As the elderly population is steadily growing worldwide, sarcopenia, the loss of muscle mass and strength due to aging, is becoming a bigger issue all over the world with notable effect on elderly health. In 2016, the World Health Organization (WHO) assigned a disease code (M63.84) to sarcopenia, emphasizing on the need for treatment development. Probiotics, live microorganisms advantageous to health, have gained attention as a potential treatment, but may cause adverse effects in immunocompromised individuals. This study investigates postbiotics—non-living bacterial products or metabolites—as safer option with immune-modulatory, antioxidant, and lipid metabolism-regulating effects. Animal experiments were conducted on 6-week-old male SD-rats to assess muscle mass and strength. Postbiotics MPG-1 prevented the loss of muscle mass and alleviated muscle strength reduction caused by dexamethasone. Molecular analysis showed postbiotics MPG-1 decreased the expression of Atrogin-1 and MuRF1, proteins involved in muscle protein degradation in the PI3K/AKT pathway, and reduced FoxO3a expression, a transcription factor that promotes autophagy. Additionally, AKT phosphorylation levels increased with postbiotics MPG-1 treatment. Further histological analyses and long-term studies are needed to confirm the link between these molecular changes and muscle fiber structure. This research gives precious intuition for sarcopenia treatment strategies.