Response of the Myocardium to Exercise

Amino acids regulating skeletal muscle metabolism: mechanisms of action, physical training dosage recommendations and adverse effects

Maintaining skeletal muscle mass is important for improving muscle strength and function. Hence, maximizing lean body mass (LBM) is the primary goal for both elite athletes and fitness enthusiasts. The use of amino acids as dietary supplements is widespread among athletes and physically active individuals. Extensive literature analysis reveals that branched-chain amino acids (BCAA), creatine, glutamine and β-alanine may be beneficial in regulating skeletal muscle metabolism, enhancing LBM and mitigating exercise-induced muscle damage. This review details the mechanisms of these amino acids, offering insights into their efficacy as supplements. Recommended dosage and potential side effects are then outlined to aid athletes in making informed choices and safeguard their health. Lastly, limitations within the current literature are addressed, highlighting opportunities for future research.

Determination of the anti-inflammatory and cytoprotective effects of l-glutamine and l-alanine, or dipeptide, supplementation in rats submitted to resistance exercise

We evaluated the effects of chronic oral supplementation with l-glutamine and l-alanine in their free form or as the dipeptide l-alanyl-l-glutamine (DIP) on muscle damage, inflammation and cytoprotection, in rats submitted to progressive resistance exercise (RE). Wistar rats (n 8/group) were submitted to 8-week RE, which consisted of climbing a ladder with progressive loads. In the final 21 d before euthanasia, supplements were delivered in a 4 % solution in drinking water. Glutamine, creatine kinase (CK), lactate dehydrogenase (LDH), TNF-α, specific IL (IL-1β, IL-6 and IL-10) and monocyte chemoattractant protein-1 (MCP-1) levels were evaluated in plasma. The concentrations of glutamine, TNF-α, IL-6 and IL-10, as well as NF-κB activation, were determined in extensor digitorum longus (EDL) skeletal muscle. HSP70 level was assayed in EDL and peripheral blood mononuclear cells (PBMC). RE reduced glutamine concentration in plasma and EDL (P<0·05 v. sedentary group). However, l-glutamine supplements (l-alanine plus l-glutamine (GLN+ALA) and DIP groups) restored glutamine levels in plasma (by 40 and 58 %, respectively) and muscle (by 93 and 105 %, respectively). GLN+ALA and DIP groups also exhibited increased level of HSP70 in EDL and PBMC, consistent with the reduction of NF-κB p65 activation and cytokines in EDL. Muscle protection was also indicated by attenuation in plasma levels of CK, LDH, TNF-α and IL-1β, as well as an increase in IL-6, IL-10 and MCP-1. Our study demonstrates that chronic oral l-glutamine treatment (given with l-alanine or as dipeptide) following progressive RE induces cyprotective effects mediated by HSP70-associated responses to muscle damage and inflammation.

The effect of milk on the attenuation of exercise-induced muscle damage in males and females

PURPOSE

The consumption of 500 ml milk following muscle damaging exercise can attenuate decreases in muscle functional capacity and increases in markers of muscle damage and soreness in males. There has been no similar research in female participants. Therefore, the aim of this study was to investigate the effects of milk consumption on exercise-induced muscle damage (EIMD) in males and females.

METHODS

Thirty-two team sport players (male n = 16; female n = 16) were randomly, but equally divided into four groups: male milk, male carbohydrate, female milk, and female carbohydrate. Immediately following muscle damaging exercise, participants consumed either 500 ml of milk or 500 ml of an energy-matched carbohydrate solution. Skeletal troponin I (sTnI), creatine kinase (CK), peak torque, counter movement jump height, 20 m sprint performance and passive and active soreness were recorded prior to and 24, 48 and 72 h post-EIMD.

RESULTS

For females, milk had a likely/very likely beneficial effect on attenuating losses in peak torque at 60°/s from baseline to 24, 48 and 72 h, and a likely beneficial effect in minimising decrements in sprint performance and soreness over 72 h. Milk was unlikely to have a negative effect on serum markers of damage from baseline to 48 and 72 h. For males, milk had an unclear effect on muscle function variables. Milk had a most likely/likely beneficial effect on limiting muscle soreness from baseline to 72 h, and a possible beneficial effect on attenuating increases in CK. The effect on sTnI was unlikely to be negative from baseline-72 h. Overall gender comparisons provided many unclear outcomes. However, female participants demonstrated smaller increases in sprint time, passive soreness, active soreness (non-dominant leg) and sTnI values.

CONCLUSION

Consumption of 500 ml of milk post-EIMD can limit decrements in muscle function in females, and limit increases in soreness and serum markers of muscle damage in females and males.

Heat shock proteins in neurodegenerative disorders and aging

Many members of the heat shock protein family act in unison to refold or degrade misfolded proteins. Some heat shock proteins also directly interfere with apoptosis. These homeostatic functions are especially important in proteinopathic neurodegenerative diseases, in which specific proteins misfold, aggregate, and kill cells through proteotoxic stress. Heat shock protein levels may be increased or decreased in these disorders, with the direction of the response depending on the individual heat shock protein, the disease, cell type, and brain region. Aging is also associated with an accrual of proteotoxic stress and modulates expression of several heat shock proteins. We speculate that the increase in some heat shock proteins in neurodegenerative conditions may be partly responsible for the slow progression of these disorders, whereas the increase in some heat shock proteins with aging may help delay senescence. The protective nature of many heat shock proteins in experimental models of neurodegeneration supports these hypotheses. Furthermore, some heat shock proteins appear to be expressed at higher levels in longer-lived species. However, increases in heat shock proteins may be insufficient to override overwhelming proteotoxic stress or reverse the course of these conditions, because the expression of several other heat shock proteins and endogenous defense systems is lowered. In this review we describe a number of stress-induced changes in heat shock proteins as a function of age and neurodegenerative pathology, with an emphasis on the heat shock protein 70 (Hsp70) family and the two most common proteinopathic disorders of the brain, Alzheimer's and Parkinson's disease.

Benefits of estrogen replacement for skeletal muscle mass and function in post-menopausal females: evidence from human and animal studies

Age related loss of skeletal muscle mass and strength accelerates with the onset of menopause in women. Recent evidence from human and animal studies provides compelling evidence for the role of estrogen based hormone replacement therapy (HRT) in maintaining and enhancing muscle mass and strength and protecting against muscle damage. The physiological mechanisms by which estrogen can positively influence skeletal muscle mass and strength and protect against post-damage inflammation and disruption are also beginning to emerge. These less well known benefits of estrogen for skeletal muscle coupled with other benefits of estrogen to bone and metabolic health in older females provide further incentives for HRT use to enhance overall health in post-menopausal women. New research also attests to the safety of shorter term HRT in younger post-menopausal females. Overall the benefits of HRT to muscle health and function could assist in offsetting age related loss of muscle mass and function and delay age related morbidity and their use for overall health benefits in aging females should continue to be evaluated.

Extracellular heat shock protein 70 (HSPA1A) and classical vascular risk factors in a general population

Atherosclerosis is a chronic inflammatory and autoimmune disease. Candidate molecules/autoantigens include heat shock proteins (HSPs); Hsp70 (HSPA1A) is one of the best studied HSPs. Various studies have shown a correlation between extracellular Hsp70 (eHsp70) and anti-Hsp70/anti-Hsp60 antibody concentration and development of atherosclerosis. A random sample of 456 people aged 40-60 (218 males, 234 females) was studied to investigate the prevalence of traditional vascular risk factors and eHsp70 and anti-Hsp70/anti-Hsp60 antibodies levels, according to the risk of vascular disease. Task Force Chart was applied for classification. Subjects were divided into three groups: G0 (with no vascular risk factor or a risk lower than 5%), n = 239; G1 (moderated 10-20% risk, who do not have established disease) n = 161; and G2 (established atherosclerosis disease) n = 52. eHsp70 and anti-Hsp70 were significantly lower in the atherosclerosis group (group 2) with respect to the other groups. Disease-free people showed the highest anti-Hsp60 concentration compared with the other two groups. A correlation has not been demonstrated between the concentrations of circulating Hsp70 (HSPA1A), anti-Hsp70, and anti-Hsp60 and classical vascular risk factors and C-reactive protein. Low levels of eHsp70 and anti-Hsp70 antibodies should be considered as candidate FRV. Simultaneous decrease of eHsp70 and anti-Hsp70 antibodies would be explained by circulating immune complex formation, and both could be proposed as biomarkers for the progression of atherosclerotic disease. Levels of circulating anti-Hsp60 antibodies may constitute a marker of inflammation in atherosclerosis.

Evidence for sex differences in cardiovascular aging and adaptive responses to physical activity

There are considerable data addressing sex-related differences in cardiovascular system aging and disease risk/progression. Sex differences in cardiovascular aging are evident during resting conditions, exercise, and other acute physiological challenges (e.g., orthostasis). In conjunction with these sex-related differences-or perhaps even as an underlying cause-the impact of cardiorespiratory fitness and/or physical activity on the aging cardiovascular system also appears to be sex-specific. Potential mechanisms contributing to sex-related differences in cardiovascular aging and adaptability include changes in sex hormones with age as well as sex differences in baseline fitness and the dose of activity needed to elicit cardiovascular adaptations. The purpose of the present paper is thus to review the primary research regarding sex-specific plasticity of the cardiovascular system to fitness and physical activity in older adults. Specifically, the paper will (1) briefly review known sex differences in cardiovascular aging, (2) detail emerging evidence regarding observed cardiovascular outcomes in investigations of exercise and physical activity in older men versus women, (3) explore mechanisms underlying the differing adaptations to exercise and habitual activity in men versus women, and (4) discuss implications of these findings with respect to chronic disease risk and exercise prescription.

Influence of sex hormones and phytoestrogens on heart disease in men and women

Cardiovascular disease (CVD) is the number one cause of morbidity and mortality in men and women worldwide. According to the WHO, by 2015, almost 20 million people will die from CVD each year. It is well established that men and women differ not only in baseline cardiac parameters, but also in the clinical presentation, diagnosis and treatment outcomes of CVD. Women tend to develop heart disease later in life than men. This difference has been attributed to the loss of estrogen during the menopausal transition; however, the biological explanations for the sexual dimorphism in CVD are more complex and seem unlikely to be due to estrogen alone. The current controversy that has arisen regarding the effects of HRT on CVD in women is a case in point. In this review, the sex-based differences in cardiac (patho-) physiology are discussed with emphasis on the impact of sex hormones, hormone receptors and diet on heart disease.

The influence of estrogen on skeletal muscle: sex matters

As women enter menopause, the concentration of estrogen and other female hormones declines. This hormonal decrease has been associated with a number of negative outcomes, including a greater incidence of injury as well as a delay in recovery from these injuries. Over the past two decades, our understanding of the protective effects of estrogen against various types of injury and disease states has grown immensely. In skeletal muscle, studies with animals have demonstrated that sex and estrogen may potentially influence muscle contractile properties and attenuate indices of post-exercise muscle damage, including the release of creatine kinase into the bloodstream and activity of the intramuscular lysosomal acid hydrolase, beta-glucuronidase. Furthermore, numerous studies have revealed an estrogen-mediated attenuation of infiltration of inflammatory cells such as neutrophils and macrophages into the skeletal muscles of rats following exercise or injury. Estrogen has also been shown to play a significant role in stimulating muscle repair and regenerative processes, including the activation and proliferation of satellite cells. Although the mechanisms by which estrogen exerts its influence upon indices of skeletal muscle damage, inflammation and repair have not been fully elucidated, it is thought that estrogen may potentially exert its protective effects by: (i) acting as an antioxidant, thus limiting oxidative damage; (ii) acting as a membrane stabilizer by intercalating within membrane phospholipids; and (iii) binding to estrogen receptors, thus governing the regulation of a number of downstream genes and molecular targets. In contrast to animal studies, studies with humans have not as clearly delineated an effect of estrogen on muscle contractile function or on indices of post-exercise muscle damage and inflammation. These inconsistencies have been attributed to a number of factors, including age and fitness level of subjects, the type and intensity of exercise protocols, and a focus on sex differences that typically involve factors and hormones in addition to estrogen. In recent years, hormone replacement therapy (HRT) or estrogen combined with exercise have been proposed as potentially therapeutic agents for postmenopausal women, as these agents may potentially limit muscle damage and inflammation and stimulate repair in this population. While the benefits and potential health risks of long-term HRT use have been widely debated, controlled studies using short-term HRT or other estrogen agonists may provide future new and valuable insights into understanding the effects of estrogen on skeletal muscle, and greatly benefit the aging female population. Recent studies with older females have begun to demonstrate their benefits.

The level of Hsp27 in lymphocytes is negatively associated with a higher risk of lung cancer

Heat shock proteins (Hsps) can protect cells, organs, and whole organisms against damage caused by abnormal environmental hazards. Some studies have reported that lymphocyte Hsps may serve as biomarkers for evaluating disease status and exposure to environmental stresses; however, few epidemiologic studies have examined the associations between lymphocyte Hsps levels and lung cancer risk. We examined lymphocyte levels of Hsp27 and Hsp70 in 263 lung cancer cases and age- and gender-matched cancer-free controls by flow cytometry. Multivariate logistic regression models were used to estimate the association between lymphocyte Hsps levels and lung cancer risk. Our results showed that Hsp27 levels were significantly lower in lung cancer cases than in controls (16.5 vs 17.8 mean fluorescence intensity, P < 0.001). This was not observed for Hsp70 levels. Further stratification analysis revealed that lymphocyte Hsp27 levels were negatively associated with lung cancer risk especially in males and heavy smokers. There was a statistical trend of low odd ratios (95% confidence intervals) and upper tertile levels of Hsp27 [1.000, 0.904 (0.566-1.444) and 0.382 (0.221-0.658, P (trend) = 0.001) in males and 1.000, 0.9207 (0.465-1.822) and 0.419 (0.195-0.897, P (trend) = 0.036) in heavy smokers] after adjustment for confounding factors. These results suggest that lower lymphocyte Hsp27 levels might be associated with an increased risk of lung cancer. Our findings need to be validated in a large prospective study.

Exercise training-induced gender-specific heat shock protein adaptations in human skeletal muscle

This study investigates the effects of short-term endurance training on heat shock protein (HSP) adaptations of male and female human skeletal muscle. The data demonstrate that females did not respond to continuous or interval training in terms of increasing HSP content of the vastus lateralis muscle. In contrast, males displayed HSP adaptations to both training interventions. These data provide a platform for future human studies to examine a potential gender-specific stress response to exercise.

Exercise physiologists talk about sex differences

The number of publications addressing sex differences and exercise physiology has increased from 12, before 1970, to as many as 1344 through October 2007, according to a recent PubMed search. The following symposium represents three distinct examples of how exercise physiologists are approaching the issue of sex differences in various aspects of physiology. Tarnapolsky presents data from studies of sex and sex hormone effects on substrate use, a factor that may distinguish between the capacities of women and men to excel at exercise performance at different durations and intensities. Harms and Rosenkranz provide insight into the potential limitations of respiratory function at increased exercise intensities in the female sex attributable, in part, to sex-based anatomic differences in respiratory anatomy. Milne and Noble discuss important findings concerning the cardioprotective aspect of exercise-induced heat shock proteins versus the inherent cardioprotection of elevated estradiol concentrations in young women. Each paper demonstrates the novel methodology and sophisticated research designs currently being employed to discern sex differences and sex hormone effects on various aspects of exercise physiology.