I noticed this tonight (again) while trying to 'grease the groove' with kettlebell cleans. I was using a weight a size larger than I normally use for stamina training, and I was keeping it to 3 reps each side, with 3-4 recovery breaths between sets.
Coach Sonnon has discussed the phenomenon of 'second wind' elsewhere, and I am sure we have all experienced various levels of heightened arousal and performance 'gates' beyond that which haven't been classified as thoroughly. But I find an unusual internal phenomenon consistently happening with kettlebell and Clubbell® lifts some minutes after the second wind has kicked in, and I am curious if anyone else has noticed it.
To be brief, whenever I work with heavier weights than usual in extended density and GTG sessions, I almost always feel something that signals 'the beginning of the end'. It's like an audible 'thump' that I feel internally, mostly in the sides of my neck and rib cage; I feel light headed for a moment, and then almost immediately move into a state of even higher arousal; I feel stronger, more reckless, and more willing to go for it no matter what the cost. However, I've learned from experience (most recently at a kettlebell seminar) that this thump is also a signal that I am very near the 'red line' where I am about to completely overload my system and crash and burn (ie, drop to the floor and suck wind like there is no tomorrow). The last few sets after this are almost always pure pleasure, no matter how bad the oxygen debt or lactic acid load, but I know that it will almost always end very soon with a bad groove or a form collapse, so I try to terminate the training after the first couple of 'wobbles' that I can't correct.
This never used to happen when I ran 10Ks etc - it seems to be unique to the stimulation to the nervous and circulatory system caused by heavy kettle and clubbells. I am sure there is an standard exercise physiology term for the 'threshold' that this signifies - I am just curious if anyone else perceives it as a 'thump', and if there is an obvious explanation why? Change in blood pressure maybe, or a shift in some patterns in the veins and arteries near my occiput?