Blood lactate accumulation and muscle deoxygenation during incremental exercise

Abstract

Near-infrared spectroscopy (NIRS) could allow insights into controversial issues related to blood lactate concentration ([La](b)) increases at submaximal workloads (). We combined, on five well-trained subjects [mountain climbers; peak O(2) consumption (VO(2peak)), 51.0 +/- 4.2 (SD) ml. kg(-1). min(-1)] performing incremental exercise on a cycle ergometer (30 W added every 4 min up to voluntary exhaustion), measurements of pulmonary gas exchange and earlobe [La](b) with determinations of concentration changes of oxygenated Hb (Delta[O(2)Hb]) and deoxygenated Hb (Delta[HHb]) in the vastus lateralis muscle, by continuous-wave NIRS. A "point of inflection" of [La](b) vs. was arbitrarily identified at the lowest [La](b) value which was >0.5 mM lower than that obtained at the following. Total Hb volume (Delta[O(2)Hb + HHb]) in the muscle region of interest increased as a function of up to 60-65% of VO(2 peak), after which it remained unchanged. The oxygenation index (Delta[O(2)Hb - HHb]) showed an accelerated decrease from 60- 65% of VO(2 peak). In the presence of a constant total Hb volume, the observed Delta[O(2)Hb - HHb] decrease indicates muscle deoxygenation (i.e., mainly capillary-venular Hb desaturation). The onset of muscle deoxygenation was significantly correlated (r(2) = 0.95; P < 0.01) with the point of inflection of [La](b) vs., i.e., with the onset of blood lactate accumulation. Previous studies showed relatively constant femoral venous PO(2) levels at higher than approximately 60% of maximal O(2) consumption. Thus muscle deoxygenation observed in the present study from 60-65% of VO(2 peak) could be attributed to capillary-venular Hb desaturation in the presence of relatively constant capillary-venular PO(2) levels, as a consequence of a rightward shift of the O(2)Hb dissociation curve determined by the onset of lactic acidosis.

Muscle capillary blood flow kinetics estimated from pulmonary O2 uptake and near-infrared spectroscopy

“…It has been generally accepted that the NIRS signal evolves predominantly from changes in oxy-or deoxy-Hb (34); however, for its relevance to the present study, this issue deserves further consideration. In rat thigh muscles perfused with perfluorocarbon to eliminate the NIRS signal arising from Hb, an interference from Mb of less than 10% was observed (40 (17). Collectively, these observations suggest that NIRS light absorption in the quadriceps muscle is mainly associated with Hb during exercise.…”

Estimated contribution of hemoglobin and myoglobin to near infrared spectroscopy

“…Using multiple wavelengths also allows for a more accurate correction of the path length variations that occur in tissue due to scattering. Wavelengths in the vicinity of 690-850 nm have commonly been used for measuring changes only in oxy- [Hb+Mb] and deoxy-[Hb+Mb] (Mancini et al, 1994, Chance et al, 1992, Grassi et al, 1999, Ferreira et al, 2005). Mancini et al (1994) attempted to validate NIRS use in humans using a continuous wave dual frequency (760-800nm) spectrometer.…”

Effect of Duration of Muscle Relaxation during Intermittent Isometric Exercises on Deoxygenation and Lactate Accumulation in Active Muscles

“…Also, an imbalance between production and outfl ow of lactate occurs intermittently, suggesting that lactate may gradually accumulate in VL. Acidifi cation of active muscles through lactate accumulation (lactic acidosis) may accelerate oxygen release from hemoglobin, resulting in increased oxygen extraction from the muscles 20,22) . Therefore, lactate accumulation in VL may be closely involved in the deoxygenation of muscles.…”