Volker Nolte reviews Coxmate GPS

 

I had the chance to use the Coxmate GPS monitor in my training and have been asked to put my feedback in writing. Before I do this, it should be clear what I am looking for in a performance monitor for rowing. I use a performance monitor in research, my coaching, as well as in my own rowing. In both cases, it is important that the monitor produces reliable and precise feedback that can be used to monitor my physical training and technique, as well as controlling tactics in races and high intensity pieces. Ideally, the monitor also has the capability to store all the data during rowing, so that they can be analyzed afterwards. I need to be able to rely on the data and see immediately if a technical modification or change in effort produces a specific feedback.

I used for my testing the new Coxmate GPS parallel to the Nielsen-Kellerman SpeedCoach Gold. I am very familiar with the NK unit and numerous tests indicated the accuracy of that unit when properly calibrated. Therefore, I consider it as the ‘Gold Standard’ so-to-speak that gives me a solid base to compare. Since I row on a lake without current that has a buoyed and surveyed 2,000m Albano Course, it is easy for me to calibrate and evaluate accuracy. The lake is wide open with no obstructions like mountains or large buildings around that could interfere with the view of satellites.

A second test battery was done by one of the most experienced and best rowers on the University of Western Ontario rowing program to receive additional feedback.

THE MANUAL

The manuals that are delivered with the unit or can be downloaded from the company’s website need improvements.

Of course, it is challenging to present information for all the many monitor options, but it is somewhat frustrating to find out features through trial and error, or to not understand others. For example, you can receive feedback about “ratio”, but the manuals don’t explain what it is.

There are also some videos available that help with the monitor and the analysis program, which are a step in the right direction, but one does not have always access to a computer where a piece of paper could be of better help.

THE MECHANICAL SET-UP

The Coxmate unit comes with three different setup options. I tried the connection to the stretcher adjustment rail and the slide on mechanism to a NK bracket.

Coxmate GPS mount spare kit

Coxmate GPS mount spare kit

A glass filled plastic pin is used for the stretcher rail connector that is supposedly pretty strong. Not only did the monitor shake on this mechanism what made it harder to read the screen, the pin actually broke when we switched the monitor from one boat to the other. This was of course our mistake and we may not have taken enough care, but this may be an area of concern that this part would need some more strengthening.

Of course, it is very handy to have such a universally usable mechanism, but I ended up using the slide on to the NK bracket.

THE COXMATE GPS MONITOR

The first thing that you realize when you turn the monitor on is the colourful touch screen. This is a nice

Coxmate GPS display 5 units

GPS display 5 units

and neat feature that opens a large number of options on each screen to immediately choose from.

According to the manufacturer’s information, the battery life is ~6 hours. We could not quite realize this length of battery life. After two normal training sessions of about 75 min each, the battery indicator showed still three bars, but it quickly went down to only one bar during the next workout. According to the manufacturer, the indication is designed to be slightly pessimistic, so you are inclined to re-charge the unit. GPS obviously uses considerable energy and the size and quality of the battery would come with a price, so you have to keep an eye on the battery indicator and accept the inconvenience charging the unit frequently.

When you set the unit to the rowing feedback screen, you are down to only two colours – black and white. You have the choice of colour combination and I liked the black numbers on white background best. This is probably an individual preference, but the thin print of the numbers should definitely be changed to be bold.

While the touch-screen is nice, ideally it should be larger. Like with the battery, a larger screen would affect the unit’s price, but the current screen size limits you with the readability of the information on the screen, especially while rowing. This is especially important for rowers that need prescription glasses.

Also, one needs to think about the number of fields you want to have displayed. Currently, you can choose between either two or five fields. The monitor lets you choose the information that is displayed, but two fields are not enough! I know the monitor gives you the option to use the ‘changing screen’ with the two field display. This means that the information switches in the two fields from stroke to stroke. Personally, I do not like this option, too much focus is needed, since one would have to keep an eye on the monitor for several strokes consecutively which takes a lot of focus away from the task to row well.

For good rowing feedback, you need the following essential data presented: stroke rate, splits or speed, distance or time! Stroke rate and speed information gives you the essential pieces of information about your performance and effort, and without distance or time, you cannot monitor training pieces. Therefore, two information fields are not enough.

However, five fields are too many. You cannot compute such a variety of data and the digits become so small that they are hard to read. As long as you can choose what you want to see, three fields would be ideal in my mind, which is currently not an option in the program.

While the screen size is already limited and with it the size of the digits, there is too much space taken by the “Ready”/”Run”/”Stop” field that is displayed next to the measurement numbers. Use different background colours or other features, like red for ‘stop’, green for ‘run’ or blinking for ‘ready’ to indicate the state in which the monitor runs at a time, but use the whole space for real information.

The monitor offers several more options like “Recall” and “Set-up” that would take too much space to discuss appropriately. It also offers to select “Workouts” and “Navigation” which are of course neat features if you like to pre-program your training or pre-set the path you want to row. Such settings would keep you on track with your training and remind you of turns or stops you have to make. It would require some preparation time to set these things up properly, but after some time of getting used to them, they could come quite handy.

Coxmate GPS rowing, crew, speed measurement, rowperfect

Three boxed Coxmate GPS units

THE DATA PRESENTED

Every rowing monitor provides time and stroke rate information. The Coxmate monitor provides these data without any magnet necessary. The built-in accelerometer starts the clock and detects discrete positions of the stroke to calculate stroke rate. Both features work well and precise and can be trusted. In fact, the manufacturer feels so confident about the accuracy of the stroke rate measurement that it is presented to one decimal place. As a rower you have to learn to interpret such data. I am not sure, if it is necessary to know whether you row 20.4 or 20.5 strokes per minute during your steady-state training? I actually believe that up to 0.5 strokes per minute is a natural fluctuation of stroke rate for every rower, so you expect to see the first decimal place changing all the time.

A very interesting feedback is speed which is obviously connected with distance measurement. Currently there are two different measurement systems on the market: impeller and GPS. It is an ongoing discussion which is better, the impeller system giving more stable feedback and instantaneous response, but needing an impeller, wires and calibration while the GPS’ big plus is convenience, since it works in any boat, is easy to install and does not need calibration. One needs to realize that the two systems actually measure two different distances/speeds: the impeller measures relative to the water and GPS measures relative to land. It remains an ongoing discussion what is better and how a rower needs to interpret the respective data especially in changing environments like wind and current. I will leave this for a different time.

However, it is important to receive accurate and stable measurements when rowing. Here is my experience with the Coxmate GPS monitor:

  • It takes about 10m until the unit starts measuring distance. This means any distance measured is off by at least 10m. On the 2,000m course that I used, the two units that I compared presented in the range of 10m exactly the same measurements. The final distance rowed was in the range of 5 – 10m to the surveyed distance for both units which I would consider very accurate.
  • When you start rowing or when you switch speed/intensity there is considerable delay with the Coxmate unit until the measurements catch up to the actual speed. It took anywhere from 7 – 12 strokes until the numbers were ‘correct’. In most of the situations one can live with the delay, e.g. when you start a long distance piece. However, if you for example plan to do high intensity pieces of short duration like 30 sec or 30 stroke pieces, you will not get any meaningful information for the first 10 strokes (except for SR). The impeller system is in these instances far better.
  • The splits presented by the Coxmate unit “jumped” quite a bit, means while I was rowing with constant speed, the split numbers varied up to +/- 5 sec from stroke to stroke. I tried different settings and combinations. The numbers became a little more stable with averaging “5” setting, but it took more strokes to get to the proper level. Again, the impeller system was much more responsive to speed changes.
  • Distance per stroke is called “cover” and could be an interesting measurement. However, I saw large variations of this data of in average ± 1 m from stroke to stroke that would not help me in my training. In one training while I was rowing at constant SR and speed, measured by the impeller system, the distance per stroke values varied even by up to

    ± 1.5 m. Rowing at constant SR and speed of course would mean also that distance/stroke is constant, which was not achieved by the GPS unit.

THE ANALYZING PROGRAM

The initial download of the analyzing program on to my computer was not straight forward. The manufacturer tries to protect from illegal downloading by having you enter some code that only buyers of the unit will receive. This may or may not be necessary – who would download the program without having a unit to use it with? – it certainly inhibited my progress, so that I had to use the company’s help to get the job done.

After downloading the analyzing program, it was easy to navigate. Downloading the data was fast and simple. One need a little bit trying, but the program is in general self-explanatory. Generating a graph of the data is easy and the graph is displayed in proper size, however the scales, especially on the vertical axis need improvements. The fonts are too small. The scales and tick marks need to show numbers.

The display of the graphs were acceptable. The splits showed the considerable variations that were discussed above. They are simply too large to help with any meaningful interpretation. Even the variations in the stroke rate seemed larger than observed during rowing. Since the magnitudes were not presented on the scale, it size of the variations can only be speculated.

IN CONCLUSION

The Coxmate GPS is clearly based on a unit that was designed for bicycling and running. The velocity in these sports are more constant, so that the measurements are more stable. In rowing, we have the situation that boat speed varies considerably over one stroke which takes in general between 1.5 – 3 sec. This situation presents for a common GPS system a huge challenge, so that we see these typical speed variations.

Additionally, there is an inherent delay in catching up to speed changes, since speed data is calculated over a number of strokes.

Finally, if you are rowing on a river with current and in wind, you need to learn to interpret the GPS feedback. All these factors are limitations of a GPS unit.

The Coxmate unit with its colour touch screen and several of its features is a good step in the right direction. Its price is certainly an advantage. Depending on the interest and expectation of the rower, this unit can be acceptable for an entrance level or recreational rower. If you are a serious trainer, you may not be completely satisfied with the current model.

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Source: Rowperfect

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