Health Benefits of Endurance Training: Implications of the Brain-Derived Neurotrophic Factor—A Systematic Review

Hindawi Neural Plasticity Volume 2019, Article ID 5413067, 15 pages https://doi.org/10.1155/2019/5413067 Review Article Health Benefits of Endurance Training: Implications of the Brain-Derived Neurotrophic Factor—A Systematic Review Włodzimierz Mrówczyński Department of Neurobiology, Chair of Biological Sciences, Poznan University of Physical Education, 27/39 Królowej Jadwigi St., 61-871 Poznań, Poland Correspondence should be addressed to Włodzimierz Mrówczyński; Received 2 November 2018; Revised 7 February 2019; Accepted 24 February 2019; Published 24 June 2019 Academic Editor: Xavier Navarro Copyright © 2019 Włodzimierz Mrówczyński. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article presents a concept that wide expression of brain-derived neurotrophic factor (BDNF) and its receptors (TrkB) in the nervous tissue, evoked by regular endurance training (ET), can cause numerous motor and metabolic adaptations, which are beneficial for human health. The relationships between the training-evoked increase of endogenous BDNF and molecular and/or physiological adaptations in the nervous structures controlling both motor performance and homeostasis of the whole organism have been presented. Due to a very wide range of plastic changes that ET has exerted on various systems of the body, the improvement of motor skills and counteraction of the development of civilization diseases resulting from the posttraining increase of BDNF/TrkB levels have been discussed, as important for people, who undertake ET. Thus, this report presents the influence of endurance exercises on the (1) transformation of motoneuron properties, which are a final element of the motor pathways, (2) reduction of motor deficits evoked by Parkinson disease, and (3) prevention of the metabolic syndrome (MetS). This review suggests that the increase of posttraining levels of BDNF and its TrkB receptors causes simultaneous changes in the activity of the spinal cord, the substantia nigra, and the hypothalamic nuclei neurons, which are responsible for the alteration of the functional properties of motoneurons innervating the skeletal muscles, for the enhancement of dopamine release in the brain, and for the modulation of hormone levels involved in regulating the metabolic processes, responsively. Finally, trainingevoked increase of the BDNF/TrkB leads to a change in a manner of regulation of skeletal muscles, causes a reduction of motor deficits observed in the Parkinson disease, and lowers weight, glucose level, and blood pressure, which accompany the MetS. Therefore, BDNF seems to be the molecular factor of pleiotropic activity, important in the modulation processes, underlying adaptations, which result from ET. 1. Introduction Endurance activity is a natural form of movement based on aerobic metabolism and repeated isotonic contractions of large skeletal muscles [1, 2]. Cycling, running, and swimming performed at low intensities from minutes to hours by at least several weeks are classical examples of such activity [2, 3]. It is commonly known that endurance training (ET), which is a form of organized and planned endurance activity, brings many health benefits by improving or restoring physical condition. Therefore, it is used not only for sport purposes but also for rehabilitation of patients with neuromuscular [4], cardiovascular [5], and metabolic [6] diseases. The influence of ET on the skeletal muscles is well known. Regular exercises increase both the density of capillaries in muscle fibers and the flow of blood to whole active muscles [7]. Moreover, endurance activity increases maximal oxygen uptake [8] and improves the ability of the skeletal muscles to produce energy through oxidative metabolism [3] due to an increase in the number and size of mitochondria in trained muscles [9]. Endurance intervention enhances the muscles oxidative capacity [10, 11], triggers the muscle to 2 produce more efficient forms of contractile proteins [12], and modifies the motor unit proportions towards more resistance subtypes [13]. However, ET not only evokes adaptive change in the morphological, metabolic, and contractile properties of trained muscles but also exerts numerous effects on tissues and organs located outside of the activated muscles, thus improving physical competence of the whole organism [14]. Regular endurance effort alterates the functional action of spinal motoneurons, which control the activity of the skeletal muscles [15–17], prevents metabolic syndrome (MetS) [18], regulates fat metabolism [19], decreases blood glucose levels [20], delays the onset of type 2 diabetes [21], and finally reduces the risk of cardiovascular diseases and heart complications and improves the cardiac function [1, 22]. Next, endurance activity also counteracts and delays the development of some neurodegenerative diseases [23, 24] and mental disorders [25]. Moreover, ET can influence the activity of hormonal [26] and immune systems [27], upregulate the level of endogenous antioxidant enzymes [28], improve the mechanical properties and mineral density of bones [29], counteract the risk of osteoporosis [30], and delay the aging processes [31]. Benefits of ET for health are so evident that this type of physical activity has been considered as a drug [32], leading to improvements in life quality and reduction of hospital admission risks [33]. Moreover, ET is often recommended as “a cornerstone in the prevention, management, and treatment of numerous chronic conditions” such as obesity, type 2 diabetes, hypertension, or coronary heart disease [34]. Up to date, reports addressing various physiological and metabolic consequences of endurance exercises [35–38], which are accessible in the PubMed databases, count more than 370000 entries. However, the described physiological, biochemical, and molecular mechanisms behind the numerous adaptations resulting from ET come from studies performed on rodents rather than human beings because it is “difficult to use humans to examine exercise training alterations in many molecular systems as well as most organ systems” [39]. Specifically, majority of studies have been performed on rats (Rattus norvegicus) or mice (Mus musculus), because these species share many common structural and functional similarities with humans and hence may shed a light on physiological mechanisms behind the observed effects of endurance exercises [40] and create a possibility to compare obtained results to these performed in humans during compatible effort intensities [41]. Experiments performed on rodents undergoing controlled ET [42] enable obtaining many biochemical, toxicological, or genetic details [43] related to the impact of endurance activity on mammalian organisms. Despite the fact that most of the studies on the effects of ET were carried out on rodents, t (...truncated)