The effect of resistance exercise on the immune cell function in humans: A systematic review

BACKGROUND

Resistance exercise is beneficial for the immune system, including decreased susceptibility to infections and improved effectiveness of vaccinations. This review aims to provide a systematic analysis of the literature regarding the impact of resistance exercise on immune cells in the blood circulation.

MATERIALS AND METHODS

The protocol of this review followed the PRISMA guidelines and registered in PROSPERO (ID: CRD42020157834). PubMed and Web-of-Science were systematically searched for relevant articles. Outcomes were divided into two categories: 1) inflammatory gene expression or secretion of inflammation-related cytokines and 2) other aspects such as cell migration, proliferation, apoptosis, phagocytosis, and redox status.

RESULTS

Thirty intervention studies were included in this review, of which 11 articles were randomized controlled trials and six non-randomized controlled trials. Although only resistance exercise interventions were included, there was a high heterogeneity regarding specific exercise modalities. The most frequently studied outcome measures were the gene and protein expression levels in peripheral blood mononuclear cells (PBMC). This review reveals that already one acute exercise bout activates the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway in PBMC. Although resistance exercise induces an acute cytosolic oxidative stress response, the antioxidant enzyme expression is improved after resistance training period. Natural killer cell activity increases in older but decreases in younger adults immediately after a resistance exercise bout. Moreover, resistance exercise improves neutrophil phagocytic activity. Finally, effects on lymphocyte proliferation remain unclear.

CONCLUSIONS

The results of this systematic review demonstrate that resistance exercise has beneficial effects on several aspects of immune cell function both in young and older individuals. Acute changes in immune cell function occur already after a single bout of resistance exercise. However, regular resistance training during several weeks seems necessary to obtain beneficial adaptations that can be related to better immunity and reduced inflammation. The effects documented in this review confirm the beneficial effects of resistance exercise in young as well as older persons on the immune cell function.

Relative energy deficiency in sports (RED-S): elucidation of endocrine changes affecting the health of males and females

The purpose of this review is to present a different perspective of the relative energy deficiency syndrome, to improve understanding of associated endocrine alterations, and to highlight the need for further research in this area. The term "female athlete triad" was coined over 25 years ago to describe three interrelated components: disordered eating, menstrual dysfunction, and low bone mass. The syndrome's etiology is attributed to energy intake deficiency relative to energy expenditure required for health, function, and daily living. Recently, it became clear that there was a need to broaden the term, as the disorder is not an issue of only three interrelated problems but of a whole spectrum of insults resulting from low energy availability (LEA; i.e., insufficient energy availability to cover basic physiological demands) that can potentially affect any exerciser, irrespective of gender. The new model, termed relative energy deficiency in sport (RED-S), has received greater scrutiny in sports medicine due to its effects on both health and performance in athletes of both sexes. RED-S results from low-energy diets (intentional or unintentional) and/or excessive exercise. Energy deficiency reduces hypothalamic pulsatile release of gonadotropin-releasing hormone, this impairing anterior pituitary release of gonadotropins. In women, reduced FSH and LH pulsatility produces hypoestrogenism, causing functional hypothalamic amenorrhea and decreased bone mass. In men, it reduces testosterone and negatively affects bone health. Moreover, LEA alters other hormonal pathways, causing physiological consequences, such as alteration of the thyroid hormone signaling pathways, leptin levels, carbohydrate metabolism, the growth hormone/insulin-like growth factor-1 axis, and sympathetic/parasympathetic tone. This review explains and clarifies the effects of RED-S in both sexes.

Exercise Regulates the Immune System

The profound effect of exercise on the normal functioning of the immune system has been well-known. Exercise and immune regulation are interrelated and affect each other. Exercise changes immune regulation by affecting leucocytes, red blood cells, and cytokines, etc. Regular exercise could reduce the risk of chronic metabolic and cardiorespiratory diseases, partially by the anti-inflammatory effects of exercise. However, these effects are also likely to be responsible for the suppressed immunity that make our bodies more susceptible to infections. Here we summarize the known mechanisms by which exercise-both acute and chronic-exerts its immune regulation effects.

Establishing a dose-response relationship between acute resistance-exercise and the immune system: Protocol for a systematic review

Exercise immunology research has traditionally focussed on aerobic-exercise, however it has become apparent in more recent years that resistance-exercise can also considerably affect host immunobiology. To date however, no systematic process has been used to establish a dose-response relationship between resistance-exercise and the immune system. The present systematic review was thus conducted to determine the dose-response effects of a bout of resistance-exercise on acute leukocyte counts. In accordance with the PRISMA guidelines, a systematic literature search was conducted in the electronic databases, PubMed, Web of Science, and Google Scholar, over the date range of 1989-2016. Following the PICO elements, eligibility criteria included: i) participants: healthy humans aged 18-40; ii) intervention: a single bout of resistance-exercise; iii) comparator: at least one comparator group; iv) outcome: acute measures of circulating leukocyte counts. Specific exclusion criteria were also applied. Risk of bias and quality of evidence was assessed using the PEDro scale. Due to the individual designs of the admitted studies, a qualitative analysis (systematic narrative synthesis) was employed in the present review. The results of the present review demonstrate that a single bout of resistance-exercise induces an acute monocytosis, neutrophilia, and lymphocytosis. It became apparent that the reviewed literature either does not consistently specify, or does not describe with sufficient detail, the time-course between the onset of exercise and the collection of blood. We recommend that researchers consider addressing this in future studies, and also collect blood measures during exercise to aid with comparison of temporal effects. Regarding the determination of a dose-response relationship, an acute neutrophilia, monocytosis and lymphocytosis appears to occur more rapidly and to a greater magnitude following a single bout of high-dose vs low-dose resistance-exercise. Mechanistically, exercise-induced cell trafficking changes are associated with mechanical, metabolic and endocrine factors. Physical aptitude of the host may also affect resistance-exercise-induced lymphocyte trafficking responses.

Effects of prolonged exercise on agouti-related protein: a pilot study

Agouti-related protein (AgRP), is a signaling peptide that affects feeding behavior, energy homeostasis, and has also been shown to stimulate the hypothalamic-pituitary-adrenal axis. The purpose of this study was to determine the effects of 90 min of treadmill exercise on circulating AgRP concentrations and the relationship of AgRP responses to cortisol. Seven young males completed a preliminary trial followed by counterbalanced experimental and control trials 4-5 weeks apart. The experimental trial began 2.5 h after consumption of a standard nutrient beverage and consisted of treadmill exercise at 60 % of previously determined VO(2max) for 90 min. Blood samples were collected before (-30 and 0 min), during (18, 36, 54, 72, and 90 min), and following exercise (20, 40, and 60 min). Blood samples were collected in a resting, control trial at the same time points as the experimental trial. Plasma lactate was significantly higher in the exercise than the control trial. Although AgRP increased from 18 min of exercise to peak at 90 min, these increases were not significantly different than values in the control trial. Cortisol responses during the exercise trial were significantly higher than the control trial. AgRP concentrations during early exercise were positively correlated with cortisol levels later in recovery. The obtained data suggest that AgRP concentrations during prolonged steady-state exercise are associated with subsequent cortisol increases, but further study is required to determine whether there is a causal effect.

The effect of exercise intensity on plasma and tissue acyl ghrelin concentrations in fasted rats

OBJECTIVE

This study was conducted to investigate the effect of exercise training and feeding status on plasma and tissue acyl ghrelin concentrations.

MATERIALS AND METHODS

Thirty-two, eight-week-old male Wistar rats (185±5g) were randomly assigned to one of four groups: high intensity (HI: 34 m/min ~80-85% VO(2)max), moderate intensity (MI: 28 m/min ~70-75% VO(2)max), low intensity (LI: 20 m/min ~50-55% VO(2)max), and sedentary control (SED) groups. All experimental groups performed a 12-week exercise program consisting of treadmill running on a 0° slope for 1 h/day, 5 days/week at their respective training intensity. Twenty four hours following the last training session the animals completed a 12h fast. Rats were then killed, blood was collected and plasma separated; the fundus and soleus muscle were excised and frozen in liquid nitrogen for later analysis. Fasting levels of circulating acyl ghrelin and acyl ghrelin content in the soleus muscle and fundus, as well as glycogen in the soleus muscle were measured. Data were analyzed using one-way ANOVA.

RESULTS

Results demonstrated that 12 weeks of exercise training combined with a 12h fast significantly increased plasma as well as soleus muscle concentrations of acyl ghrelin in the HI and MI groups (p<0.05) and reduced acyl ghrelin concentrations in the fundus (p<0.05).

CONCLUSION

The results of the study indicate that chronic treadmill exercise training enhances fasting plasma acyl ghrelin in an intensity-dependent manner which is accompanied by a significant increase in soleus muscle and reduction in fundus acyl ghrelin levels.