Andrew Flatt
@andrew_flatt
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Professor and Researcher. Interested in the application of HRV in sport, exercise, and health.
Joined October 2012
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1. We tracked heart rate variability in college football players from day 1 of preseason training through to the national championship. Some key findings & thoughts discussed in the thread below.
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I’ve been trying to further understand long-term health concerns in strength/power athletes.
Why do they seem to get no mortality benefit from years of RT-based exercise? I don’t believe this is all explained by drugs.
Some relevant findings/thoughts in the thread below.
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Many heavyweight strength athletes have metabolic syndrome
Cardio 3x/wk improves their cardiometabolic biomarkers without affecting weight class
& doesn’t seem to ↓ performance.
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Concussion decreases HRV. Aerobic exercise increases HRV. New study finds Aerobic exercise improves recovery time from concussion.
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Aortic stiffness increases with age & impairs cardiovascular, renal, & cognitive function.
Aerobic exercise seems to be the most effective way to improve aortic compliance.
Be very cautious of social media fitness trainers who discourage cardio.
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The concurrent training research shows that gains in strength & muscle mass are minimally affected by aerobic exercise if it’s programmed appropriately.
Neglecting cardiovascular health when building size & strength is a choice, not a requirement.
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High blood pressure is a leading risk factor for CVD
Exercising at 50% VO2max for 40 min = ↓ BP for 7-10 h in people with elevated BP
40 straight min = 7 h of ↓ BP
40 intermittent min (10 min/h x 4 h) = 10 h of ↓ BP
Don’t underestimate easy cardio
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1. Learning about HRV from a wearable company is like learning about nutrition from a supplement company. Expect exaggerated claims about HRV & how accurately their tool can measure it. HRV is useful, but body batteries, % recovery, & readiness scores are marketing hype.
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HRV at bedtime predicts subsequent sleep quality. Have a pre-bedtime routine that increases parasympathetic activity to improve sleep. 10 min of paced diaphragmatic breathing is an effective strategy.
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Inactivity = faster ↓ in HRV & aortic compliance with age, contributing to health consequences shown below.
Habitual aerobic exercise = ↑ HRV & aortic compliance, contributing to ↓ risk.
Benefits apply to younger & older adults. Best to start young.
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Endurance training alone or endurance + resistance training, but not resistance training alone, increases HRV in healthy middle-aged adults.
Vagal-related protective effects seem to come primarily from aerobic exercise.
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Intense lifting repeatedly spikes blood pressure & afterload, which can cause the heart to thicken & the aorta to stiffen. While adaptive short term, these effects may not be inconsequential for everyone long term. Heavy lifting should be counterbalanced with aerobic exercise.
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↓ HRV lets you know that the body is currently coping with something non-specific. You can often train & perform well in this situation, but the adaptive response may be somewhat delayed or blunted as the brain prioritizes what it considers the more urgent task(s).
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Aerobic exercise seems to be the most effective way to limit or reverse the age-related decline in HRV.
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Parasympathetic functions relevant to athlete health & recovery:
↑ Sleep/Rest
↑ Digestion
↑ Energy storage
↑ Growth/Repair
↑ HRV
↑ Training response
↓ Sympathetic activity
↓ Arousal/Anxiety
↓ Inflammation
↓ Oxidative stress
↓ Heart rate
↓ Blood pressure
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Stress, sleep, & parasympathetic activity are key contributors to individual variation in training responses, & they’re interrelated.
↑Pre-bed HRV = ↑sleep
Pre-sleep slow paced breathing = ↑HRV & ↑sleep
↑Sleep = ↑next-day HRV
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High fit athletes typically have higher/more stable HRV, reducing HRV sensitivity to perceived stress & workload, possibly due to ↓ parasympathetic withdrawal/faster recovery. This seems to help them better tolerate (via ANS) instances of ↓ sleep,↑ life stress,↑ load, etc.
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Muscle growth/repair is strongly supported by parasympathetic function. Highly anabolic periods of the day are aligned with largely parasympathetic endeavors such as sleep & restful downtime. Withdrawn PNS activity = poor sleep = poor recovery. You can’t grow if you’re all go.
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Inflammation, oxidative stress, & sympathetic activity strongly contribute to various major diseases & are inhibited by parasympathetic activation.
Too much emphasis on HRV’s role in acute “readiness” & performance, not enough on its role in long-term health & adaptation.
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Post-training parasympathetic reactivation is delayed by ↑ lactate/metabolites, ↑ body temperature, & dehydration.
Accelerating HRV recovery requires La/metabolite clearance, body cooling, & hydration.
Slow breathing may help a little but doesn’t really address these factors.
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Training & non-training stress compete for body resources. To prioritize training adaptation, minimize competing sources of stress. Stable routine/lifestyle facilitate reliably predictable demands, support efficiency in energy provision/allocation, & make training more effective.
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Aerobic fitness is protective against the negative effects of chronic stress in ways that strength & power are not. A competitive season is chronic stress, particularly for the less fit players.
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A problem with “readiness” is that athletes can perform well when unwell & underperform when well. It’s a poorly defined marketing term that implies a reliable association. We can’t infer health/wellbeing from performance markers, or performance from health/wellbeing markers.
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Restoration of HRV to baseline following several nights of 50% sleep restriction takes 3 nights of 8h sleep. Timely find considering we just finished final exams. Likely implications for fatigue/recovery, possible implications for performance & injury risk
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A common misconception is that HRV should consistently agree with subjective status.
The ANS responds & adapts to external demands that you may feel (e.g. work stress, physical stress), but also to internal demands that you may not (e.g. fluid balance, blood pressure control).
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Too much emphasis on finding novel hacks and methods to stimulate parasympathetic activity to increase HRV.
Not enough emphasis on addressing the major factors that are suppressing it.
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A hard pill to swallow for some of us in S&C. Strength training has numerous health benefits. But we need to be mindful of context. Being ~250 lb, exposure to chronically high volumes of static hemodynamic stress, & fearing aerobic exercise is not good for cardiovascular health.
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1. Evidence-based strategy to ↑HRV & cardiovascular health:
- Get a dog (↑HRV in dog-owners)
- Take it for long walks (nature, Vit D, exercise)
- Keep it close (HRV↑/BP↓ when nearby)
- Love it back
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Personal story about:
-being a former D-lineman, powerlifter, & coach
-stressful PhD
-stiff arteries, high lipids & body mass
-priority shift from performance to health
-changes in HRV & other biomarkers
-how/why I improved my cardiovascular health
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The top 2 health/fitness trends of the next year in no specific order:
- zone 2 training
- disregarding aerobic fitness
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Having a newborn with health issues has been stressful, but I’ll be damned if the most parasympathetic times of my day aren’t when finally I get to sit back & hold her in my arms. Five weeks old & stronger than I’ll ever be.
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Do cardio and lift, but especially do cardio.
Here, in adults with overweight or obesity, aerobic exercise alone or combined resistance plus aerobic exercise, but not resistance exercise alone, improved composite cardiovascular disease risk profile.
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Slow-paced breathing with or without HRV biofeedback = routine maintenance and support for the autonomic nervous system.
Benefit/effort ratio is unmatched.
Some of the physiological effects:
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Aerobic fitness not just for sport demands. Supports recovery & stress buffering.
“Good physical fitness, especially good aerobic endurance capacity, is an important protective factor against health-threatening reactions to acute psychosocial stress.”
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Endurance athletes would benefit from more lifting, as many strength coaches will be quick to point out. Strength athletes would probably benefit from more aerobic work and stretching. Not sure this gets pointed out as often.
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The goal with data (HRV, sleep) should be to “use it” sparingly. An intelligent training approach & self-care routine predominately reflect decent trends. No change needed most days. The feedback helps fine-tune supportive behaviors & is handy when life throws you a curveball.
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Factors that help ↑ HRV:
- perceived safety
- connectedness
- predictability (routine)
- work autonomy
- aerobic exercise
- nutrition (fruit/veg, oily fish)
- early dinner
- adequate sleep
- Vit D
- healthy body comp
- modest kcal deficit
& address suppressive factors below:
@andrew_flatt
What does the data show regarding how to improve balance? For many of us with sympathetic dominance
@by
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Quick-start guide to reduce confusion with HRV:
1. Learn about HRV from coaches/researchers, not tech companies
2. Use an independently validated tool
3. Ignore proprietary “readiness”/recovery scores
4. Interpret raw data in context with other status metrics
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Cardiac adaptations to various sports & exercise modalities based on their static vs dynamic components.
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HRV is less confusing when you zoom out & add context.
Many apps are zoomed in & make a lot of assumptions.
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Sample: untreated (no BP drugs) & resistant (high BP despite ≥3 BP drugs) hypertensives
Intervention: 1 year walking (≤3.5 mph), 30-60 min/day, 5-6 days/wk
Results: systolic BP ↓ 8 mmHg for untreated, ↓ 10 mmHg for resistant
Conclusion: walk 1 h/day
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I’m a fan of active recovery & certain modalities, but rest days with no or minimal team obligation are underrated. Few things allow players to shut it down & recover better than simply knowing there’s nothing on the calendar tomorrow. Typically see a nice HRV bump the next day.
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New from our lab:
Higher/more stable daily HRV was generally associated with superior cardiovascular (↓blood pressure & aortic stiffness), metabolic (↓body fat, glucose, & LDL) & psychoemotional (↓perceived stress) health in young adults.
Full text:
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It’s tempting to train through periods of high stress, but studies show ↓ acute recovery, ↓ chronic adaptation, & ↑ injury/illness risk.
Monitor: subjective markers for context/perception of stress; HRV for impact/magnitude of stress.
Manage: Adjust training; address stress.
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Four weeks of HRV biofeedback training (slow paced breathing to maximize HRV) reduced TNF-α (an inflammatory cytokine) & improved resting HRV vs no improvements in the control group. Higher resting HRV was associated with lower TNF-α.
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When introducing athletes to tracking (HRV/sleep/wellness), I assure them that their scores have almost no impact on acute performance, but they’re important for health & getting more out of training longterm. Emphasizing the performance angle is incorrect & creates data anxiety.
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HRV (RMSSD) reference values from a massive sample of healthy men and women.
n = 84 772
age range = 13–91 years
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Not all resistance training effects are desirable.
New study shows that 10 weeks of traditional RT caused ↓ cardiovagal baroreflex sensitivity, ↓ HRV, & ↑ blood pressure responses to isometric exercise in healthy young adults.
Solution: add cardio.
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Led by MS student, Tom Nagel, we showed that ↑VO2max was strongly related with ↓aortic stiffness in firefighters, independent of body fat.
Stiffness values were consistent with men 10-15 yrs older.
Cardio reduces aortic stiffness.
RT does not.
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↑ blood pressure activates the vagus via stretch-sensitive arterial baroreceptors to ↓ BP.
Large artery stiffness = ↓ baroreflex, promoting ANS imbalance & ↑ BP.
Aerobic exercise = ↓ aortic stiffness,↑ baroreflex & HRV, & ↑ BP regulation.
Don’t discourage cardio.
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My take on “just lift; be lean”:
- Lifters who are mesomorphic, >200 lb, &/or Black, can have high blood pressure despite lifting & being lean.
- It downplays the unique cardio-protective effects of aerobic exercise & the importance of aerobic fitness for long-term health.
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One of the main reasons why aerobic exercise and diet reduce blood pressure is because of their positive effects on autonomic function.
They increase parasympathetic activity and reduce sympathetic activity.
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HRV, sleep, & subjectives are indicators of health, not performance. Better status metrics = better health = better long-term adaptation. Staying healthy should be a priority if long-term performance is a goal.
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Being disappointed that your HRV isn’t reduced when you have a night of poor sleep or feel some stress is like being disappointed that you didn’t bruise when you got bumped.
Stable trend despite disturbances > being hypersensitive. It’s a characteristic of elite athletes.
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Acute effects of water immersion on cardiac-parasympathetic activity:
Warm water = ↓ HRV
Thermoneutral water = ↑ HRV
Cold water = ↑↑ HRV
Pros & cons to cold tubs. Avoid when prioritizing muscular adaptions. Consider when prioritizing ANS recovery.
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The link between vagal function & chronic diseases is under appreciated.
Effects of parasympathetic activation:
-↓HR, ↑HRV
-↓sympathetic effects
-↓inflammation
-↑NO
-↑redox regulation
-↑mitochondrial biogenesis/function
-↑calcium regulation
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Staying up later on weekends increases sympathetic activity, aortic stiffness, & morning blood pressure surge.
Circadian disruption = ANS disruption = ↓HRV.
Performance may/may not be affected, but the adaptive response probably is.
Likely less negative effects in high fit.
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ANS imbalance is mechanistically involved in the development of various chronic diseases. Countermeasures are required for most people.
Practical approach:
- Track HRV
- Observe effects of lifestyle behaviors
- Gravitate to those that facilitate higher/more stable values
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Exercise is the best way to ↑ HRV.
Some potential mechanisms:
↑ insulin sensitivity, stress buffering, NO, aortic compliance, & baroreflex sensitivity
↓ total/visceral fat, inflammation, oxidative stress, RAAS, & sympathetic activity
Our new paper
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HRV-based recovery scores can be misleading. HR is constantly being modulated to meet current demands, recover from recent demands, or prepare for anticipated demands. Apps don’t know which is the case, & implications differ when it’s a recovery issue vs stress/lifestyle issue.
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HRV tends to peak in summer (so might performance). Example data below (standing values). Possible contributing factors:
- Circannual drop in cortisol
- Greater intake of fresh produce (antioxidants)
- Peak Vit D
- Higher activity levels
- Better mood?
- Less work stress?
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New summary of lifestyle behaviors that reduce your risk of atherosclerosis.
Or, that improve your HRV. They’re the same.
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Here’s my understanding (correct me):
Some RT reduces risk. A lot of RT may increase risk.
Some AE reduces risk. A lot of AE continues to reduce risk or doesn’t increase risk.
Doing both is best, but they are not the same, & data currently suggest more time devoted to AE.
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Deloading when objective and subjective markers are suppressed is probably more effective than deloading at predetermined timepoints based on hypothetical needs. Effective deloads can be much shorter than 7 days.
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HRV correlates with numerous health, lifestyle, & fatigue-related markers, but it can’t correlate with all of these at all times. Heavy influence from one factor can obscure its relationship with another. It’s versatile but sensitive. ANS is important but complex. Context is key.
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New paper describing how chronic stress contributes to cardiovascular disease. I can’t think of a better tool for tracking & managing stress than HRV. It naturally promotes behaviors that increase parasympathetic activity & results are seen in the data.
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Autonomic activity helps explain inter-individual training responsiveness.
Higher baseline HRV is associated with superior adaptation to endurance training.
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The brain instinctively shifts energy away from recovery when stress loads are high to address more urgent tasks.
You can choose to train through it or you can adjust.
One decision prioritizes training. The other prioritizes training adaptation.
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Whenever I see an article on the health benefits of exercise, it always surprises me if there’s no specific mention of improved autonomic regulation.
Aerobic exercise is one of the best ways to reduce sympathetic activity.
Some reasons why that’s important in figures below.
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Slow-paced breathing for 15 min each evening across a 30-day period increases subjective sleep quality and HRV compared to control (15 min social media) in healthy young adults.
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HRV is modifiable at older ages, but young adulthood may be a critical time period in which efforts to increase/maintain values could help mitigate the age-related decline.
It’s likely easier maintaining higher values from your 20-30s vs substantially increasing them at 50.
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Efforts to improve HRV need to consider mental health. Excessive worry, anger, & dwelling on negative thoughts can act like an anchor weighing it down. This may help explain some cases of individuals who have lower HRV despite high fitness.
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Common misconception… HRV is not an objective measure of how you subjectively feel. Don’t be disappointed when these don’t align. Associations are occasional. Both offer unique insight regarding status/adaptation. Neither predict performance.
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How excessive artificial light at night can negatively affect autonomic activity, reflected in increased HR and blood pressure, and reduced HRV.
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Why not just use HR instead of HRV?
Because they’re different.
In this example, look how much better parasympathetic HRV markers discriminate healthy vs clinical circadian profiles of cardiac-autonomic activity.
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Athletes who best tolerate increased training stress have had prior exposure and/or very high aerobic fitness. These players show the least reductions in HRV & subjective markers despite accumulating the greatest external loads. No substitute for high fitness in younger players.
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Excess stress impairs performance, increases catabolic hormones & compromises sleep & recovery. Stress is hard to avoid, but developing better coping strategies helps reduce its effects. Diaphragmatic breathing increases parasympathetic activity & would be a good place to start.
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Under appreciated effects of moderate intensity cardio.
- Lowers blood pressure & aortic stiffness to a similar degree as HIIT
- Lowers blood pressure more than higher intensity steady state
- Has minimal recovery demand & may rather serve as active recovery
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It would be tough to find a bigger proponent of HRV tracking than me.
Here’s my response to “Why does someone need to track their HRV?”.
“You will realise that you should perform daily exercise or be less sedentary, prioritise quality sleep, eat well, quit smoking, limit alcohol, manage stress, foster good relationships and budget periodic downtime.”
—
@Andrew_Flatt
via
@JoelSnape
on tracking
#HeartRateVariability
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Since ~2010, sports science research progressively de-emphasized daily HRV values in favor of trend characteristics, including direction of the rolling average & magnitude of fluctuation. Proprietary readiness & % recovery scores overemphasize the importance of today’s value.
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ANS function helps link sleep with health.
Parasympathetic activity & its protective effects peak during sleep.
Blunted nocturnal HRV is associated with various chronic diseases.
Inadequate sleep = limited relief from sympathetic effects.
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When you learn what factors contribute to low HRV scores, you can reduce their frequency. This results in higher & more stable values, which is associated with better health, better recovery, & better training adaptation. More behavior modification, less program modification.
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Considerable overlap exists between factors that affect cardiac-autonomic & metabolic health, such as:
- Exercise
- Diet
- Sleep
- Stress
Increased RHR/reduced HRV is one of the earliest signs of metabolic dysregulation.
Improving HRV likely improves a lot more than just HRV.
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HRV should peak during sleep.
Light-dark stimuli, meal timing, temperature, & physical activity affect 24 h ANS activity patterns.
Disturbed circadian variation in ANS function (partly driven by late meals) thought to promote hypertension, metabolic disorders, & weight gain.
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In trained individuals, non-training stress tends to affect ANS activity more so than the training stress that they’re accustomed to.
This means that lower/less stable HRV often reflects the stress that diverts energy away from recovery processes & impairs training adaptations.
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When tasked with recovering from training & coping with excess stress, recovery loses every time. Energy is diverted from muscle growth/repair to sustaining the alarm response by shifting from anabolic to catabolic processes, & from parasympathetic to sympathetic activation.
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I recently had COVID. Nocturnal (Oura) & post-wake standing HRV showed highly divergent recovery patterns post-symptoms. This is problematic for guiding training. Here’s my attempt at interpreting the data & some current thoughts on “readiness” scores.
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How mental stress originates in the brain, alters autonomic regulation, and consequently promotes cardiovascular diseases/events and end organ damage.
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When HRV is only thought of as a training tool, the behavior modification benefits related to improved sleep, diet, attention to recovery, & management of non-training stress get overlooked.
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Sympathetic hyperactivity stiffens arteries, impairs baroreflex function, reduces vagal activity, & promotes further sympathetic activation via a positive feedback loop.
This causes sustained hypertension & damages vital organs.
Prevented or reversed with aerobic exercise.
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Low HRV but otherwise healthy?
Rule out family history of hypertension (FHH).
Offspring of hypertensives often have ↓ HRV, even when normotensive, & have ↑ risk of future hypertension.
Notable findings, with good news (hint: exercise/fitness helps a lot), in thread below.
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High aerobic fitness helps compensate for poor health and a poor lifestyle.
Mortality risk is substantially lower in high fit vs low fit individuals who are:
- obese
- hypertensive
- less active
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Aortic stiffening increases cardiovascular risk.
Training Rx to limit the age-related increase in aortic stiffness:
- moderate aerobic exercise
- 4-5 days/week
- 30 min/session
Less aortic stiffening also helps preserve baroreflex sensitivity & HRV.
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Stress-related sleep loss is an example of the brain prioritizing coping with perceived threats at the expense of personal health & recovery. This often explains cases of lower/less stable HRV in athletes despite minimal changes in training load.
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High stress impairs training adaptations & cardiometabolic health (e.g.↑glucose, ↑BP, ↓HRV).
Not a time to chase PR’s, but not a time to be sedentary.
Rx = familiar submaximal lifting + cardio.
Maintain training effects, manage BP/glucose, & get a parasympathetic stimulus.
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Altered ANS function largely contributes to the stress-related health toll.
Increasing parasympathetic (↓sympathetic) activity is like putting a buffer b/w your health & the damaging effects of chronic stress.
Aerobic exercise is the best way to improve ANS regulation & ↑HRV.
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Be cautious with wrist-worn wearables. Hard to measure HRV when they cannot consistently measure HR. The tech will continue to improve but I worry the wrist may be too “noisy”.
Review of Validity and Reliability of Garmin Activity Trackers
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Old lesson from this & other similar occasions:
- powerlifting wasn’t great for my HRV
- adding aerobic exercise improved it while I continued lifting heavy
- effects likely occurred sooner than chronic adaptations (body fat, VO2max)
- the stimulus alone seemed important
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Potential implications of sustained ↓ in HRV:
-sleep disturbances
-↑ infection risk
-catabolic>anabolic processes
-fatigue-related injury
-cardiovascular maladaptations
May precede performance decrements.
Less common in high-fit players.
Avoidable if tracking.
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Various “hacks” promoted to increase HRV primarily have transient effects. They have their place, but if the goal is long-term improvement, addressing the factors below that are most relevant to you is typically the way to go.
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