Saturday, February 10, 2018

Technical Analysis of a 1:38:00 RAK Half Marathon

Going sub 1:40:00 in any half marathon is considered a decently competitive time achievement for age groupers.

Consider that this year at the RAK Half, only 12% of the competing runners (both male and female) posted a gross time better than 1:40:00 and the rest 88% were slower. By net time, I assume this percentage will be still lower.

In this year's RAK Half, I bested the previous year's race time by nearly 14 minutes and certainly, I've never run a half this fast since college years, so therefore it is an all-time PB at this distance.

What does it take to run sub 1:40:00? I would like to share some of my own data to shed some technical light on the subject.

Note : Please click all images to zoom in.

Race Day Ambient Conditions

The morning of race saw a starting time temperature of 15 deg C, 88% humidity with 11 kph northerly winds (most likely measured at 10m height off the ground). Barometric pressure was 1014mbar. 

Between 7 and 9am, the temperature rose maybe 2 degree C at most.

These conditions yield a calculated air density of 1.2203 kg per cubic meter and a WBGT (wet bulb globe temperature) of around 16 deg C. 

Race Course

The AIMS certified course is 21.1 km long. The course is mostly very flat with 30-40m of total ascent making it suitable for a flat out race.

Incline data as a function of distance :

Weight Trend 

The trend of weight (without shoes etc) several weeks leading into the race is shown below. The weight trend hovers over 62-63 kg. At the time of the race, adding the mass of shoes and running attire to that figure would put me at a racing weight of approximately 63 kg.

HRV Trend 3 Weeks Before Race

A monitoring of daily heart rate variability 3 weeks from race day revealed that :

1) RMSSD fluctuated with highs reaching the weekend (Friday) of weeks 3 and 2 before the race. Hourly tapering of runs (last 2 weeks) showed a decrease in daily RMSSD.

2) Log transformed RMSSD normalized to R-R intervals, an indicator of fatigue, actually increased during the time 3 weeks before the race and declined during the last taper week.

Not reading too much into this but 1) and 2) might indicate a readiness to perform & heightened parasympathetic activity during tapering period. My weekly hours and average training paces for the last 3-4 weeks to the race are included in the 3rd plot below.

Certainly interesting and deserves more study.

HR Trimp Performance Chart Trend

The following image shows TRIMP performance chart (generated in Golden Cheetah) along a 2.5 month period from Nov 20 2017 to race day on Feb 9 2018  (I ran a 10K race in early November 2017 so I chose to start tracking PMC then). 

While absolute values are not important, the trend says I was more or less in a maintenance phase in the months of Nov and Dec by running an average of 3-4 km every day. In the month of January 2018, I picked that dosage upto >4 km every day. Therefore, I accumulated some residual fatigue indicated by the stress balance line (yellow) following which a taper period relaxed the stress balance to -4 just before race day. Overall fitness (blue line) increased gradually to a peak a week before race day. 

It is interesting to keep the -4 stress balance in context with the race performance achieved at the race. Atleast what the curve shows is that I went into the race slightly fatigued but not at a level that made me dysfunctional.  

Certainly, a performance management chart can be made using the language of external power and RSS, but to me, TRIMP and HR based PMC is much more trust-able when I want to assess heart stress.

Race Data

Aggregated run data is shown below from several devices, namely the Polar V800, Runscribe+ (beta) and Stryd powermeters.

Net Time : 1:38:00 (Data from GPS and 2x accelerometers)
Pace : 4:32 min/km | 7:18 min/mile | 13.23 kph | 8.22 mph | 3.67 m/s

Ave. External Running Power : 234 Watts  (to move center of mass)
Ave. External Power to weight ratio : 3.7 W/kg  
External Power Intensity : 95-98 % of Critical External Power 
Basis of Critical Power : Exponential fit over 90 Day power duration curve
Normalized External Race Power : 233 W

GOVSS Power : 373 W (a proxy for internal + external run power)

Ave. Heart Rate : 190 bpm
Racing HR as %  : 91% (Karvonen method)
HR Zone Distribution (Polar) 

Total Steps : 18,584 
Ave. Step Length : 1.16 m | 3.8 ft
Ave. Stride Length : 2.32 m | 7.6 ft
Ave. Step Rate : 191 steps a minute
Ave.  Stride Rate : 95 strides per minute 

Estimated Vertical Oscillation of Center of Mass : 0.061 m
Ave. Ground Contact Time : 0.215 seconds
Estimated Leg Spring Stiffness : 11 kN/m

Ave. Impact Shock : 12.2 G (correlates with vertical ground impact force)
Ave. Braking Shock : 10.6 G (correlates with horizontal braking forces)

Kinematic Variables & Their Distribution Over Time 

The following series of time series screenshots show box plot distributions of kinematic variables, something I really like. On the Y-axis is dependant variables of interest (such as ground contact time) and on the X-axis is time. 

Step Rate 
Half way point
Median : 189 spm
Overall, high cadence and very even throughout. 

Ground Contact Time
Half way point
Median : 0.218 s
Overall, low GCT and very even which speaks for the evenness in step rate and footstrike type.

Flight Ratio
Half way point 
Median : 30.9%
Overall, a slightly fluctuating proportion of flight time around the 30% mark. In all my past data at these paces, I have not seen numbers substantially higher than 30%.

Stride Length 
Half way point 
Median : 8.4 ft (2.56 m)

Stride Length (Left/Right Distribution)
A bit doubtful on the data but interestingly, it's showing that a decrease in SL in one of the feet is complemented by an increase in the other foot. The dark blue curve must be for the right foot. I'd have to continue to monitor this in past and future data to understand if this is a real variation between left and right sides or just noise.

Footstrike Type
Half way point 
Median : 9 (Between midfoot and forefoot)
This data comes from accelerometers strapped to the heel but eitherway, the indication is not far from what I thought it'd be. 

Impact Force
Half way point
Median : 12.4 G
This is not an indication of actual force but certainly a proxy for negative vertical acceleration. 5-15 Gs is a normal range. 

Braking Force
Half way point 
Median : 10.9 G
This is not an indication of actual force but certainly a proxy for negative horizontal acceleration. 4-13 G's is a normal range.

Run Power (GOVSS)
Half way point 
Median : 421.6 W
GOVSS power involves a computation of internal and external power to run and uses an efficiency correction upon metabolic demand. In other words, this plot gives an indication of total metabolic demand with time.

Pace and Power Splits

Maximum variation in pace = 21 seconds/km.


Readers might recall my post on my dismal performance in the same race in 2017. In that year, I dragged myself across the finish line in 1:52:00 and went back home pissed and determined to get better next year. 

In that post, I revealed pace and power histograms and some other interesting metrics. This season, a self-coached and methodical running streak from September 2017 resulted in a strong performance and a 12th place in my age category. 

I still think the most basic of all tools - a training log and a simple stopwatch - should inform most runners how structured their plans are, if they are making improvements and how much rest they are getting in between. 

The plethora of data metrics from inertial measurement units, heart rate monitors and GPS devices are nice to have and for the added tradeoff in analysis time, you get some marginal improvements in information which may or may not suit everyone.

Yet, we should not lose sight of the forest for the trees. Summing up some greater generalities about achieving sub 1:40:00, I have the following points :

1) Specificity of training : Commit a purpose to most runs, if not all runs.

2) Reverse your gear : Work backwards from shorter distances. You must break barriers in short distance (aerobic) racing to get faster at longer distances. Remember our friend, Riegel? A 44:00 10K will lobby harder for your sub 1:40:00 half campaign than one slower. 

3) Run slow to run fast :  Increase volume of low intensity runs and optimize volume of fast runs. 

4) Be a good guest : Our friend is Mr. Improvement, we'd like him in our house. Complement training sessions with adequate rest in between; an extensive endurance run may take 8-12 hours for supercompensation timing while an intensive anaerobic training session might require 40-60 hours for the same.  Doing stupid things when these bodily changes are taking place will shut the front door on Mr. Improvement. Corny, but this is fact. 

5) The journey counts : Take a year to work towards the half marathon goal of 1:40:00. Run with friends, run often, have fun.

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