Leucine supplementation does not attenuate the decline in daily muscle protein synthesis rates or preserve leg muscle mass during leg immobilization in young or older adults: a double-blind randomized trial
Study Details
This double-blind randomised trial examined whether leucine could preserve muscle protein synthesis (MPS) and muscle mass during 3 days of unilateral leg immobilisation in 48 recreationally active adults 🔍
Participants included 24 younger adults (~23 y) and 24 older adults (~69 y), with an equal male split 👥
They consumed either 5 g leucine or 5 g carbohydrate 3×/day with their main meals during immobilisation 🥄
Key Findings
📉 Daily MPS was ~15% lower in the immobilised versus non-immobilised leg in younger adults
📉 In older adults, MPS fell by ~23%, indicating a greater suppression of protein synthesis during disuse
↔️ However, leucine did not attenuate the reduction in MPS in either age group
🦵 Quadriceps cross-sectional area decreased by ~1.2% in younger adults and ~1.1% in older adults after only 3 days
↔️ Leucine also failed to preserve quadriceps muscle size versus carbohydrate placebo
👴 Although older adults experienced a larger suppression of MPS, the actual rate of muscle loss was not significantly different between age groups
⚡ These findings highlight how rapidly muscle tissue responds to disuse, with measurable atrophy developing in just a few days
🧬 Leucine can stimulate MPS under normal conditions, but during immobilisation this anabolic signal appears insufficient to overcome disuse-induced anabolic resistance
⚠️ The study examined only 3 days of complete leg immobilisation, so findings may differ during longer periods, partial loading or rehabilitation
Conclusion
During injury or immobilisation, leucine alone should not be expected to preserve muscle; maintaining safe mechanical loading where possible, alongside sufficient total protein and rehabilitation strategies, is likely to be more important ✅
Reference
https://www.sciencedirect.com/science/article/pii/S0002916526000146
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