The aim of this study was to evaluate the effect of long-term running training on muscle strength of men aged 50 and above. The study involved two groups of men aged 50 and above: physically active (E, n = 34) and inactive (NE, n = 20). Body composition was assessed with the electrical bioimpedance method. The isometric maximum voluntary contraction (MVC) was the main measurement. The value of muscle torque achieved by a group of synergists (operating in the given joint) during a short isometric contraction was evaluated. Ten groups of flexor and extensor muscles of the elbow, shoulder, hip, knee, and torso joints were measured. In addition, a 3 s measurement of grip strength of the right (Fr) and left (Fl) hand was taken using a hand dynamometer. The obtained values enabled to calculate the symmetry index (SI). Men who had been running regularly were characterized by a significantly lower strength level (p < .05). Results in the NE group were determined to a great extent by significantly different body weights (p < .001) and a significantly higher body fat mass (FAT) content (p < .001). SI was statistically higher in the reference group (p < .05). Long-distance run training reduces FAT while maintaining a high level of muscle strength. These studies indirectly confirm the effect of strengthening slow-twitch motor units in men aged 50 (Doherty & Brown 1993; Kanda & Hashizume 1989). In addition, stimulating the body through physical effort helps it also to maintain a high level of strength symmetry, which is a preventive factor in reducing the number of injuries.
Keywords: body composition; muscle strength; running training; sarcopenia; symmetry.