Ladder resistance training (LRT) provides sufficient mechanical stimulation to induce increases in cross‐sectional area in most types of skeletal muscle; however, some types of muscles with certain m...

During almost one-third of our life, maturation of the nervous system promotes strength and muscle mass increase. However, as age advances, the nervous system begins to suffer a slow and continue reduction of its functions. Neuromuscular junction (NMJ) is one of the structures of which change due to aging process. Physical training leads to significant adjustments in NMJs of young and aged animals. Nevertheless, studies that aimed to investigate this effect have, in many cases, methodological variables that may have some influence on the result. Thus, this study aimed to carry out a systematic review about the effects of exercise training on the NMJ compartments of young, adult and aged animals. We searched PubMed, Google Scholar, Science Direct, Scielo and Lilacs databases for animal experimental studies that studied exercise effects on the NMJs components across age. After inclusion and exclusion criteria, we included nine articles in systematic review and two for meta-analysis (young/adult NMJ). We identified that exercise training cause NMJ hypertrophy on young animals and NMJ compression on aged ones. However, many methodological issues such as age, skeletal muscle and fibers type, and type of exercise and training protocol might influence the results.

Thirty male 20-months-old Wistar rats were divided into groups: IC – initial control (n = 6), FC – final control (n = 6), AC – anabolic hormone control (n = 6), ST - strength trained (n = 6) and STA - strength trained with anabolic hormone (n = 6). All groups were submitted to adaptation, familiarization and maximum load carrying test (MLCT). Strength training (6-8x / session with loads of 50 to 100% MLCT, 3x/week and pause of 120 seconds) was performed in ladder climbing for 15 weeks. The administration of testosterone (TP) was performed 2x/week (10 mg/kg) in animals in the AC and STA groups. After the experimental period, animals were euthanized and the tibial nerve and plantaris muscle removed and prepared for electron transmission and histochemistry. To compare the groups we used one-way ANOVA (post hoc Bonferroni), student's t-tests for pre vs post (dependent and independent variables) comparisons and significance level set at p ≤ 0.05. The following significant results were found: a) aging decreased the number of myelinated axon fibers; b) use of isolated TP increased the diameter of myelinated fibers, along with increased thickness of myelin sheath.; c) ST increased area of myelinated and unmyelinated fibers, together with the myelin sheath. These changes made it possible to increase the area occupied by myelinated fibers keeping their quantity and also reduce the interstitial space; d) association of anabolic steroid and ST increased the area of unmyelinated axons and thickness of the myelin sheath. Compared to ST, both strategies have similar results. However, Schwann cells increased significantly only in this strategy.