Half-Marathon Alstertal

Sunday, I was racing the second leg of my Autumn campaign, a half-marathon along the river Alster in Hamburg.

Photo by Haemmboerger

It was a great day for a running race – a perfect sunny autumn day. After the morning fog cleared, the sun came out and it was nice and warm, but not too hot. My guess for the temperature was around 20°C – about 72°F.

Race report

I was going into the race with a goal of running sub-1:40 which translates to a 4:45 pace. After my speed session on Tuesday, I wasn’t sure if I’d be able to manage going that fast. But I was very confident to be able to go 5min/k pace which would be sub-1:45. So I decided to build my speed during the race, but still start reasonably fast to run a good time.

I was warming up while it was still pretty cold (the sun hadn’t come out yet), but I was already getting thirsty. So before starting I made sure to sip some extra water. (I had already decided not to race with my FuelBelt and left it at home.) By the time the race started, the sun was out in full force and it was getting quite toasty.

During the first k of the race, the pace was quite slow as there were still slower people in front of me. (Both because I lined up with a couple of friends towards the back, and you have the usual slower people that want to start at the front.) Passed the first k in about 5:30, but then it was thinning out quite well and I didn’t really have a problem to run my pace.

After the first 5k (split: just over 24 minutes) I had made up the time lost in the first k and I knew I was on track for a decent time. During the second 5k I tried to pace myself – I knew that more hills were to come and it was still a bit to go. Also, I got these usual doubts .. “I’m going pretty fast, not sure if I can hold this for another 15k”.

But everything went well. I was able to pick up the effort and the pace a bit, and by the 15k mark I knew that I had 1:45 pretty much in the bag, but I probably wouldn’t be able to make it in sub-1:40. I was working pretty hard and picking up quite a few people, but the last two k or so are just borderline hard. I managed to come in after 1:40:39 (by my own watch), well spent and needing a few minutes to get my breath and smile back.

I was pretty happy with the way things worked out, I managed to pick up the pace and effort ( even if it wasn’t quite enough to go sub-1:40). I felt pretty strong during the race, and I hope that my training during the next few weeks allows me to get some more faster next time around.

Racing with a GPS watch

This was also my first race with my new GPS watch, and I was looking forward to seeing how accurate the GPS data would be. Most of the race course was under pretty thick tree cover, so it would be quite hard work for the GPS unit. Also, having run the race quite often in past years, I knew that the race course would be pretty accurately measured, so it was a good basis for comparison. If the course was off at all, it was long, especially with the little deviation made necessary by building activities.

The GPS track ended up being a bit off course (maybe by 10 or 15 meters). The following screenshot from Google Earth shows the out and back section that were on the same path on the upper bank of the river that shines through the trees:

But I don’t think that this is really an issue. The total distance as measured was 20.49k – compared to the half-marathon distance of 21.1k it was maybe 3% percent off. For distance, that is not really a problem – 3% accuracy is probably much better than what you can get from any other way of measuring or guesstimating. It’s also good to know that the GPS distance is shorter than the “real” distance. My explanation for that is that there were quite a few turns on the course, and with positions saved every 10 meters or so, some of these turns get “flattened out” – makes sense to me.

But looking at this 3% accuracy gets tricky when you want to pace off the GPS unit, especially at the “sharper end” of my speed. 3% at a 5min/k pace is a difference of almost 10 seconds. This can make a big difference. I’m also not sure if the pace that the watch displays is going be “slower” than the real pace. When looking at the watch, the pace I was seeing was almost always quicker than the real pace. So, the pace displayed is a good indicator, but certainly not good enough to pace off it. “Perceived Effort”, HR and clock time with the course markers still seems to be more reliable. But the GPS is one more measurement that may point to being off, and it will be sufficient to keep the pace in check during the first few k’s in the IM marathon.

All in all, the Garmin 405 passed this test easily. I’m still very much impressed with the unit!