The gut-muscle-brain axis, acting as a three-dimensional interactive network that mediates neurodegenerative diseases and sarcopenia, plays a core regulatory role in the pathological progression of Parkinson’s disease (PD). This article provides a systematic review of how gut microbiota dysbiosis within this axis influences the balance of muscle protein synthesis and degradation via microbial metabolites, how myokines secreted by skeletal muscle in turn modulate neuroinflammation and the function and integrity of the intestinal barrier, and the molecular mechanisms underlying the bidirectional propagation of α-synuclein among the gut, muscle, and brain. Incorporating the latest clinical evidence, it further explores targeted intervention strategies such as probiotics and combined exercise-nutrition approaches, aiming to offer new perspectives for the precision prevention and management of sarcopenia in elderly PD patients.