Garmin FR620 – max curiosity

In mid December 2013 I bought a Garmin Forerunner 620 (FR620); my first ever GPS watch. I bought it primarily because my trusty Garmin FR60 was becoming less trusty, partly because Garmin were offering a 30% pre Christmas discount and perhaps partly because I had sprained my ankle earlier in the month and was feeling a little sorry for myself. However this post isn’t a review of the 620, though if you need one you’ll be hard pressed to find one more thorough than that at DC Rainmaker’s blog, nor is it an investigation or explanation of the 620’s VO2 max feature provided by Firstbeat Technologies; since I have little or no insight to provide. I am just curious to know where the 620’s estimate of my VO2 max is going …

historic VO2 max graph to 8 June 2014

My FR620’s various revisions of its estimate of my VO2 max. Taken from the ‘classic’ view at Garmin Connect.

Whilst not every graph tells a story this one does: Point A is New Years Eve 2013 and my first run with the 620. Previously it had remained shiny and new in its box, or at least on my wrist in purely decorative fashion, and had never been used. An initial value of 50 seems to have been the 620’s default starting point. Fitness wise I was about three weeks complete rest off full fitness having sprained my ankle earlier in December. By point B in mid February 2014 I’d returned to full training and was about to PB at the Brighton Half Marathon though my time, 88:16, was well short of the 74:50 predicted by the 620! At the end of April point C was my first run for 43 days, having sprained my ankle for a second time on 18 March, hence the straight line immediately preceding it. The 3 point drop in VO2 max estimate would seem a reasonable reflection of 6 weeks rest. A few days into May I reset my 620 to address an apparent issue and it appears to have returned to its default estimate of 50. Point D is a couple of runs after this reset. Point E is the 620’s latest estimate after five weeks or so of regular running. The table below summarises the five points and the 620’s associated race time predictions alongside my current PBs.

point date VO2 max 5k 10k HM marathon
A 31 Dec 2013 51 20:24 42:19 1:33:41 3:15:07
B 13 Feb 2014 63 16:19 33:53 1:14:50 2:36:33
C 30 Apr 2014 60 17:01 35:20 1:18:04 2:43:12
D 7 May 2014 50 20:50 43.12 1:35:40 3:19:08
E 15 June 2014 57 18:04 37:29 1:22:53 2:53:05
current PBs 18:55 39:33 1:28:16 none

Reviewing the rise from A through B it appears the 620 was initially acquiring data on my fitness, revising its estimate of my VO2 max accordingly and that it had settled on a figure somewhere between 60 and 63 since it had ceased to rise even before the tail off in fitness to C due to inactivity. Whilst the initial shape of the graph is understandable the actual VO2 max estimate at B seems excessive. Or at least the related race predictions seem highly optimistic given my current targets.

In this initial period I am not entirely sure that I had entered good estimates of my maximum or resting heart rates into the 620 and in fact it may have been an adjustment to one of these entries which prompted the end of the relentless rise in VO2 max estimate just after point B. I have assumed for now that these inaccurate entries were the reason for the apparent over estimation of my VO2 max / race performance.

At the point of reset I ensured accurate estimates were entered; 172 for my maximum HR and 45 for resting HR. The maximum HR may even be a little conservative; it’s the maximum value I’ve recorded during the closing seconds of a 5k PB. The resting HR I am more confident of as it is the average of a series of careful measurements which themselves varied very little. Either way these values should not encourage the 620 to over estimate again. Perhaps coincidentally the 620’s latest race predictions at point E appear just about realistic given my current PBs, or at least the 5k does; as the race distance increases the predictions again disappear into what I would consider unattainable optimism. The difference from event to event though I expect is more to do with my own ability/preference for shorter distances rather than any error in the 620’s VO2 max estimation.

So, as I said at the outset, at this point I am curious to know just where the VO2 max estimate is going: If it continues to revise its estimate upward along a similar trajectory to that originally recorded from A to B, I will probably have to conclude that the feature is interesting, but not useful except perhaps as a measure of relative fitness. On the other hand it may be that the more accurate values for maximum and resting HR enable the 620 to come to a more believable conclusion. Unfortunately as my ankle continues to falter in its recovery I’m again inactive as a runner so there’ll be no new data for the 620 to consider in the short term. Given that points A and B were just over 6 weeks apart and the 620 was still revising its VO2 max estimate it would seem that more than 6 weeks running, and all of it at full fitness and running health, are required to enable the 620 to settle on its best estimate.

I’ll post again when points F and G come to pass …


Success! [5:2 Diet, Epilogue i]

Those of you who have been enthralled by my recent series of posts (the precursors to this post being chapters one, two and three) regarding my attempts to control my eating and lose a small amount of weight will perhaps be disappointed that we are entering the epilogue. (For completeness the effective prologues “Can’t Weight!” and “Redemption?” should also probably be included as part of the canon.) However, I cannot contain my satisfaction a moment longer. I weighed in this morning at 67kg!

something something

Weight change from 25 March to 9 June 2014 achieved using Fast Diet approach to weight control.

Whilst 67kg is strictly short of my 66kg running weight goal, I decided this morning – a scheduled fast day; currently Mondays and Thursdays – not to fast and to adopt a practice of weighing in on each scheduled fast day and only fasting if I weigh more than 67kg. This formalises what I have been doing by feel over the past few weeks. On a few scheduled fast days I have either skipped the fast entirely or modified the day so that I have eaten a light breakfast and even lighter lunch as normal, but have then also eaten a light dinner rather than omitting it entirely as has become my habit. The Fast Diet book suggests moving from a 5:2 pattern to a 6:1 pattern as an option to maintain weight which is essentially what I have begun to do.

The last few weeks have been successful not only in that I have effectively achieved my weight goal, but also that I have not binge eaten either. As a direct tool for weight loss the Fast Diet has certainly worked for me. But more than that, and the core reason why I intend to continue fasting as part of my lifestyle, I have found that each fast day effectively resets and re-calibrates my physical sense of hunger, re-sensitises me mentally to my eating choices and reasserts my control over eating and my weight.

As of the last few weeks I am back to running around 20 miles a week and I’m aware that there is still significant recovery required; for my sprained right ankle which is still noticeably ill at ease in comparison to the left one, for my cardiovascular system as it adjusts to my renewed activity after 6 sedentary weeks and for my body composition; dieting as I have been and mostly without exercise I have certainly lost significant muscle as well as fat. I’m looking forward to returning strength, fitness and my next PB!

Stillman running weight

I first came across the Stillman running weight formula sometime in 2012 although I can no longer find the particularly thorough article in which I first read about it. The formula presumably comes from the pre internet age as I can only find it referred to indirectly online and even then some articles* appear to have been published offline before appearing online.

The formula reflects the simple observation that elite runners are typically lighter than non-runners (of healthy weight) and that as the event distance increases so the athlete tends to be proportionally even lighter. Whether there was any physiological justification of the formula is not clear from the articles I’ve seen; it may be that Dr Stillman derived the formula mathematically to best model the weight of elite runners at the various event distances. I’m writing about the formula not to prescribe a particular running weight as “right”, but purely because I’ve used it to set a personal running weight goal and found using it interesting.

The formula uses imperial units for both weight and height and though I’ve seen the formula re-expressed to use metric units I’ve found it simpler to convert my metric height to feet and inches via Google and subsequently convert the imperial weight value produced to kilogrammes. If imperial units meet all your needs it’s a calculation that can easily be done mentally.

The formula can be expressed concisely in two steps:

Calculate a base value for a healthy, non-active individual by adding 5½ lbs (male) or 5lbs (female) for every inch in height over 5 feet to 110lbs (male) or 100lbs (female).

Modify the base value reducing it by a percentage dictated by event type; sprinters 2½%, hurdlers 6%, middle distance runners 12% and long distance runners 15%.

In my case, a five foot ten inch male, the base value is calculated as:

10 x 5.5 + 110 = 165 lbs = 11 stone 11 lbs = 74.8kg

And modified as below for each event type. [Note  the additional information on what constitutes a sprinter, hurdler etc.]

event type reduction weight BMI
non-active 11 stone 11 lbs 74.8kg 23.7
sprinter (100m – 400m) 2½% 11 stone 7 lbs 73.0kg 23.1
hurdler (100m – 400m) 6% 11 stone 1 lb 70.4kg 22.3
middle-distance (800m – 10K) 12% 10 stone 5 lbs 65.9kg 20.8
long-distance (10 miles plus) 15% 10 stone 0 lbs 63.6kg 20.1

I spent some time considering my racing weight in the context of the formula during early and mid 2012 and in the process decided I was most definitely a middle distance, not a long distance, runner. That is quite likely the case as subsequent performances over 800m, 1500m and one mile would appear to confirm, but at the time it was more in the harsh light of the results produced by the formula. When I first completed the calculation, the goal weight for even a middle distance runner seemed to border on the impossible; I had come close to 70kg / 11st as an adult, but only momentarily. Nonetheless by the time I set my running targets for 2013 I had fixed my goal at 66kg / 10st 5lbs / BMI 20.8.

By August 2012 I’d come close to 70kg / 11st as an adult, but only momentarily.

By August 2012 I had come close to 70kg / 11st as an adult, but only momentarily.

Writing now, within 2kg of my goal weight, it doesn’t seem extreme to any degree; it’s remarkable what a change of position does for perspective. I’ve read that every pound of excess weight lost can be expected to produce a two seconds per mile increase in pace …

event PB weight at PB hypothetical PB
at 66.0kg
800m 2:25.9 71.6kg 2:13.6
1500m 5:18.2 71.2kg 4:56.8
1 mile 5:31.7 73.7kg 5:08.8
5k 18:55 73.5kg 17:13
5 mile 31:36 71.5kg 29:35
10k 39:33 71.6kg 37:00
10 mile 66:41 71.3kg 62:48
half marathon 88:16 73.2kg 81:20

There are some pretty exciting numbers there! I’m looking forward to achieving my goal weight, returning to full fitness after my recent ankle sprain and then rigorously testing out my new physique to see just how much difference it makes.

* See articles at Serpentine and Horwich RMI Harriers club sites.