Thursday, March 8, 2012

Parasympathetic Overtraining and the Endurance Athlete-

"Why can't I get my heart rate up to its usual rate on my run or ride?" "Why is my heart rate so much lower than usual when I work out?" Scour the internet, try to find why you can't perform a given workout at your usual heart rate, and you will almost definitely be misled. The form of overtraining most endurance athletes are most susceptible to is rarely discussed. In turn, a form of overtraining with completely opposing signs and symptoms is discussed. This drives endurance athletes whom are overtrained or on the verge of being overtrained to keep on digging that dangerous hole which is overtraining, and prevents them from reaching their potential.

Several years ago I began to research the topic of overtraining in endurance athletes. It confounded me that even in mainstream publications focusing on runners and triathletes, i.e. endurance athletes, the information being published was not relevant to our particular situation as endurance athletes. The majority of published information readily available discussed only one of the two types of overtraining. Most of these articles wholly ignored and failed to mention that overtraining comes in two forms; Sympathetic and Parasympathetic. In only discussing the type of overtraining known as Sympathetic, endurance athletes have been misinformed entirely of what overtraining is and how it presents itself.

The Sympathetic Nervous System controls the fight-or-flight response. This response releases the hormones; cortisol, epinephrine (which is also known as adrenaline), and norepinephrine. Epinephrine’s job is to increase heart rate during periods of stress and high activity. Epi, as it is also called, also constricts blood vessels which elevates blood pressure and helps to get blood to muscles which demand it. Cortisol, like Epinephrine is also produced in the Adrenal Glands during fight-or-flight. Cortisol is responsible for increasing blood sugar in the body to provide readily available and fast burning fuel. During fight-or-flight Cortisol also suppresses the immune system and aids in fat metabolism.

The Parasympathetic Nervous System controls "rest and digest" hormones as opposed to fight-or-flight. Its job is to allow for digesting food and relaxing. It works mostly by inhibiting uptake of hormones involved in fight-or-flight response such as epinephrine and cortisol.

Sympathetic Overtraining refers to an overactive sympathetic nervous system producing TOO MANY stress hormones. This is typically brought on by too much anaerobic work or work near lactate threshold. Parasympathetic Overtraining refers to a sympathetic nervous system which has been so taxed, which may be fatigued, and the Parasympathetic Nervous System, actually begins to gain control over the weak and fatigued SNS. This is confusing language because both forms of overtraining actually involve over stimulation of the Sympathetic Nervous System, as it is responsible for raising heart rates even during aerobic exercise. The difference is where the balance of power falls. As stated, in Sympathetic Overtraining, the SNS is overactive, and in Parasympathetic Overtraining the SNS is underactive or "fatigued" and unable to produce the necessary hormones to raise heart rate. It is unfortunate the labels stuck, and the titles are as they are.

When most magazines and internet sources are discussing overtraining, they usually refer to the symptoms that are present in sympathetic overtraining;

• Fatigue

• Trouble Sleeping

• Weight loss

• Decreased performance

• Frequent illness and colds

• Overuse injuries become present

• Elevated morning heart rate

• Elevated cortisol levels

The only two symptoms which are not subjective are an athletes morning heart rate, and an athletes cortisol levels. Unfortunately, these two factors are usually NOT affected during overtraining by endurance athletes! Even subjective symptoms like an inability to sleep are opposite during Parasympathetic overtraining. During parasympathetic overtraining, one might be able to sleep like a baby for 12 hours per night. This is because there is no sympathetic stimulation to "stress" the athlete preventing restful sleep. Also in the same vein, athletes experiencing parasympathetic overtraining might notice an INCREASE in weight and body fat percentage or no change at all, as cortisol is not burning fat and harvesting glucose, the opposite is actually occurring in the body. The body digests everything and takes fuel in the bloodstream to digest it and store it.

Endurance athletes are likely to see overtraining presenting itself in an, INABILITY TO MAINTAIN A "NORMAL" HIGH HEART RATE RELATIVE TO PERCEIVED EFFORT. What this means is that if an athlete always averages about 140 beats per minute during a given workout, and over several weeks, the athlete finds that even with the same or even a higher effort, he is at a lower heart rate, like around 125, he may be overtrained.

{One method I found to monitor the state of my training, was to log my rate of perceived effort for given workouts, relative to my average heart rate. My RPE scale was 1/20, and HR was in beats per minute. There are multiple ways to track this. You could even give each day a ratio value, like say your RPE was 15 out of 20, and your HR was 155. Your load that day could be .75 (which is RPE 15/20) multiplied by 155, which equals 116.25. You can track this value daily, during overtraining your RPE might be 15/20 but your HR for the workout was only 139 giving your daily number a value of .75*139= 104.25 The purpose of this article is however bringing light to overtraining athletes, NOT discussing methods of prevention. That will be a later topic, as we must also focus on the third variable to assessing daily load, which would be volume!}

If you went on most internet forums, and inquired on why your heart was low for a given workout, the answers that are available are absurd. Most of the respondents are laymen at best, with ZERO understanding of physiology, and they actually reply that it is due to advanced fitness, larger cardiac output, etc! True, true, with greater fitness comes lower heart rates for given efforts, but this is so gradual and unnoticeable in the short term it isn't applicable to overtraining. If overtraining was occurring it is likely that a heart rate for a given workout would be possibly ten beats per minute lower or even more! Heart rates lowering due to advanced fitness occur in timeframes that are so long they become baselines which gradually shift, they would not lower 10 beats or more for a given workout in a period of only one month.

Unfortunately, what I have presented here is mere anecdotal evidence, but IT IS MY HYPOTHESIS. There are many other merely anecdotal research articles which tell stories of German cyclists and Ironman Triathletes experiencing the exact same phenomenon and after taking time off, resting and recuperating only doing exercise which was at VERY low intensity under 110 beats per minute, the athletes were once again strong, performing at normal HR expectations. This may take anywhere from days to weeks or more. I do know, from experience, that it has generally taken me two months at very low intensities to recover, and as a counter balance now, I make sure to track my heart rate constantly. I do not work out at or above lactate threshold more than 15% of my weekly miles or volume...This was also the foundation of Ironman Champion Mark Allen's training program.

The only time we become stronger as athletes is when we recover. Overtraining is in direct conflict with getting faster, and as much of a science the endurance sports are and have become, it is amazing I have to piece together various 1st hand research regarding adrenal fatigue and second hand and anecdotal stories and research regarding Heart-Tired Syndrome which is what Parasympathetic has been written about before. With much research I have determined the cause to be a weakened adrenal system, but the heart and body are complex. Conduction delays in the heart cannot be ruled out, with many athletes being diagnosed with cardiac arrhythmias who overtrain, and also with the endocrine system at play I haven't even mentioned how the heart cannot beat fast without an adequate supply of glycogen!

In regards however, to the common issue of endurance athletes being incapable of elevating their HR for a given workout to their "normal" HR, we must first look to Parasympathetic Overtraining. Unfortunately, there is no diagnosis medically for this as many cardiologists and doctors have absolutely ZERO idea what is at play here.

Signs and Symptoms of Parasympathetic Overtraining are as follows. (These S&S may or may not include all ;)

• Fatigue

• Depression

• Decreased Performance

• Achy legs at night


• Possible craving of carbohydrates and caffeine

• Overuse injuries

• Normal heart rate while at rest or LOWER HR than usual

• Low Blood Pressure

The craving of carbohydrates is a response by the body to provide quick burning fuel which usually provides ample energy supply. Many Ironman and Ultra running athletes know that when they "bonk" or "hit the wall" that their HR plummets. This is not because of overtraining in a one day event, but because the body only functions at high levels while it has an adequate carbohydrate supply. The body can store approximately 2000 calories, (if the athlete is superbly trained at an elite level), and once the body has no more glycogen, (AKA "Carbs") to burn, the body must resort to burning fat as fuel which is much more inefficient.

Athletes who do not race with heart rate monitors could not witness this phenomenon. In the comments field below, please comment on stories from your races of over 3 hours in which you noticed your heart drop during an endurance race. As stated before, this article is anecdotal, yet I want all of the stories I can get to study the situation of HR and power, as well as HR and overtraining.

Hopefully this data can be objectified. In the next few days I will post links to all the articles which discuss Heart Tired syndrome I found online, as well as those which are relevant in regards to overtraining, Parasympathetic Overtraining, and Adrenal Fatigue/Insufficiency.

Please comment on this article and don't hesitate to ask questions and bring up other possible causative factors.

PS- Sorry if this piece doesn't flow well...I sort of whipped it out in a rush and haven't really proof read or edited yet...but hey, the important stuff is present!


  1. i agree with you completely troy. I know that when I feel fatigued and try to go out for a run/ride, I have a hard time getting my HR up with the same RPE. When I'm rested, I can run faster and get my heart rate higher and hold it longer. After a few days of hard training, that last day is difficult for me to complete the sets at the efforts required. However, after taking a full day of recovery, I'm typically back to feeling again and my HR is back where it should be.

    I would also be interested in tracking HR in the morning before getting out of bed. If it's much lower than normal, is that a sign of over training that can be reliable before going out and even attempting a workout?

  2. Interesting thought with lower HR in the morning...Tracking can only help! It'll be interesting to look at the data over an entire year...I know that looking at the HR data from my 100 milers has been eye opening in terms of dialing in proper pacing.
    There are a lot of studies that involve using resting AM heart rate while laying down and then upon rising too, like orthostatics...we'll have to dive into the study and post it.

  3. This is great stuff. I've never had a long term "overtraining" issue that kept my HR low, but have had this happen in some races. I ALWAYS train with a HR monitor, and generally follow the Mark Allen/Maffetone advice of training the endurance engine (I do some 'speed work' at marathon pace though).

    I'm new to Ultras, but here is my (limited) HR experience in race, two of which had a HR drop:

    Race 1. American River / 50 Miles. Being 40 at the time, my Mark Allen/Maffetone HR training limit was 145. This was my first ultra (or really any race; had never done a marathon) so I played it conservatively and did the first several hours limiting HR to 138. This turned out to be TOO SLOW, and I ended up running a negative split for a race that is flat for the first half and rolling/uphill for the second. I was one of four people in the entire field who ran a neg split. HR never dropped like you're discussing and I was able to keep it high the entire second half (~165).

    Race 2: a very hilly 50 miler in the UK. Being my second race, and knowing I started AR50 too slow, I decided to see if I could start faster. That was a mistake. I allowed myself a limit of 155 for the first half, and about three quarters of the way through the race my effort was jacked high, but my HR just would NOT go above 135 without a massive spurt or sprint. I am great at my nutrition, so it wasn't glycogen depletion: I just pushed myself too hard for the first 6 or so hours (finished in ~9.5 hours) I thought the inability to get my HR up to even 145 was a weird fluke.

    Race 3: First 100 (Javalina in 2010). Now I was smarter. I kept my HR at/below 143 for the first third, then allowed it up to 150, and then up to 160 (my max HR at the time was ~183). This worked great, and I ran the second half only 12% slower than the first half. Obviously, as I'd expected, as I got more dehydrated/lower blood volume, my HR would keep rising for the same effort level. Then around mile 80 or 85, my HR starts dropping, even though my perceived effort is the same or higher. In fact, I was so worried about it that at mile 90 before my last lap I asked the medical people to take my blood pressure, which they said was just fine. So out I went (and got fourth, so clearly I wasn't doing anything too wrong).

    I had no idea WHY I couldn't get my HR up though; again, as blood volume decreases, HR should go _up_ for the same perceived/actual effort. But at some point, it just started dropping, which is why I was worried about my blood pressure? Was my heart failing? What the heck was going on?

    From what you've written, it sounds like parasympathetic ... um... well not really overtraining since we're talking discrete events, but overexertion.

  4. One other note on use of HR for overtraining: from what I've read, if you take your HR before you get out of bed every morning, it MAY help you diagnose overtraining/getting sick, but people report sometimes a few days lag. Like it's not fast enough of an indicator. Perhaps that's a sign of parasympathetic overtraining vs your HR rising in the morning in a more timely fashion for sympathetic overtraining.

    Allegedly the way to REALLY check this is not HR, but heart rate variability (HRV). This is the variation in HR between your breathing in and out, and you want it to be high. When it decreases, it's a sign of overtraining/stress, etc. Will that work for parasympathetic overtraining? I dunno, but it's worth a try.

    Apparently some of the polar watches/bands can measure HRV, but I'm a garmin/Ant+ guy. Suunto supposedly also has a model that does it. I JUST found an iPhone app that'll do HRV with the garmin stuff, although you have to buy a little ant+ dongle. I'm going to give that a try (the app is sweetbeat). Also, the following that's coming out MAY do HRV, but they haven't said so yet, and it doesn't need a chest strap (allegedly):

    I'm curious what you think about HRV every morning as a more refined measure of checking for overtraining. Could be a great tool.

  5. I have the same issues. When im fatigued, my hr is lower than normal for a given rpe/pace. It takes more than one full day of rest to fix it though. Im feeling bad right now and plan on doing no more than 3 hours of cardio for the next five days. I gotta get over this funk!

  6. KenZ,
    Great data, and congrats on a well run race at Javalina!To only see a 12% decrease shows good pacing. My data has been similiar in reference to 100 mile events. Always dropping towards the end. I would be willing to wager that in your case, it was glycogen depletion. In going closer to your Lactate Threshold the second half of the race, you body burned through its glycogen reserves. The most well trained athletes in the world can only store about 2000 calories of carbs, (glycogen), therefore, if you crested 150, you were burning a higher ratio of carbs, leaving you empty at the end. I would assume this happens to all of us in a hundred mile race. the body simply can't digest more than a few hundred calories per hour, leaving us at a major deficit in events lasting much longer than 8 hours.

    As far as Heart Rate Variance, I have heard the same! I have understood that over time, variance may only be tracked using resting HR and then again immediately after standing up in the morning, (just like orthostatic BP in the med field...). I haven't heard much in relation to resting HR compared to respirations.

    Thanks for the great data and keep it up!

  7. Eureka! This is exactly what has happened to me! I'm an endurance mountain bike racer and I just completed two of the hardest weeks of training in my program. The first week I was ok, but early on during the second week the over training set in. During a Threshold workout on Wednesday it was getting difficult for me to maintain the HR required for the workout. I took a rest day and did a Tempo workout on Friday only to cut it short because once again I couldn't keep my HR up and my legs felt really heavy. Saturday was my endurance day and I couldn't even get my HR up high enough for the warm up let alone the Tempo and Threshold stages in the training. I was cashed and had to give up early. Everything you read is a high HR is the sign for over training, not lower. Thank you for posting this! It explains everything!

  8. Troy, I just found this through a Google search for parasympathetic over training in endurance athletes. I am an IM athlete, just recently finishing my second IMWI. About 6 weeks from IM, end of July 2012, I experienced exactly what you are talking about in your blog! Yes, abnormal low hr during threshold runs, cardiac arrhythmia, extreme fatigue. Always feeling tired, no motivation to train. I went ahead a finished the IM, but it was a very long day...I basically willed myself to finished because my body would not go seemed like there was no spark plug, no energy! It is about 3 weeks from IM and I am just realizing what I did to my body.I Haven't had the energy to do anything since that day....I am trying to get a handle on this and why I performed so poorly...I think I am figuring it out. I am resting. But what happens after rest, what is the path forward, how do I now train?

    1. Kathy, sorry for the delay in responding. I'm hoping you have since recovered. To address future athletes with the same problem though, I typical have prescribed two weeks of zero activity followed by two weeks of zone one activity with cut hours. by zone one, I typically mean NO MORE than 120 beats per minute, and definitely NO racing for two months.

  9. Just diagnosed with this problem after several visits to cardiologists. I am a 42 year old endurance runner that did two-a-days regularly for years until last year. I now have absolute Bradycardia and in a deep hole I must now dig out slowly. Always thought I was getting more fit as my resting HR dropped. Last year, I became more puzzled by why my race performance declined and was experiencing other symptoms such as dizziness and shortness of breath. I thought I wasn't training hard enough or was overweight.

    My plan is to slowly jog with forced walk breaks for about 6 months and see what happens. Total bummer, but it could be a lot worse. Now wondering if a low WBC is related to this as well. I had a low WBC, but felt great so thought it was just endurance runner related. Now think it might be OT related. Not sure what lies ahead after taking it easy for 6 more months (would make it a year total). Seems like the symptoms will come right back once I start training again. Human body is a amazing thing and has a stubborn memory as well.

  10. Hey Bob,

    Sorry to hear it. Regarding your WBC, this can be dilutional. meaning that you have a normal count of WBC's but as an athlete you have a higher than normal volume of blood plasma, this results in a lower "normal" number of WBC. Most athletes including myself that I have ran a CBC on actually show only like 3 to 3.5 on their WBC counts. Best of luck in recovery!

  11. I have just read this article after searching for a reason why my HR was lower today when my perceived effort was quite high. Having just spent 12 days at altitiude climbing Mount Elbrus I returned home to take part in a 100 mile road bike ride (which was hard and I knew I should be resting) followed by an endurance MTB ride 7 days later covering 48 miles and many steep, long hills. I still declined to rest and converted to the treadmill as it was less than two weeks from my return from the mountains (higher red blood cell count) and I felt tired but mentally prepared to continue training. I ran a steady run on the treadmill for 42 mins after a strength training session; my average HR was 136 and max HR was 143. The following night was a boxing session and the night after (yesterday) I performed another strength training session followed by a 45 minute run on the treadmill at 9 km/hour. I felt good on this run and my average HR was 139 and max HR was 143 (I am a reasonably fit 45 year old). My Garmin 910xt does measure HRV and provides a value called 'Training Effect'. Yesterday my Training Effect was 4.2 - Highly Improving - BONUS!!! However today I decided to push myself into one more session in the gym followed by another run on the treadmill. Knowing I was tired I decided to run at the same pace as yesterday (9km/h) to monitor the value of training effect ( I was expecting the value to remain the same or reduce). After 5 minutes of running I felt very tired but my heart rate was around 8 bpm lower than yesterday for the same pace so I pushed myself to run for 20 minutes before I knew something was wrong. My bpm was low compared to my perceived effort. When I returned home and downloaded the data from the watch my training effort was a whopping 5 - OVERTRAINING. It's a pity the watch doesn't offer this training effect value while training so I could have stopped earlier.

    I hope this helps towards your research, if you have any questions just ask....


  12. Troy

    What you have written up is very interesting and summarises an experience I went through many years ago that was diagnosed as overtraining syndrome, or underrecovery syndrome by Dr Richard Budgett, the former Olympic rowing champion who had been working with Haile Gabrselassie on the issue.

    He recognised that my constant colds and stomach aches were not just a bug and something very different, primarily because I had gathered some very detailed stats from my rowing training, which is exactly as you describe.
    We used to do 40-60minute ergos and sit at a set heart rate - say 150bpm, spend 5 minutes or so steadily getting up to speed and then keep power output (measured by split/500m on the concept 2) gradually reduced over time, as the HR creeps up so that power decreases over time, but HR remains constant. After time is up we wrote down the distance covered in metres. Every week I could repeat the exercise and over a season would add 20m or 50m to the 10000m or so covered, depending on the time of course. This accurately measured tiny improvements and was great encouragement over a long season.

    What I then noticed was then with a set HR I could go further and futher, which made me THINK that the training was working, but as you point out, it wasn't that at all. My heart was exhausted and could elevate itself to the same levels easily, so I has pushing harder and harder and therefore getting higher scores in metres from the machine, and all because I thought a lower HR meant getting fitter - a real paradox that encouraged me to push more and I didn't recognise the dangers until I has a constant cold and got very lucky to meet Gebrselassie's wife, who is also a Dr, who recognised what was going on and put me in touch with Dr Budgett - who incidentally had seen dozens of rowers, just like me, pushing too hard as that is the the mantra in rowing, without realising what was happening.

    Many years later, having had a break from hard trainning I'm now trying endurance racing and suspect that the heart palpitations I'm experiencing and low blood pressure may be a form of the same thing. As you mention, lots of very low rate exercsie is the key to recovery - feels counter-intuitive, but I did the same thing and it worked a treat - just hard to convince yourself that it's the right thing to do.

  13. Nice to finally see an article that verifies what I have experienced instead of the exact opposite. As a cyclist, I have found that if I put too many very high intensity rides together, my heart rate during a ride drops drastically and refuses to get anywhere near my max heart rate. I also feel sluggish and have to keep slowing my pace. Conversely, I have been off of the bike for as much as a week, and performed much better than expected, with a heart rate higher than I thought possible.