The Diary of a CEODr. Stacy Sims: Why women need different training rules
Sports scientist Stacy Sims explains why male-data fitness backfires; cycle-aware fueling, heavier resistance work, and creatine carry women through menopause.
CHAPTERS
- 0:00 – 23:30
Why Women Aren’t Just Smaller Men in Sports Science
Sims explains how nearly all existing exercise and nutrition protocols are based on male participants, and how that skews both guidelines and outcomes for women. She shares the formative experiences that revealed this bias to her and led to a career focused on sex differences in physiology.
- •Most sports science studies recruit young men; women are excluded due to menstrual-cycle ‘complexity’ and funding/comfort constraints.
- •Textbooks and academic language default to male models, with women often appearing only in sections on problems like anemia or energy deficiency.
- •Sims’ own data as a female participant were thrown out as ‘anomalous’ because they didn’t match male patterns—later traced to menstrual-cycle phase shifts.
- •Her early realization of sex-based exclusion, including being told she couldn’t be a Ranger or SEAL ‘because you’re a girl’, drove her research agenda.
- 23:30 – 41:00
Dr. Stacy Sims’ Background and Research Focus
Sims outlines her academic and athletic CV, from competitive endurance sport to research at Springfield, AUT, and Stanford. She describes how questions from her own racing and teammates shaped her studies on heat, hydration, menstrual phases, and contraceptives.
- •Master’s and PhD in exercise physiology and metabolism; PhD on sex differences in heat acclimation and hydration, including menstrual-cycle and oral-contraceptive effects.
- •High-performance lab work at Stanford combined human performance with public health and women’s health initiatives around hormone therapy.
- •Current roles include leading PhD students at AUT (NZ) and adjunct lifestyle medicine research at Stanford.
- •Her approach: take real athlete problems (heat, fueling, phase) into the lab, then apply high-performance insights back to everyday women.
- 41:00 – 59:00
Core Physiological Sex Differences: Muscle, Fat, Heart, Lungs, Q‑Angle
The conversation dives into the biological differences between male and female bodies that shape performance and injury risk. Sims covers in‑utero differences, puberty changes, muscle-fiber types, fat distribution, and structural aspects like Q‑angle that influence movement.
- •Even in utero, male fetuses are more likely to miscarry under maternal stress; XX vs XY respond differently.
- •Men are born with more fast-twitch fibers (power/speed); women with more endurance-type fibers and mitochondria (better at long, slow efforts).
- •Puberty widens girls’ hips and shoulders, lowering center of gravity and increasing Q‑angle at the knee, altering running and landing mechanics.
- •Women have higher essential body fat (~12% vs men’s 4–8%) and typically more total body fat at a given ‘healthy’ composition.
- •Women’s hearts and lungs are smaller relative to size, with lower hemoglobin and blood volume, limiting peak power and sprint performance but not necessarily endurance potential.
- 59:00 – 1:22:00
Q‑Angle, ACL Injuries, and How Women Should Train to Stay Safe
Sims explains why women suffer ACL injuries at rates 3–4 times higher than men and what can actually be done to prevent them. She connects structure (Q‑angle), neuromuscular patterns (quad dominance), and inadequate grassroots coaching to this injury epidemic.
- •Wider hips increase Q‑angle, meaning landing forces aren’t evenly distributed through the knee, especially in cutting and jumping sports.
- •Women tend to be quad-dominant, under-using hamstrings and glutes, which further destabilizes the knee.
- •Observational data suggest a 3:1 or 4:1 female-to-male ratio for ACL tears; 30 players missed the 2023 Women’s World Cup with ACL injuries.
- •Effective prevention hinges on strengthening the posterior chain (hamstrings, glutes, calves) and training explosive lateral movements and single-leg jumps.
- •Professional organizations like FIFA now include ACL-prevention warmups, but grassroots and youth sports often neglect these critical drills.
- 1:22:00 – 1:46:00
Male vs Female Metabolism: Why Calories-In-Calories-Out Fails Women
The discussion shifts to metabolic sex differences, focusing on the hypothalamus, kisspeptin neurons, and energy availability. Sims explains why popular regimes like fasted training, intermittent fasting, and low-carb diets often work for men but backfire for women.
- •The hypothalamus is the brain’s metabolic control center; in women it is far more sensitive to low energy and carbohydrate availability.
- •Men can dip as low as ~15 kcal/kg fat‑free mass before endocrine disruption; women require ~30 kcal/kg FFM to avoid dysfunction.
- •In women, low-carbohydrate or low-calorie states quickly trigger conservation: downregulated thyroid, menstrual disruption, increased fat storage, and lean-mass loss.
- •A common female pattern—black coffee, fasted workout, delayed first meal—drives muscle catabolism; Sims urges pre‑workout protein (+/- carbs) for women.
- •Evolutionarily, women’s systems protect against pregnancy in times of famine by shutting down reproduction, whereas men lean out and enhance fuel systems to ‘hunt’.
- 1:46:00 – 2:21:00
Fasting, Keto, Autophagy, and Exercise as a Stronger Longevity Lever
Sims critiques the blanket promotion of intermittent fasting, warrior fasting, and ketogenic diets for women. She contrasts male and female responses and emphasizes that exercise itself is a more robust and safer driver of autophagy and longevity.
- •Warrior fasting (20:4) in men can improve metabolic flexibility, glycemic control, and fat loss; in women it raises fasting glucose, increases fat storage, and suppresses thyroid within days.
- •The ‘data’ popularizing fasting mostly stem from obese, sedentary, often male clinical populations and do not translate to active women.
- •For women, the safest and most beneficial ‘fast’ is circadian-aligned: finish dinner 2–3 hours before bed and eat within 30 minutes of waking to blunt cortisol.
- •True ketogenic diets (70–80% calories from fat) sharply reduce gut-microbiome diversity, undermining vitamin synthesis, serotonin production, and sex-hormone recycling—especially problematic for women.
- •Exercise, particularly vigorous and resistance training, induces autophagy, growth hormone, and ‘cell clean-up’ more powerfully than fasting, without the collateral hormonal damage for women.
- 2:21:00 – 2:53:00
Creatine, Vitamin D, Iron, Omega‑3: What Women Actually Need
The conversation turns practical with supplements. Sims debunks myths around creatine ‘bulking’ women, highlights vitamin D’s systemic importance, clarifies iron deficiency norms, and explains when Omega‑3 is useful.
- •Creatine myths: it’s seen as a male bodybuilder supplement that causes weight gain; in reality, low-dose creatine (3–5 g/day) benefits women’s gut, brain, and muscle without significant water gain.
- •Women naturally have ~70% of men’s creatine stores and experience improved gut-lining integrity and reduced GI distress with supplementation.
- •Randomized trials show creatine (3–5 g/day) can help women exit depressive episodes more effectively when combined with SSRIs.
- •Vitamin D3 is involved in nearly every system—muscle, bone, brain, immunity—and is widely deficient due to limited sun and dietary sources.
- •Lab ‘normal’ iron ranges are drifting downward as populations get sicker; athletic women usually require ferritin ≥50–100 for good performance, not the lab cutoff of ~26.
- •Omega‑3s become more relevant in late 30s/40s as estrogen’s anti-inflammatory effects wane; testing and targeted fish oil can support cellular health.
- 2:53:00 – 3:36:00
Sleep, Jet Lag, and Chronobiology Differences Between Men and Women
Sims unpacks how men and women differ in circadian timing, sleep architecture, and responses to jet lag. She connects these differences to hormone pulses, appetite regulation, and practical strategies for eating and sleeping.
- •Women’s melatonin peak tends to occur earlier (around 9 p.m.) than men’s (10–11 p.m.), giving women slightly shorter circadian cycles.
- •Sex hormones alter sleep stages; late luteal phase and PMS often fragment women’s sleep via increased core temperature and melatonin changes.
- •Women generally suffer more with westward jet lag, whereas men fare worse flying east, due to differences in circadian length.
- •For women, eating soon after waking helps blunt the natural morning cortisol spike; skipping breakfast prolongs stress signaling and worsens appetite regulation.
- •Late-night eating disrupts parasympathetic recovery during sleep, increases carb cravings, and encourages hedonistic, not homeostatic, eating the next day.
- 3:36:00 – 4:46:00
Perimenopause and Menopause: Reverse Puberty, Not a Personal Failure
This section focuses on perimenopause as a multi-year, system-wide hormonal transition that many women mistake for personal burnout or depression. Sims reframes it as reverse puberty, outlines its metabolic consequences, and clarifies the role of menopause hormone therapy.
- •Perimenopause typically starts mid‑30s to 40s and can last 15+ years; symptoms include poor sleep, mood changes, abdominal fat gain, performance decline, and altered lipids/glucose.
- •Many women were historically dismissed with, ‘You’re just stressed; here’s an SSRI,’ rather than being told they’re in perimenopause.
- •Falling estrogen reduces anti-inflammatory capacity and impairs use of free fatty acids, shifting more fat into visceral stores around organs.
- •Menopause hormone therapy should be seen as low-dose symptom management, not full ‘replacement’ to stay young or prevent dementia.
- •Exercise priorities shift toward high-intensity intervals and power-based resistance training (less total volume, more intensity) plus high-protein, high-fiber diets to preserve muscle, bone, and metabolic health.
- •With the right lifestyle and, where appropriate, hormone therapy, life on the other side of menopause can feel stable and good again.
- 4:46:00 – 5:00:00
PCOS, Endometriosis, and Using Training & Environment as Therapy
Sims briefly addresses how conditions like PCOS and endometriosis change the training and recovery picture. She notes emerging perspectives on endometriosis and how high-intensity work can help counter insulin resistance in PCOS.
- •Endometriosis may have inflammatory plus infectious components; modulating systemic inflammation (e.g., via cold exposure timed around ovulation) may reduce ectopic endometrial growth.
- •PCOS is characterized by higher androgens and significant insulin resistance; women benefit from structured high-intensity intervals and resistance training to improve glucose handling.
- •Because cycles are irregular in PCOS, women can’t use menstruation as a reliable stress marker; tools like heart-rate variability become more important.
- •Lifestyle levers (sleep, stress management, nutrition quality) remain central in both conditions, alongside medical care.
- 5:00:00
Cycle Literacy, Tracking, and Why Men Must Join the Conversation
The episode closes with a call for menstrual and menopause literacy for everyone, not just women. Sims and Bartlett reflect on how little is taught in schools and how understanding female physiology improves relationships, coaching, and healthcare.
- •Typical 28-day textbook cycles are rare; normal cycles can range 21–40 days with varied bleed patterns.
- •Changes in cycle length or bleed pattern are early, powerful markers of stress and low energy availability in active women.
- •Teen girls with irregular periods are often handed oral contraceptives as a blunt tool instead of investigating underlying causes like stress, under-fueling, or conditions like PCOS/endometriosis.
- •Men benefit from understanding menstrual cycles and menopause because they interact daily with women as partners, colleagues, parents, and coaches.
- •Sims emphasizes empowering girls (and boys) to ask questions and understand physiology, given that most health curricula have dropped robust menstrual education.
