If your microphone is overly sensitive, there are a few things you can try to mitigate this, currently:
Turning down the overall microphone volume(and disabling any volume boost options) in the control panel
Helps a bit, but doesn't remove the issue.
Decreasing the "Command Weight" option in the "Recognition" tab of the VoiceAttack "Options" window
Increasing the "Minimum Confidence Level" option in the "Recognition" tab of the VoiceAttack "Options" window
Still it keeps picking up my "sighs" and if I further tweak the values, it stops recognizing all-together.
You may also want to read the "I'm not saying anything but VoiceAttack keeps hearing things" section of this topic.
No ambient noise in the room. I actually have my VR setup in a completely different room that the computer is in.
Also, no speech engine "training" available in my Windows, since the language is different from default english. (FYI, I find this odd that even with other language in Windows you can't train the speech engine in English.)
If it's picking up sighs and exhaling specifically, you may want to reposition the microphone relative to your nose and mouth. Even with a windscreen/pop filter that'll get picked up pretty loud(making a minimum volume level less effective at preventing this).
It's a headset mic. A flexible one. I've even turned it "backwards", so it's basically pointing to back of my ear, still picks up me exhaling.