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  • Title: Recovery of microvascular PO2 during the exercise off-transient in muscles of different fiber type.
    Author: McDonough P, Behnke BJ, Musch TI, Poole DC.
    Journal: J Appl Physiol (1985); 2004 Mar; 96(3):1039-44. PubMed ID: 14607847.
    Abstract:
    The speed with which muscle energetic status recovers after exercise is dependent on oxidative capacity and vascular O(2) pressures. Because vascular control differs between muscles composed of fast- vs. slow-twitch fibers, we explored the possibility that microvascular O(2) pressure (Pmv(O(2)); proportional to the O(2) delivery-to-O(2) uptake ratio) would differ during recovery in fast-twitch peroneal (Per: 86% type II) compared with slow-twitch soleus (Sol: 84% type I). Specifically, we hypothesized that, in Per, Pmv(O(2)) would be reduced immediately after contractions and would recover more slowly during the off-transient from contractions compared with Sol. The Per and Sol muscles of six female Sprague-Dawley rats (weight = approximately 220 g) were studied after the cessation of electrical stimulation (120 s; 1 Hz) to compare the recovery profiles of Pmv(O(2)). As hypothesized, Pmv(O(2)) was lower throughout recovery in Per compared with Sol (end contraction: 13.4 +/- 2.2 vs. 20.2 +/- 0.9 Torr; end recovery: 24.0 +/- 2.4 vs. 27.4 +/- 1.2 Torr, Per vs. Sol; P <or= 0.05). In addition, the mean response time for recovery was significantly faster for Sol compared with Per (45.1 +/- 5.3 vs. 66.3 +/- 8.1 s, Sol vs. Per; P < 0.05). Despite these findings, Pmv(O(2)) rose progressively in both muscles and at no time fell below end-exercise values. These data indicate that, during the recovery from contractions (which is prolonged in Per), capillary O(2) driving pressure (i.e., Pmv(O(2))) is reduced in fast-compared with slow-twitch muscle. In conclusion, the results of the present investigation may partially explain the slowed recovery kinetics (phosphocreatine and O(2) uptake) found previously in 1) fast- vs. slow-twitch muscle and 2) various patient populations, such as those with congestive heart failure and diabetes mellitus.
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