Why Your Training Isn't Building Muscle Anymore in Perimenopause, and How to Fix It

Sims sets up the perimenopausal transition as a period where the usual adaptive response to training is blunted because estrogen directly modulates myosin. Without sufficient estrogen signaling, muscles lose integrity and don't hypertrophy from moderate work. The fix is to dramatically alter the training stress: pick up heavy weights. This forces the neuromuscular system into a high-demand state, ensuring that the contractile proteins get a clear 'grow' signal. It's not just about lifting—it's about lifting with enough load that you can't easily breeze through; volume goes down so that intensity can stay high, avoiding the cortisol spike of prolonged sessions. She stresses this can be initiated even years after menopause, because the desensitization persists, and the body still needs those external mechanical signals.

Sims highlights protein as a critical but often underestimated piece for women who have historically been cautious about eating ample protein. She positions protein timing around lifting as a way to capitalize on the anabolic window created by heavy training. For endurance athletes who may be used to carb-centric fueling, this is a mindset shift. The recommendation is not just a general 'eat more protein' but strategically linking it to the moments when muscle is most receptive to repair signals.

Sims draws on her own experience as an Ironman and competitive cyclist to empathize with the shock of this advice, but she is adamant that the physiology demands it. She describes the classic endurance athlete's plateau: feeling stuck, doing hours of moderate work, and getting slower or softer. The root cause is a mismatch between the stress applied and the body's hormonal state. By flipping the model—building resilience and strength through high intensity first—the body can actually handle and benefit from some endurance later. It’s a periodized shift where speed and power become the foundation, not an afterthought.

Sims argues that estrogen has abundant receptor sites on myosin, one of the key contractile proteins. As estrogen levels fluctuate and eventually fall during the perimenopausal transition, those receptors become desensitized, meaning myosin no longer responds robustly to the usual contraction signals. Consequently, muscle fibers don't generate as much force and are less likely to undergo repair and hypertrophy from moderate training. The solution is not just 'keep training' but to introduce a stress that bypasses this desensitization: heavy lifting that forces the nervous system to recruit a large number of muscle fibers, thereby sending a strong signal to myosin that it must work and regenerate. This concept shifts the focus from hormonal supplementation to mechanical override.

Sims notes that once women hit menopause and the hormone fluctuations settle, the body becomes exceptionally efficient at 'long and slow' efforts, which can lead to a progressively slower pace and stalled body composition improvements. The common habit of doing 2–4 hour moderate sessions raises baseline cortisol, and with cortisol already elevated in this phase, the body gets a signal to break down lean mass—since active muscle tissue is energetically costly—rather than building it. Additionally, that level of stress isn't strong enough to stimulate protein muscle synthesis or a robust central nervous system response. Therefore, she flips the hierarchy: use high-intensity work to maintain power and speed, build resilience, and only then add in some endurance. Coming from an Ironman, rowing, and bike racing background herself, she acknowledges the mental hurdle but insists the body needs this prioritization to preserve lean mass and performance.