I am hoping to get an explanation for a puzzling issue that I have regarding my cycling heart rate. First, I know that an athlete's HR is typically lower during cycling than in running [at any given level of effort] due to the smaller muscle mass involved. However, in my case this is dramatically so and I am wondering why and, secondly, if certain types of training can help me close the gap.
Here are the facts ...
I am 40 years old and primarily cycle on a road bike [although I have recently purchased a Kona mtn bike and am enjoying that as an alternative workout]. My bike training is geared for triathlons [Olympic distance] and I am a runner first [recently qualifying for Boston in 2006 with a sub 3:20 marathon - at my current fitness I am a sub 1:30 half marathoner and 40min 10K runner]. Relative to my age group, biking is my weakest discipline in triathlon with my bike split for a 40K Olympic bike leg at about 75 minutes.
As a runner, my HRmax is 180bpm and my lactate threshold is 157bpm. I do my "tempo" running (sustained intensity runs) at 150-155bpm and my interval running just above 157bpm. On the bike however, my HR on a tempo ride on a trainer for 30' with legs burning is typically only 125-135bpm. This is 20-30 bpm lower than an equivalent perceived effort during a tempo run. During a tempo ride on roads, my HR is up to 10bpm higher than on the trainer, but that still puts me 10-20bpm below my tempo running HR.
One theory I have is that, as a marathoner, my running muscles are well developed allowing oxygen consumption to be my main performance limiter. Contrarily, as a relatively weak biker, my bike muscles are taxed way before my aerobic system. If this is true, then big gear, low cadence grinding should help me build up my bike muscles and close the gap. Comments?
Finally, can anyone tell me if my situation is common or uncommon? Are there better ways to close the gap? Should I even bother trying?
Thanks in advance!