More Stryd Experiments

In my previous post I described my first impressions of the Stryd running power meter. I've now had a chance to do a few more interesting runs and so far the power readings are looking pretty good.

Lactate Threshold Session

The first run I did since my last post was a Lactate Threshold session. This was 6km long with about 1.5km warm-up and then the remainder at my lactate threshold pace of 3:58/km. This is the pace I ran my fastest half marathon at and gives me an average heart rate of somewhere in the high 160's.

This run was recorded using the Stryd Beta iOS App synced straight to the Stryd Power Center (all graphs below are extracted from Power Centre). I also ran with my Suunto Ambit3 paired with a different heart rate strap to compare data sets. Happily the data from Stryd Power Centre matches pretty closely to that recorded by the Ambit3

Power vs Elevation vs Heart Rate

This graph shows plots for the LT part of the run with power in orange, heart rate in purple and elevation in pink. It's quite obvious to see that I had big power spikes on each of the two small hills that made up the run (around 8 minutes and 16 minutes in). You can also see a power drop during the downhill section (10 minutes).

Certainly something to work on in the future is trying to smooth these spike by adjusting effort and pace in order to maintain a steady power level throughout the run. I believe that this is much more the objective when running with power as the primary metric.

As expected, my heart rate gradually raises over time as I start to tire and this is usually what I see when I'm trying to maintain a consistent pace for a period of time. What is interesting is that average power output seems to remain fairly steady even though heart rate is going up.

What's also very noticeable is the steep rise in heart rate corresponding to the power spikes on the hills and that although my heart rate decreases after each hill it never returns to the level that it was at before that hill. I would expect that by trying to smooth out the power spikes on those hills, I would also get a much lower heart rate increase and perhaps be able to achieve a lower average for the same pace across the whole run. Something to test out in a future session and a good long term goal to aim for.

Power vs Pace

The second graph plots for the LT part of the run with power in orange and pace in blue. Not sure what happened between 12 and 13 minutes into the run as my Ambit3 didn't record such a pace fluctuation, so I'm going to assume this is just a data anomaly with the iPhone GPS readings.

What you can see from this graph is that I maintained a consistent pace across the whole run, even though there were a few small hills along the way. This consistent pace is the cause of the power spikes and heart rate raises on the hills. Again, next run the aim will be to try to keep a consistent power and let the pace vary as necessary.

Average Power Output

If I exclude the power spikes, caused by inconsistent pacing on the hills, and focus just on the two flat sections where power was steady I'm achieving an average power output of 345 watts (4.6 watts/kg). This seems fairly consistent with my 250 watts (3.3 watts/kg) recovery pace output and gives me a fairly decent baseline power figure for future Lactate Threshold sessions and half marathon efforts.

Track Intervals Session

The second run that I did was a session on the track. The entire session is shown on the plot below with power in orange, heart rate in purple and pace in blue:

This was all recorded on my Ambit3 using a second HRM strap to capture the heart rate data (as dual power and heart rate from Stryd to Ambit3 doesn't currently work). The session was divided as follows:

• Minutes 0 to 5: 800m easy warm-up
• Minutes 7 to 13: drills (skips, high knees, heel flicks etc.)
• Minutes 13 to 22: short sprints (about 30m at 80% effort)
• Minutes 22 to 55: intervals – pyramid of 200-400-600-800-600-400-200m efforts with the same distance as the previous interval jogging recovery between each
• Minutes 55 to 60: 800m easy cool down

Zooming in on just the intervals pyramid, we get the following graph:

Overall

The one thing you can clearly see is how well power tracks pace and reacts almost instantaneously. Given these were all fairly short bursts, heart rate is also following along quite well, but you can clearly see the lag at the end of each interval as it slowly returns to the recovery level. You can also see how my max heart rate increases each interval, making it a less than ideal measure of intensity compared to power.

Intervals

Power levels look pretty consistent as I would expect. The power for the first 200 is higher than any other interval (the last 200 was slow as I had a sore calf muscle at this point). The 400's have a higher power than the 600's and the 800. Both of the 600's and the 800 have a raising power towards the end as I pushed a bit harder.

Interestingly most of the intervals have a power dip at some point around the middle, probably indicating that I'm going off too fast and then slowing down too much in compensation. This isn't really noticeable on the pace graph, so either the stryd is giving me a valuable insight (which I suspect is actually the case) or it's not got it's power measurement quite right. Certainly something to play around with on my next track session.

The average power figures for each interval are:

200	402 watts
400	388 watts
600	358 watts
800	369 watts
600	362 watts
400	388 watts
200	377 watts

It's good to see that each interval either side of the pyramid has roughly identical average power. Interesting also how the 800 interval has higher watts than the 600's. However, looking at the pace graphs, I started out the 800 a bit too fast, which probably accounts for this figure.

One other thing I learnt is that using this data I am able to work out an approximate 3 minute sustainable power of something around 370 watts (4.9 watts/kg).

Recoveries

Between each interval there was a recovery period of the same distance as the interval just completed. I'm running all of these pretty steady and consistently at a relaxed pace of about 5:40-5:50 per km. Both the pace and power seem quite steady.

What is interesting from these is that average power is around 250 watts, whereas a previous recovery run had me being able to maintain 250 watts off a much faster 5:10/km pace. My suspicion is that this clearly shows a drop in running form due to fatigue from a hard interval (although see the next section also for another idea). Clearly something to work on is focusing on the power during these recoveries and trying to keep it as low as possible by maintaining good running form even though fatigued.

Warm-up and Cool-down

One slightly strange observation from this session was during the warm-up and cool-down laps. Given that these were on the track and an average pace of about 5:30/km I would have expected much lower power readings than the 250 watts that I have seen during recovery runs at 5:10/km pace on undulating roads. Instead, my power was still averaging out at about 250 watts.

I have three hypothesis to play with here:

• I run less efficiently while warming up and when tired at the end of a hard session (quite likely, but easily tested)
• 250 watts is some magical minimum figure of the amount of power that I require to get me running and I can only go up from that point
• My optimum efficiency pace is about 5:10/km and trying to run slower than that actually requires me to compromise my running performance (e.g. slower cadence, shorter strides) and that's less efficient and needs more power

This is definitely another area to play around with a bit more. I'm doing some slow runs with my children at the weekend, so will see how the results of these compare.

Multi-Terrain Run

The final run that I did was a multi-terrain recovery run. This wasn't anything particularly special as it was pretty slow and in horrible wet weather. Basically I just ran round a field five times while my boy was football training on the pitch in the middle! However what is interesting is the power map generated by Stryd Power Centre:

This map is coloured by power, with a scale from green being the areas of lowest power on the run and red being the areas of highest power, with orange being the middle between the two. Pace was a steady 5:30/km for the entire run and the terrain is pretty much flat the whole way round (3m elevation change round the whole 1km loop).

What is very evident from this picture is the change of power with the change of running surface. The bottom right section is mostly green and corresponds with a tarmac footpath and car park. The right hand side is the highest power and this corresponds to the transition from tarmac to longer grass. The entire top is in longer grass, except for the very small section directly above the football pitch that was well manicured. The left hand side was short grass but slightly wetter, while the bottom left was another area of well manicured grass.

This looks like conclusive proof that Stryd is correctly calculating differences in power requirement for running at an identical pace on different running surfaces.