Impact of a single bout of high-intensity interval exercise and short-term interval training on interleukin-6, FNDC5, and METRNL mRNA expression in human skeletal muscle

Background: Exercise promotes numerous phenotypic adaptations in skeletal muscle that contribute to improved function and metabolic capacity. An emerging body of evidence suggests that skeletal muscle also releases a myriad of factors during exercise, termed "myokines". The purpose of this study was to examine the effects of high-intensity interval training(HIIT) on the acute regulation of the mRNA expression of several myokines, including the prototypical myokine interleukin-6(IL-6), and recently identified myokines fibronectin type III domain-containing protein 5(FNDC5)(irisin) and meteorin-like protein(METRNL).Methods: Both before and after a 20-day period of twice-daily high-volume HIIT, 9 healthy males(20.5 ± 1.5 years performed a standardized bout of high-intensity interval exercise(HIIE; 5 × 4 min at ~80% pretraining peak power output) with skeletal muscle biopsy samples(vastus lateralis) obtained at rest, immediately following exercise, and at 3 h recovery.Results: Before training, a single bout of HIIE increased IL-6(p < 0.05) and METRNL(p < 0.05) mRNA expression measured at 3 h recovery when compared to rest. Following 20 days of HIIT, IL-6 and FNDC5 mRNA were increased at 3 h recovery from the standardized HIIE bout when compared to rest(both p < 0.05). Resting METRNL and FNDC5 mRNA expression were higher following training(p < 0.05), and there was an overall increase in FNDC5 mRNA post-training(main effect of training, p < 0.05).Conclusion: In human skeletal muscle(1) an acute bout of HIIE can induce upregulation of skeletal muscle IL-6 mRNA both before and after a period of intensified HIIT;(2) Resting and overall FNDC5 mRNA expression is increased by 20 days of HIIT; and(3) METRNL mRNA expression is responsive to both acute HIIE and short-term intense HIIT. Future studies are needed to confirm these findings at the protein and secretion level in humans.

Effects of resistance training on cardiovascular health in non-obese active adolescents

AIM:To determine the benefits of a 10-wk resistance training programme on cardiovascular health in nonobese and active adolescents.METHODS:This is a pragmatic randomised controlled intervention.The study was carried out in a Hong Kong Government secondary school.Thirty-eight lean and active boys and girls were randomised to either the resistance training group or the control group.Students in the resistance training group received in-school 10-wk supervised resistance training twice per week,with each session lasting 70 min.Main outcome measures taken before and after training included brachial endothelial dependent flow-mediated dilation,body composition,fasting serum lipids,fasting glucose and insulin,high sensitive C-reactive protein,24-h ambulatory blood pressure and aerobic fitness.RESULTS:The only training related change was in endothelial dependent flow-mediated dilation which increased from 8.5%to 9.8%.A main effect of time and an interaction(P<0.005) indicated that this improvement was a result of the 10-wk resistance training.Main effects for time(P<0.05) in a number of anthropometric,metabolic and vascular variables were noted;however,there were no significant interactions indicating the change was more likely an outcome of normal growth and development as opposed to a training effect.CONCLUSION:Ten weeks of resistance training in school appears to have some vascular benefit in active,lean children.

Eccentric exercise-induced muscle weakness abolishes sex differences in fatigability during sustained submaximal isometric contractions

Background:Females are typically less fatigable than males during sustained isometric contractions at lower isometric contraction intensities.This sex difference in fatigability becomes more variable during higher intensity isometric and dynamic contractions.While less fatiguing than isometric or concentric contractions,eccentric contractions induce greater and longer lasting impairments in force production.However,it is not clear how muscle weakness influences fatigability in males and females during sustained isometric contractions.Methods:We investigated the effects of eccentric exercise-induced muscle weakness on time to task failure(TTF)during a sustained submaximal isometric contraction in young(18-30 years)healthy males(n=9)and females(n=10).Participants performed a sustained isometric contraction of the dorsiflexors at 35°plantar flexion by matching a 30%maximal voluntary contraction(MVC)torque target until task failure(i.e.,falling below 5%of their target torque for>2 s).The same sustained isometric contraction was repeated 30 min after 150 maximal eccentric contractions.Agonist and antagonist activation were assessed using surface electromyography over the tibialis anterior and soleus muscles,respectively.Results:Males were~41%stronger than females.Following eccentric exercise both males and females experienced an~20%decline in maximal voliuntary contraction torque.TTF was-34%longer in females than males prior to eccentic exercise-induced muscle weakness.However,following eccentric exercise-induced muscle weakness,this sex-related difference was abolished,with both groups having an"45%shorter TTF.Notably,there was~100%greater antagonist activation in the female group during the sustained isometric contraction following exercise-induced weakness as compared to the males.Conclusion:This increase in antagonist activation disadvantaged females by decreasing their TTF,resulting in a blunting of their typical fatigability advantage over males.

Skeletal muscle mechanisms contributing to improved glycemic control following intense interval exercise and training

High-intensity and sprint interval training(HIIT and SIT,respectively)enhance insulin sensitivity and glycemic control in both healthy adults and those with cardiometabolic diseases.The beneficial effects of intense interval training on glycemic control include both improvements seen in the hours to days following a single session of HIIT/SIT and those which accrue with chronic training.Skeletal muscle is the largest site of insulin-stimulated glucose uptake and plays an integral role in the beneficial effects of exercise on glycemic control.Here we summarize the skeletal muscle responses that contribute to improved glycemic control during and following a single session of interval exercise and evaluate the relationship between skeletal muscle remodelling and improved insulin sensitivity following HIIT/SIT training interventions.Recent evidence suggests that targeting skeletal muscle mechanisms via nutritional interventions around exercise,particularly with carbohydrate manipulation,can enhance the acute glycemic benefits of HIIT.There is also some evidence of sex-based differences in the glycemic benefits of intense interval exercise,with blunted responses observed after training in females relative to males.Differences in skeletal muscle metabolism between males and females may contribute to sex differences in insulin sensitivity following HIIT/SIT,but well-controlled studies evaluating purported muscle mechanisms alongside measurement of insulin sensitivity are needed.Given the greater representation of males in muscle physiology literature,there is also a need for more research involving female-only cohorts to enhance our basic understanding of how intense interval training influences muscle insulin sensitivity in females across the lifespan.

Adipose-brain crosstalk: do adipokines have a role in neuroprotection?

Accumulating evidence from epidemiological and experimental studies indicate that obesity,and its related metabolic consequences of insulin resistance and type 2 diabetes,are associated with accelerated cognitive decline(Yates et al.,2012).The etiology of neurodegeneration in obesity is undoubtedly complex,with vascular,metabolic,inflammatory,and structural changes all likely to play a role(Yates et al.,

Possible role of microparticles in neuroimmune signaling of microglial cells

Aim:Submicron fragments termed microparticles(MPs),derived from all major central nervous system cell types including neurons and glia(microglia,astrocytes,oligodendrocytes),have emerged as novel intercellular signaling agents.This study tested the hypothesis that MPs derived from activated microglia,which represent the mononuclear phagocyte system in the brain,could induce pro-inflammatory and cytotoxic responses of microglia in an autocrine or paracrine manner.Methods:Human THP-1 monocytic cells were used to model human microglia.MPs derived from these cells were reapplied to THP-1 cells and their secretion of neurotoxins and cytokines was measured.Results:When exposed to lipopolysaccharide(LPS)or mitochondrial transcription factor A in combination with interferon(IFN)-γ,THP-1 cells released MPs.When reapplied to THP-1 cells,MPs induced the release of secretions that were toxic to human SH-SY5Y neuroblastoma cells,as well as monocyte chemoattractant protein-1.The cytotoxicity of THP-1 cells induced by MPs derived from IFN-γplus LPS-treated THP-1 donor cells was enhanced in the presence of IFN-γ.The MPs released by THP-1 cells were not directly toxic towards SH-SY5Y cells.Conclusion:Our data support the hypothesis that activated microglia-derived MPs could act as signaling agents that are recognized by microglia to cause pro-inflammatory and cytotoxic responses.