Integrative myofibrillar protein synthesis does not differ between young to middle-aged males and females

Dietary protein ingestion stimulates myofibrillar protein synthesis (MPS) to support adequate quality and quantity of skeletal muscle protein mass. Hence, the stimulation of MPS is essential for maintaining or improving physical performance and overall quality of life. However, whether sexual dimorphism exists on the regulation of daily MPS remains largely unknown. Objectives: This study aimed to conduct a secondary analysis on participants consuming moderate to high protein intake to determine whether differences exist between males and females in free-living MPS. Hypothesis: We hypothesized that there would be no differences in integrated daily free-living MPS between males and females. Methods: Sixty males and females (mean age 32 ± 11 years; BMI: 25.3 ± 3.7 kg·m 2 ; 40 males, 20 females) were loaded (5 mL·kg -1 ) with deuterated water (D 2 O) and subsequently consumed daily maintenance doses (0.625 mL·kg -1 ·d -1 ) during a short-term (1 week) resistance training program. Saliva and muscle biopsies were collected at baseline and after 1 week of the intervention to measure total body water (TBW) enrichment and MPS. MPS was calculated from the change in myofibrillar protein-bound enrichments between muscle biopsies and TBW enrichment multiplied by 3.7. Data were analyzed using mixed effects models. Results: All participants consumed dietary protein levels greater than the current RDA (1.14 ± 0.05 g·kg -1 ·d -1 ). There were no differences in MPS between males (1.68 ± 1.64 %·d -1 ) and females (1.70 ± 2.07 %·d -1 ). Discussion: We demonstrated that integrated MPS do not differ between males and females. Our integrative MPS results corroborate findings from acute MPS studies that show sex is not a regulatory factor for muscle protein turnover in healthy young and middle-aged adults. This study was funded by the Beef Checkoff This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.