Clarifying Gas Exchange Testing, Blood Lactate Testing and the use of INSCYD analytics.

Respiratory gas exchange (Gx) testing collects ventilatory measurements used to assess fitness and create evidence-based exercise/training prescriptions. One measure is the identification of two clearly defined physiological events, or turnpoints, in the rate of oxygen uptake and carbon dioxide expulsion (see figure 1). Identifying these turnpoints is a practical way to establish training zones and assess strengths & weaknesses in one's fitness. Furthermore, Gx testing protocols provide in-depth analysis of fuel utilization to assess nutrition-related variables, such as FATmax, VO2max, Anaerobic Threshold, and Running Economy.

Figure 1.

Synopsis of information obtained from Gx testing: VO2max, Ventilatory Thresholds, FATmax, & Zones of intensity.

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Respiratory gas exchange (Gx) measurement and blood lactate testing are used to examine the body's metabolic response to exercise. Both methods look at what's happening in the muscle cells indirectly. Gx testing measures cellular changes occurring during exercise via the lungs by sampling breath -by- breath concentrations of oxygen and carbon dioxide at the mouth. Blood lactate testing measures the appearance of lactate in the blood, where working muscles during exercise produce this lactate. Blood lactate concentrations increase at higher metabolic demand as the rate of lactate production exceeds the body's capacity to clear it. By examining the distinct inflection points along a curve of either oxygen uptake or blood lactate concentration per unit of work (watts) or speed (pace) specific training recommendations and training zones can be prescribed. Therefore, both methods are valid for examining level of conditioning and for making exercise/training prescriptions.

However, a standard blood lactate step-test does not provide the same level of depth as gas exchange (Gx) step-test measurements. The resulting blood lactate curve does not provide data related to cycling and running economy, fuel utilization (carbohydrate & fat), or VO2max, whereas Gx testing provides all the above. At Endurance, we employ our experience using INSCYD software to extract more insight from blood lactate sampling. In the lab we combine blood lactate sampling with Gx measurements to obtain a complete metabolic profile of an athlete. For blood lactate testing in the field our diagnostics allow us to capture variables such as maximal fat burning, maximal lactate production (VLamax) and anaerobic threshold without the need for Gx. Although this method of testing is more accurate with the use of Gx, we can obtain robust information with the convenience of sampling closer to home, or on the road. 

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References:

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Lucia et al. Analysis Of the Aerobic-Anaerobic Transition In Elite Cyclists During Incremental Exercise With The Use of Electroymyography. Br J Sports Med. (1999); 33: 178-185.

Faude, Kindermann & Meyer. Lactate Threshold Concepts: How Valid Are They? Sports Med. (2009); 39 (6): 469-490.

Jones & Carter. The Effects of Endurance Training On Parameters Of Aerobic Fitness. Sports Med. (2000); 29(6): 373-386.

Olbrecht, J., et al. "The importance of a calculation scheme to support the interpretation of lactate tests." D Maclaren, T Reilly, A Lees A (Eds). Swimming Sciences VI, Biomechanics and Medicine. London: E & FN Spon (1992).