A Method for Monitoring Fitness and Avoiding Overtraining Using the Ithlete App

 My Basic Endurance Training Philosophy

It is my belief that the balancing act of approaching optimal fitness can best be accomplished through an improved understanding of the ways in which activity and rest progressively complement each other. Thus in order to experience sustained improvement as an endurance runner it is necessary to master the subtle balance between the act of running, and the process of recovery. Fitness improvements take hold as adaptations take place during recovery from exercise, not during the act of running. The stimulus from active exercise disturbs the bodies homeostasis, and when the exercise is repeated consistently the body then responds in turn with numerous adaptations. As an example two such adaptations in response to consistent running are  mitochondrial bio-genesis ( in both the muscles and the brain), and increased capillarisation, which each help to improve running economy.

This is how researchers Stanley, Peak & Buchheit put it in a recent review 'Cardiac parasympathetic reactivation following exercise: implications for training prescription'  for the journal Sports Medicine:

"The objective of exercise training is to initiate desirable physiological adaptations that ultimately enhance physical work capacity. Optimal training prescription requires an individualized approach, with an appropriate balance of training stimulus and recovery and optimal periodization."

 
 Yet in my opinion most runners place too much emphasis on the act of running ( often trying to keep to a rigid training schedule), and place too little awareness on the body's response to training during recovery.  This can lead to a less than optimal progression of fitness in 1 of 2 ways:

1. Too much running volume, or too much running intensity, with insufficient recovery. This will likely result in at best less than ideal progress (or worse lead to injury or over-training syndrome).
    
2. Too little training, and too much downtime. This will result in less than ideal fitness gains. There are days when the body and mind are primed to make ideal use of a strenuous workout. Going too easy or skipping a workout on these may be an opportunity lost.

 On the other hand, if subjective awareness of the body's response to training is combined with reliable objective bio-markers ( such as HRV ), then endurance training may be adjusted to fit the body's readiness on any given day.

Using HRV as a Biomarker to Inform Training

 Now that I have laid out my basic philosophy I would like to delve into some tools I will be using to help guide my objective understanding of how well I am responding to training. I will be using HRV   data obtained from a simple app available for i-phones or tablets (ithlete). So far it has been my experience that the HRV data can ( if used properly ) greatly inform a runners knowledge of the state of their fitness and recovery. Collection of HRV data used to be time consuming and expensive, but now requires only a 10 dollar app and a bluetooth heart monitor (in addition to the smartphone or tablet most of us already own ).  Each Ithlete app  collection session only takes 1 minute, results are instantaneous and are kept in history for reference, and there are some nice automatic graphs produced as I will show below. As a quick disclaimer I do not work for Ithlete or benefit in any way by promoting their product.

Based on my personal  experience and a fairly thorough scouring of the research I believe the most informative use of the HRV data for monitoring endurance training  requires consistent tracking of 3 types of HRV readings. It can also be useful to keep track of your training load ( TL) with miles run or a more complex measure that includes training intensity. This may sound like a lot to do, but remember this only requires less than 5 minutes of total collection time. Below are the types of HRV collection I find most informative collectively. I will follow with a graphic example of the approach using my recent data, and will finish with some of the peer reviewed research that describes why this approach can be so useful.

The three types of HRV information I will collect & present are:

1. Morning Resting HRV (mrHRV) - A Good measure of overall well-being prior to daily stress accumulation
   .
2.  Morning Standing HRV (msHRV) - A Good measure of the current state of the bodies resilience to physical stress.
   
3. Evening HRV (eHRV) - When the bodies homeostasis has been disturbed from an exercise session it requires more than usual amount of oxygen to support the adaptation process. This is known as excess post exercise oxygen consumption (EPOC). Taken at rest each evening, (eHRV) shows how hard & how quickly the body is working to return to it's morning resting state.

It has been my experience that a larger the gap  between morning standing HRV and morning resting HRV ( in other words mrHRV minus msHRV) indicates better resilience. This formula informs the capability of parasympathetic withdrawal (and sympathetic activation) to a low level of physical stress and is I think the best indicator of exercise readiness.

There are two very informative findings that relate to these HRV measures from the work of Stanley, Peak & Buchheit that I sourced above:
 

• Complete cardiac parasympathetic reactivation requires up to 24 h after low-intensity aerobic exercise, 24–48 h after threshold-intensity exercise and least 48 h after high-intensity exercise. Individuals with greater fitness are more resilient to training stress and require less time to recover.
  
• Metaboreflex stimulation (e.g. muscle and blood acidosis) is likely a key determinant of parasympathetic reactivation in the short term (0–90 min post-exercise), whereas baroreflex stimulation (e.g. exercise-induced changes in plasma volume) probably mediates parasympathetic reactivation in the intermediate term (1–48 h post-exercise).

 The first finding provides a clue for why including a large percentage of low intensity training may be important for sustained fitness improvements allowing sufficient recovery each day while establishing the necessary volume of training. Since threshold and interval training require more recovery time it is not wise to schedule these sessions back to back unless possibly in an overload phase prior to a race taper.

The second finding points to the importance of examining standing HRV in addition to resting HRV. The orthostatic challenge involved in standing makes (mrHRV-msHRV) a better proxy for exercise-induced changes in plasma volume then mrHRV alone.  

I say this in part because an earlier study of Dr Bucheitts 'Exercise-induced plasma volume expansion and post-exercise parasympathetic reactivation' which demonstrated the following phenomenon:

 "significant increase in all vagal-related HRV indices (and a decrease in the sympathetic related index) 2 days following a single bout of supramaximal exercise"

 This result indicates that high intensity exercise can lead to a super-compensation effect whereby resting (not standing) HRV is elevated 2 days after the exercise. A resting HRV that is elevated due to a supercompensation effect however, shoud not necessarily be interpreted as an indicator improved readiness for a difficult workout.


Thus (mrHRV-msHRV) would seem better equipped to identify the lingering effects of threshold and high intensity workouts on current exercise readiness, especially if HRV appears to rise in the initial days after threshold or high intensity exercise. I have seen exactly this pattern occur as I will show below.

Edit -- I have seen some conflicting results in the following week. In some cases high msHRV seems to indicate good fitness readiness. As usual with a closer look things are not so simple as they seemed with limited data. I have a feeling that acute fatigue, & long term fatigue have differing effects that may reverse some training interpretations.

My HRV Training Graph for 1 Week

 Due to the superior graphic tracking capabilities of the ithlete package I will use it to track my results. Ithlete allows me to simultaneously graph training load against changes in HRV both supine at rest and standing at different time points (within the day, and day to day). This will allow me to clearly display and examine 3 key indicators relevant to training. Here is an example:

Here is how to interpret the graph:

The green dots represent morning resting HRV (mrHRV) - This informs the  health of the parasympathetic nervous system at rest. It is a good measure of overall well-being prior to daily stress accumulation. My scores which tend to range in the 80's are quite high for my age group (probably in the top 1%). It is not uncommon for those doing a lot of running to have a high HRV. The blue line represents a rolling average of the mrHRV score. If the green dot drops one standard deviation below the blue line for 1 day a relatively easy training day is recommended. If the green dot drops below the blue line for 2 consecutive days a day off is suggested.

The height of the vertical white lines on any given day represents morning resting HRV minus morning standing HRV (mrHRV-msHRV). For example, in the graph above on Tuesday my morning resting HRV was 82, and my morning standing HRV was 48 so that (82-48=34).   The length of this line informs the capability of parasympathetic withdrawal (and sympathetic activation) to a lower degree of stress ( in this case the stress of standing, which is referred to in the literature as an orthostatic challenge). The 34 point HRV difference is a large gap indicating that this would be a good day for a challenging workout. As mentioned above it is my view (supported by literature and subjective experience ) that this is the best HRV indicator of exercise readiness. Generally I find the longer this vertical line is, the better I am prepared for a good training session.

The purple bars represent the training load in the form of miles run which I manually entered. It can be useful to compare HRV levels to this measure over from the previous day in order to see how a hard or easy training day effects the trend in resting HRV or the exercise readiness on any given day. Generally this is confirmed as tall purple bars ( high training load ) tend to lead to lower HRV the following day. It is also important however to keep in mind the intensity of the run as well as the research findings I bulleted above indicate that it is high intensity exercise that is likely to have the biggest effect on the vertical white lines (lowering exercise readiness ).

I would stress here that HRV is just one tool. Results need to always be interpreted with care taking into account subjective feelings of fatigue and soreness, sleep patterns, diet, emotional state, and of course the relationship between HRV results and the intended goals of recent training. For example I tend not too place much validity on my Saturday morning results as my dietary patterns on Friday evening are quite different in preparation of a long run on. I also tend to get less and lower quality sleep Friday nights.

Example of Daily HRV Interpretation and Usefulness

 

The first thing to notice regarding the resting HRV is it tends to be lower after long runs. This is expected . So for example on the first Sunday resting HRV with a score of 80 approaches the blue line which is about a standard deviation below it's typical level. This drop was in response to a 20 mile run on the previous Saturday. While the 20 mile run was at a comfortable overall pace this training load  was enough to provide a useful training stimulus without dropping the resting HRV too drastically. The shorter vertical line on Sunday completes this coherent picture and suggesting some limited exercise readiness and thus relatively easy training day.

On Sunday I restricted my running to just 7 miles, although I also taught a tai chi class and did some weight training. Monday was a very easy day with just 5 miles of easy running . Coinciding with the easier training loads are a gradual increase in resting HRV on Monday Tuesday and Wednesday reflected by the rising green dots. While the highest resting HRV score ( 88 ) is seen on Friday, Tuesday reflects the best exercise readiness level as indicated by tall white vertical line.

On Wednesday I completed a moderately taxing 15 miles that included 3 miles at marathon pace effort in the evening. As expected there was a resulting dip in my resting HRV the following morning. On Thursday I only ran 6  miles, but I did run steep long hill in the morning at a fairly high intensity. On Friday morning my resting HRV was quite high (88), leading me to suspect a transeint super-compensation effect of the prior higher intensity work-outs. I became especially wary noticing that the exercise readiness measure (mrHRV-msHRV) was somewhat low (88-67=21). In response I planned for an easy day which turned out to be a very good idea. On my easy 2.5 mile jog into work I began experiencing some reactive hypoglycemia symptoms* which I am prone to. I was able to avoid a full on event, but had I just trained with a hard effort based on the high morning resting HRV score (88) the results would likely not have been pleasant.

I should also mention that you can also see evening HRV (eHRV) in the deflection of the slope of the white line from one day to the next. Evening HRV which is taken at 9pm, had a score of 71 on Monday evening and 76 Tuesday evening. These evHRV scores as expected are lower then the mrHRV scores on the same day which were 80 and 82 respectively. This shows that excess post exercise oxygen consumption was likely occurring in the evening. By the following morning however resting HRV continued to rise showing the importance of a good nights sleep.

* notes this was the 2nd time I experienced reactive hypoglycemic symptoms with a pattern of high resting HRV and a low exercise readiness measure (mrHRV-msHRV).

**I also identified  what appears to be a mild allergic reaction to cashews and peanuts based on their effect on morning resting HRV. Resting HRV was substantially lower on mornings when I had eating substantial amounts of these nuts ( especially the cashews ) on the prior evening.

My mrHRV had dipped a bit Saturday morning. I had taken in extra carbs the evening before and had woken up quite early for this reading so I went ahead with my long run for Saturday. This was an important run for me nearing the peak of my marathon training cycle. I had been running lots of volume but a strained hamstring had prevented any faster running. With the hamstring feeling better I wanted to get a substantial number of miles a my ideal goal marathon pace. This graph includes the Saturday run and Sunday morning HRV results:

On my 18.5 mile Saturday run I included a 2 mile warm-up followed by 10 miles at ideal marathon pace (8 min miles), followed by 4 miles at a comfortables pace, and finally another 2 miles close to marathon pace at the end. After this run I am thinking my current fitness probably supports 8:10 min marathon pace but 8 flat may be stretching it. Sunday morning (April 20th) HRV results show that I am still recovering from that run. My mHRV is a bit low but more importantly the short white vertical line indicates low exercise readiness. This is also in line with my subjective sense, so as a result I will skip my planned morning easy run and check HRV again later in the day to see if an easy evening run makes sense. I am already at about 60 miles for the week so even though I had planned for 67 a day off would not hurt if waranted.

Edit -- I have seen some conflicting results in the following week. In some cases high msHRV seems to indicate good fitness readiness. I have read multiple recent studies making the case for using weekly HRV averages rather than daily values. The daily values are more contain more noise ( more variable ) which clouds interpretation. In my soon to come update I will include weekly averages as well as a weekly fitness test indicator.

Some links to peer reviewed research for those interested:

 

On the use of HRV in monitoring fitness training

see Simon Wegerifs excellent summary  of Dr. Martin Buchheits research here  

A few of the interesting findings

• Participants with the highest starting HRV were the fastest runners, but those with lowest starting HRV showed the most improvement.
• All 11 responders showed increases in their morning HRV, and the ones with the largest gains in performance showed the biggest increases in HRV.
• An improvement of 10% in 10k run time required an average of 15% improvement in morning HRV, though two participants who achieved improvements of 15% in HRV achieved a more modest 3-4% improvement in 10k time.

Buchheit M, Chivot A, Parouty J, Mercier D, Al Haddad H, Laursen PB, Ahmaidi S.

Eur J Appl Physiol. 2010 Apr;108(6):1153-67. doi: 10.1007/s00421-009-1317-x. Epub 2009 Dec 22.

http://www.ncbi.nlm.nih.gov/pubmed/20033207

also

"In conclusion, when controlled for changes in body mass

occurring as a result of growth and maturation, substantial

improvements in submaximal exercise HR and Ln rMSSD

(but not HRR) are highly predictive of improvements in maximal aerobic speed"

 M. Buchheit,  M. B. Simpson, H. Al Haddad,  P. C. Bourdon,  A. Mendez-Villanuev
* note that Ln rMSSD is the HRV measure Ithlete uses

And

"Cardiorespiratory fitness can be efectively improved during endurance training by using daily HRV for exercise prescription. A lower-intensity training stimulus, whenever attenuated vagally mediated HRV occurs, might be benificial to gain favorable response in endurance training."

 Antti M. Kiviniemi ·Arto J. Hautala ·Hannu Kinnunen · Mikko P. Tulppo 2007

 "Results of recent studies support the hypothesis that assessment of ANS functioning includes important information concerning acute and chronic physiological processes before, during and after aerobic exercise training stimulus. Moreover, we show that daily assessment of ANS activity could serve as an indicator of appropriate physiological condition for aerobic training."

Hautala AJ¹, Kiviniemi AM, Tulppo MP. 2009

 

 

More on the importance of testing HRV standing as well as supine

"Exercise-induced changes in sympathetic and parasympathetic ANS control differ, depending on posture and period of measurement. Exercise induced changes in parasympathetic and sympathetic outflow, respectively, can be extracted from measurements from supine, through the orthostatic response, to standing, thereby detecting changes in ANS that are otherwise obscured.
"However, this study also clearly demonstrates the novel relationship between HRV indicators and indicators of physical fitness during an orthostatic stressor. Participants with greater physical fitness showed increased responsiveness (indicated by increased sympathetic activity and vagal withdrawal) to the orthostatic challenge." 

 
Grant CC¹, Viljoen M, Janse van Rensburg DC, Wood PS. 2012

Relationship between exercise capacity and heart rate variability: Supine and in response to an orthostatic stressor 

"However, this study also clearly demonstrates the novel relationship between HRV indicators and indicators of physical fitness during an orthostatic stressor. Participants with greater physical fitness showed increased responsiveness (indicated by increased sympathetic activity and vagal withdrawal) to the orthostatic challenge. "

Catharina C. Grant^a,  Jimmy R. Clark^b, Dina C. Janse van Rensburg^a, Margaretha Viljoen^c
2009

also see Andrew Flatts Ithlete blog