Muscle Gains Boost from Re-Training After Exercise Breaks, Study Shows

Recent research suggests that taking a pause from endurance training does not negate muscle development; in fact, retraining can lead to even greater muscle growth. A study conducted on mice demonstrated that animals which engaged in voluntary running on a wheel for four weeks, paused for four weeks, and then resumed training for another four weeks experienced unexpected and significant muscle gains. Notably, the second training phase resulted in larger muscle fibers compared to the initial session, despite the mice exercising less intensely during this period.

The investigators from the University of Illinois at Urbana-Champaign explored the molecular basis of this phenomenon. They found that gene expression related to mitochondrial function was significantly enhanced after the second bout of exercise. Mitochondria, known as the energy factories of cells, seem to play a critical role in muscle memory, priming the muscles to respond more vigorously upon retraining.

Interestingly, even when the mice were subjected to a high-fat diet that typically impairs muscle development, the repeated exercise still produced comparable muscle growth, indicating that the exercise-induced muscle memory could override dietary disadvantages.

The research also involved a washout period to assess whether initial adaptations from exercise dissipated over time. Results showed that most early adaptations faded during this break, yet the benefits of the second exercise bout persisted and led to increased muscle mass—up to 30% more in the legs. The gene analysis suggested that the mitochondria’s boost was key to this enhanced response.

Professor Diego Hernandez-Saavedra and Ph.D. candidate Clay Weidenhamer highlighted that exercise intensity and mitochondrial health are vital, with aerobic activity contributing to muscle growth—a concept sometimes underestimated compared to weight training. Their findings open new avenues for strategies aimed at preserving muscle health during aging or counteracting effects of poor diet, potentially leading to interventions for frailty and metabolic disorders.

This study, published in the American Journal of Physiology-Cell Physiology, emphasizes the importance of mitochondrial function and muscle memory in physical training, providing promising insights for both health professionals and fitness enthusiasts.

Source: https://medicalxpress.com/news/2025-09-retraining-lapse-muscle-gains.html