The measurement of blood lactate concentrations during exercise has been performed since the early 1920's. Since this time the increase in blood lactate has been interpreted as a marker for increased glycolytic metabolism, which in turn has been interpreted as a sign of anaerobiosis. During the last decade the connection between blood lactate accumulation and anaerobiosis has been controversial, and it remains so today. Regardless of the controversy, blood lactate increases during incremental exercise have been repeatedly used to predict/explain aerobic exercise performance. The point at which blood lactate accumulation increases abruptly has been termed the lactate threshold (LT). This lab will provide you with experience in performing an enzymatic spectrophotometric blood lactate assay of serial blood samples collected during an incremental cycle ergometer exercise test, and using the Beer-Lambert Law to calculate lactate concentrations.

Experimental Procedures:

Collect blood from a subject via an indwelling venous catheter during incremental exercise to VO2max.  Also use indirect calorimetry.  I recommend drawing blood samples (2 mL) every min from rest to 5 min, then every 0.5 min to 10 min, then again every min to fatigue.  Have the blood samples clot and then centrifuge to remove the serum for your samples.

Methods

I have posted the directions for the lactate assay on this website linked to the section on "Assays".  Follow these procedures for making your reagent cocktail.  Perform your assays in duplicate at 340 nm, and remember to add your sample volume of distilled water to your blank tubes.  Zero the spectrophotometer to the blanks, and then read your absorbance for each sample.

Data Analyses:

* Graph Watts vs. lactate and visually identify and label the LT.

* Graph the relationship between VO₂, % VO₂max and blood lactate. Visually identify and label the LT.

* Also detect the LT by performing log transformations of the lactate data and graph the results. HINT - for the log transformations you will need to develop multiple regression equations for subsets of the data and use the point of their intersection as the LT (see the references !!!).  I have an equation in Prism that does this for you.

* Detect the ventilation threshold via your method of choice.  If present, identify a threshold change in VO₂.

* Which method of LT detection, or VT, would be the most accurate? Why?

* What argument exists that may indicate that it is inappropriate to use the LT concept to evaluate blood lactate accumulation during incremental exercise?

* Are the patterns of muscle and blood lactate accumulation during incremental exercise similar? If so, does this evidence support or negate the concept of a threshold alteration in muscle energy metabolism?

all suitable references can be obtained from the following manuscripts!!!

Beaver W.L., K. Wasserman and B.J. Whipp. Improved detection of the lactate threshold during exercise using a log-log transformation. J. Appl. Physiol. 59:1936-1940, 1985.

Chwalbinska-Moneta J., R.A. Robergs, D.L. Costill and W.J. Fink. Threshold for muscle lactate accumulation. J. Appl. Physiol. 66(6):2710-2716, 1989

Robergs R.A., J. Chwalbinska-Moneta, J.B. Mitchell, D.D. Pascoe, J. Houmard and D.L. Costill. Blood lactate differences between arterialized and venous blood. Int. J. Sports Med. 11(6):446-451, 1990