Friday, December 14, 2012

Garmin Forerunner 610

At the Low-Key Hillclimbs awards party this year, I received an extremely generous gift from some friends this Christmas: a Garmin Forerunner 610. They had observed I'd been running with my Edge 500 coupled with a Garmin wrist strap, a functional if somewhat klunky solution to on-the-run GPS.

In the rain at CIM it wasn't easy for me to see the Edge 500 screen: water droplets and low ambient light made for poor viewing conditions. So I decided early on to run blind: go on perceived exertion. This made sense to me in any case since, lacking any training data in the wet and windy conditions, I didn't know what my target pace should be anyway. So after getting a 5 km split, I allowed the Edge to flop upside down on my forearm where it was located (I had a gel under my compression sleeve which occupied the normal watch position). I left it there to collect data silently for post-run analysis (it was issuing beeps every 5 km, but during the constant rain of the run I didn't notice any of these).

The Edge is designed for cycling, and while riding I would have been able to see the screen better. While riding the unit sits stationary upon my stem, my head stays in a stationary position relative to the stem, and so there's better opportunity to focus. When running I'm bouncing up and down, making focusing on the screen more challenging.

Before talking about the Forerunner, I will link to the DC Rainmaker review. He does incredible product reviews, and I won't attempt to reproduce any information contained there. I'll assume you've read that review, and will instead focus on my perceptions. Rainmaker's focus is a bit different than mine: for example he devotes several paragraphs and photos to the device's packaging.

One issue I always worry about is weight. My Forerunner 610 with its integrated strap has a mass of 77.5 grams. On the other hand my Edge 500 with its auxilliary strap has a mass of 59 grams for the Edge itself + 17 grams for the strap totalling 76.3 grams. The difference is 1.2 grams. This weight difference is obviously insignificant, and would change if I trimmed the straps to better fit my rather low-circumference wrist.

The issue of watch weight is interesting, however. Wrist weight must be supported by arms, which can fatigue from the isometric load (although I had no arm fatigue problems during the CIM, so isometric loading of arms may be an issue only with ultra events, if at all). Arm motion is like a pendulum: they swing through a point of minimum potential energy and maximum kinetic energy, reach a point of maximum potential and minimum kinetic energy, then fall back again. This in principal takes no energy: a pendulum can swing a long time without energy input. But arms are connected by muscles, tendons, skin, and clothing. Each of these dissipates energy. The result is arm motion comes with a certain energy cost. The question is whether adding mass to the wrist changes this energy cost. I don't see a reason it should. For example, when I'm carrying a really significant load in my hand, for example a water bottle or food I've picked up on a lunch run, I swing the arm holding the load less than the other. So I suspect the more mass loaded on my arm, the less I swing it. So I'll assume the mass on the wrist is the same as mass on the body.

Running speed is generally considered to be inversely proportional to total mass. I have generally made the mistake of assuming this is true: but analysis suggests otherwise. If I uniformly increase the mass of all parts of the body, then speed should indeed be inversely proportional to mass, neglecting mass-dependent differences in run efficiency (for example, if I had zero mass I couldn't run at all, since I would have no grip on the road). But I concluded using energy analysis that on level ground the energy cost of running should be relatively equally partitioned between center-of-mass motion and foot-and-leg motion. If I add 1% to the center-of-mass, and this mass is inert other than the ballistic trajectory of the center of mass, then this should increase my total energy cost by only 0.5%, not 1%, and should therefore reduce my speed by only 0.5%. In contrast, if I add the same mass to my foot, that would slow me substantially more than 1% (it's been documented 100 grams of foot mass, well under 1% total body mass, on average decreases speed by approximately 1%).

If I weigh 59 kg with clothing, the load of an additional 1.2 grams, assuming it affects only center-of-mass motion energy, is 0.12 seconds per my CIM time. Obviously that's totally insignificant in comparison to other differences between the two. On the other hand, if I compare the Edge versus no GPS, that's 8.0 seconds (8.1 seconds for Forerunner versus no GPS). 8 seconds is more significant: if 1000 runners are finishing per hour that could well be a loss of 2 places. But I gain enormous benefit from having post-race data, so even if you think the watch provides no utility during the run itself, I consider an 8-second price worth paying. On the other hand, it takes very little improvement in pacing optimization to gain back those 8-seconds, I suspect, so I think the GPS is win-win. (and I'm comparing here versus a bare wrist, versus my wristwatch the difference would be less).

wrist shot

The Edge 500, despite being slightly lighter, looks like a cycling computer jury-rigged onto my wrist, which is exactly what it is. In contrast the Forerunner looks like a real watch. The Edge 500 with its old Forerunner strap is uncomfortable: the straps, if tight enough to keep it from moving around, dig into my skin, so I prefer wearing them over sleeves. The Forerunner strap is comfortable: it is strap is broad and supports the weight of the GPS unit nicely. I have no problem wearing the Forerunner all day while I wouldn't consider doing that with the Edge 500.

The screen layout is nice and simple. The buttons to start and stop the timer are easy to hit when I want to hit them, but unlikely to be accidently pressed when I don't. And unlike the Edge it has a touch screen which is easy for switching between virtual screens. For scrolling through menus it's a little less than optimal, as it's easy to accidently select menu options when touching the screen to scroll it. But fortunately it's not necessary to change menu options too often. The touch screen is an obvious upgrade for the successor to the Edge 500.

An obvious difference is that pace is provided as time/distance, rather than the distance/time typically preferred by cyclists. That Garmin couldn't squeeze time/distance into the Edge 500's numerous field options provided for customization is slightly cynical: it's an obvious attempt at differentiation to encourage multi-sport athletes to buy both an Edge and a Forerunner since runners generally prefer time/distance by convention, while cyclists prefer distance/time.

There's also a "virtual partner" for pacing. This is nice: you set up a target pace, and it tells the distance and time relative to the virtual pacer. This seems enormously useful for trying to hit a marathon BQ time target. But I don't want to sell short the Edge 500: it also has a similar option. If you go to "workouts" you can define a workout of distance 42.2 km (marathon distance), then set a target range for speed from 12.35 kph (3:25 marathon) to 14.06 kph (3:00 marathon). The idea is to keep my speed within a target band, the 3:00 pace set on the fast side for downhills. I didn't do this for CIM, and that was likely a mistake, although the screen visibility and alarm audibility issues in the rain would still apply.

But apparently I'm not the only one who finds audible alarms not 100% sufficient. The Forerunner additionally has a vibration option. Every km, for example, it buzzes my wrist, and a split appearts on the screen. The Edge 500 has an alarm but no vibration.

I did my first medium-length run with the Forerunner, 10 miles around Sunnyvale, and it was very nice. I ran with it again the next day with another ten miles on the Steven's Creek Trail. I liked the fact that every km my wrist vibrated and I could see my pace from that km. Runs in autocentric suburbia are frustrating due to long-cycle traffic lights (in contrast my runs in San Francisco have surprisingly little stopping except for a few key street crossings). These result in delays which tend to pad the km average pace. But despite this it's useful.

The default main "timer" screen has three fields: time, distance, and last lap pace. The obvious omission is current pace. Current pace with GPS is always tricky, as small errors in position can result in large errors in current pace. I know with the Edge 500 I've found using current speed to guide my pacing unreliable and even depressing. I'll be going at what I consider a good clip, look down, and see I'm well under my target pace. Or I'll be running at what feels to be target pace and the speed display tells me I'm well over. I think I have a better feel for present pace than the unit is able to provide. However, pace for the previous km will be much better assuming the GPS signal is good (for example, I'm not running between tall buildings or in a canyon). That help calibrates my perceived pace. For example, at CIM during miles 20-26 when both legs were hurting I thought I was running substantially faster than post-race data analysis revealed. I could have easily picked that up from km lap data. The Edge 500 is perfectly capable of showing the same data, and indeed I had it set up to give me 5 km splits, but I wasn't using the data I had available. But the message here is I think the default screen on the Forerunner is probably good.

But there's space for two optional screens, and all screens are customizable. I activated one of the optimal screens and put distance, instant pace, and elevation. Elevation is nice for trail runs which tend to have long climbs and elevation can be a good guide to distance to the top. I was a bit surprised I didn't see "total elevation gain" as an option, but that's of questionable utility anyway.

When I ran using current pace, it was surprisingly stable, free from the wild deviations of the Edge 500. But the Edge series is optimized for cycling, where rapid accelerations are common, and the cyclist wants the numbers to respond within a small number of seconds. However, with the Forerunner, optimization is for running, where typically a runner plods along at a fairly steady pace. Thus the Forerunner evidentally uses considerable time-smoothing for its current pace number. I could see this when I would briefly slow and then return to my original pace, and it would take close to 30 seconds for the speed to recover. But an advantage of all of this smoothing is the instant pace agrees fairly well with the split which shows up when my next kilometer's auto-lap completes.

The uploading of data I don't find as convenient as the Edge. The Edge mounts as a USB drive, while the Forerunner requires comminication via a browser plug-in. With Garmin Connect, I had no problems, but with Strava I had difficulty getting my most recent activity to appear. Curiously, if I uploaded with Garmin Connect first, then uploaded to Strava, I always saw my most recent activities. One thing worth checking out for this purpose is the Suunto ANT+ Sport USB stick (see Rainmaker review).

For GPS comparison I did my second 10-mile run, and out-and-back on the Steven's Creek Trail in Mountain View, California, with both the Forerunner 610 and my HTC Incredible phone running the Strava Android app. The app was in a belt pouch with my wallet-type-stuff, while the Forerunner was on my left wrist. Out near the San Francisco Bay, with few obstructions, the phone seemed to be slightly better: the outward leg and the return leg were somewhat tighter. In particular, I did a jog right-left across a bridge which narrowly constrained my path, and the phone showed the outbound and inbound trajectories essentially overlapping, while the Garmin had a clear gap. But then when I got in among obstructions, trees lining a path through an office park recently taken over by Google, I thought perhaps the Garmin looked slightly better: there was in particular a little lateral jog in the Android data which wasn't evident on the Garmin. I had the Garmin on "smart recording" while the Android samples at 3-second intervals. I will try putting the Garmin on 1-second sampling to see if that changes things. The difference in sampling rates can affect the tendency to see route anomalies. In summary I can't say for sure which was better. GPS data quality wouldn't be a deciding factor in which I used.

So overall I really like it. It's definitely the GPS souce of choice for me my next marathon, which looks to be Napa on 2 March.

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