Lactic acid has been cast in the role of nemesis, as the necessary evil to higher athletic performance; not just in rowing, but in many sports over the years. The scientific knowledge, however, has advanced in recent decades and lactic acid seems to play a more complex role than is often assumed.
“First of all,” explains Dr Trent Stellingwerff, lead of Innovation and Research at the Canadian Sport Institute Pacific, “we should call what we are measuring lactate and not lactic acid. Within the muscle, 99 per cent of the lactic acid (LaH) separates immediately into lactate (La-) and hydrogen ions (H+). It is the H+ that is the problem.”
“Lactate is both fuel and metabolic waste product,” says Alex Hutchinson, author of the Sweat Science articles for runningworld.com . “The body has different ways of mobilising its fuel stores and it all depends on when you need the fuel.”
“When you are performing over your V02 max (maximal aerobic capacity),” says Stellingwerff, “you have to draw on anaerobic metabolism to provide the required energy. A 2000m rowing race is done at 98 to 110 per cent of power at V02 max. This is why rowers produce so much lactate.”
“Professional marathoners, by comparison, run at 85-90% of V02 max and would probably never have a lactate measurement over 4 mmol (millimoles),” he says, “but in rowers it can be around 15-18 mmol and sometimes even a bit higher.”
Measuring lactate, however, is an indirect measure, since it is not the lactate itself that causes the acidosis (or drop in pH inside the muscles). The hydrogen ions (H+) produced with the lactate cause the drop in the muscle’s pH. Normal pH in the body is 7.2, but can drop as low as 6.6 if it were to be measured in rowers after a race, according to Stellingwerff.
“The burn you feel,” he says, “the toxic feeling you get later in races is the H+ causing the drop in pH. That sends a signal back to all the enzymes to slow and stop producing energy.” 
As well as directly causing a lot of pain through acidification, this drop in pH may have other effects on performance. “Because you are disrupting the normal contraction cycle of the muscle,” says Stellingwerff, “I would imagine that there could be an impact on the central nervous system as well.”
“It is unclear exactly what is happening,” points out Hutchinson, “but it does appear that there are various places along the central nervous system that are responding to fatigue. If you exercise one arm very hard for instance, the other will also be tired. This non-local fatigue is mediated by the central nervous system and is one of the best pieces of evidence that fatigue isn’t just in muscles.”
So, although lactate does not appear to be what is causing the 'burn.' it is what coaches and sports scientist tend to measure. But why measure it in the first place and how is the information useful?
“It’s a matter of convenience,” says Hutchinson. “Lactate is simple to measure and although it doesn’t cause the burn on its own, it does give an indirect sense of what is going on in the muscles.”
“Lactate is an important molecule to measure in the right context,” says Stellingwerff, “but it can be over-measured.” Stellingwerff knows rowing well as he worked for a number of years with the Canadian senior men’s rowing team as head of physiology.
Stellingwerff identifies three situations in which a sport scientist might measure lactate in an athlete:
1)      Standardised testing such as a step test to assess aerobic/anaerobic fitness
2)      As a means to qualify/quantify a set workout to assess if the workout is having the desired effect
3)      Regular monitoring of training adaptation and fatigue during a recurring set workout
“The big thing,” says Stellingwerff, “is consistency of measuring the same thing each time. Anyone can take a lactate, but it takes a lot of time to understand what that value means. There are so many variables and you have to be careful of not just taking a lactate sample and making an assumption on that alone.”
“I think when you measure lactate,” he says, “you should also be measuring heart rate (HR), the athlete’s rate of perceived exertion (RPE) and some objective external measure like boat speed. It is the integration of many variables, that might include lactate, which allows for the correct interpretation.”
“The biggest mistake possible,” says Hutchinson, “would be to take lactate measurements and say this person is or isn’t good enough. To me it is a tool to assess how an athlete is progressing over time.”
So, measuring lactate may not be as all-important on its own, as is often assumed. It does. however, remain an important component of training and preparation for elite rowers in their pursuit of high performance.