Train.Red is a small wearable sensor that sits directly on a working muscle — your quads, calves, or wherever the effort is concentrated. Using near-infrared light, it measures muscle oxygen saturation (SmO2%): the balance between how much oxygen is being delivered to that muscle and how much it's using, updated in real time as you train.
Most training data — heart rate, pace, power — is a whole-body number. It's useful, but it doesn't tell you which muscle is actually struggling, or how close it is to its limit. SmO2 does: it shows local fatigue building before it shows up in your pace or your form, and it shows exactly how quickly a muscle recovers once you back off.
Where INSCYD builds your whole-body metabolic profile and the ramp test benchmarks your functional engine, Train.Red zooms in on the muscle itself — live, during the sets and intervals you're actually training. Together, the three give a complete picture: what your body can do, how it holds up under sport-specific demand, and what's happening inside the muscle while it's happening.