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Sympathetic Arousal and Heart Rate Variability

Understanding mental health and stress management is crucial for clinics aiming to improve patient care and deliver better mental health outcomes. Two critical metrics in this area are Heart Rate Variability (HRV) and Sympathetic Arousal (SA). HRV measures the variation in time between consecutive heartbeats, reflecting the balance between the sympathetic and parasympathetic branches of the autonomic nervous system (ANS). The parasympathetic system helps the body relax and recover, while the sympathetic system prepares the body for action, often called the “fight or flight” response.

Parasympathetic vs Sympathetic Branch

Assessing the parasympathetic branch through short term HRV is relatively straightforward as it involves analyzing the time-domain (e.g., RMSSD) and frequency-domain (e.g., high-frequency power) components of heart rate signals. Short term HRV represents a complex relationship between the sympathetic and parasympathetic systems (Shaffer, 2017). This influence is generally consistent and can be easily isolated, making it more straightforward to evaluate ”rest and digest’ activities compared to the complexities of measuring the sympathetic system.

While HRV can provide some insights into the body’s autonomic function, it is not a reliable marker for directly assessing sympathetic arousal, or the body’s response to stress. Measuring the sympathetic side of the ANS is challenging because its signals often overlap with parasympathetic signals and are highly variable. The sympathetic nervous system (SNS) triggers rapid physiological changes in response to stress, such as increased heart rate, vasoconstriction, and heightened alertness. Unlike the parasympathetic system, which can be measured under controlled conditions, sympathetic activation is dynamic, context-sensitive, and transient. These rapid, variable responses are difficult to capture consistently using HRV alone, as HRV lacks the specificity to distinguish between sympathetic and parasympathetic contributions in real-time.

Introducing Sympathetic Arousal

We introduce Sympathetic Arousal (SA), a precise and sensitive marker for real-time stress and anxiety management. SA provides targeted insights into stress responses, enabling timely interventions for well-being. Clinics can use SA to track, understand, and respond to patient stress, leading to more effective treatments and improved mental health outcomes.

How is Sympathetic Arousal Measured?

During stress or excitement, the body’s nervous system causes the tiny blood vessels in your skin to tighten, reducing blood flow. This is part of the “fight or flight” response, preparing the person for action by sending more blood to the muscles and heart. When you’re calm, your skin gets more blood flow, and when you’re stressed, less blood flows to the skin. This change in blood flow can be used to measure how stressed or emotionally aroused a person is—this is the essence of Sympathetic Arousal measurement.

We are excited to have partnered with Philia Labs, developer of a cutting-edge AI-powered algorithm using Biostrap’s high-definition PPG Waveshape features to track these subtle changes in blood to measure Sympathetic Arousal.

This algorithm has been trained on stressor timings (Udhayakumar et al, 2023) and microneurography (Rahman et al 2024, under review) , a gold-standard technique that records real-time nerve activity by inserting a microelectrode into a peripheral nerve. This invasive method directly measures the signals in the sympathetic and parasympathetic nerves, offering precise insights into the autonomic nervous system’s activity. By leveraging this AI-driven measurement method, we can access previously unattainable insights with HRV alone.

Measuring Sympathetic Arousal and HRV Together

By combining HRV and Sympathetic Arousal measurements, clinics gain a more comprehensive understanding of physical and emotional stressors affecting their patients. This dual approach enables earlier interventions and more personalized wellness plans, which can translate into better patient outcomes and overall mental health improvement. Key benefits include:

  • Detecting early signs of chronic stress and anxiety by identifying physiological changes that are linked to prolonged stress responses. This is key for preventing burnout and maintaining employee well-being.
  • Providing more accurate mental health assessments beyond HRV.
  • Identifying specific stress triggers for better management and coping strategies, allowing clinics to understand what stressors may lead to heightened arousal in patients and adjust treatment plans accordingly.
  • Removing guesswork from evaluating intervention efficacy by objectively measuring changes in sympathetic and parasympathetic arousal. Improvements in sympathovagal balance can ensure that treatment efforts are making an impact on health and well-being outcomes.
  • Benchmarking best practices for increased ROI by determining which wellness strategies provide the most effective reduction in stress and improving overall employee outcomes.

 

Monitoring Fatigue

Fatigue is a state of physical or mental exhaustion that results from prolonged activity, stress, or lack of rest. It can manifest as reduced energy levels, impaired concentration, and diminished physical or cognitive performance due to prolonged sympathetic dominance (Tanaka, 2015). Benefits of monitoring both HRV and Sympathetic Arousal can be helpful for fatigue in the following ways:

  • Spotting physical and mental exhaustion patterns early, allowing for proactive adjustments in workloads or daily routines.
  • Tailoring fatigue management strategies at scale to improve overall well-being by creating individualized treatment plans that consider the recovery and arousal aspects of a patient’s health.

How Sympathetic Arousal Can Be Used For Your Business

Sympathetic Arousal (SA) is more than just a stress metric—it’s a powerful tool that can transform mental health care, performance optimization, and stress management across various fields.

Healthspan & Longevity Clinics: Chronic stress accelerates aging by over-activating the sympathetic nervous system, leading to inflammation, oxidative stress, cellular damage, and increased risk of age-related diseases like cardiovascular issues and cognitive decline. Monitoring Sympathetic Arousal (SA) helps detect and manage stress early, enabling healthspan clinics to create personalized plans that slow aging, enhance recovery, and promote long-term vitality for healthier, longer lives.

Elite Athletes: Stress disrupts athletic performance by impairing recovery, increasing the risk of injury, and reducing focus and endurance due to prolonged sympathetic nervous system activation. By tracking Sympathetic Arousal (SA), excessive stress can be identified, allowing athletes and coaches to optimize recovery, balance training, and minimize the risks of burnout and injury.

First Responders & Military Personnel: Chronic stress and fatigue in first responders (e.g. Police, firefighter, EMTs) and military personnel impair decision-making, reduce endurance, and heighten the risk of injury or burnout. Prolonged exposure without recovery increases vulnerability to PTSD and other mental health issues, impacting long-term resilience. By monitoring Sympathetic Arousal (SA) in real time, stress can be managed during critical operations, improving performance and reducing the long-term risks of burnout and PTSD.

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References

Shaffer, F. (2017, September 28). An Overview of Heart Rate Variability Metrics and Norms. PubMed. Retrieved October 11, 2024, from https://pubmed.ncbi.nlm.nih.gov/29034226/

Tanaka, M. (2015, September 29). Frontier studies on fatigue, autonomic nerve dysfunction, and sleep-rhythm disorder. NCBI. Retrieved October 11, 2024, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4621713/

Udhayakumar, R. (2023, August 30). Measurement of stress-induced sympathetic nervous activity using multi-wavelength PPG. Royal Soc. Open Science. Retrieved October 11, 2024, from https://doi.org/10.1098/rsos.221382

Ziegler, M. (2012). Chapter 61 – Psychological Stress and the Autonomic Nervous System,. Primer on the Autonomic Nervous System (Third Edition). Retrieved October 11, 2024, from https://doi.org/10.1016/B978-0-12-386525-0.00061-5

 

 

 

 

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Fatigue happens after all difficult exercises. Running a mile gets harder after you’ve already run two. Powerlifting becomes more challenging after multiple reps. Recognizing this fatigue is how we continue pushing ourselves to run further distances and lift heavier weights, growing faster and stronger with every workout.

However, consistently overtraining to the point of exhaustion can cause the brain to become chronically tired. Known as central nervous system (CNS) fatigue, this condition is marked by decreased functioning in the part of the brain responsible for voluntary movement.

While some people debate what causes it, many athletes and active individuals have struggled with the long-term side effects of CNS fatigue. Read on to learn what CNS fatigue is, how to spot the symptoms, and when it’s time to step back and recover.

Understanding the Central Nervous System

Most mental and bodily functions are controlled by the central nervous system (CNS), which is comprised of the brain and spinal cord. The brain interprets everything we see, hear, feel, smell, and taste. The spinal cord is responsible for sending messages about these experiences into the body to elicit a reaction. Speech, memory, movement, and general awareness are all a direct result of a properly functioning nervous system.

The CNS also enables us to engage in physical activity — it’s what helps us run, squat, and lift on command. Specifically, the motor cortex is the area of the brain responsible for helping us plan and execute voluntary movements. Located in the brain’s frontal lobe, the motor cortex is divided into multiple sections that govern different movements and responses.

One important area of the motor cortex is the primary motor cortex, which helps us control different parts of the body on queue. The primary motor cortex helps us learn new athletic skills and complete them faster and more efficiently through repetition.

What is CNS Fatigue?

The brain and spinal cord are designed to give us freedom of movement, but chronic overtraining can fatigue the central nervous system to the point of inefficiency. This is called central nervous system fatigue, or CNS fatigue.

So you might be wondering, what causes CNS fatigue? One of the leading causes is extending oneself during workouts, though it can also be caused by poor sleep and nutrition. CNS fatigue is thought to be most common among weight lifting and strength training athletes, but it can happen to anyone engaging in high-intensity exercise. Plus, everyone has a different work capacity, meaning that some people may be able to endure more strenuous exercise before experiencing CNS fatigue.

Overtraining and CNS fatigue are sometimes put into the same category, but one is more serious than the other. Overtraining is a common side effect of trying a new and rigorous exercise routine, and it can usually be overcome with a few days of adequate rest and nutrition. In contrast, CNS fatigue results from chronic muscle fatigue and is more difficult to overcome.

What are the Symptoms of CNS Fatigue?

According to the late Olympic coach Charlie Francis, CNS fatigue is caused when high-intensity work occurs too often during training or when high-intensity exercise persists even in the presence of fatigue from a previous workout. When the motor neurons responsible for voluntary movement are forced to fire very quickly and very often, they get tired.

This results in CNS fatigue — where a person’s neurons don’t fire as quickly as they should. When the brain doesn’t send messages to the body to move quickly, a person isn’t able to exercise at the same rate as before.

CNS fatigue also inhibits muscle regrowth, which reduces exercise performance. For example, lifters may start to notice that they’re not building muscle as quickly as before or that their training program has become less effective.

Unlike peripheral fatigue, the normal muscle tiredness that occurs after lactic acid buildup from a workout, chronic CNS fatigue causes persistent symptoms that interfere with a normal workout regimen.

Signs of CNS fatigue is irritability and emotional changes. It also disrupts sleep patterns and can cause either food cravings or loss of appetite, all of which can exacerbate a heightened emotional state.

Another core symptom of CNS fatigue is a weakened immune system. If you find yourself feeling sluggish throughout the day and you’re getting sick more often than normal, it could be a sign your body is struggling to fight off everyday pathogens.

 

The Role of HRV in Monitoring CNS Fatigue

Heart Rate Variability (HRV) is increasingly recognized as a powerful tool in assessing the state of the autonomic nervous system, making it an essential metric for understanding central nervous system (CNS) fatigue. HRV measures the variations in time between consecutive heartbeats and reflects the balance between the sympathetic and parasympathetic nervous systems.

HRV as a Marker of Stress and Recovery

When the body is under stress, whether due to physical exertion, mental stress, or CNS fatigue, the sympathetic nervous system is activated. This can lead to a decrease in HRV, signaling that the body is in a state of heightened alertness or stress. On the other hand, high HRV typically indicates strong parasympathetic activity, suggesting the body is in a relaxed and recovered state. For athletes and high performers, HRV is a critical metric for tracking recovery and avoiding overtraining.

HRV and CNS Fatigue

CNS fatigue is often harder to detect than muscular fatigue, but HRV provides an indirect window into the health of the nervous system. Prolonged periods of low HRV can be an indicator that the CNS is under strain, even if physical symptoms are not yet apparent. Monitoring HRV over time allows for better management of training loads and recovery, helping to prevent burnout and optimize performance.

Practical Applications

Integrating HRV into a recovery protocol for individuals experiencing CNS fatigue can help tailor interventions. For example, if an athlete’s HRV remains consistently low, this could signal the need for extended rest, nutritional adjustments, or even changes in training intensity. Conversely, an increase in HRV after a rest period could indicate successful recovery and readiness to resume activity.

Overcoming CNS Fatigue

Rest is the first and most important way to overcome CNS fatigue. Sleep helps your body recover and promotes muscle growth, which ensures your workouts remain effective. In addition to getting enough sleep each night, you’ll also want to schedule adequate downtime between workout sessions.

Workouts that require more muscle activation, such as heavy weight lifting or spinning, should be balanced with more rest, and you should have a post-workout recovery plan that includes proper nutrition.

Similarly, meditation can help reduce the mental and bodily stress associated with CNS fatigue. Whether you’re already experiencing fatigue or you’re working to prevent it, a regular meditation practice can clear your mind and help you get back in the game.

1. Change Your Workouts

Your workouts are also going to need to change if you want to overcome CNS fatigue. Studies show that muscular fatigue occurs more with endurance exercises like long-distance running or bicycling.

Rather than decreasing your training volume and working out less, you can simply change what you’re doing so that you’re still increasing your heart rate without enduring prolonged exercise.

Coach and bodybuilder Jason Ferruggia suggests using straps and deadlift variations when lifting weights. This reduces the need to grip the bars tightly, which can ease CNS stress. Similarly, switching to fat bars when lifting weights can reduce stress on the nervous system.

Training sessions that alternate muscle groups on different days are a great place to start. You may also consider turning to low-intensity exercises like swimming or cycling for short periods.

2. Alter Your Lifestyle

Many people who suffer from CNS fatigue also have busy, stressful lives. Learning to say no to tasks, events, and outings that don’t serve you can help you create more space for rest.

Being more mindful about what you do and how you spend your time can retrain the brain to act normally, rather than overfiring. Reducing daily stress is an important aspect of overcoming CNS fatigue, as it’s a result of chronic stress on the mind and body.

Additionally, neurotransmitter imbalances are associated with CNS fatigue. Changing your diet can help you rebalance serotonin and dopamine to get back to feeling your best. In addition to eating a diet low in refined sugars and processed foods, you can boost your body’s stress response by supplementing with fish oil, curcumin (found in turmeric), glutamine, and amino acids like tyrosine.

3. Strengthen the Motor Cortex

Strengthening the brain (and the motor cortex in particular) can also help you overcome CNS fatigue so you can return to your normal workouts. Repeating the same low-intensity workouts on alternating days can retrain the brain to work out without getting excessively fatigued. It can also help you create muscle memory in new areas of the body.

Overcoming CNS Fatigue for Health and Prosperity

Fatigue is a normal side effect of exercise. But if you’re feeling chronically irritable, tired, and like you can’t exercise to your fullest capacity, you may be experiencing CNS fatigue.

CNS fatigue is when the motor neurons in the brain don’t function as efficiently as they should, which takes a major toll on your ability to perform at your best. Fortunately, getting enough rest and taking care of your body can help you overcome this challenging, yet common condition so you can achieve optimal health.

 

Reading time: 5 min

Why Am I Always Tired?

Occasional tiredness is normal, especially after a schedule change or a late night. But if you’re feeling tired all the time, you may be severely impacting your ability to function at optimum levels. Feeling tired all the time likely means you’re struggling with sleep efficiency.

Sleep efficiency is the percentage of time spent in a deep sleep while you’re in bed. Normal sleep efficiency levels are 85% or higher. Less may signify a sleep disorder or medical condition.

Tiredness and Sleep Efficiency

People who aren’t hitting a high sleep efficiency mark are likely experiencing sleep deprivation, which can cause a host of mental and physical problems. For example, sleep is the period where your brain processes and catalogs the day’s events and turns them into memories. Not having this time can lead to short and long-term memory issues.

Sleep deprivation can also cause mood and behavioral changes, making a person feel moody, anxious, and even depressed. Being tired all the time also leads to brain fog, which can make it harder to perform daily duties at home and work. Brain fog contributes to poor concentration and focus, memory problems, and lack of mental clarity.

Physically, lack of sleep can weaken a person’s immune system and make them more susceptible to illness and disease. High blood pressure, weight gain, and increased risk of heart disease are all associated with chronic sleep deprivation. Plus, the confusion and bad balance caused by poor sleep put a person at a higher risk of accidentally injuring themselves or others.

Medical Conditions and Tiredness

Several medical conditions can also contribute to decreased sleep quality. For example, sleep apnea is a condition where a person involuntarily stops breathing during the night.

Sometimes people with sleep apnea are awoken by their own gasping, choking, or snoring, which can disrupt sleep cycles. Sleep apnea can cause a person to feel tired upon waking because their sleep was consistently interrupted — even if they don’t remember it.

Other medical conditions that can lead to sleep apnea include autoimmune diseases, such as lupus, arthritis, and Sjögren syndrome. Additionally, persistent fatigue can be caused by mental health conditions like depression, anxiety, and chronic stress.

Stress can have a direct effect on how tired you feel physically. When you anxiously ruminate or overwork your brain to the point of exhaustion, you burn through glucose — the brain’s fuel for working hard. This causes adenosine to rise, which blocks the release of the brain’s feel-good chemical, dopamine. Less dopamine leads to less motivation, which makes you less inclined to do anything mentally or physically, increasing overall fatigue.

Chronic Fatigue Syndrome

Another underlying condition that causes extreme tiredness is chronic fatigue syndrome (CFS). This causes exactly what it sounds like: chronic fatigue.

Chronic fatigue syndrome isn’t associated with any underlying disorders, though some specialists say it is induced by viral infections, stress, hormonal changes, or weakened immune systems. Women in their 40s and 50s tend to be the most commonly affected by this condition.

While everyone with CFS experiences different symptoms, it’s most commonly diagnosed when a person’s fatigue persists for at least six months and causes a significant reduction in their ability to perform everyday tasks.

Additionally, chronic fatigue can’t be cured by bed rest or significant periods of rest. CFS patients always wake up feeling tired, no matter how long they’ve slept. Chronic fatigue can manifest physically too, leading to muscle pain, joint pain, and swollen lymph nodes.

How to Stop Feeling Tired

If you’re feeling tired all the time, it might be time to change your sleeping, eating, and activity habits. Here’s how to stop feeling tired and improve your sleep quality to feel happier, healthier, and more well-rested.

Reduce Refined Foods and Increase Whole Foods

Most people understand that a balanced diet is important for maintaining physical health. But people don’t always associate unhealthy food with tiredness, even though it can be a major culprit of fatigue.

Reducing carbs like white breads, muffins, pastries, processed foods, and sweets can prevent bursts and dips in energy levels, especially when swapped for healthy foods like low-sugar fruits, vegetables, and lean protein.

Change When and How You Eat

If you skip breakfast, you could be setting yourself up for a day of sleepiness. While some people wait until lunch to eat due to fasting diets or busy schedules, studies have shown it may increase inflammation throughout the body

The quantity that you eat plays a role in how tired you feel too. Overeating or under-eating can both cause fatigue, so it’s important to practice portion control when it comes to meals. Getting enough whole grains, healthy fats, protein, and vegetables can boost energy levels after mealtimes, rather than draining them.

Stay Active and Lower Stress

As mentioned above, stress is a major contributor to tiredness. It can also rob you of quality sleep by keeping you up late into the night.

Getting regular exercise is one of the best ways to combat persistent stress. Instead of reaching for a cup of coffee, getting in a brisk 15-minute walk in the morning can boost circulation and increase cognitive sharpness, setting you up for an energized day.

While moving more may seem like the opposite of what you want to do when you’re tired, it works. “If you aren’t moving around, your body doesn’t need to use many resources to create energy, so energy production is low and you feel tired, fatigued, and unmotivated,” says doctor Roger Adams.

Once you start moving for at least 15 minutes, Adams says, your body will create enough energy to meet this demand. Another benefit of getting enough physical activity is that it can help you sleep better for longer.

Hydrate and Reduce Caffeine Intake

Many people turn to a cup of coffee for their morning energy boost, but this is a common cause of fatigue. There are several reasons why coffee causes low energy, especially when consumed regularly.

Mainly, coffee is a diuretic, meaning it causes a person to pass urine more often than normal. Diuretics can quickly lead to dehydration if a person isn’t drinking enough water. Dehydration increases heart rate and lowers blood pressure, both of which cause a person to feel more tired.

The negative effects of dehydration are why, even if you’re not a coffee drinker, getting enough water is essential to staying energized. One way to make sure you stay hydrated is to keep a glass of water or water bottle by your bedside or work table throughout the day. This way, getting enough water feels less like a chore and becomes a normal part of your everyday life.

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Get Your Energy Back

If you’re always feeling tired although you get enough sleep, it could be a sign that you’re suffering from a medical condition, so it’s important to talk to your doctor. But changing your daily habits can help you get back into dreamland faster. What you eat and how often you exercise are directly correlated with how tired you feel.

If you’re wondering how to stop feeling tired, you already have everything it takes to get back to feeling energized. Tiredness and sleep deprivation can have a major impact on your physical and mental health, so it’s important to take action and adopt healthy habits today.

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