Dempsey55

I'm 22, 6'4", and weigh about 205 lbs. A good bit of muscle. I ride MTB and ride pretty technical single track at a rather advanced level. The main issue I run into is my heart can't keep up with my technical riding, or so I assume. I regularly find that I can ride well at 90% of my max 193 bpm rate. I get bored if I ride at anything less. I feel bonk coming after about 45 minutes of that, but can usually finish out the last 20 minutes at a lower intensity without suffering at a Cat 2 pace.

Do I need to build my base by riding at a lower intensity to see any results? Is sucking up my "fastest lap time at the trailhead" ego the only way to improve my races over an hour?

Using HRM training alone; is it remotely beneficial to my endurance capabilities to continue riding this way? If not, what do you ultra-endurance guys suggest? I feel like I ride painstakingly slow either on the road bike or the mountain bike below 85%.

Is there a reason why I'd have a naturally higher exercising rate, while a low RHR?

gregf83 

That doesn't sound unusual or abnormal.
It doesn't sound like you're bonking, rather you're just fatiguing. I don't know what you've done for base training but generally building a base involve lots of volume at a lower intensity done in the off season. Once you have a solid base built you start adding intensity with intervals. You might want to read Friel's training bible for some insight into periodized training.

What kind of results you're looking for? You're a pretty big guy to expect to do well on a hilly mtb course.

I don't know what that means but the way to get faster is to improve your power/weight ratio. 205lbs is too heavy so you need to lose some weight to begin with.

What does your typical training week look like? How many hrs/wk are you riding? Length of typical ride? MTB only or road and MTB?

I don't know what you mean by a high exercising rate. Your HR sounds normal for a young man.

chasm54

First of all, you aren't "bonking". A bonk is a precipitous loss of energy because you have depleted you glycogen reserves. What you are talking about is riding at a level of intensity that is above your threshold, and which you cannot maintain for an hour. And that answers your question about whether you have a "naturally high exercising rate". Clearly you haven't, or you'd be able to keep going.

Your endurance will improve to a degree if you keep doing this, because you'll probably raise your lactate threshold a bit. But it won't improve as much as if you did longer, rather less intense training at something like 90% of your lactate threshold instead of 90% of your MHR. An hour is quite a short ride. You need to spend more time if you want to build an aerobic base.

Carbonfiberboy 

Ah, you're just easily bored. As they say, MTB riding is physical, road riding is mental. Do you train on a road bike? Many MTB riders do most of their training hours on the road to deepen their base, get in proper interval training, etc.

Dempsey55

Thanks guys! Yeah you guys are right. My rides are usually around 2 hrs long. I need to get out and spin for longer periods of time on the fireroads. The races are 1.5 hrs long in my class, so I try to keep them above that. But I think I need to focus more on determining my LTH and working off that alone instead of with the pack. I was getting concerned when I felt like I had plateaued as far as my lap times were concerned when riding to exhaustion after 1.5 hrs at race pace. I need to get on the road bike and spin my way to efficiency. Thanks!