In mid-December the first BSXinsight wearable lactate threshold monitors will begin shipping.

Announced back in March via a Kickstarter campaign, the US$369 devices slip inside a calf compression sleeve, where data is recorded for post-workout upload via a smartphone app.

The end result, the company claims, is lactate threshold data that can inform training, previously only available to athletes via pin-prick blood tests done in medical centres and high-end training facilities.

Instead of the lab-standard model of measuring lactic acid in the blood every few minutes, the BSXinsight monitors muscle oxygenation via a light array shined into the calf. BSXinsight then runs an algorithm to give users lactate threshold (LT) power and heart rate numbers, plus training zones based on percentages of those figures. 

“Lactate threshold is the gold standard of performance testing, and the blood-testing method has been around for 50 years,” said Dustin Freckleton, president and co-founder of BSXinsight.

“Researchers discovered that by doing these incremental testings [as power and/or pace ramps up], taking blood samples along the way, and plotting results of lactate concentrations, you see this thick hockey stick curve towards the end. What that spike represents is the point at which the athlete moves from a predominantly aerobic state to an anaerobic state.” 

The original idea for BSXinsight was to beam real-time data to Garmin or other cycling computers via an ANT+ signal, and that may still come in version 2.0. The current unit, however, will be started and stopped by a smartphone app, and information will be transmitted to for analysis. The app walks riders through a progressive LT test, as well, to be done on a trainer with a power meter.

The BSXinsight measurement is done with standard LED bulbs.

“Each type of light interacts differently with different type of tissues,” Freckleton said. “Some reflect light, some are absorbed. Based on those interactions of distortion and absorption, we are able to determine what is going on inside the muscle.”

While the company recommends using the unit for lactate threshold tests every few weeks, BSXinsight can also give daily feedback on muscle oxygenation levels. And, very much unlike lab LT test equipment, the unit is designed to be worn while riding outside. 

But what exactly would a cyclist do with muscle oxygenation data? Freckleton and other physiologists admit that this is still exploratory, “similar to where heart-rate and power data were when they first came out,” Freckleton said. “There are no clear guidelines as to how to use it.”

The main premise and selling point of the device for now, however, is a way to measure or at least approximate a rider’s lactate threshold. In rough terms, lactate threshold is closely associated with the maximum level of sustainable output. If you can quantify this point, either in power output or in heart rate, you can more effectively train to improve it.

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A common way to approximate a lactate threshold test without lab gear is to ride as hard as you can for an hour, then look at your average power and/or heart rate for the last 20min of the effort. This could be called your LT power or heart rate.

Traditional LT tests involve pricking a rider’s finger every few minutes to measure lactic concentration as power is incrementally increased

In the lab, lactate threshold tests typically involve ramping up power (usually by 20 watts every four minutes), and measuring lactic acid by taking small blood samples from the fingertip, looking for the point when lactic acid starts to spike.

The team behind BSXinsight are hoping that having a portable consumer unit that calculates lactate threshold without the pin pricks — or the lab costs — could find a market among cyclists, runners and triathletes. 

The US$299 running version will pair with heart-rate monitors. The US$369 cycling version will pair with heart-rate monitors and power meters, via ANT+, but not cadence sensors, at least for now. And there is also a US$419 multisport version. All come with a 30-day money-back guarantee. BSXinsight is still awaiting product certification approval outside the US, but Freckleton expects to have that soon.

The BSXinsight device comprises an LED emitter plus a pair of photodetectors that measure the scattered light 

So does it work?

At FasCat Coaching in Boulder, Colorado on Friday, several high-level coaches gathered for a demonstration. Present among them was Neal Henderson, a veteran coach who was worked with several Olympians and world champions. Henderson said that there is “certainly reason to believe a correlation between muscle oxygenation and lactate threshold, but it is all about the algorithms. I want to see the data under the hood.”

Freckleton said coaches will have access to complete data sets from BSXinsight files, downloadable in .csv files, while consumers can just look at the more layman-friendly dashboard on

At the demonstration, BSXinsight enlisted a local cyclist to perform a LT test using both the pin-prick method and a BSXinsight unit simultaneously. The pin-prick data returned interesting results, with a dip in lactic acid at the 340w mark relative to measurements at 320w and 360w, which several coaches in attendance chalked up to sodium contamination from the rider’s sweat.

Still, Freckleton called the LT power from the pin-prick test at 360w, while using BSXinsight determined the rider’s LT power at 374w. An LT test done the prior week on the same rider at FasCat Coaching resulted in a 355w LT.

Rob Pickels, a sports physiologist at the Boulder Center for Sports Medicine, said that while he “absolutely sees a correlation” between muscle oxygenation and LT, the current technology and science around it “is exploratory.”

But the same goes for lactic acid, he said. “If anyone can tell you specifically what causes fatigue, then they are the smartest person in the world,” Pickels said. The BSXinsight unit, he said, “is very interesting. I’m not ready to say it’s absolutely ready, but I am interested.”

(Images: Ben Huang / Immediate Media)


Would you use a lactate threshold monitor like BSXinsight? Let us know in the comments!

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