Capillary‐to‐sarcolemma distance and location of cytochrome c oxidase: Insights for maximal O₂ uptake and muscle lactate release in trained athletes

Mean capillary‐to‐sarcolemma diffusion distance (mCtSDD) is conceptually critical for exchanges of both gases and metabolites between muscle and blood. However, the importance of this distance for maximal oxygen uptake () and muscle lactate release in highly‐trained athletes remains unexplored. Furthermore, the importance of intramyocyte location of cytochrome c oxidase (COx) activity and remains obscure. Seventeen highly‐trained lightweight oarsmen performed a maximal incremental exercise test to assess and its associated power (), as well as a 3 min 110% exercise to estimate the net lactate release rate at exercise completion [NLRR(0)]. A vastus lateralis muscle biopsy allowed analysis of muscle microvasculature indices [capillary density (CD) and mCtSDD] and location‐specific COx activity. Significant correlations between mCtSDD and both ( r = −0.76, P < 0.001) and NLRR(0) ( r = −0.63, P = 0.00724) were found. Correlations between CD and or NLRR(0) were also found ( r = 0.50, P = 0.0397 and r = 0.49, P = 0.0483, respectively). COx activity was higher in the pericapillary and subsarcolemmal domains than in the intramyofibrillar counterpart (location effect: P < 0.001). Pericapillary and subsarcolemmal COx activities were significantly associated with ( r = 0.59, P = 0.0322 and r = 0.58, P = 0.0387, respectively), in contrast to its intramyofibrillar counterpart ( r = 0.48, P = 0.096). mCtSDD was significantly associated with and muscle lactate release rate in highly‐trained endurance athletes. Pericapillary and subsarcolemmal COx activity was also associated with . image Key points Because it is a carrier‐free area, the capillary‐to‐sarcolemma diffusion distance is conceptually critical for exchanges of both gases and metabolites between muscle and blood. In the present study, we proposed a new index estimating the mean capillary‐to‐sarcolemma diffusion distance (mCtSDD). In the present study, mCtSDD was closely correlated with and the net lactate release rate estimated at exercise completion. The importance of intramyocyte location of cytochrome c oxidase (COx) activity and remains obscure in highly‐trained athletes. Pericapillary and subsarcolemmal COx activity was higher than its intermyofbrillar counterpart. Pericapillary and subsarcolemmal COx activity was significantly associated with in highly‐trained endurance athletes.