Critical speed in the rat: implications for hindlimb muscle blood flow distribution and fibre recruitment
- 15 December 2010
- journal article
- Published by Wiley in Journal Of Physiology-London
- Vol. 588 (24), 5077-5087
- https://doi.org/10.1113/jphysiol.2010.198382
Abstract
Critical speed (CS) constitutes an important metabolic and performance demarcator. However, active skeletal muscle blood flow distribution specifically surrounding CS remains unknown. We tested the hypotheses that CS could be accurately determined in the running rat and that measurement of hindlimb inter- and intramuscular blood flow below and above CS would support that the greatest muscle fibre recruitment above, relative to below, CS occurs in the predominantly glycolytic muscles. Seven male Sprague-Dawley rats performed five constant-speed tests to exhaustion at speeds between 95 and 115% of the speed that elicited to determine CS. Subsequent constant-speed tests were performed at speeds incrementally surrounding CS to determine time to exhaustion, V(O2), and hindlimb muscle blood flow distribution. Speed and time to exhaustion conformed to a hyperbolic relationship (r(2) = 0.92 ± 0.03) which corresponded to a linear 1/time function (r(2) = 0.93 ± 0.02) with a CS of 48.6 ± 1.0 m min(-1). Time to exhaustion below CS was ∼ 5× greater (P < 0.01) than that above. Below CS V(O2) stabilized at a submaximal value (58.5 ± 2.5 ml kg(-1) min(-1)) whereas above CS (81.7 ± 2.5 ml kg(-1) min(-1)) increased to (84.0 ± 1.8 ml kg(-1) min(-1), P > 0.05 vs. above CS). The 11 individual muscles or muscle parts that evidenced the greatest blood flow increases above, relative to below, CS were composed of ≥ 69% Type IIb/d/x muscle fibres. Moreover, there was a significant correlation (P < 0.05, r = 0.42) between the increased blood flow above expressed relative to below CS and the percentage Type IIb/d/x fibres found in the individual muscles or muscle parts. These data validate the powerful CS construct in the rat and identify that running above CS, relative to below CS, incurs disproportionate blood flow increases (indicative of recruitment) in predominantly highly glycolytic muscle fibres.This publication has 45 references indexed in Scilit:
- Effects of neuronal nitric oxide synthase inhibition on resting and exercising hindlimb muscle blood flow in the ratJournal Of Physiology-London, 2010
- The O2cost of the tension-time integral in isolated single myocytes during fatigueAmerican Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2010
- Nitric oxide synthase inhibition during treadmill exercise reveals fiber-type specific vascular control in the rat hindlimbAmerican Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2010
- Reproducibility of endurance capacity and V̇o2peak in male Sprague-Dawley ratsJournal of Applied Physiology, 2009
- Reporting ethical matters in The Journal of Physiology: standards and adviceJournal Of Physiology-London, 2009
- Muscle metabolic responses to exercise above and below the “critical power” assessed using31P-MRSAmerican Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2008
- Inter- and intrastrain variation in mouse critical running speedJournal of Applied Physiology, 2005
- Hyperbolic relationship between time‐to‐fatigue and workloadEquine Veterinary Journal, 1999
- Metabolic and respiratory profile of the upper limit for prolonged exercise in manErgonomics, 1988
- Effect of varying exercise intensity on glycogen depletion in human muscle fibresActa Physiologica Scandinavica, 1985