SPIRE and PortaMon: Do You Need Both Signals?

Artinis published a piece on combining muscle NIRS with HD-EMG a few months back, and we reposted it here because it explains the two techniques cleanly. What I want to add is the part that matters when you are deciding whether to actually buy the pairing, not just read about it.

Two signals, two different questions

HD-EMG answers one question: what is the nervous system telling the muscle to do. Firing rate, recruitment, conduction velocity. NIRS answers a different one: does the muscle have the oxygen to do it. Neither instrument alone tells you which one is actually limiting performance when a subject fatigues. Force output collapses and you are left guessing whether the brain stopped asking or the muscle stopped delivering.

That is the whole reason to run two machines instead of one. It is also the reason not to buy both if the study only needs one answer.

Why we added the pairing to the catalogue

NBT has carried Artinis fNIRS for years. TMSi, which makes the HD-EMG side, is now part of Artinis, and PortaMon plus SPIRE is the combination the two companies actually engineer and support together, not something we bolted on ourselves. We put up a dedicated product page for it, with the specs, the FAQ, and where it will not help you.

Where it earns its price

• Separating neural fatigue from metabolic fatigue in a sports science or rehabilitation protocol
• Tracking whether a training block is improving oxygen delivery or improving motor unit recruitment, because those call for different training
• Spatial mapping work where oxygenation data needs to be tied to a specific region of the same HD-EMG grid

Where it does not

If the question stops at whether the muscle is firing, buy the SPIRE alone. If it stops at whether the muscle is oxygenated, buy the PortaMon alone. Both stay on the surface, so intramuscular EMG or any tissue depth beyond a few centimeters is out of scope for either one, combined or not.

The Artinis piece is worth reading for the physiology. Whether your protocol actually needs both signals or just one is a conversation worth having before the quote, not after.

Adapted from Artinis' blog post Integrating muscle NIRS & HD-EMG: Gain advanced muscle insights.