Garmin Training Plan Confusion!

I'm using a Garmin Forerunner 405CX watch and following Garmin's Training Plan - Level 2. 

Today's Week 2 run was to be 5x2 mins at 10k effort with 60 secs jog between efforts. I understand 10k effort to mean 92-94% of my Maximum Heart Rate (is that the same as Heart Rate Reserve?) of 185bpm, but I could barely reach 170bpm and had trouble sustaining that for 30 seconds, let alone 2 mins!

I'm assuming that I'm doing something wrong here. And with my troubled relationship with science and numbers, that doesn't entirely surprise me.

Help!

I have run 10k in 59 mins, but I didn't have a heart rate monitor then, so I don't know what my heart rate was, but I don't imagine it was anything near 92-94% of my maximum.

That sounds too high for a 10k pace. 

Is that a calculated max or measured ?

And I'd just go from your pace - so you'd be running at just over 10kph for 2 mins ?

Cougie, sorry - I didn't understand what you meant in your second and third sentence.

Why do you think your maximum heart rate is 185bpm?

If you can't deal with the heart rate/ effort levels maybe it would be easier to run to pace... if you've run a 10K in ~1hour, your 10K pace is 10kph so do 5x 2minutes at 10kph rather than at 92-94% max heart rate.

And no, Maximum Heart Rate is not the same as Heart Rate Reserve

Chimpster: I think my MHR is 185bpm because I measured it with a heart rate monitor. I'll try the 5x2 mins at 10kph; that seems to make sense really.

The Garmin training plan tells me that a long run should be 65-75% of MHR, threshold run should be 80-85% of MHR, etc, but on the Garmin Connect site which stores all my activity data,  there's a table with a column for bpm, and a column for %HRR. I was assuming that 122-135 bpm = 50-60 %HRR meant that I should set my watch to ensure my heart beats 122-135bpm if I want to run at 50-60 percent of my MHR. Perhaps I've misunderstood something here!

Heart rate reserve (HRR) = heart rate max (MHR) - resting heart rate (RHR)

i.e your HRR depends on your personal resting heart rate, which will be affected by your level of fitness.

Its ok - you've told us now that you measured your HR max and didnt calculate it using the flawed 220- your age sum.

Your 10k pace is about 10 kilometers per hour ?

So if you ran at 10kph - that IS your 10k pace ? "10k effort"