After performing heavy (near-max) sets of squats, benchpresses, and deadlifts, I move on to unweighted chins, some dumbbell work, and cleans with very light weight to practice form.

During the chinup sets I've noticed that my heart rate is skyrocketing by the 7th or eighth rep, and I am forced to stop the set due to feeling generally fatigued; no gas in the tank, slightly nauseous. I can perform at least 14-16 reps if I do chin-ups on their own w/o prior lifting.

Is this fatigue a symptom of glycogen deficiency? Or are there other mechanisms of action - it feels like my heart rate is skrocketing way too fast for the amount of work I'm doing. With chin-ups I generally stop due to muscle failure along with burning pain in the arms...not exhaustion.

This happens the lightweight cleans and isolation exercises as well -not just chins - after the powerlifts.

I'd like to understand the exact mechanism of action this type of fatigue occurs through - why my heartrate skyrockets and I become less functionally efficient later in the workout.

Links, science-based answers appreciated.