Rethinking Aging: A Systems-Based Model of Neuromuscular Decline

As we age, the gradual loss of motor units — vital nerve-muscle connections — undermines movement control and coordination. Contrary to the view that this decline is confined to individual muscles, research on lifelong athletes reveals that even with targeted training, widespread motor unit degradation still occurs. This paper introduces the Systemic Motor Unit Integrity Hypothesis, which proposes that maintaining neuromuscular health requires body-wide activation, not just localized efforts. According to this model, degradation in undertrained areas can destabilize the entire neuromuscular network, leading to reduced synchronization, impaired control, and systemic decline, even in strong muscle groups. To explain this, the Network Degradation Model is presented, framing aging as a cascading breakdown of neural signals triggered by regional motor unit loss. This perspective shifts the focus from isolated muscular atrophy to preserving whole-system coherence, with implications for future training strategies, intervention design, and research on movement longevity.