The limits of lactate
Blood Lactate levels are important
Of all the physiological measurements made when testing cycling performance, the level of lactate in the blood is, without doubt, one of the most important.
Why is that? Well, the level of blood lactate during exercise shows how efficiently the muscles can utilise fuel and convert it to energy. In highly trained cyclists, the muscles can sustain a very high power output with little accumulation of fatiguing lactate, which basically means that they can pedal harder for longer, without being forced to slow down by muscle fatigue.
In lesser-trained cyclists, lactate begins to accumulate at much lower power outputs, resulting in a lower sustainable power output. Also, study after study has shown that for any given individual, a lower level of blood lactate for a given sustained power output (for example as a result of an interval training programme) results in better performance.
In other words, blood lactate is seen as a reliable performance barometer, with lower levels equating to better endurance performance. However, new research by New Zealand scientists suggests that a simple ‘one-off' test of blood lactate following a session of intense exercise might not be sufficient - something that could have significant implications for cycling coaches.
In the study, the researchers set out to investigate how reliable and consistent blood lactate measurements were by taking repeated measurements over time. To do this, 12 healthy, fit male cyclists performed three separate series of power tests on different occasions.
Each series of power testing was identical and consisted of power tests at four exercise intensities: 45 per cent (very light), 60 per cent (light), 75 per cent (moderately hard) and 90 per cent (very hard) of maximum oxygen uptake. The cyclists' levels of blood lactate were measure pre-test then at the end of every fifth minute, either until the end of the test or until the point at which the cyclists could no longer keep going.
In a nutshell
Over the group as a whole, the power outputs at 45 per cent, 60 per cent, 75 per cent and 90 per cent of maximum oxygen uptake averaged 142, 196, 248 and 302 watts respectively across the three testing sessions. What was really interesting however was the variability of the lactate measurements between different testing sessions.
Although you'd expect to get pretty much the same blood lactate measurement for the same power output, what the researchers actually observed was quite a big degree of inter-session variability.
Indeed, when they compared the same power outputs in different sessions, they found differences in the measured levels of blood lactate of between 9 and 21 per cent!
The implications here are fairly obvious. A coach might be very encouraged to see a drop of 10 per cent in lactate levels at the end of a constant power test following a training programme. But if the session-session variability can be as great as 21 per cent, it would be hard to know how much of the drop was down to an actual improvement in the cyclist's fitness and how much was down to simple variability between testing sessions.
As the authors point out, their results suggest that coaches should try and factor in the occurrence of testing variability by assessing it as part of their testing. They also suggest that coaches should definitely not rely on a single test of blood lactate at the end of an exercise test as an accurate indicator of change in performance over time as it's likely to be insufficiently accurate.
J Sports Med Phys Fitness. 2012 Dec; 52(6): 575-82.