So you’ve finally sprung for a coach. You’re tired of your friends dropping you on the tamest of false flats. Your coach explains that the only way to effectively write a training plan based on power numbers is to first determine — scientifically — what your numbers are. It’s time for a lactate threshold test.

Now, if everything goes to plan, you get in an easy ride the day before. You go to bed early. You get a good breakfast the morning of the test.

Of course, things never go to plan, and your kids were up until 2 a.m. Now your exhaustion is going to render this test fundamentally useless, but you’ve already booked the lab. You go and do it anyway. Your coach gives you a lactate threshold power number and builds your next four weeks of training around it, but that number doesn’t mean a lot.

Then in a few months, you go through the whole process again. You begin to wonder how many times your finger can be pricked before you lose all feeling for good.

Until now, a lactate threshold test in a lab with a blood draw was the only way to accurately measure a rider’s lactate threshold. BSX Insight is a new device designed to guide you through the process and give you a test that measures your levels of deoxygenated blood. It then compares those levels to known trends in the relationship between deoxygenated blood levels and the production of lactate. The test can even be done at home with a trainer, a powerful fan, power meter, and the new $370 BSX Insight — Cycling Edition.

The Insight tethers to your ANT+ devices, such as a power meter and a heart rate monitor, and then feeds that information to your phone, along with data on blood lactate levels. This is where things get interesting: the BSX Insight device measures the levels of deoxygenated blood using an LED light that looks through your skin on the back of your calf and into your blood stream. The BSX software — its secret sauce — then takes those oxygenation levels and converts them to a lactate threshold number. No more finger pricks every few minutes.

We tested the BSX Insight over the course of several months and while our experience didn’t confirm the scientific perfection of the BSX, it did speak to the Insight’s value. When we first received it, our tester was coming back from the flu, but we wanted to get to testing. A week of laying around and popping meds is not ideal preparation, and power numbers were embarrassingly low. The BSX came in handy in this scenario because we did not have to schedule time in a lab and spend money on testing that could have led to an inaccurate assessment.

Source Endurance Training Center of the Rockies is just down the street from the VeloNews office, and coach Zack Allison was more than happy to follow the BSX guidelines while testing blood lactate the old-fashioned way.

The BSX test starts at a very low wattage, after the rider puts in basic info and pairs his or her power meter. Every three minutes the wattage ramps up 20 watts. We went through the testing on a Lemond Revolution trainer the first time, and then on a Computrainer at the Source Endurance Training Center. Doing the test on the Computrainer was much easier, as all we needed to focus on was pedaling — the Computrainer kept the power numbers where the BSX mobile application said it needed to be.

“What I’ve found while researching the validity of measuring the deoxygenated blood at the calf is actually really accurate from a scientific point,” Allison said. “But it’s comparing apples to oranges in some ways because its tough to say that every person’s blood lactate and deoxygenated blood levels move along identical scales.”

Of course, this is coming from a professional coach whose lifeblood is the intricate numbers from his athlete’s power meters. Most of us simply don’t care about that level of testing. For those of us that do, the Insight could still be a vital tool that could quickly pay for itself if you’re doing lactate threshold testing every other month.

“It’s good for the price tag,” Allison continued. “People have to be careful of all of the variables, and if they’re doing a step test on their own, because when you’re in a lab for a lactate threshold test, the lab controls those variables for you.”

That brings us to the most important piece of the puzzle — preparing for the test. Riders need to be well hydrated, have a fully charged Insight device, have plenty of fans, and be in a cool place. Riding on an ergometer helps, but is not necessary as long as you have a reliable trainer. The lead-up to any lactate threshold test matters just as much as the test itself.