Does testosterone increase muscle protein synthesis and lean mass?

Testosterone functions as a potent anabolic regulator of skeletal muscle, particularly relevant for maintaining physical function and metabolic health during aging. While often discussed in a male context, research confirms that testosterone significantly influences muscle protein dynamics and body composition in women.

Clinical evidence and effectiveness

Clinical studies, including randomized controlled trials (RCTs) in postmenopausal women, demonstrate that testosterone administration enhances lean body mass and reverses aspects of sarcopenia.

• Muscle Protein Synthesis (MPS): Testosterone significantly increases the muscle protein fractional synthesis rate. In studies of postmenopausal women, testosterone administration has been shown to boost MPS by approximately 50%.
• Body Composition: Longitudinal data indicates that supplemental testosterone increases lean mass and improves muscle strength. These effects are particularly pronounced when baseline levels are low, suggesting a restorative role for the hormone in aging populations.
• Metabolic Correlation: Increases in lean mass are associated with improved glucose disposal capacity, as skeletal muscle serves as the primary site for insulin-mediated glucose uptake.

Mechanistic explanations

The anabolic effects of testosterone are mediated through genomic and non-genomic pathways within the myofibers:

• Androgen Receptor (AR) Signaling: Testosterone binds to the AR, which then translocates to the nucleus to act as a transcription factor. This upregulates myogenic genes such as MYOD1 and FST (follistatin), which promote muscle growth and satellite cell activation.
• Intracellular Pathways: Testosterone modulates anabolic tone via the Akt/mTORC1 signaling pathway, a master regulator of protein translation. While some studies in women show gains in muscle mass without significant changes in specific downstream markers like S6K1, the overall metabolic shift remains strongly anabolic.
• Protein Degradation: Emerging evidence suggests testosterone may also preserve muscle by suppressing degradation pathways, specifically those mediated by FoxO3a, thereby balancing protein turnover in favor of synthesis.

Bottom line

Testosterone is a robust anabolic agent that increases muscle protein synthesis and lean mass in women. It works through androgen receptor-mediated signaling to upregulate growth-related genes and stimulate protein translation via the mTORC1 pathway.