Ellis, D. S., Taylor-Mason, A., & Miller, B. F. (2006). A sodium-lactate infusion does not change time-trial performance in cyclists. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 650.

"Reasoning dictates that if two things correlate, they may be causally related. Therefore, many have implicated lactic acid production (HLa), and its subsequent dissociation into a hydrogen ion (H+) and lactate ion (La-) as causative to fatigue. HLa is 99% in the form of La- at the physiological pH of the body. Therefore, during routine blood sampling it is the [La-], not [HLa] that is being measured. Nonetheless, blood [La-] is still used as a reference point of exercise prescription by sport scientists with the theory being that this is the point below which La- and H+ production can be accommodated and exercise sustained".

This study determined whether 20-km cycling time-trial performance is different in the same subject exercising at two different lactate concentrations. Highly trained male cyclists (N = 9) completed a 20-km cycle ergometer time-trial. Ss performed a lactate infusion trial and a control saline infusion trial. The lactate infusion was conducted at rates previously observed to raise blood lactate by 2 mmol in trained Ss.

The increase in lactate ion over time was significantly different between two conditions. Average time to complete the time-trial and average watts did not vary between conditions. Blood [Glu], RPE, VO2, RER, HR, and hematocrit were not different between trials.

Implication. Increased blood lactate ion does not increase fatigue or perceived fatigue. It does not alter cardiac or respiratory parameters. It is an inappropriate method for quantifying training intensity.

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