Journal of Applied Physiology AJP: Heart and Circulatory Physiology
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J Appl Physiol 87: 348-355, 1999;
8750-7587/99 $5.00
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Vol. 87, Issue 1, 348-355, July 1999

Blood lactate accumulation and muscle deoxygenation during incremental exercise

Bruno Grassi1, Valentina Quaresima2, Claudio Marconi1, Marco Ferrari2, and Paolo Cerretelli1

1 Istituto di Tecnologie Biomediche Avanzate, Consiglio Nazionale delle Ricerche, I-20090 Segrate (MI); and 2 Dipartimento di Scienze e Tecnologie Biomediche, Università di L'Aquila, I-67100 L'Aquila, Italy

Near-infrared spectroscopy (NIRS) could allow insights into controversial issues related to blood lactate concentration ([La]b) increases at submaximal workloads (w). We combined, on five well-trained subjects [mountain climbers; peak O2 consumption (VO2peak), 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 [O2Hb]) and deoxygenated Hb (Delta [HHb]) in the vastus lateralis muscle, by continuous-wave NIRS. A "point of inflection" of [La]b vs. w was arbitrarily identified at the lowest [La]b value which was >0.5 mM lower than that obtained at the following w. Total Hb volume (Delta [O2Hb + HHb]) in the muscle region of interest increased as a function of w up to 60-65% of VO2 peak, after which it remained unchanged. The oxygenation index (Delta [O2Hb - HHb]) showed an accelerated decrease from 60- 65% of VO2 peak. In the presence of a constant total Hb volume, the observed Delta [O2Hb - HHb] decrease indicates muscle deoxygenation (i.e., mainly capillary-venular Hb desaturation). The onset of muscle deoxygenation was significantly correlated (r2 = 0.95; P < 0.01) with the point of inflection of [La]b vs. w, i.e., with the onset of blood lactate accumulation. Previous studies showed relatively constant femoral venous PO2 levels at w higher than ~60% of maximal O2 consumption. Thus muscle deoxygenation observed in the present study from 60-65% of VO2 peak could be attributed to capillary-venular Hb desaturation in the presence of relatively constant capillary-venular PO2 levels, as a consequence of a rightward shift of the O2Hb dissociation curve determined by the onset of lactic acidosis.

lactate threshold; near-infrared spectroscopy


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