Resistance training (RT) may induce transient changes in endothelial and autonomic patterns. Static stretching (SS) performed at the end of an RT session may alter the temporal course of recovery of these responses. This study investigates whether SS following RT modulates acute endothelial, autonomic, and haemodynamic recovery compared with RT alone. Twenty-seven healthy males completed three experimental sessions in a randomized-crossover design: RT, RT + SS, and control condition (CC). RT consisted of two upper-body resistance exercises (bench-press and seated-biceps curl), while RT + SS included the same RT protocol followed by SS of the same muscle groups. Flow-mediated dilation (FMD
Skeletal muscle responses to exercise depend on contraction mode, which alters the balance between perfusion, oxygenation, and metabolic demand. However, how these physiological responses differ across muscles remains unclear. This study investigated contraction mode-dependent MRI responses in lower-leg muscles using quantitative T2*, T2, and T2′ measurements. Nineteen healthy female participants performed isometric and isotonic plantar flexion in a randomized crossover design. MRI measurements were obtained during inter-set rest periods and the post-exercise recovery phase in the medial gastrocnemius (MG), lateral gastrocnemius, soleus, and tibialis anterior. Time-course changes were analyzed using linear mixed-effects models, and response magnitude was quantified using peak and area under the curve (AUC). Isotonic contraction produced significantly greater T2* responses than isometric contraction, particularly in the medial gastrocnemius (MG), during exercise and early recovery (all false discovery rate-corrected p ≤ 0.027). T2 also showed smaller differences in MG at selected recovery time points, whereas no significant differences were observed in other muscles. Linear mixed-effects models revealed a main effect of contraction mode, and peak and AUC analyses demonstrated that both the magnitude and persistence of responses were greatest in MG. In contrast, T2′ did not show contraction mode differences. Contraction mode influences muscle responses in a muscle-specific manner, with MG showing the greatest sensitivity. The greater sensitivity of T2* may reflect its responsiveness to the combined effects of hemoglobin oxygenation-related susceptibility, microvascular blood volume, and water-related tissue changes. These findings provide insight into muscle-specific MRI responses and may inform the optimization of rehabilitation strategies.
Mobility in humans and all animals depends on the co-ordinated progress of essential steps linking electrical action potentials along the surface membrane of muscle fibres to the increased cytoplasmic Ca2+ concentrations that activate the contractile proteins. Excitation–contraction (EC) coupling is the transformation of an electrical signal into a massive release of Ca2+ from intracellular Ca2+ stores. We consider the evolution of our knowledge of the structures and proteins that underlie skeletal muscle EC coupling, unanswered questions and future developments that will reveal the fundamental molecular events of the coupling process. The deeper understanding gained with future developments will reveal the molecular basis of muscle weakness related to mutations in EC coupling proteins or result from fatigue and aging. The benefits will flow on to the rational design of therapies to increase muscle strength in the many situations where muscle weakness is related to changes in EC coupling.
Acute cardiovascular recovery from exercise remains poorly characterized in young Black men, a population at elevated cardiovascular risk. Therefore, we compared integrated hemodynamic and cardiac autonomic responses following aerobic (AE) versus resistance exercise (RE) in this group. Fifteen Black men (18–29 years) completed counterbalanced bouts of AE (30 min cycling, 65
Transient CO2 inhalation-induced dilation of the internal carotid artery (ICA), an index of cerebrovascular endothelial function, is partly mediated by cerebrovascular CO2 reactivity (CVR) via increased shear stress. Although CVR is attenuated under hypocapnia relative to normocapnia, it remains unclear whether the reduction in CVR affects ICA shear-mediated dilation. To address this knowledge gap, ICA shear-mediated dilation and ICA blood flow reactivity to CO2 ( Q̇_ICA -CVR) were measured under normocapnia (Con) and hyperventilation-induced hypocapnia in 15 healthy adults (11M/4F, 25 ± 3 years) on two separate visits. Shear-mediated dilation was induced by elevating end-tidal CO2 partial pressure (PETCO2) by 10 mmHg above the pre-inhalation baseline for 30 s and calculated as the percentage increase in the peak diameter relative to the baseline diameter. The Q̇_ICA -CVR was assessed using a 3-min PETCO2 elevation (+ 10 mmHg) and expressed as the change in ICA blood flow divided by the change in PETCO2. Hypocapnia decreased Q̇_ICA -CVR (P = 0.02), shear-mediated dilation (4.12 ± 1.90
This study investigated the effects of velocity and load on lower limb neuromuscular synergy during the concentric phase of the squat to inform resistance training design. Surface electromyography (sEMG) signals from lower limb muscles were collected during squats performed under two loads (40
To investigate the acute effects of concurrent exercise (CE), resistance exercise (RE), and moderate-intensity continuous exercise (MICE) on cerebrovascular reactivity (CVR) to hypocapnia. Twenty-four healthy young adults (12 males) completed four 30-min, time-matched experimental visits in a randomised order: seated rest (CON), RE (4×10 repetitions of four exercises at 70
High-altitude exposure combined with physical activity triggers complex systemic adaptations. However, multidisciplinary longitudinal investigations into these multiorgan responses remain limited. This prospective observational study aimed to investigate the cardiovascular, metabolic, renal, and hepatic responses to a subacute high-altitude expedition. 21 Caucasian participants (14 men and 7 women) participated during a Himalayan trek expedition up to 5050 m. Measurements included: cardiovascular parameters (HR, BP) evaluated at five points (baseline (T0), intermediate ascent (T0a), peak (T1), intermediate descent (T1a), post-trek (T2)); comprehensive biochemical parameters (renal, hepatic, and lipid markers) collected at four time points: baseline (T0), peak altitude (T1), post-trek (T2), and a several-month follow-up (T3); body weight at three points (T0, T1, T2) and dietary intake. Ascent induced significant increases in HR and BP, with DAP remaining elevated during descent. At peak altitude, the A/G ratio decreased while U/C and GFR increased, alongside reductions in creatinine and body weight. Despite a severe energy deficit (44–52
Maximal lactate accumulation rate (vLamax) is commonly used as a surrogate of anaerobic glycolytic power. Conventional protocols calculate vLamax as a mean rate over a fixed sprint window after subtracting an alactic phase, even though glycolytic flux rises, peaks, and declines within seconds. Fixed-duration protocols may therefore underestimate the instantaneous peak rate. Seventeen elite track cyclists performed 12 s and 60 s maximal isokinetic sprints with continuous power, gas exchange, near-infrared spectroscopy, and blood lactate. Total metabolic energy (from dynamic gross efficiency), aerobic energy, and phosphocreatine energy were reconstructed, and the glycolytic residual gave vLa(t), vLamax, and time to peak. The indirect assessment yielded higher vLamax than the gold standard (0.91 ± 0.18 vs. 0.82 ± 0.17 mmol/L/s; p < 0.001), while predicted 12 s lactate accumulation matched measured values (7.67 ± 1.77 vs. 7.58 ± 1.60 mmol/L; p = 0.464). Peak vLa occurred at 9.1 ± 1.4 s, before the 12 s endpoint. A single maximal sprint suffices to reconstruct the individual glycolytic flux trajectory (its onset, peak, and post-peak decline), and the cumulative lactate accumulation was independently validated against a separate 12 s sprint. On this basis, fixed-duration protocols appear to underestimate instantaneous peak vLamax by averaging across the post-peak decline (mean bias 10
Virtual reality (VR) reduces experimental and clinical pain, but whether these effects extend to naturally occurring muscle pain (NOMP) during exercise remains unclear. This study examined whether immersive nature-based VR attenuates NOMP and improves motor performance during prescribed and self-regulated exercise. Two within-participant crossover studies were conducted involving 12 (Study 1) and 24 (Study 2) healthy participants. In Study 1, participants completed a stepped incremental cycling task to exhaustion. In Study 2, participants performed self-regulated intermittent isometric handgrip contractions at light (13/100) and strong (50/100) perceived effort. Tasks were completed under immersive VR (nature scene), two-dimensional sham, and no-intervention control conditions in pseudo-randomised, counterbalanced orders. Pain onset, NOMP intensity, perceived effort, and time to exhaustion were assessed in Study (1) Muscle pain intensity and force production were measured in Study (2) Repeated measures ANOVAs and assessed main condition effects. Immersive VR did not delay pain onset (p=.159) , prolong time to exhaustion (p=.204) , or lower perceived effort compared within sham or control conditions (p^' s>.215) . A small, yet practically meaningful, reduction in NOMP intensity occurred early during cycling (F_2,22=4.518,p=.023, η _p^2=0.291[0.002,0.500]) but was not sustained at later phases of the task (p^' s<.369) . In Study 2, NOMP intensity (p=.815) and force production measures (p^' s<.325) were similar across conditions. Nature-based immersive VR had limited effects on NOMP and motor performance. Pain types that are peripherally driven, like NOMP, may be less affected by VR interventions which target central mechanisms of pain modulation. Thus, hypoalgesia effects with VR are potentially pain-type dependent.
This study investigated the neuromuscular differences between glucose (GLU) and fructose (FRU) ingestion on central and peripheral fatigue development and blood glucose responses during endurance cycling to failure. Seven young, recreationally active participants (4 males, 3 females) completed a randomized, single-blinded crossover study involving three conditions: GLU, FRU, and placebo (PLA) ingestion. Participants cycled at an intensity set at their maximal lactate steady state until task failure while consuming PLA, or 60 g/h of GLU or FRU. Heart rate and ratings of perceived exertion (RPE) were assessed every 5 min whereas neuromuscular function of the knee extensors and capillary blood glucose and lactate were assessed every 20 min. GLU ingestion significantly increased time to task failure ( 25
Sit-to-Stand (STS) is a demanding postural task whose performance becomes challenging with aging. While muscle synergy analyses have helped describe its modular control, most evidence is based on unilateral EMG, which can characterize within-limb structure but cannot test whether the two sides share stable motor modules or reveal subtle inter-limb compensations in an apparently symmetric task. This study investigated the effects of aging on the neuromuscular organization of STS by examining bilateral muscle synergies and their relation to the whole-body center-of-mass (CoM) kinematics. Seventeen young and sixteen older healthy adults performed a 30-s STS test while kinematic data and bilateral muscle activity from seven trunk and lower-limb muscles were collected. Synergies were extracted using non-negative matrix factorization and linked to CoM behavior through a mapping approach that associates synergy recruitment with regions of the CoM kinematic state space. Four synergies were sufficient to reconstruct the activation patterns, with highly consistent structure between limbs and no age-related differences in synergy number or spatial structure. Older adults, however, showed broader activation duration (p = 0.02) and earlier recruitment timing (p = 0.009) of the synergy associated with trunk flexion and forward momentum generation. Furthermore, this anticipatory shift was consistent with the elderly’s CoM trajectory entering the corresponding high-probability region earlier along the anteroposterior axis in the CoM–synergy mapping. These findings suggest that while the fundamental bilateral modular architecture of STS is preserved with aging, its temporal precision and coupling with whole-body mechanics become less distinct, reflecting adaptive strategies to maintain stability during postural transitions.
Portable near-infrared spectroscopy (NIRS) enables cost-effective monitoring of muscle oxygen saturation (SmO2) during exercise, presenting a promising alternative for delineating exercise intensity domains. This study investigated whether SmO2 breakpoints (BP1 and BP2) can provide accurate estimates of ventilatory thresholds (GET and RCP). Twelve male Tier 3 triathletes completed an outdoor incremental TestVAM. Vastus lateralis SmO2 was recorded using NIRS, alongside pulmonary gas exchange measurements. BP1 and BP2 were identified visually. Heart rate (HR) and running speed at BP1, BP2, GET, and RCP were extracted. The intraclass-correlation coefficient (ICC) was calculated and equivalence between SmO2 breakpoints and ventilatory thresholds was assessed with equivalence bounds set at 5 bpm for HR and 0.5 km h−1 for speed. The ICC(3,1)abs was poor to moderate for all comparisons (range: 0.18–0.69). HR and speed between BP1 and GET were not equivalent (p > 0.91), with GET occuring ealier in both HR (p = 0.014, Δ = − 9.92 bpm, 90
Skeletal muscle strength is multifactorial. Although associated, skeletal muscle size and strength often change disproportionately following resistance training with different loading paradigms. Examining strength relative to muscle size has been used to evaluate the potential contribution of muscle growth or other factors (e.g., neural or intramuscular adaptations) that occur with strength changes. Moreover, as muscle size could explain differing strength between individuals, comparisons of strength per unit of muscle size are sometimes used to account for differences in strength related to size. Several analytical approaches can be used to account for or hold muscle size fixed when evaluating strength. Based on prior work in sports medicine and other fields, we explored the use of ratio normalization and multiple regression techniques. Data from NHANES (1999–2002) and a previous investigation from our group were used in analysis demonstrations. In synthesizing and applying recommendations from previous work, we highlight some nuances and complexities with ratio normalization that may not be readily apparent without testing assumptions.
Lifestyle habits in young adult women and health maintenance are crucial for lifelong disease prevention in middle-aged and older adults. Evidence regarding associations between free-living physical activity (PA) and glucose tolerance in non-underweight, non-overweight young adult women remains limited. We examined associations between glucose tolerance-related blood markers and PA indices, including intensity-specific PA and energy expenditure variables, using validated objective measures in normal-weight young adult women without an exercise habit. This exploratory cross-sectional study enrolled 28 healthy young adult women (22 ± 2 years; body mass index, 20.9 ± 2.3 kg/m2) without regular exercise habits. Under free-living conditions, daily energy expenditure and PA intensity distribution (percentage time in light, moderate, and vigorous activity), sedentary behaviour (SB) and daily step count were assessed using doubly labelled water and an accelerometer. The muscle insulin sensitivity index (MISI), hepatic insulin resistance index (HIRI), and whole-body insulin sensitivity were calculated from oral glucose tolerance test blood biochemistry data. The mean PA level was 1.58 ± 0.16, corresponding to a low-to-moderate range. Fasting blood test values did not indicate impaired glucose tolerance. In single correlation analyses, MISI demonstrated significant negative correlation with
To identify sex-related differences in fractionated reaction time (FRT) and assess the relationship between corticospinal excitability and inhibition and FRT of the first dorsal interosseous (FDI) muscle. Twenty-three healthy males (24.8 ± 2.8 years) and 23 healthy females (24.1 ± 3.6 years) completed 30 trials each of a simple and go/no-go (GNG) reaction time test. Participants abducted their index finger as fast as possible in response to a visual stimulus. FRT splits the reaction time response into the following segments: Premotor time (PMT; duration between stimulus onset and start of muscle activity), motor time (MT; duration between the onset of muscle activity and initiation of force production), and total reaction time (TRT; duration between stimulus onset and force production), were determined for each trial. Corticospinal excitability and inhibition of the FDI were assessed through the amplitude of the motor evoked potential normalized to Mmax (MEP/Mmax), and duration of the corticospinal silent period (CSP), respectively. Simple MT (p < 0.01), GNG MT (p < 0.01), and GNG TRT (p < 0.01) were significantly longer in females compared to males. Remaining FRT measures were not significantly different between sexes (p ≥ 0.06). Corticospinal excitability was similar between sexes (p = 0.21), while corticospinal inhibition was greater in males compared to females (p = 0.02). No significant correlations were present between FRT and corticospinal measures (r ≤ 0.33; p ≥ 0.13). Males begin to produce force sooner and have greater corticospinal inhibition. However, there was no relationship between FRT and corticospinal communication.
