With the addition of two new models - the Polar S625X and the S725 - there are even more Polar S-series heart monitors to choose from. Here is what you need to know to decide on the right model for your sport - whether it's running, cycling, duathlon or triathlon.

Triathlon and Duathlon
Polar threw us a curve here because the 700 series monitors ( S710, S720, S720i) have always been the right choice for multisport, while the S610 and S610i were for runners. That was then, the S625X is now. The S625X proves out to be the best multisport training tool ever made. They have added an inertial technology footpod which ships with the S625X, to give running distance and pace. This is the same technology as in the Nike running products except smaller, lighter, and more water resistant, and claiming longer battery life (we haven't tested that claim ourselves yet).

The S625X has a nice set of features and options for multisport. Most important, of course, is that it is compatible with all of the Polar cycling inputs (speed, cadence, and even power) - giving it all the cycling features of the S720i. If you are considering moving up from the S510 or S520, those speed and cadence wireless sensors you have now will work on your new S625X.

If you are a runner or triathlete that has been waiting to buy a downloadable monitor - you are lucky you waited. The S725 (and S720i) models are not compatible with the footpod. But the 625X ships with a footpod, and is compatible with all the Polar cycling sensors. This means that you can combine the S625X (shipped with a footpod) with the inexpensive speed and cadence monitors ( or the power option instead) and have a complete system for both running and cycling with every type of data Polar creates. If you start with the S725, you won't get the running speed and distance data.

We wanted to be sure you were getting all the cycling features with the 625X, so we did a comparison between the models regarding the cycling features, and there is nothing missing in the S625X (plus cycling options). It still supports configurations for two bikes. It stores just as much training data. It has the same altimeter features (missing in the earlier S610i). We have used the S625X and S725 side by side in every type of cycling situation. There is no advantage to training with the S725. Be sure to purchase the add-on speed sensor if you want speed and distance data for the bike. (And consider getting the optional cadence or power sensors.) In short, the S625X is a great monitor for the athlete who wants to have it all (both running and cycling speed data).

Our pick for triathletes and duathletes - the Polar S625X.

Cycling
If you are a cyclist that is not interested in running - even as cross-training - then we suggest the S725, (or the current model the S720i). It comes down to price, and there is not much difference. The S725 ( and the S625X as well) includes the improved LCD display first introduced in the S720i. They both also include the new WearLink chest strap that many people find more comfortable. The S725 does add one unique feature over the S720i - the Mobile connectivity feature. This feature allows you to store and analyze your training data on the Nokia 5140 mobile phone. The S725 has a charcoal plastic cover (looks very nice) instead of the metal cover of the S720i. It almost makes it seem smaller - but that's an illusion. The form factor is the same for S720i, S725 and S625X.

If you have been getting by with the S510, be aware that moving up to any of these models brings you to a whole new level of convenience, features, and simplicity of operation. Now is definitely the time to make your move.

Our monitor pick for pure cyclists is either the S725 or S720i. Choose the S725 if you want a cycling monitor with the soft Wearlink chest strap (normally a $50 upgrade), or the Nokia cell phone feature (upload your workout on the fly). The S725 (and S625X) also have a feature that allows you to display heart rate as a % of your max - instead of as an absolute HR number. If these features are important to you, choose the S725 for cycling. Otherwise, save yourself a few dollars and go with the S720i - which is a bargain right now - priced at about $40 less than the S725.

Running
The introduction of the S625X is the start of a new day for runners. Although Polar still markets it as a heart rate monitor, they may soon find, as did Nike and Timex, that the chest strap quickly becomes an afterthought. This may start a whole new movement back to using pace as the method of choice for measuring intensity of workouts. (With heart rate still being an important measure of how hard you are working to keep that pace.) Pace is how running used to be measured, and heart rate came on as an objective measure when you were not at the track. Now there is an objective measure that is with you all the time, as heart rate is, and which directly relates to what we treasure as a sign of improvement - finish time.

We have reworked PC Coach with this in mind. Heart rate is now just one of several possible data types, all on an equal footing. If you leave the chest strap in the drawer, no problem. Using checkboxes at the top of the downloaded data screen, PC Coach lets you choose to graph heart rate, pace, altitude - or any combination of the three.

Polar is not the first to introduce the speed and distance monitor. Nike brought a very similar product to market two years ago, and is now in a second generation. Timex has on the market a GPS based product that is also into a second generation. Both companies made some mistakes in their first generation, but now have ( or very soon will have) reliable products for sale. Garmin has also released a GPS based product for runners. PC Coach currently supports downloading from the Timex models and all of the Polar models, and plans to support the Nike and Garmin downloading products as well. Each of these other products has its merits. But if you want Polar quality, take a look at the S625X.

The S625 inertial system is based on a very precise measurement of your foot's acceleration in various planes. An on-board computer combines the outputs from these very tiny accelerometers, and calculates the stride length for every single stride, as it happens. This is one reason why it is so much more precise than a pedometer, which requires you to enter your stride length at the beginning. This technology is so vastly more precise than a pedometer that they should not even be mentioned in the same article, so I'll stop. Polar promises 97% accuracy out of the box for the S625X, and 99% once you calibrate it at the track, which only needs to be done once ( It remembers the calibration when you change batteries).

It is, by my observations, much less accurate than that if you integrate walking in your workout. It also loses accuracy as you move away from the pace you used while calibrating, either faster or slower. The further you are from calibration pace, the less accurate it is. Nevertheless, the advantages over a GPS system are compelling: it works in cities, it works on trails through the trees, and it is unnoticeable on your shoe. And of course, Polar has done such a good job integrating it with the S-series functionality, that the result is a wonderful combination of ease of use, feature-richness, accuracy, and practicality.

My bet is that the S625X will quickly become the new king of running training tools. Now we can bring back pace as important guidance in our training. I don't think it will take us very long. And new possibilities for combining pace and heart rate information in our training methods will take us to the next level.

Our pick for runners who wish to train using pace along with heart rate - the Polar S625X.