The concept of “muscle memory” is well established, referring to the phenomenon whereby previously developed muscle can be regained more readily following a period of detraining. It is commonly believed that these effects are attributed to additional nuclei acquired during training, which are permanently retained even if you stop working out. But is this really how muscle memory works? A recent review by Serrano et al (PMID: 40768525) challenges this conventional explanation, suggesting that the mechanisms underlying muscle memory may be more complex than previously thought. Some key takeaways: --Although short periods of detraining generally result in little change in myonuclear number, evidence from both animal and human studies suggests that myonuclei may be lost with prolonged detraining or muscle atrophy. At a minimum, the evidence remains conflicting, calling into question the notion that myonuclei are permanently retained. --Methods matter. Accurately counting myonuclei is technically challenging, and differences in measurement techniques may help explain conflicting findings. --The mechanisms remain unresolved. Retained myonuclei may contribute to muscle memory under certain conditions, but the evidence does not establish that they are the sole—or necessarily primary—mechanism. --Other factors may contribute. Persistent molecular adaptations, particularly epigenetic changes that regulate gene expression, have been shown to enhance the hypertrophic response when resistance training is resumed (e.g., PMID: 40183698). Bottom line: Muscle memory is a well-established phenomenon, but the notion that it is driven solely by the permanent retention of myonuclei is increasingly being questioned. While retained myonuclei may contribute to this effect, lasting molecular modifications may also play an important role in facilitating muscle regrowth when training resumes. pmc.ncbi.nlm.nih.gov/article…