aerobic VS anearobic MHR ? for any endurance racers

Cre8veLifeR

OK. I am wondering what to do...I am 42, so according to the Karvonen THR scale my MHR is 178.

I am training for a triathlon in May (it's only a sprint) and I run a lot anyway, do high-impact dance, swim, cycle, etc.and I am in very good cardio health. I forget my V02 Max but it was in the "excellent" category.

When I am doing a cardio workout I am consistently training at around 153-155 BPM and can sometimes get around 163 - 169 BPM if I run hard. The lower end already puts me in the anearobic training zone since it's about 85% of my MHR. I can comfortably carry on a conversation and do not get winded. Over 163 BPM I am definitely breathing harder but don't feel like I am overexerting myself though it's considered "max effort" zone. I can easily complete an 8K without slowing or tiring out at this pace.

My question is, to put myself in an aerobic training zone my THR should be below 142 BPM but I feel like I am barely moving, but is that where I should be training to improve my cardio endurance, or a combination of both? I know pace is the most important aspect of a race...The race is a 750-meter swim, 20k-bike ride and a 5k-run. I figure it will take me an hour an a half to complete. If I keep my training in the anearobic state am I going to tire out even though if's a comfortable running pace for me? Looking for training advice from people who know or who have done this sort of endurance training before! This is my first endurance race other than a 1/2 marathon.

TIA!