Monday, July 9, 2018

Battery for Garmin Glo

Need a new battery?

I've used a Garmin Glo Bluetooth GPS for a few years now.  It does a great job giving a fast, accurate GPS position to an iOS or Android devices and is very useful for things like in-aircraft applications, where you may want a more sensitive GPS receiver than the one in your phone.

It's available in new and refurbished versions online for reasonable pricing, typically less than US$99.  However, after a few years, the batteries fade, and if you haven't used it for awhile, the battery may not work at all, due to a cut-off circuit within the battery in case of very low voltage.  To get around this I've "jumped" the battery (using a 9V Ni-Cad) battery to get it working again, but often when you're at this point, you probably just need a new one.

That said, it's almost impossible to find a replacement battery for it.  The local Garmin distributor here in Hong Kong won't sell it, Garmin USA doesn't sell it, and even if you find one online, chances are the seller won't ship it to you due to dangerous goods restrictions on Li-Ion battery shipments.

The spare battery has had different part numbers over the years, all of which are discontinued or seem impossible to find:

Well, here's the secret:

It turns out that you can use a standard battery for a Nokia 3600 phone, and it'll work perfectly.  Chances are your local phone shop has dozens of these on-hand and can't sell them because no one uses these old, but once extremely popular, Nokia phones.  The Nokia part number is NK3600, and it is the exact same spec as the Garmin Glo battery.  Now you know! Use this information at your own risk, it's not something that Garmin saw fit to tell me, but it just works.

Garmin Glo Battery Issues and Status Indications

While troubleshooting my previously dying Garmin Glo battery, I noticed some not-so-intuitive LED status indications.  Aviation retailer Transair, has a good video that demonstrates this. It is very easy to mistake the "battery faulty" indication for the "battery charging normally" indication.

Green/Amber LED
  • Green-Green-Amber lights blinking: normal charging.  After a full charge, the LED goes off completely and you can unplug the mini-USB charger. A good battery should give you 10-12 hours of use.
  • Green-Amber / Green-Amber (alternating) lights blinking: fault with the battery, you probably need a new one.
  • Green solid light: GPS is connected to satellites.

Blue LED
  • Blue light blinking: looking for a Bluetooth device to pair with.
  • Blue solid light: paired with said device.

Thursday, January 4, 2018

Oval Chainrings as Treatment for a Hamstring Injury

I have to start this post by saying I've always been the world's biggest skeptic when it comes to oval chainrings. When I first started working in a bike shop in the mid-eighties, Shimano had a huge marketing push on Biopace, claiming less effort and fresher legs. Despite what Sheldon Brown said, I could never feel any benefit to chainrings that were anything but round.

Photo credit: Ebay seller bicyclists_retreat

Fast-track to the 21st century, when in 2014 I listened with pleasure as one of my favourite podcasters, Tri-Talk's David Warden, completely trashed Rotor's Q-rings. In Episode 71, triathlon coach Dave Warden put the Q rings through a trial using Computrainer, side by side with regular round rings. In this N=2 experiment, he found that power output using Q rings was significantly less than round rings. The experiment appears to be very well designed, controlled and executed. However, though I think Dave's methodology and knowledge are great, I acknowledge that it's one guy's experiment, and certainly not up to the standard of a peer-reviewed study. Still, after listening to the podcast, you will seriously doubt any potential benefit of Q-rings. Dave himself has said he has since stopped recommending Q-rings to his coached athletes.

So I must say I was intrigued when Bradley Wiggins won the Tour de France using Osymetric rings in 2012. Chris Froome also started using them in 2011 as he says in this Cycling Weekly video, and has won three Tours on them.  

Photo credit: Cycling Weekly

Osymetric rings have significantly more ovality than anything I have seen before. They are quite different from Biopace (which seemed to have misplaced the ovoid altogether) and much more exaggerated than Rotor's Q-rings. A bit more research in the company revealed that it was a small operation run out of France by Jean-Louis Talo, with no affiliation to any major parts manufacturer and their marketing machines. He didn't actually sponsor any of the riders using his chainrings, and some have had to request waivers from their sponsors to use them! Interesting, and very unusual for the world's best pros to use specialized equipment not for any money, but only because it gives them a performance advantage.

Still, I was doubtful... until... I developed a serious chronic case of proximal hamstring tendinopathy. I had been struggling with it for nearly a year. It's a somewhat uncommon running injury that is very hard to get rid of, described beautifully in this video by Dr. Jason Metzl. I blame long runs on rolling hills, terrain I can't really avoid where I live. The main symptoms are a loss of running speed and power, pain just below the butt when running uphill, and a sharp pain when sliding the leg back (doing a motion like scraping mud off your shoe). Thankfully, it hurt a lot less to ride a bike (compared to running), but I could feel it as a uncomfortable niggle. As a precaution I lowered my saddle somewhat, and raised the cockpit, which reduced the niggle, and I hoped that it would help the recovery (having stopped running altogether). But it occurred to me that a chainring designed to eliminate the "dead spot," that exact bit of the pedal stroke at the bottom where you "scrape" back, might eliminate the niggle. I now had an excuse to overlook my skepticism and slap some oval rings on my bike! Just like Wiggo and Froomie!

And the crazy thing is that it worked. Immediately I could feel that any soreness I felt at the bottom of the pedal stroke was gone. Where running was a 8/10 on the pain scale, and normal bike riding a 3/10, riding with Osymetric rings was a 1/10. I didn't now have to forego my favorite sport of cycling because I had injured myself running! Life was good again!

Osymetric Rings on my tri bike.  And yes, the shifting is absolute crap.

Within a few months of riding with oval rings my injury completely disappeared. A few months of riding on Osymetric oval rings did what nearly a year of physiotherapy, including deep tissue work, stretching, and acupuncture, could not do.

This result is completely unscientific, N=1, but it is consistent with what we know about muscle firing. It does make sense that unloading those muscles and tendons in the kinetic chain behind the leg would help an injury there heal. With a round chainring, there is significant recruitment of the hamstring (biceps femoris) at the dead spot at the bottom of the stroke, as shown in the image below, derived from electromyography (EMG) data, and it makes sense that a very oval ring might push some of load that further up the downstroke, to the quads (vastus medialis, intermedius and iateralis and rectus femoris). 

Image credit: Stephen Thordarson

Unfortunately the only studies that have been done on oval rings seem to be manufacturer-sponsored, and designed to show a power benefit, or a reduction in effort (heart rate, lactate, VO2). And all the studies are unconvincing if not dubious. Good summaries of the available literature can be found here and here.  My own rudimentary research doing FTP tests on different days, on the same course, in similar environmental conditions, showed no clear power benefit (and no handicap either).  Oval rings can exaggerate power readings on a crank-based powemeter, so I used a hub-based Powertap, 

It would be interesting to see if the rationale for oval rings could be made more convincing if the studies focused on helping riders deal with pathologies like hamstring tendionopathy, or in that vein, how it might reduce the loads on running muscles, which could make triathletes that much more comfortable after a transition from bike to run.

Disclosure: This unit was provided to my shop by the local distributor at wholesale pricing.  Pricing was somewhat more than comparable round chainrings from Sram or Shimano.  I received no benefit from any manufacturer in writing this article.