Increased maximal oxygen uptake after sprint-interval training is mediated by central haemodynamic factors as determined by right heart catheterization.

There is a lack of knowledge regarding the contribution of central and peripheral factors to the increases in VO2max following sprint-interval training (SIT). This study investigated the importance of maximal cardiac output (Qmax ) in relation to VO2max improvements following SIT and the relative importance of the hypervolemic response on Qmax and VO2max . We also investigated whether systemic O2 extraction increased with SIT as has been previously suggested. Healthy men and women (n = 9) performed 6 weeks of SIT. State-of-the-art measurements: right heart catheterization, carbon monoxide rebreathing and respiratory gas exchange analysis were used to assess Qmax , arterial O2 content (ca O2 ), mixed venous O2 content (cv O2 ), blood volume (BV) and VO2max before and after the intervention. In order to assess the relative contribution of the hypervolemic response to the increases in VO2max , BV was re-established to pre-training levels by phlebotomy. Following the intervention, VO2max , BV and Qmax increased by 11% (P < 0.001), 5.4% (P = 0.013) and 8.8% (P = 0.004), respectively. cv O2 decreased by 12.4% (P = 0.011) and systemic O2 extraction increased by 4.0% (P = 0.009) during the same period, both variables were unaffected by phlebotomy (P = 0.589 and P = 0.548, respectively). After phlebotomy, VO2max and Qmax reverted back to pre-intervention values (P = 0.064 and P = 0.838, respectively) and were significantly lower compared with post-intervention (P = 0.016 and P = 0.018, respectively). The decline in VO2max after phlebotomy was linear to the amount of blood removed (P = 0.007, R = -0.82). The causal relationship between BV, Qmax and VO2max shows that the hypervolemic response is a key mediator of the increases in VO2max following SIT. KEY POINTS: Sprint-interval training (SIT) is an exercise model involving supramaximal bouts of exercise interspersed with periods of rest known for its efficiency in improving maximal oxygen uptake (VO2max ). In contrast to the commonly accepted view where central haemodynamic adaptations are considered to be the key mediators of increases in VO2max there have been propositions highlighting peripheral adaptations as the main mediators in the context of SIT-induced changes in VO2max . By combining right heart catheterization, carbon monoxide rebreathing and phlebotomy, this study shows that increases in maximal cardiac output due to the expansion of the total blood volume is a major explanatory factor for the improvement in VO2max following SIT, with a smaller contribution from improved systemic oxygen extraction. The present work not only clarifies a controversy in the field by using state-of-the-art methods, but also encourages future research to investigate regulatory mechanisms that could explain how SIT can lead to improvements in VO2max and maximal cardiac output similar to those that have previously been reported for traditional endurance exercise.

Functional Limitations and Exercise Intolerance in Patients With Post-COVID Condition: A Randomized Crossover Clinical Trial.

Importance: Many patients with post-COVID condition (PCC) experience persistent fatigue, muscle pain, and cognitive problems that worsen after exertion (referred to as postexertional malaise). Recommendations currently advise against exercise in this population to prevent symptom worsening; however, prolonged inactivity is associated with risk of long-term health deterioration. Objective: To assess postexertional symptoms in patients with PCC after exercise compared with control participants and to comprehensively investigate the physiologic mechanisms underlying PCC. Design, Setting, and Participants: In this randomized crossover clinical trial, nonhospitalized patients without concomitant diseases and with persistent (≥3 months) symptoms, including postexertional malaise, after SARS-CoV-2 infection were recruited in Sweden from September 2022 to July 2023. Age- and sex-matched control participants were also recruited. Interventions: After comprehensive physiologic characterization, participants completed 3 exercise trials (high-intensity interval training [HIIT], moderate-intensity continuous training [MICT], and strength training [ST]) in a randomized order. Symptoms were reported at baseline, immediately after exercise, and 48 hours after exercise. Main Outcomes and Measures: The primary outcome was between-group differences in changes in fatigue symptoms from baseline to 48 hours after exercise, assessed via the visual analog scale (VAS). Questionnaires, cardiopulmonary exercise testing, inflammatory markers, and physiologic characterization provided information on the physiologic function of patients with PCC. Results: Thirty-one patients with PCC (mean [SD] age, 46.6 [10.0] years; 24 [77%] women) and 31 healthy control participants (mean [SD] age, 47.3 [8.9] years; 23 [74%] women) were included. Patients with PCC reported more symptoms than controls at all time points. However, there was no difference between the groups in the worsening of fatigue in response to the different exercises (mean [SD] VAS ranks for HIIT: PCC, 29.3 [19.5]; controls, 28.7 [11.4]; P = .08; MICT: PCC, 31.2 [17.0]; controls, 24.6 [11.7]; P = .09; ST: PCC, 31.0 [19.7]; controls, 28.1 [12.2]; P = .49). Patients with PCC had greater exacerbation of muscle pain after HIIT (mean [SD] VAS ranks, 33.4 [17.7] vs 25.0 [11.3]; P = .04) and reported more concentration difficulties after MICT (mean [SD] VAS ranks, 33.0 [17.1] vs 23.3 [10.6]; P = .03) compared with controls. At baseline, patients with PCC showed preserved lung and heart function but had a 21% lower peak volume of oxygen consumption (mean difference: -6.8 mL/kg/min; 95% CI, -10.7 to -2.9 mL/kg/min; P < .001) and less isometric knee extension muscle strength (mean difference: -37 Nm; 95% CI, -67 to -7 Nm; P = .02) compared with controls. Patients with PCC spent 43% less time on moderate to vigorous physical activity (mean difference, -26.5 minutes/d; 95% CI, -42.0 to -11.1 minutes/d; P = .001). Of note, 4 patients with PCC (13%) had postural orthostatic tachycardia, and 18 of 29 (62%) showed signs of myopathy as determined by neurophysiologic testing. Conclusions and Relevance: In this study, nonhospitalized patients with PCC generally tolerated exercise with preserved cardiovascular function but showed lower aerobic capacity and less muscle strength than the control group. They also showed signs of postural orthostatic tachycardia and myopathy. The findings suggest cautious exercise adoption could be recommended to prevent further skeletal muscle deconditioning and health impairment in patients with PCC. Trial Registration: ClinicalTrials.gov Identifier: NCT05445830.

The impact of atypical sensory processing on adaptive functioning within and beyond autism: The role of familial factors.

LAY ABSTRACT: Individuals diagnosed with autism tend to process sensory information differently than individuals without autism, resulting for instance in increased sensitivity to sounds or smells. This leads to challenges in everyday life and may restrict the individual's daily functioning. How direct this link is, however, is currently unclear. We investigated this question in 289 twins of whom 60 were diagnosed with autism and further 61 were diagnosed with other neurodevelopmental disorders. We looked at the association between unusual sensory processing and adaptive skills, both across individuals and within-twin pairs, testing whether individuals with higher levels of atypical sensory processing showed reduced adaptive skills compared to their twins. Since twins share 50%-100% of their genes and part of their environment (e.g. family background), associations within-twin pairs are free from effects of these familial factors. We found that an increased sensitivity to, as well as the avoiding of, sensory input (hyper-responsiveness) was linked to reduced adaptive skills across individuals-but not within-twin pairs. We also found an association between the degree to which individuals seek for sensory input (sensation seeking) and reduced adaptive skills, but only in individuals diagnosed with autism. The results suggest that sensory hyper-responsiveness has negative effects on individuals' general ability to function, but that this link is influenced by familial factors and hence not direct. In addition, sensation seeking behaviors might have a negative impact on adaptive skills specifically in autistic individuals.

Material properties of plasticized hardwood xylans for potential application as oxygen barrier films.

Free films based on glucuronoxylan isolated from aspen wood were prepared by casting from aqueous solutions and drying in a controlled environment. Addition of xylitol or sorbitol facilitated film formation and thus examination of the material properties of these films. The mechanical properties of the films were evaluated using tensile testing and dynamic mechanical analysis in a controlled ambient relative humidity. The strain at break increased, and the stress at break and Young's modulus of the films decreased with increasing amounts of xylitol and sorbitol due to plasticization. At high amount of plasticizer, it was found that films with xylitol gave lower extensibility. Wide-angle X-ray scattering analysis showed that xylitol crystallized in a distinct phase, which we believe contributes to the more brittle behavior of these films. The effect of the plasticizers on the glass transition temperature was determined using dynamic mechanical analysis and differential scanning calorimetry. An increased amount of plasticizer shifted the glass transition to lower temperatures. The effect of moisture on the properties of plasticized films was investigated using water vapor sorption isotherms and by humidity scans in dynamic mechanical analysis. Sorption isotherms showed a transition from type II to type III when adding plasticizer. The films showed low oxygen permeability and thus have a potential application in food packaging.