Life, Running, & Medicine.
Notes on life as I see it.

Sunday, April 13, 2008

Re: The Lactate Threshold

In reference to Brian's question about the lactate threshold (LT):
[Insert here a disclaimer that (a) I am not an exercise physiologist and (b) everything published below is available from a quick google search]
LT is essentially a physiologic state at which lactate begins to accumulate in your body (your blood specifically).  For energy, your body breaks down glucose into an intermediary called pyruvate.  Under aerobic conditions your body then must INPUT a little energy into the Kreb's Cycle to fully break the pyruvate down and get OUT the most energy possible.  This is very efficient and allows for the maximal "bang for the buck" in terms of energy per sugar molecule.  The problem is that when your body is really pushing hard you run out of the energy needed to jump start the Kreb's Cycle, so the pyruvate can't get fully metabolized.  This is when we switch to anaerobic metabolism.
In anaerobic metabolism the pyruvate gets fermented into lactate, which created energy as byproduct.  It is faster but produces far less energy per sugar molecule.  The lactate accumulates either until you rest and it gets converted back into pyruvate and enters the Kreb's Cycle, or it finds its way to the liver to get turned into sugar.  Basically, lactate accumulation is a marker for your body entering an anaerobic state.
We care about LT because studies have shown that LT is the best predictor of endurance sport success.  In other words, winning runners have to run faster to accumulate lactate than losing runners.  It follows then that training to specifically raise your LT will get us quicker faster.  This is a little odd because we generally consider distance running to be an aerobic sport, so it is counter-intuitive that training anaerobically is useful.  I think of it as improving aerobic 'reserve'.  Most recommendations for improving LT have to do with training at or just above your personal LT.  Interval and Fartlek trainings aim to do this (interval trainings shoot well above your LT, Fartlek aim to be just at or slightly above).
Really determining your LT requires serial blood tests at various training intensities, to literally measure when lactate blood levels start to rise.  This is preposterous for most of us.
The two easiest (but less accurate) methods for determining LT are the following:
  1. Heart Rate Method.  At 85-90% of maximal heart rate (MHR=220-age) you are at your LT.  For those badly out of shape its more like 60% of MHR (in which case you shouldn't be doing LT training yet).  This varies between individuals so I would make sure this is concordant with the Race Pace method below (for runners).
  2. Race Pace Method.  Your 15K race pace roughly approximates your LT.  If you run less, use your 10K pace minus 20 seconds or your 5K pace minus 30 seconds.
In short, LT training aims to be an efficient method of training for endurance events (do fewer miles but do them harder). 
Good sources for LT info:

1 comment:

Matthew Barrowclough said...

Thats the most scientific and obsessive definition of LT. I wouldn't think anything less from you Aaron =)

Here is the general definition for everyone to understand: LT is the highest output you can sustain for 15-30min before exhaustion completely takes over.

Training above your LT raises your LT, which provides you with being able to run faster for longer. By training above LT, you train your body to deal with the pains and exhaustion that is accompanied with such activity. Most runners don't train this part of their engine which is why they aren't able to get faster. Once you have the endurance to finish a 10k,20k, half, or full then you need to transition into more power/speed training. The sessions should be shorter but the intensity is much higher.
Rule: If you never incorporate any above threshold work into your training then you are very unlikely to experience gains in your speed.

Marathoners have very high LTs, whereas sprinters rely on their massive VO2 and anaerobic limits. LT is very trainable, whereas V02 is largely genetic but is still quite trainable but not to the extent of LT. Everyone who wants to improve should incorporate above LT/LT training.

Matty B