.10 vs. TEMP: 0.81 ± 0.11 g/min; P = 0.002) lower in HOT than in TEMP, respectively. Total carbohydrate oxidation (P = 0.111) was not significantly different between trials, resulting in a greater contribution from endogenous sources in HOT versus TEMP (2.10 ± 0.35 vs. 1.86 ± 0.30 g/min; P = 0.020). Gastrointestinal temperature and heart rate (P < 0.001) were greater in HOT. Even with adequate hydration, running in a hot environment reduced exogenous carbohydrate.NEW & NOTEWORTHY This study showed that exogenous carbohydrate oxidation is reduced by ∼20% during running in the heat, even while controlling fluid intake to maintain euhydration, highlighting that heat stress alone impairs exogenous carbohydrate use. These findings suggest a lower exogenous carbohydrate oxidation and a greater reliance on endogenous stores when exercising in the heat, independently of the effects of dehydration.