Threshold measurement

The term 'Threshold' is loose and in exercise physiology circles there are many thresholds defined but yes, when talking about training for endurance events it generally refers to blood Lactate Threshold (LT)or a closely related proxy. In power training circles most folks refer to FTP or Functional Threshold Power which is loosely defined as the highest steady state power a rider can sustain for roughly an hour under ideal conditions which include sufficient recovery, good nutrition and hydration and sufficient motivation (e.g. a race situation).

You'll also see reference to Anaerobic Threshold or AT which is a dated term that's fallen out of favor as there is no crisply defined changeover point between aerobic and anaerobic metabolism but for all practical purposes it is also a proxy for LT. Even LT gets confusing as there are various definitions ranging from a fixed (typically 1mmol) rise in blood lactate levels above a baseline level or a transition point from a linear portion of the lactate/intensity curve to an exponential portion of the same curve but in the end they're all attempting describe a point below which you can sustain for long periods and above which you'll fatigue much more quickly.

For training purposes your field tested 'Threshold' HR of 178 bpm is mostly what you care about as that's an indication of the intensity level that you can sustain for a very long time presumably under steady heavy loading. A lot of folks estimate this by taking the average HR for the final 20 minutes or so of a full out and steadily paced 30 minute time trial like effort. This cuts out the first six to eight minutes it takes for your HR to catch up with the effort (HR lag) but your full hour value is likely very similar as that lag period gets averaged out during the longer interval. On days when you want to target Threshold training you'll want to do steady 10 to 30 minute or longer intervals targeting a minimum of 95% of that Threshold HR or ~170 bpm.

It's possible your Threshold HR increased, but that's not very typical and it's not an indication of improved or necessarily decreased fitness. Your Threshold HR doesn't typically increase as a result of improved fitness, there may be small changes and it can decrease during the first five to eight weeks of steady training as heart stroke volume increases, But typically after that initial period of training Threshold HR doesn't change much but the intensity (i.e. power) you can sustain at that same Threshold HR increases. IOW your heart beats at roughly the same rate during Threshold efforts but you generate more power and go faster on the bike.

Here's a good link describing training levels and what physiological systems they target that gives reference to percentages of Threshold HR as well as Threshold power: http://home.trainingpeaks.com/articles/cycling/power-training-levels,-by-andrew-coggan.aspx

-Dave

In the years when i used to race i was into the anaerobic threshold training concept. Dividing training days during the week as aerobic or anaerobic rides. The anaerobic threshold being the limit zone between the two (and also a training zone on its own). Quite simple, the hard stuff was anaerobic and the lengthy rides aerobic, easy frameset to distribute interval training, sprinting, climbing, endurance, etc.

Quoted post said:

Originally Posted by wysinwyg [IMG]/img/forum/go_quote.gif[/IMG]

First of all when people talk of 'threshold' are they referring to lactate threshold? Is there some other type of threshold?

I'm reading here that your threshold is the heart-rate you can sustain for an hour.

It all depends on who is doing the talking - the average competitive cyclist will almost exclusively be referring to POWER threshold which is technically called Functional Threshold Power (FTP). It's funny but you've obviously heard enough about FTP to know that it is supposed to represent the level you can work at for about an hour. However, this is NOT what is represented when referring to LACTATE Threshold. This obvious and easy confusion is something we are now saddled with ever since the first serious book on Power Training came about by Coogan and Allen. I wish they had named FTP something like MSP for Maximal Sustainable Power, or anything that was different than using a term that was already in the scientific journals for years and years and associated with heart rate.

The word Threshold was previously spoken of in respect to Heart Rate responses to training - ie Lactate Threshold, Ventilatory Threshold and the old term now out-of-favor Anaerobic Threshold - all of which lined up almost at the same heart rate response, and thus the shortening of the term to "Threshold". It was just easier to represent the concept - but it was always a METABOLIC concept related to HEART RATE. It represents that point where your lactate accumulation is far outstripping the ability of your muscles to flush that lactate - or in the case of ventilatory measurement, it is a second and dramatic inflection in breathing response and CO2 processing.

Hence the LENGTH OF TIME you can spend at this heart rate is not what makes it your "Threshold", instead it is the occurrence of measurable physiological markers that determine what this is - this is the reason you took the lactate test - to measure where that is for you.

So, in answer to your question about being more or less fit - it more represents how your body has learned to tolerate working at or above your Threshold Heart Rate. To some degree, if you can tolerate longer periods or higher heart rates above your THR, then that would indeed indicate improved fitness.

Quoted post said:

Originally Posted by liveon2wheels [IMG]/img/forum/go_quote.gif[/IMG]

I wish they had named FTP something like MSP for Maximal Sustainable Power, or anything that was different than using a term that was already in the scientific journals for years and years and associated with heart rate.

It was just easier to represent the concept - but it was always a METABOLIC concept related to HEART RATE.

I think you'll find it's the other way round. It's always been a metabolic concept related to work rate (power).

Heart rate has always been incidental when talking about threshold, which has always been about a work rate (power) that elicits changes in metabolic function such as onset of acidosis, and physiologists were primarily interested in the work rate (power), O2 utilisation, blood lactate concentration and/or perceived exertion. A look through a good ex phys text book on "threshold" and you probably won't even see HR mentioned.

When HR monitors became more common, that's when people started to look more at what HR happened to be doing and started attaching an unwarranted significance to it.

Nowhere in the science journals did anyone use the term Functional Threshold Power (FTP) prior to Dr Coggan coining the term. And since FTP is clearly defined by its author, there is no confusion on what it means. The real confusion comes from use of terms like "anaerobic threshold", which is neither, and pretty meaningless.

Lactate threshold is defined typically as the work rate (power) that elicits an increase in BL of 1mmol/L over baseline levels, or around 2.5 mmol/L. It typically occurs at a work rate ~ 15% lower power than FTP.

damn you just beat me to that response! Grrrrrrr! [IMG]/img/vbsmilies/smilies/eek.gif[/IMG]