PDF Summary:ROAR, by Stacy T. Sims

Female athletes face unique physiological challenges that affect their training, performance, and recovery—but most training advice is based on male physiology. In ROAR, Stacy T. Sims explains how women can optimize their athletic performance by understanding their hormones and menstrual cycles.

Sims shows how different phases of the menstrual cycle affect energy levels, recovery time, and training capacity. She provides strategies for adjusting nutrition and training schedules to work with your body's natural rhythms rather than against them. You'll learn why women need different fueling strategies than men, how to prevent injuries related to female biomechanics, and why strength training becomes increasingly important as you age. This guide offers practical tools for tracking your cycle, planning your workouts, and supporting your body's specific needs at every life stage.

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For example, people with type 1 diabetes must carefully balance carbohydrate intake with insulin dosing to avoid hypoglycemia during exercise. Those with type 2 diabetes or prediabetes may need to limit carbohydrate intake to manage blood sugar levels, especially if they’re insulin resistant. Women with PCOS often have insulin resistance and may benefit from lower carbohydrate diets to improve metabolic health. In these cases, a registered dietitian or endocrinologist can help you develop an individualized nutrition plan that considers your specific medical needs, training demands, and hormonal fluctuations.

Monitoring & Readiness Adjustment

Sims explains that monitoring HRV can help track recuperation and preparedness. HRV is the fluctuation in the duration between heartbeats. It shows how the parasympathetic and sympathetic divisions of the autonomic nervous system interact, where the former handles rest and digestion and the latter deals with fight or flight responses. An increase in HRV indicates that your body can handle stress effectively. When it declines, you're less able to cope with stress. Sims points out that heart rate variability is a useful measure of recovery, but female hormones influence it, which means the figure might not be accurate.

(Shortform note: To understand how female hormones affect HRV, researchers conducted a systematic review and meta-analysis of studies examining changes in cardiac vagal activity across the menstrual cycle. They found that HRV is higher during the follicular phase (when estrogen is high and progesterone is low) and lower during the luteal phase (when progesterone is high and estrogen is low). The researchers explain that these hormonal fluctuations affect the baroreflex, which is a mechanism that helps regulate blood pressure and heart rate. The baroreflex sends signals to the heart’s pacemaker cells, which control the timing of each heartbeat. When estrogen and progesterone levels change, they alter the baroreflex’s signaling, leading to changes in HRV.)

In females who haven't gone through menopause, HRV is affected by their monthly cycles. During the follicular stage, when hormones are at their lowest, HRV peaks. Once ovulation occurs and progesterone levels increase, it activates the body's fight-or-flight response, leading to a rise in resting heart rate and breathing rate, and a drop in HRV. Due to these autonomic nervous system changes affecting HRV, your recovery measurements will consistently be lower in the late luteal phase than in the follicular phase. You may have recuperated, but since the devices' algorithms don't consider hormonal fluctuations, they might incorrectly indicate a low-recovery score that suggests your recovery isn't complete even though it is. Hormonal birth control can affect HRV.

(Shortform note: Researchers have found that factors like sex, age, and hormonal status can shift resting HRV values. They recommend interpreting HRV scores in the context of an individual's baseline rather than using fixed cutoffs. This approach accounts for individual variability and physiological changes, such as those occurring during the menstrual cycle.)

HRV rises in the initial days of beginning hormonal contraception, yet it drops significantly during the active pill weeks, reaching its lowest level in the initial two days of the placebo pill, then rising again. For women going through perimenopause, the proportions of hormones are entirely changed, and for those postmenopausal, they are steady, which alters how hormones affect the vagal nerve. In each situation, there's increased fight-or-flight response and decreased rest-and-digest response, particularly following menopause. During menopause, HRV drops, establishing a different standard afterward.

(Shortform note: While Stacy T. Sims describes a pattern of heart rate variability (HRV) changes in women using hormonal contraception and those going through menopause, it's important to note that this pattern may not apply to all women, especially those using menopausal hormone therapy (MHT). According to researchers, postmenopausal women using MHT had HRV values similar to those before menopause. This suggests that the drop in HRV and the establishment of a new standard after menopause, as described by Sims, may not occur in women using MHT. The study highlights the importance of considering individual differences and treatment options when discussing HRV changes in women during different life stages.)

Current wearable technology doesn't recognize these adjustments, and their existing algorithms are unable to predict accurate recovery. Sims suggests tracking patterns in your heart rate variability, breathing rate, and sleep quality. If you notice a drop in heart rate variability and an increase in your rate of respiration, especially if your sleep isn't as good, it's a signal to ease up. Boosting HRV requires intervening and triggering parasympathetic reactions by changing your habits.

Advances in HRV Research and Wearable Technology

Since the publication of ROAR, research on HRV has advanced, and wearable technology has improved. A 2022 study found that HRV changes during the menstrual cycle are predictable, with a decrease in HRV during the luteal phase and an increase during the follicular phase. This means that wearable technology can now account for these changes in their recovery algorithms, rather than treating them as random noise. Wikipedia contributors note that HRV is a complex measure influenced by many factors, including age, fitness level, and stress. This complexity makes it challenging to interpret HRV data accurately, but advances in machine learning and data analysis are helping to improve the accuracy of HRV-based recovery algorithms.

Sims says that wearables such as the Oura Ring and Whoop Strap can provide insights into your trends in recovery and readiness. These devices leverage HRV to gauge your readiness and rest levels. These tools are especially helpful because they let you view the general patterns in your physiology, enabling you to evaluate and modify the effectiveness of new exercise methods, diet changes, and lifestyle strategies. They also aid in maintaining consistency. People don't enjoy receiving low ratings, so realizing that staying awake for another installment of your Netflix marathon or refilling your wine glass before sleep will cost you wellness points (in addition to genuinely damaging your real-world well-being and functioning) will likely motivate you to make better choices.

The Downside of Wearables

One potential downside of using wearables like the Oura Ring and Whoop Strap is that you may become overly focused on optimizing your sleep and recovery scores. This can lead to a phenomenon known as “orthosomnia,” where the pursuit of perfect sleep metrics actually causes anxiety and disrupts your sleep quality. The constant monitoring and analysis of your sleep data can create a feedback loop of stress and worry, making it harder to relax and fall asleep naturally. This paradoxical effect undermines the very goal of using these devices—to improve your overall well-being and recovery. To avoid this pitfall, use the data as a general guide rather than an absolute measure of your health. Focus on how you feel and listen to your body’s signals, rather than becoming fixated on achieving perfect scores.

Lifecycle, Recovery & Optimization

Sims explains that women's recovery requirements differ and that their recovery window is shorter than men's. They struggle to retain muscle and are more prone to challenges in performance in hot conditions. Some items marketed to women to address these disadvantages might even worsen the situation.

(Shortform note: The textbook Physiology of Sport and Exercise by W. Larry Kenney, Jack H. Wilmore, and David L. Costill, provides experimental evidence that women and men have different physiological responses to exercise, including cardiovascular, metabolic, and thermoregulatory differences. These differences are influenced by factors such as ovarian hormones, which affect heart rate, core temperature, skin blood flow, sweating, and substrate utilization.)

In this section, we’ll look at daily support for women in sports, and training adaptation and lifecycle considerations.

Daily Support for Female Athletes

Sims asserts that female athletes need a balanced intake of carbs, proteins, and fats. Carbohydrates are the body’s main source of energy, protein is a structural component of every cell and tissue, and fat assists the body in absorbing vitamins.

Carbs are vital for daily health. They fuel the mind and nervous system, aid in the body’s fat burning, and preserve muscle by stopping protein from being used as a primary energy source. Protein is crucial for women, as our hormones frequently cause us to experience catabolism. Protein is also necessary to facilitate fat loss, as it keeps the muscles repairing and rebuilding, which allows carbohydrates to refuel the muscles and liver, thus allowing fat stores to stay empty.

Sims recommends a daily nutrition breakdown of approximately 40% carbohydrates, 30% protein, and 30% fat.

Alternative Macronutrient Recommendations

The Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine have a different take on the ideal macronutrient breakdown for athletes. In a joint position stand, they recommend that athletes consume 3-12 grams of carbohydrates per kilogram of body weight per day, depending on the intensity and duration of their training. They also suggest a protein intake of 1.2-2.0 grams per kilogram of body weight per day, with the higher end of the range recommended for athletes engaged in intense training or trying to lose weight. For fat, they recommend that athletes consume 20-35% of their total daily calories from fat, with an emphasis on healthy unsaturated fats.

Training Responses and Life Stage Considerations

Sims points out that training adaptations can be affected by factors like nutrition, menstruation, and hormonal contraceptives. Training adaptations are the changes that happen in your body from exercising, like increased fitness and strength.

Menstruation can affect these adaptations. You can leverage this information to plan your exercise and rest periods for better long-term results. Hormonal contraceptives can dull your body's ability to adapt to training and make it challenging to notice endocrine changes because of underfueling. Another element is diet. Consuming protein pre- and post-workout can enhance how muscles adapt, while antioxidant supplements can impair adaptations to resistance training.

The Dangers of Underfueling

The “endocrine changes because of underfueling” that Sims refers to are the hormonal disturbances that occur when you don’t eat enough to support your training. This is known as relative energy deficiency in sport (RED-S). When you chronically underfuel, your body goes into conservation mode, suppressing hormones like thyroid, reproductive, and metabolic hormones. This can lead to a cascade of problems: irregular or absent periods, low bone density, poor recovery, and increased injury risk. The scary part is that these hormonal changes can be subtle and easy to miss, especially if you’re on hormonal contraceptives that mask menstrual irregularities.

In this section, we’ll explore physiological state and how you adapt to training, in addition to strength, biomechanics, and injury prevention.

Physiological State & Training Adaptation

Sims says that people who are expecting can benefit from consistent workouts. It enhances physical fitness, prevents gaining too much weight and diabetes during pregnancy, uplifts mood, improves posture, muscle strength, balance, and stamina, aids sleep, and prepares the body for labor. It also enhances placental growth and the development of the fetus. It helps the baby develop a strong cardiovascular and endocrine system and a healthy metabolism, reducing the risk of childhood obesity and diabetes. Sims suggests that pregnant women should do moderate exercise for at least 30 minutes nearly every day of the week.

(Shortform note: While exercise during pregnancy offers numerous benefits, it may not be safe for everyone. For example, women with high-risk pregnancies, such as those with a history of preterm labor, placenta previa, or certain heart or lung conditions, may need to modify or restrict their physical activity. In these cases, exercise could potentially exacerbate complications or pose risks to both the mother and the developing fetus.)

Sims also notes that women need more heat adaptation sessions than men. Heat adaptation sessions are workouts in high temperatures that acclimate your body to the heat. Women need more of these because they sweat less and begin sweating at a later point during exercise, making it harder for them to cool down. However, with enough heat-based workouts, women can increase their heat tolerance beyond men's.

The Risks of Heat Adaptation Sessions

While heat adaptation sessions can help you acclimate to high temperatures, they can also increase your risk of exertional heat illness (EHI). EHI is a condition that occurs when your body overheats during exercise, and it can lead to symptoms like dizziness, nausea, and even organ failure. To avoid EHI, gradually increase the intensity and duration of your heat adaptation sessions over time. This allows your body to adjust to the heat without becoming overwhelmed. Additionally, pay attention to your body's signals and stop exercising if you experience symptoms like dizziness, nausea, or confusion.

Strength, Biomechanics & Injury Prevention

Sims emphasizes that strength training is essential for women to preserve their muscle mass and prevent injury. Women naturally possess less muscle than men, and they lose muscle mass at a faster rate as they age because their hormones aren’t conducive to muscle making. Building strength is the sole method for preserving muscle tissue. It also strengthens connective tissues, which aids in injury prevention. Sims emphasizes that strength training is particularly crucial for women over 40, since aerobic exercise doesn't lead to significant changes in muscle mass.

(Shortform note: Sims’s claim that building strength is the sole method for preserving muscle tissue may be an overstatement. Research on older adults suggests that maintaining muscle mass depends on a combination of factors, including adequate protein and energy intake. While strength training is important, it may not be sufficient on its own to prevent muscle loss, especially in older women. This suggests that a more comprehensive approach, including dietary considerations, may be necessary for optimal muscle preservation.)

Sims explains that women have unique biomechanics that require specific injury prevention strategies. Women naturally possess a curved lower back, possibly shorter Achilles tendons, and a broader pelvis that causes a knock-kneed posture. These factors make effective mobility a higher priority than flexibility. Women are also at greater risk for injury because of their muscle imbalances and movement patterns.

(Shortform note: The combination of a curved lower back, shorter Achilles tendon, and broader pelvis can increase injury risk by altering the line of force through the hip, knee, and ankle during dynamic movements. This configuration can amplify out-of-plane joint torques, which require greater control and strength to manage. Mobility training, which emphasizes controlled movement through load-bearing ranges of motion, better prepares the body to handle these complex forces than static stretching alone.)

Sims suggests that intense power training through lifting heavy weights purely for strength activates your neuromuscular system and engages the maximum number of fibers in your muscles. It also activates those powerful, energetic type II fibers, which are crucial for speed and the first to deteriorate. Studies indicate that one main cause of older endurance athletes' reduced speed is their muscles don't contract as rapidly and forcefully as before. Strength training can prevent—and correct—this decline. To prevent injuries, Sims advises wearing heels as little as possible, strengthening your core to protect your joints, switching from crunches to planks, aiming for optimum mobility instead of flexibility, and maintaining the strength of your glutes and hips to enhance balance and stability.

(Shortform note: While Sims recommends minimizing the use of heels to prevent injuries, there are situations where a heel lift can be beneficial. For example, sports medicine specialists Nicola Maffulli, Perumal Sharma, and K. L. Luscombe explain that a temporary heel lift can help reduce strain on the Achilles tendon during the early stages of rehabilitation for Achilles tendinopathy. This approach is often combined with an eccentric loading program, where the height of the lift is gradually reduced as symptoms improve.)