Threshold Intervals

Perennial_Quest said:

What does it mean if one day you cannot reach your target Heart Rate or find it takes longer to build up to it than it usually does, weather conditions being the same and route.Also I had two days rest before-hand so fatigue would not come into it.Is this a good or bad thing or something that just sometimes happens.I previosly had no problem getting up to 92 percent of my max if i wanted but yesterday it took longer and found it more difficult to reach my target HR.

Ahhh... the variability of heart rate.
But to your question: what it actually means will depend and can be difficult to put a finger on. One of the main problems is that heart rate is a reflection/indirect measure of many physiologic phenomena, all of which can influence the actual number you see from day to day and within a single ride.
My overall advice, however, is to be sure and factor in RPE whenever training with heart rate. Whether or not you decide to (or should) keep pushing yourself depends on what your curent goals are and your experience as a cyclist...and willingness to suffer. I can tell you that a sluggish or slightly lower than normal heart rate response does not mean that you are not putting out the same power as when your HR was slightly higher/more responsive.
Also, if it's just one random day, I wouldn't give it a 2nd thought: multiple days would suggest some significant state of fatigue for which you will want to make a conscience effort to recover from.

Smartt/RST said:

Ahhh... the variability of heart rate.
But to your question: what it actually means will depend and can be difficult to put a finger on. One of the main problems is that heart rate is a reflection/indirect measure of many physiologic phenomena, all of which can influence the actual number you see from day to day and within a single ride.
My overall advice, however, is to be sure and factor in RPE whenever training with heart rate. Whether or not you decide to (or should) keep pushing yourself depends on what your curent goals are and your experience as a cyclist...and willingness to suffer. I can tell you that a sluggish or slightly lower than normal heart rate response does not mean that you are not putting out the same power as when your HR was slightly higher/more responsive.
Also, if it's just one random day, I wouldn't give it a 2nd thought: multiple days would suggest some significant state of fatigue for which you will want to make a conscience effort to recover from.

I've noticed the same thing. One day my HR seems really responsive and follows my subjective efforts quickly and easily right up to near HRmax, and other days reaches a 'brickwall' limit as low as HRmax-20. I recognise this is down to incomplete recovery, but what is it that is un-recovered ? - Is it my legs, too tired to generate enough stimulus to get my HR going, or does the heart muscle itself need to rest ? - or is it a combination. I wonder about this as often in this situation my legs feel good, but my HR just won't climb.

DavidM said:

I've noticed the same thing. One day my HR seems really responsive and follows my subjective efforts quickly and easily right up to near HRmax, and other days reaches a 'brickwall' limit as low as HRmax-20. I recognise this is down to incomplete recovery, but what is it that is un-recovered ? - Is it my legs, too tired to generate enough stimulus to get my HR going, or does the heart muscle itself need to rest ? - or is it a combination. I wonder about this as often in this situation my legs feel good, but my HR just won't climb.

There are several "seperate", but interdependent physiologic systems involved that effect your HR, ability to recruit muscle, hormonal release, etc, etc. Suffice to say, this is the underline "problem" with monitoring HR alone; the actual number you are seeing is influenced by a multitude of factors, identifying why it's higher or lower than normal is essentially impossible on a day-to-day basis.