Experimental Physiology最新文献

We evaluated the feasibility and efficacy of a 2-week training programme comprising resistance vibration exercise (RVE) without and with artificial gravity (AG). Participants (n = 24) were divided into three groups: (i) URVE: upright loaded squat exercise; (ii) HRVE: horizontal loaded squat exercise; and (iii) AGRVE: loaded squat exercise conducted on a short-arm human centrifuge. All participants followed the same protocol and were exposed to the same ground reaction force, whilst performing exercise comprising bilateral squats, triple extension squats and single/bilateral calf raises. Before and after the 2-week training period, we measured thigh and calf muscle strength with isokinetic dynamometry, muscular power with a jump test, volume with functional muscle magnetic resonance imaging, and body composition with dual-energy X-ray absorptiometry. All groups showed significant improvements in eight-repetition maximum squat strength (P < 0.0001, G > 0.80), whilst only the AGRVE group demonstrated a small effect in jump height (G = 0.26). The AGRVE group significantly increased knee extension and flexion maximum voluntary contraction (MVC), with no comparable changes in the HRVE or URVE groups. The AGRVE group increased total thigh muscle volume (P = 0.03), with notable hypertrophy in the vastus medialis, semitendinosus, and vastus intermedius muscles. These findings demonstrate that AGRVE is significantly superior to HRVE and URVE in enhancing knee MVC and thigh muscle volume, thus indicating that artificial gravity improves the outcome of resistance vibration exercise in ambulatory participants.

Due to a lack of technical capacity to directly visualise and quantify microvessels in the skin, little is known regarding regional and/or sex differences. We compared diameter, velocity, flow and density at four regional sites using a novel optical coherence tomography (OCT) approach. OCT and laser Doppler flowmetry (LDF) were performed on the back, forearm, foot and thigh in 30 healthy adults (15♂ 15♀; 31 ± 6years) at rest (33°C) and after 30 min of local heating (LH; 44°C). At baseline, larger diameter, speed, flow, density and LDF flux were recorded on the back than other sites (P < 0.017). In response to LH, the smallest changes in OCT-derived diameter were observed on the back (Δ12 ± 6 µm) and foot (Δ13 ± 6 µm vs. forearm 17 ± 5 µm; thigh Δ18 ± 5 µm, all P < 0.005 vs. foot, back). The back exhibited the smallest change in density (back Δ19 ± 7%, forearm Δ24 ± 5%, thigh Δ26 ± 6%, foot Δ26 ± 8%, P < 0.02 vs. back) whilst the foot exhibited the smallest changes in speed (foot Δ27 ± 14, back Δ58 ± 22, forearm Δ47 ± 17, thigh Δ48 ± 11 µm/s, P < 0.001 vs. foot) and flow (Δ135 ± 60, back Δ204 ± 76, forearm Δ212 ± 60, thigh Δ247 ± 51 µL/s, P < 0.001 vs. foot). When sites were grouped, males had larger baseline diameters (♂ 45 ± 3 vs. ♀ 42 ± 3 µm, P = 0.019) and flows (♂ 109 ± 20 vs. ♀ 93 ± 17 µL/s, P = 0.025) whilst females exhibited larger LH-induced changes in speed in the thigh (♀ Δ53 ± 10 vs. ♂ Δ43 ± 10 µm/s, P = 0.014) and density in the forearm (♀ Δ26 ± 4 vs. ♂ Δ21% ± 6%, P = 0.006). Regional differences exist in OCT-derived cutaneous microvascular diameter, speed, flow and density at baseline and in response to LH. Males showed larger cutaneous diameter and flow at baseline, while females exhibited larger changes in the speed and density outcomes in response to local heating.

Aldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme that plays an important role in aldehyde detoxification. A large percentage (30-50%) of the East Asian population carry a single point mutation in the ALDH2 gene (ALDH2*2 variant) that causes a severe reduction or lack of ALDH2 enzyme activity, and leads to disrupted cellular homeostasis due to the accumulation of toxic reactive aldehydes. The ALDH2*2 variant has been associated with several degenerative diseases, with evidence suggesting a link to cardiovascular disease, potentially mediated by endothelial dysfunction. This, however, remains to be confirmed. We aimed to investigate whether the ALDH2*2 variant is associated with impaired endothelial function in young, healthy East Asians. Twenty-two participants were genotyped and divided into non-carriers (ALDH2*1/*1; n = 12; 7 females and 5 males; age = 23 ± 3 years; height = 167.4 ± 8.7 cm; body mass = 60.1 ± 9.0 kg) and carriers (ALDH2*1/*2 and ALDH2*2/*2; n = 10; 8 females and 2 males; age = 24 ± 5 years; height = 162.6 ± 10.1 cm; body mass = 62.1 ± 9.7 kg) of the ALDH2*2 allele. Endothelial function was assessed via flow-mediated dilation (FMD) following current guidelines. Carriers displayed lower FMD, either absolute or relative, which was not statistically significant but approached significance (unpaired t-test) (FMD%: non-carriers = 10.2 ± 1.9% vs. carriers = 8.1% ± 3.1%, P = 0.079, effect size: Cohen's d = 0.82; FMD_abs: non-carriers = 0.32 ± 0.06 mm vs. carriers = 0.26 ± 0.09 mm, P = 0.082, effect size: Cohen's d = 0.78). In conclusion, our data seem to suggest that the ALDH2*2 variant impairs endothelial function even in young and healthy individuals without the presence of other stressor agents. Future studies with larger sample size are necessary to confirm our findings.

The endothelium plays a pivotal role in regulating cerebrovascular blood flow, and its dysfunction increases the risk of cerebrovascular disease. Endothelial shear stress, a primary mechanical stimulus for endothelial nitric oxide production, is a key modulator of vascular adaptation. In recent years, transient hypercapnia-induced flow-mediated dilation of the internal carotid artery (ICA-FMD) has emerged as a valuable in vivo approach for assessing cerebrovascular endothelial function in humans. This review first synthesizes methodological advances in ICA-FMD assessment, emphasizing the importance of transient carbon dioxide (CO₂) inhalation, normalizing ICA-FMD to the shear stress, and consideration of unique ICA haemodynamics. Second, it consolidates mechanistic insights and conditions for improving ICA-FMD, elucidating effective and ineffective strategies. Intermittent hypoxia-induced increases in shear stress improve ICA dilatory response, underscoring the pivotal role of shear rate. Although ICA blood flow during exercise has been extensively studied, data on shear rate during exercise are limited. Moderate-intensity leg cycling that avoids hyperventilation and elevates end-tidal CO₂ partial pressure increases ICA shear rate and augments post-exercise ICA-FMD, whereas higher-intensity exercise or small-muscle exercise fails to produce similar benefits. These observations suggest that a threshold shear stimulus may be required for post-exercise improvements in ICA-FMD. Future research should establish standardized methodologies, define the shear stimulus threshold, elucidate the time course of vascular adaptations, and extend investigations to populations at elevated cerebrovascular risk. Translating these mechanistic insights into clinical strategies has the potential to optimize cerebrovascular endothelial function and thereby contribute to the prevention of cerebrovascular diseases.

Synaptic input to the motoneuron pool is altered during fatiguing muscle contractions. In humans, the corticospinal tract is often studied, with equivocal findings regarding its role in the reduction of force. To date, the involvement of the reticulospinal tract during states of fatigue has not been explored. Fourteen participants (28 ± 6 years, nine males) visited the laboratory twice, first for a familiarisation, then for an experimental trial. Participants completed a 5-min sustained elbow flexor contraction at an intensity eliciting 40% of the EMG recorded during a maximal isometric voluntary contraction (MVC). Before, during and after the contraction, transcranial magnetic stimulation and electrical cervicomedullary stimulation were used to elicit motor evoked potentials (MEPs) and cervicomedullary evoked potentials during the silent period (SP-CMEPs), respectively, with CMEPs also being evoked in combination with a startling acoustic sound (CMEPcon). Electrical stimulation of the brachial plexus was used to evoke maximal compound action potentials of the elbow flexors (M_max). The 5-min contraction induced a 53% loss of force (P < 0.001), with no change in background EMG (∼4% M_max, P = 0.293). Neither MEP amplitude (P = 0.246) nor CMEPcon ratio (P = 0.489) was altered during the contraction, whereas CMEP and SP-CMEP amplitudes were reduced by ∼20% and 50%, respectively (P < 0.001) and remained depressed post-task. The results suggest that neither corticospinal nor reticulospinal tract excitability was altered during a 5-min constant-EMG task at 40% maximal EMG. Instead, the aetiology of the neural contribution to fatigability appeared to be primarily related to the loss of motoneuron excitability.

This study investigated the acute effects of two isoenergetic high-intensity interval exercise (HIIE) sessions, running (HIIE-RUN) and cycling (HIIE-BIKE), on post-exercise oxygen consumption ( ${\dot{V}}_{O_2}$ ), carbon dioxide production ( ${\dot{V}}_{C{O}_2}$ ), substrate oxidation and 24-h energy intake (EI) in men with overweight or obesity. Twelve fasted men (44.4 ± 14.5 years; body mass index: 28.3 ± 1.9 kg m^-2) completed both HIIE sessions. ${\dot{V}}_{O_2}$ and ${\dot{V}}_{C{O}_2}$ were measured before, during and after exercise, while substrate oxidation was calculated before and after exercise. The rate of perceived exertion was recorded during each exercise. Appetite was assessed throughout each session using a visual analogue scale (VAS) and EI was recorded via a 24-h dietary questionnaire. Both exercise modalities resulted in similar energy expenditure (EE), but HIIE-BIKE elicited a significantly higher respiratory exchange ratio (P = 0.002). No significant effect of exercise modality or time × modality interaction was observed for ${\dot{V}}_{O_2}$ and EE during the post-exercise period. Fat oxidation was significantly increased during recovery compared with the pre-exercise levels (P < 0.001), but did not differ between modalities. Appetite and 24-h EI were unaffected by the exercise modality. In men with overweight or obesity, isoenergetic HIIE-RUN and HIIE-BIKE seem to induce comparable post-exercise ${\dot{V}}_{O_2}$ , EE and substrate oxidation during the 2-h recovery period. Both modalities similarly promoted fat oxidation without specific dietary compensation observed.