Tuesday, 3 December 2013

Detraining - what happens when you take it easy for a month

After my last race of the year, the Jedburgh Thee Peaks Ultra, I decided to take the month of November off training and just run when the sun was out and just for fun.  I ran a total of 58 miles in November, compared to 185 miles in October when I trained for and raced at Jedburgh.  This month I'm now returning to training but keeping things easy to gently ease myself back.

What has surprised me is just how quickly I have lost fitness over the past 5 weeks since Jedburgh, I have noticed that I am getting more muscle fatigue and even have had Delayed Onset Muscle Soreness (DOMS) in the days after even modest runs.  My heart rate for a given pace is also higher, and the calories per mile reported by my HR monitor for each runs has risen steadily through this period.

The average effective efficiencies (normalized for hills and distance) of my runs tell the sorry tale of the de-training I've seen - I averaged 82 calorie/mile for October, 87 for November and 90 for the two runs I've done so far this December.  That's a 10% reduction in efficiency in just five weeks and I didn't even stop running completely, just reduced by mileage from 45 miles/week to 13 miles/week.

I am quite perplexed by the extent of de-training I've seen, is this normal, is that what others see as well?  My scientific inclination is also drawn to finding out in what ways my body has changed during this period of lighter mileage and de-training.

My own thoughts are really just a jumble of possibilities:

  • Mitochondria populations in my muscles has decreased through lack of need for them all
  • Muscles have atrophied through lack of stimulus
  • Muscles have begun rebuilding after a big month of running and the newly configured muscles need to developed aerobically before I see the benefit
  • My aerobic fast twitch muscle fibres due lack of aerobic exercise have reverted to being more like fast twitch fibres rather than aerobic fibres
  • Weight changes - I might have put on roughly 1% in weight, pretty negligible but I guess it'll account for a tiny bit of the loss of efficiency
  • Blood volume has reduced
  • Loss of adaptations for heat loss

I suspect the last two might well be the most significant factors, but I've never read a paper or articles discussing de-training so it's all just speculation.  One thing I have noticed is that calories reported in the first mile of running has only gone up around 3% but the average has gone up 10% showing that I have much more significant HR drift than I did prior to taking it easy.  This makes me suspect that my ability to handle the accumulation of heat has been significantly impaired as I find it difficult to recoil my muscle fibres and populations of Mitochrondia have been slashed enough to explain a 10% loss in efficiency.

If you have insights please leave a comment as I'd love to know what others think might be happening when we de-train.  As I get back into training it'll be interesting to see how quickly my efficiency returns, fingers crossed it won't be months before I get back to near where I was back in October.


  1. It might not all be detraining - it's also wetter and muddier underfoot. The colder temperatures might affect efficiency of your muscles and respiration? Winter clothing is probably also a bit harder to run in than shorts and t shirt.

    I'd be really interested to know, how do you calculate (and normalise) your average effective efficiency?

    1. The underfoot conditions haven't been too different, and the colder temperatures do generally reduce my HR for a given pace - the coldest day in the last week of training I posted my best figures for 5 weeks, while it was warmer today I my efficiency is down by a few percent.

      Clothing may make a small difference, but I suspect it's main effect will be on how easy it is to get rid of excess heat than the weight or effect on ease of movement. I think if I match the clothing to the conditions well I don't see much effect.

      Normalizing my efficiency is a bit of black art that I've developed through logging my average HR, calories estimated from my HR monitor, the distance and elevation/descent of my runs from GPS logs. I've developed a mathematical formula that combines the distance, elevation/per mile and calories per mile to provide an "effective efficiency" which normalizes the calories per mile. I'm still experimenting with different formula and coefficients to get a best fit through my data, while not perfect it's become reliable enough to know roughly how fit I am.

      I've used this data and formula to estimate race finish times, but again it's still a black art, things like adrenalin on the day, weather conditions on the day, under foot conditions all play a part which you can't easily factor in. The more races I do the better results I'm getting as I tweak the way I calculate things.

      As the methods I'm using are still evolving I not yet confident enough to publish all the details. I currently use a spreadsheet to do the maths which I'm happy to publish but without alot of explanation it'd be different to know what it all means. Long term this type of analysis could be done via phone apps and online training logs. I few of the skills (I'm real-time graphics software consultant for living) required to contribute to such a project but alas not enough time.