Human function emerges from dynamic interactions among physiological systems. While decades of research have provided understanding of individual systems, how musculoskeletal, cardiovascular, and respiratory systems coordinate as an integrated network during exercise remains unclear. We characterized multisystem coordination during cardiopulmonary exercise test (CPET) of incremental cycling. Twenty-six young adults performed a graded cycling test until exhaustion (25 W/min). Continuous synchronized recordings included electromyography from bilateral vastus lateralis (Leg) and erector spinae (Back), three-lead electrocardiography, and respiratory waveform via chest belt. Multisystem coordination was assessed using Amplitude-Amplitude Cross-frequency Coupling (ACFC), which quantifies the dynamic co-modulation of signal amplitudes. ACFC yielded three network-based markers: inter-muscular, cardio-muscular, and respiratory-muscular coupling. Analyses compared the Beginning (first third) and End (last third) of the test. At the Beginning, inter-muscular coupling was strongest within the Leg–Leg sub-network. At the End, Leg–Leg coupling decreased by 30
Intermittent exogenous ketosis via ketone monoester (KE) ingestion has been shown to enhance physiological responses and reduce acute mountain sickness (AMS) symptoms during acute normobaric hypoxia. Its effects during early acclimatization to terrestrial high-altitude, however, remain unclear. Thirty-four participants were randomised to an intermittent exogenous ketosis (IEK, n=17) or placebo (PLA, n=17) group and underwent a near sea level trial (295 m) without supplementation, followed by a four-day sojourn at 3375 m during which they received regular KE (IEK) or placebo (PLA) supplements. AMS symptoms, hematological markers, and resting ventilatory, cardiovascular, and cerebral tissue oxygenation responses were assessed each day upon waking, at midday, and before sleep throughout the exposure. KE consistently elevated circulating β-hydroxybutyrate post-ingestion (P<0.001), confirming intermittent exogenous ketosis in the IEK group. AMS incidence peaked at 25–35
This study examines the effects of cigarette smoking (CS) on post-exercise cardiovascular re-stabilization following high-intensity interval exercise (HIIE) in physically active smokers. Fifteen physically active male smokers completed three conditions, including the CS, sham smoking (SS), and non-smoking (NS) in a randomized crossover design. In each condition, participants performed 20 mins of HIIE followed by one of the assigned smoking conditions. Cardiovascular function indices such as heat rate (HR) heart rate variability (HRV), brachial-ankle pulse wave velocity (baPWV), ankle-brachial index (ABI), peripheral oxygen saturation (SpO2), blood lactate concentration (BLa), and perceived recovery scale (PRS) were evaluated at baseline, immediately post-exercise, post-smoking, and 45 min post-exercise, whereas endothelial function (flow-mediated dilation, FMD) was assessed at baseline and 45 min of post-exercise. Significant interaction effects were observed for HR (p<0.001, ES (effect size, partial eta squared) = 0.11), HRV indices (lnLF: p=0.009, ES =0.21; lnHF: p=0.001, ES = 0.23), FMD (p<0.001, ES =0.22), and SpO₂ (p=0.018, ES = 0.22). The CS condition showed delayed HR and HRV recoveries compared with the SS and NS conditions. FMD was significantly lower in both the CS and SS conditions than in the NS condition, with a greater reduction observed in the CS condition. SpO2 returned to baseline levels 45 min post-exercise in the NS condition, showed a trend toward recovery toward baseline in the SS condition, and did not significantly recover to baseline in the CS condition. baPWV, ABI, BLa, and PRS showed no significant differences among conditions. CS delayed post-HIIE recovery of HR and HRV (lnLF, lnHF), impaired endothelial function and delayed SpO2 restauration. Therefore, avoiding CS immediately after HIIE may help preserve normal post-exercise cardiovascular early recovery after HIIE in physically active smokers.
The interpolated twitch technique (ITT) is often used to assess voluntary activation (VA); however, its effectiveness depends on the muscle tested. Using single pulse stimulation, VA of the dorsiflexors is overestimated. Therefore, the purpose of this study was to investigate whether using a doublet provides a more sensitive measure of VA in the dorsiflexors. Participants (n = 14, 7 females) performed isometric dorsiflexion contractions in a 45º plantar-flexed position from 10 to 100
Blood flow restriction (BFR) is a widely used exercise modality in sport; however, evidence supporting its use in individuals with overweight remains limited. This study evaluated whether home-based BFR training provides additional benefits over conventional resistance training in this population. Twenty-seven participants were assigned to BFR (n = 13) or non-BFR (n = 14) groups for a 6-week (3x/week) home-based strength program via videoconference. Assessments included body composition (DEXA), glucose and lipid metabolism, knee extensor/flexor strength, and gait analysis (energetics, biomechanics and preferred walking speed). No group × time interactions were observed for any outcome, indicating no BFR-induced benefits. Across both groups, trunk lean mass increased (BFR: 27.2 ± 4.3 to 27.9 ± 4.5 kg; non-BFR: 25.4 ± 4.0 to 25.8 ± 4.4 kg; P = 0.007). HDL-cholesterol decreased (P = 0.008) and glycated haemoglobin increased (P < 0.001), both statistically significant but clinically negligible and directionally unfavourable. Isometric knee-extension peak torque increased (BFR: 186 ± 50 to 222 ± 80 Nm; non-BFR: 183 ± 81 to 204 ± 90 Nm; P < 0.001), with parallel gains in isokinetic concentric extension and flexion at 30°/s, 90°/s, and 180°/s (all P ≤ 0.032). Gait analysis showed no changes. Six weeks of remotely supervised bodyweight resistance training improved knee extensor and flexor strength in sedentary adults with overweight or obesity. Under the present conditions, adding BFR did not provide evidence of additional benefit for strength, body composition, metabolic markers, or walking outcomes. The trial was registered in advance at ClinicalTrials.gov with the identifier NCT05371119 on 12 May 2022.
A single bout of unaccustomed eccentric exercise can protect against subsequent strength loss and soreness, with protection sometimes transferring to the unexercised contralateral limb. The contralateral repeated bout effect (CL-RBE) may be relevant for muscle–tendon units with comparatively small fascicle strains during eccentric tasks, such as the triceps surae, but has not been established in this muscle group. We tested whether unilateral eccentric heel drops produced evidence consistent with the CL-RBE in the triceps surae and whether its expression differed after 2- and 7-day interbout intervals. Twenty-four participants completed 225 unilateral eccentric heel drops (ECC1), then repeated the task on the opposite limb (ECC2) after 2 days (2D, n=12) or 7 days (7D, n=12). Maximal voluntary isometric plantar-flexor torque (MVIC) and soreness were assessed at baseline (PRE) and post-exercise. Surface electromyography (sEMG) amplitude (root mean square, RMS) and median frequency (MDF) were quantified during each bout. At 48 h, normalised MVIC torque was higher after ECC2 than ECC1 in 2D (10.8
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
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.
