Steps taken, distance traveled, even your heart rate -- your fitness tracker can already tell you plenty about your workout. But how do you really know if your body is working at its optimum level? A new device could make that easier. The BSXinsight is the first wearable to track your lactate threshold, and is available today (March 31) from $300.

If you're not familiar with what your lactate threshold is, that's the point during exercise at which lactic acid accumulates in your blood stream faster than your body can get rid of it. Being able to keep exercising at the same intensity while maintaining a low amount of lactate production means you're improving in fitness, BSX says. The company also said that lactate threshold is considered the gold standard of performance measurement by professional athletes.

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Traditionally, getting an accurate measurement of your lactate threshold would require taking a blood sample (a pinprick to your finger, earlobe or thumb) during a workout session, but the BSXinsight system uses an optical sensor to read your blood oxygen level. BSX then translates that information to your blood lactate level. 

The calf-worn BSXinsight transmits information to a paired device in real time via Bluetooth 4.0, and a companion app for both iOS and Android analyzes your performance and encourages you to speed up based on how you're doing. The app will also tell you what to do over the next six to eight weeks to get the most out of your training. In addition to your lactate threshold, the BSXinsight also tracks your heart rate and calories burned.

Over time, working out with the BSXinsight is supposed to give you a better understanding of how hard you should be working to maximize performance instead of relying on a gut feeling to tell if you're overexerting or not pushing hard enough.

Originally a Kickstarter project, the now-funded BSXinsight is available in running ($300), cycling ($370) and multisport ($420) editions. Stay tuned for a full review.

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