Journal of applied physiology最新文献

Body sizes and shapes vary widely, even among healthy adults, resulting in diverse muscle sizes, strengths, and performance capacities. This study developed an artificially intelligent (AI) algorithm to segment individual muscles and bones from whole body MRI scans of 102 healthy adults (49 males, 53 females) aged 18-50 yr, generating three-dimensional (3-D) segmentations of 70 muscles and 13 bones spanning the upper limbs, trunk, and lower limbs. We quantified muscle volume, asymmetry, and fat fraction at whole body, regional, and individual-muscle levels, and examined how these properties correlate with body size and skeletal dimensions. Fat fraction and asymmetry varied across muscles and were generally similar between sexes; however, the distribution of muscle volume across the body differed between females and males. Across all predictors tested, total bone volume showed the strongest correlation with total muscle volume (r² = 0.85), followed by femur volume, height × mass, mass, height, and BMI. At the individual muscle level, the associated bone volume consistently explained more variance in muscle size than anthropometric predictors. Correlations between muscle volume and body-size parameters were significantly different between males and females, whereas bone-volume correlations showed no significant sex differences. These results suggest that skeletal dimensions-reflecting an individual's "frame size"-are stronger determinants of muscularity than body size metrics and explain the observed sex differences in muscle sizes. This work presents a comprehensive in vivo muscle-level dataset to date, introduces a novel framework for analyzing muscle-bone correlations, and provides reference data for applications from clinical diagnostics to athletic performance and musculoskeletal modeling.NEW & NOTEWORTHY This study presents the most comprehensive in vivo dataset of full-body muscle and bone volumes in healthy adults, showing that skeletal dimensions are the strongest predictors of muscularity, with height × mass emerging as the second-best predictor.

There is a metabolic cost associated with stabilizing walking, but it remains unclear to what extent stabilizing walking in the sagittal plane contributes to this cost. Furthermore, strategies for stabilizing walking in the sagittal plane vary with speed, but it is unclear whether this also leads to a speed-dependent metabolic cost of stabilizing walking. Here, we explored the metabolic cost of stabilizing walking in the sagittal plane across speeds and its relationship with control strategies. To this aim, we applied continuous treadmill belt speed perturbations (a standard deviation of 0.13 ms^-1) to 22 healthy individuals walking at 0.8, 1.2, and 1.6 ms^-1. We evaluated changes in metabolic energy consumption and control strategies between perturbed and unperturbed walking and explored relationships between energy consumption and control strategies. Perturbations induced larger increases in metabolic rate and changes in control strategies at slower than faster walking speeds, suggesting that walking is more robust against perturbations at faster speeds. Perturbations increased the metabolic rate by 16.7% at the slowest vs. 4.6% at the fastest walking speed. When perturbed, subjects took shorter, wider, and more variable steps and variability in ankle muscle activation increased, but most changes were larger at slower speeds. Metabolic rate increased more due to perturbations in individuals who reduced step length more, that is, relied more on anticipatory adjustments of the walking pattern. Our findings are especially relevant to explain the increased metabolic cost of individuals with mobility impairments, who often walk slower and have altered walking control.NEW & NOTEWORTHY Stabilizing walking requires more active control in the frontal than in the sagittal plane. Nevertheless, we demonstrated that there is a considerable energetic cost associated with stabilizing walking in the sagittal plane, especially at slower speeds. This cost is higher in individuals who adjusted their average walking pattern more when walking was perturbed. Diseases that affect both walking speed and control might therefore have a disproportionately large effect on the metabolic cost of walking.

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.

The purpose of this study was to determine whether racing a 50-km ultramarathon alters behavioral and electrophysiological (EEG) indices of executive function. Seventy-six recreational runners (37 ± 10 yr; 39 F, 37 M) completed EEG assessments before and immediately after the race at one of six ultramarathons. Executive function was evaluated with a visual oddball task, with accuracy and reaction time as behavioral markers, N2 as an index of inhibitory control, and P3 as an index of attentional allocation. Motivation [Sport Motivation Scale (SMS)] and negative affect [Depression, Anxiety, and Stress Scale (DASS)-21] were assessed 7-14 days before the race. Average race time was 7 h 54 min (±2 h 8 min), with 2.5% (±1.7%) body mass loss. Reaction times were 2.2% shorter post race (P < 0.0001), alongside a 14% increase in variability (P < 0.0001). N2 and P3 amplitudes decreased by 28.1% (P = 0.008) and 17.9% (P < 0.0001), respectively, with P3 latency reduced 3.4% (P < 0.001). Larger N2 reductions were associated with higher identified (r = 0.29, P = 0.013) and introjected (r = 0.29, P = 0.012) motivation, whereas greater P3 reductions correlated with higher DASS-21 scores (r = -0.69, P < 0.001). Racing an ultramarathon reduced neural activity related to inhibitory control and attentional allocation, resulting in shorter, more variable behavioral responses. Associations with affective state and motivation subtypes measured in the weeks prior suggest that prerace psychological factors may influence cognitive resilience during ultramarathon competition.NEW & NOTEWORTHY Here we report the first large-sample electrophysiological evidence that ultramarathon racing reduces neural activity associated with executive function, leading to shorter but less precise behavioral responses.

Transspinal evoked potentials (TEPs) elicited by transcutaneous spinal cord stimulation (tSCS) share some neurophysiological similarities with the H-reflex evoked by peripheral nerve stimulation (PNS). The purpose of this study was to further compare these two responses during and/or following different external interventions, known to activate Ia afferents. Fourteen volunteers took part in two experimental sessions, where PNS and tSCS promoted the same afferent solicitation of soleus muscle (target muscle). During the first experimental session, modulations of H-reflex and TEP were examined after 20 s of neuromuscular electrical stimulation delivered both at low and high frequency. During the second experimental session, changes in both responses during and following local vibration and passive stretching were evaluated. Results showed no differential modulation between the two soleus responses across the four tested interventions (all P > 0.25). Both H-reflex and TEP significantly decreased following low-frequency electrical stimulation (P = 0.001), whereas no significant modulation was observed after high-frequency stimulation (P = 0.08). Similar amplitude reductions between the two responses were also observed during local vibration and passive stretching (P < 0.001). In addition to the similar modulation of soleus responses, modulations of tSCS-evoked responses in synergist muscles during the low-frequency train, as well as in both synergist and antagonist muscles during local vibration and passive stretching, have also been observed. These results provide further evidence of the similarities between H-reflex and TEP, while highlighting the potential of tSCS to concomitantly assess multiple muscles modulations.NEW & NOTEWORTHY This study provides evidence that soleus H-reflex, induced by peripheral nerve stimulation and soleus transspinal evoked potential, elicited by tSCS, exhibit similar modulations during and after interventions known to vary afferent input to spinal motoneurons. It further reveals the impact of these interventions on multiple lower limb muscles, highlighting the significant advantage of using tSCS-evoked responses as a powerful tool to assess modulations of the neuromuscular system.

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.

This study investigated the acute effects of passive stretching on microvascular oxygen partial pressure (PmvO₂) and hypoxia-inducible factor-1α (HIF-1α) expression in rat skeletal muscle, focusing on stretch intensity and duration. Twenty male Wistar rats were assigned to either a stretch or sham group. In Study 1, the soleus muscle was passively stretched at varying intensities by changing its length from the optimal length (L_O) by 2, 4, 6, 8, and 10 mm, while PmvO₂ was simultaneously measured. In a separate experiment, the muscle was stretched from L_O to 8 mm and maintained in the stretched position for 2 hours, whereas in the sham group it was kept at L_O throughout. After stretching, the muscle was rapidly frozen, and HIF-1α mRNA was quantified by real-time PCR. Passive stretching induced an acute, intensity-dependent decrease in PmvO₂. Values during high-intensity stretches (6-10 mm) were significantly lower than in the sham group (25 ± 9 vs. 39 ± 7 mmHg, L_O vs. 8 mm; P < 0.05). Sustained 8 mm stretching caused a rapid decline in PmvO₂ within 40 s, followed by a stable low plateau for 2 hours (time F = 11.2; group F = 17.9; interaction F = 2.10; P < 0.01). Interestingly, 2 hours of stretching reduced HIF-1α mRNA expression. These findings demonstrate that passive stretching elicits an intensity-dependent and sustained reduction in microvascular PO₂, which may suppress HIF-1α mRNA expression in skeletal muscle.

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.