It depends. For 10 RM, it's probably more like ~7 reps total. Anything 5 RM and under, you're most likely getting full recruitment from the first rep though. Assuming the RM is accurate and all the other factors that effect performance that day, as well as assuming proper form, no form breakdown in later reps, etc etc. I wouldn't get too caught up on which specific rep is the first one where you start getting full recruitment, it's just important to realize that it is a sliding scale where the lighter the load, the more reps needed before full recruitment and vice versa. I'm sure that Blade has elaborated on this in the myo-reps documentation since the system is basically based around this idea.