I wanted something that could record running distance, and was torn between getting a Garmin ForeRunner 301 (which uses GPS to measure distance) and a Polar S625x (which uses inertial sensing to measure distance). Ultimately, after a thorough search of the newsgroups to find out what other's experiences were, I chose the Polar ... seemd that the Garmin had too many problems maintaining a lock on satellites in mountainous / forested conditions, and there were reports that its heart rate monitor would give erroneous data after about 2 months of use.
So, I made the mail order purchase of the Polar unit:
And out of the box it's worked great! Here's what the thing does. If you go out running, you strap on the heart rate monitor chest strap, attach the intertial foot pod to your shoe, and run. The watch constantly monitors and records your heart rate, your running pace, and even your altitude and the air temperature. The chest strap is the new all-fabric style, and I was surprised that it was even more comfortable than my previous monitor strap (a Polar T61). The foot pod is so light that I don't even feel it on my shoe:
Polar claims the accuracy of the interial measurement system is 97% without calibration, and that goes up to 99% once the foot pod is calibrated for a particular runner's style. On my first long run (10 miles) with the unit, where I had a measured distance to compare to, the S625x was actually 99.3% accurate! Pretty amazing to me, that distance can be calculated so accurately simply with inertial sensing.
The altimeter has a resolution of 5 feet, and routinely shows the elevation profile of a local run that I do that has only 50 feet of elevation change.
For use while biking, the watch gets data from a wireless speed sensor mounted to the front fork:
After the workout, I download the data to my laptop using a wireless infrared link -- the IR window is barely visible on the top of the watch. Downloading takes just a few seconds.
The software that comes with the watch is really nice. The program starts off with a calendar, that shows the last workouts -- color coded to activity (in this case, green for running and blue for cycling):
And at the end of each week is a summary of workout intensity, color coded by heart rate zones.
Each individual workout has details shown in a graph with heart rate, altitude, and speed. For example, a typical run has a graph like this:
The top red line is the heart rate, the thin red line is altitude, and the blue line on the bottom is running speed. The chart below the graph shows total distance, calories, average heart rate, fraction of the run that was ascending versus descending versus level, etc.
Data from cycling looks similar:
And each workout has a page where I can enter details about what the ride or run was like -- the use of a happy face + slider bar is rather humorous, since as the slider bar moves up and down the face goes from smiling broadly to severely frowning. A good quick way to characterize a workout! The details page also breaks the workout down into time spent in each heart rate zone:
Overall, the S625x works really well -- accurate recording of heart rate, cycling distance, and running distance. Right now I'm not using it for advanced training, but instead to simply keep track of how I've been exercising from week to week.
So, would this watch be useful for adventure racing? I think yes, but wonder if it might be considered TOO useful. Of course the cycling and heart rate functions are useful, and the altimeter would be great for navigational purposes, but having super-accurate distance readouts while on trekking legs would be awesome! Especially night-time trekking -- I can imagine it would be a fantastic way to keep track of distance covered in the absence of many of the landmarks we'd use during daylight.
The question is, would inertial distance sensing give athletes the same competitive "advantage" that GPS would, and thus would these devices be frowned upon in AR? Conversely, I've heard it argued that GPS doesn't make adventure racers to any faster or get there any more accurately ... and what's the difference between a foot pod for measuring running distance and a cycling computer measuring cycling distance?
Fun stuff!
Dave
