Exercise and COVID-19: exercise intensity reassures immunological benefits of post-COVID-19 condition.

Any form of physical activity, including exercise, has various benefits at the physiological (improving cardiac and respiratory functions, increasing skeletal muscle mass, and maintaining homeostasis) and psychological levels (improving cognitive function, reducing anxiety and depression) which help to combat any type of infection. In contrast, the infectivity ratio could reduce the physical activity of an individual, such as performing a habitual exercise. Adaptation to different exercise strategies including intensity and duration may better increase physical performance and improve the symptoms. For example, low to moderate intensity perhaps fails to induce this adaptive process, while high-intensity of exercise compromises immune health. This can aggravate the infection rate (Open window theory). However, high intensity with a shorter time produces various morphological alterations in the primary organs including the lungs and heart, which facilitate life support in COVID-19 patients. However, less information about exercise protocols failed to assure the benefits of exercise to COVID-19 patients, particularly post-COVID-19 conditions. Therefore, this review will answer how exercise intensity is crucial to reassure the exercise benefits for promoting safe participation before infection and post-COVID-19 conditions.

Redox status biomarkers in the fast-twitch extensor digitorum longus resulting from the hypoxic exercise.

The fast-twitch muscle may be affected from over-produced reactive oxygen species (ROS) during hypoxia/hypoxic exercise. The study aims to investigate redox status biomarkers in the fast-twitch extensor digitorum longus (EDL) muscle after hypoxic exercise. Male Sprague Dawley rats (eight-week-old) were randomly divided into six groups of the experimental "live high train high (LHTH), live high train low (LHTL) and live low train low (LLTL)" and their respective controls. Before the EDLs' extraction, the animals exercised for a 4-week familiarization period, then they exercised for four-weeks at different altitudes. The LHTH group had higher ratios of lipid hydroperoxides (LHPs) than the experimental groups of LHTL (p=0.004) and LLTL (p=0.002), while having no difference than its control 'LH'. Similarly, a higher percentage of advanced oxidation protein products (AOPP) was determined in the LHTH than the LHTL (p=0.041) and LLTL (p=0.048). Furthermore, oxidation of thiol fractions was the lowest in the LHTH and LH. However, redox biomarkers and thiol fractions illustrated no significant change in the LHTL and LLTL that might ensure redox homeostasis due to higher oxygen consumption. The study shows that not hypoxic exercise/exercise, but hypoxia might itself lead to a redox imbalance in the fast-twitch EDL muscle.

"Live High Train Low" Hypoxic Training Enhances Exercise Performance with Efficient Redox Homeostasis in Rats' Soleus Muscle.

Çolak, Ridvan, Eda Agascioglu, and Ufuk Çakatay. "Live high train low" hypoxic training enhances exercise performance with efficient redox homeostasis in rats' soleus muscle. High Alt Med Biol. 22:77-86, 2021. Background: Different types of hypoxic training have been performed to improve exercise performance. Although both "live high train high" and "live high train low" techniques are commonly performed, it is still obscure as to which one is more beneficial. Materials and Methods: Eight-week-old male Sprague-Dawley rats were randomly divided into aforementioned experimental groups. After a familiarization exercise (4-week, ∼15-30 minutes/day) at normoxia, all rats exercised (4-week, ∼35 minutes/day) at hypoxia with their pre-evaluated maximal aerobic velocity test. The soleus was extracted after the test following 2 days of resting. Results: The live high trained low group displayed better performance than the live high trained high (p = 0.031) and the live low trained low (p = 0.017) groups. Redox status biomarkers were higher in the live high trained high group except for thiols, which were illustrated with no difference among the groups. Further, contrary to total and protein thiols (r = 0.57, p = 0.037; r = 0.55, p = 0.042 respectively), other redox status biomarkers were observed to be negatively correlated to exercise performance. Conclusions: The live high trained low group could consume more oxygen during exercise, which might lead to having a better chance to ensure cellular redox homeostasis. Therefore, this group could ensure an optimum exercise performance and anabolic metabolism.

Impaired redox homeostasis in the heart left ventricles of aged rats experiencing fast-developing severe hypobaric hypoxia.

Despite its rare occurrence, humans and animals have been prone to getting fast developing severe hypobaric hypoxia. Understanding the redox homeostasis related response of an aging heart to this type of hypoxia are crucially important, since the metabolism of myocardial tissue depends on the redox status of proteins. Rodents can tolerate hypoxic stress better than human subjects. This study was aimed at investigating the effects of fast developing severe hypobaric hypoxia on redox status biomarkers; such as, advanced oxidation protein products (AOPP), lipid hydroperoxides (LHPs), protein carbonyl groups (PCO), protein thiol groups (P-SH), and total thiol groups (T-SH) on the myocardial left ventricles of young and aged Wistar rats. The rats were gradually ascended and exposed to an 8000-meter hypobaric hypoxia. While AOPP levels showed no difference, the TSH and PSH concentrations decreased, and the PCO and LHP increased in both of the hypoxic groups than the controls. The TSH and PSH were lower, and AOPP, PCO and LHP were found to be higher in the elderly hypoxic groups than in the young ones. The significant outcome of the study represents that an 8000-meter hypobaric hypoxia could be considered as a severe hypoxic stress, but not life-treating for the rats and would affect both the young and aged left ventricles similarly in respect to impaired redox status. However, if the percentage increases are taken into consideration, it seems that the higher rate of protein oxidation occurs in young hearts; meanwhile aged hearts are more prone to T-SH oxidation.

Phospholipid fatty acid pattern and D-glucose metabolism in muscles from omega3 fatty acid-depleted rats.

A depletion in long-chain polyunsaturated omega3 fatty acids may affect fuel homeostasis. In such a perspective, the present study deals mainly with the in vitro fate of D-[U-(14)C]glucose in hemidiaphragms, stretched soleus and plantaris muscle pieces obtained from normal and omega3-depleted rats (second generation) and incubated in the absence or presence of insulin. When so required, the omega3-depleted rats were injected 120 min before sacrifice with either a omega3 fatty acid-rich medium-chain triglyceride:fish oil emulsion (FO) or a control medium-chain triglyceride:olive oil emulsion (OO). The content of the soleus muscle in long-chain polyunsaturated omega3 fatty acids was severely decreased in the omega3-depleted rats, and modestly albeit significantly increased after injection of FO to these animals. In stretched soleus muscles from OO-injected omega3-depleted rats, the absolute values for glycogen synthesis measured in the absence or presence of insulin were about twice higher than in normal animals. In the OO-injected omega3-depleted rats, insulin augmented the output of (14)C-labelled amino acids, whilst such was not the case in normal animals. These and other findings suggest a lower catabolism of D-glucose relative to the anabolic process of glycogen synthesis and a lower availability of endogenous amino acids in the muscles of omega3-depleted rats, as compared to those of control animals. The prior injection of FO to the omega3-depleted rats restored a normal value for the paired ratio between the output of (14)C-labelled amino acids and acidic metabolites, but further increased glycogen net synthesis. It is proposed, therefore, that the perturbation of d-glucose metabolism in muscles from omega3-depleted rats involves a multifactorial determinism, only some of the concerned factors being susceptible to rapid correction after enrichment of cell phospholipids in long-chain polyunsaturated omega3 fatty acids.

Opposite effects of D-fructose on total versus cytosolic ATP/ADP ratio in pancreatic islet cells.

D-fructose (10 mM) augments, in rat pancreatic islets, insulin release evoked by 10 mM D-glucose. Even in the absence of D-glucose, D-fructose (100 mM) displays a positive insulinotropic action. It was now examined whether the insulinotropic action of D-fructose could be attributed to an increase in the ATP content of islet cells. After 30-60 min incubation in the presence of D-glucose and/or D-fructose, the ATP and ADP content was measured by bioluminescence in either rat isolated pancreatic islets (total ATP and ADP) or the supernatant of dispersed rat pancreatic islet cells exposed for 30 s to digitonine (cytosolic ATP and ADP). D-fructose (10 and 100 mM) was found to cause a concentration-related decrease in the total ATP and ADP content and ATP/ADP ratio below the basal values found in islets deprived of exogenous nutrient. Moreover, in the presence of 10 mM D-glucose, which augmented both the total ATP content and ATP/ADP ratio above basal value, D-fructose (10 mM) also lowered these two parameters. The cytosolic ATP/ADP ratio, however, was increased in the presence of D-glucose and/or D-fructose. Under the present experimental conditions, a sigmoidal relationship was found between such a cytosolic ATP/ADP ratio and either (86)Rb net uptake by dispersed islet cells or insulin release from isolated islets. These data provide, to our knowledge, the first example of a dramatic dissociation between changes in total ATP content or ATP/ADP ratio and insulin release in pancreatic islets exposed to a nutrient secretagogue. Nevertheless, the cationic and insulinotropic actions of d-glucose and/or d-fructose were tightly related to the cytosolic ATP/ADP ratio.

Adenine nucleotide pattern in rat pancreatic islets exposed to nutrient secretagogues.

The effects of D-glucose, D-mannose, D-galactose, Dglyceraldehyde, pyruvate, L-lactate, 2-ketoisocaproate, L-leucine, and/or L-glutamine on the ATP and ADP content of rat isolated pancreatic islets were reevaluated in order to compare changes evoked by these nutrient secretagogues in the islet ATP content and ATP/ADP ratio to their effects upon insulin release. Although being compatible with the fuel concept for nutrient-stimulated insulin secretion, the results of this study also argue against the monolithic view that the adenine nucleotide pattern in islet cells represents the sole coupling factor between metabolic and more distal events in the process of nutrient-stimulated insulin release.