The purpose of this study was to use ³¹P-magnetic resonance spectroscopy to examine the relationships among muscle PCr hydrolysis, intracellular H⁺ concentration accumulation, and muscle performance during incremental exercise during the inspiration of gas mixtures containing different fractions of inspired O₂ (FI_O2). We hypothesized that lower FI_O2 would result in a greater disruption of intracellular homeostasis at submaximal workloads and thereby initiate an earlier onset of fatigue. Six subjects performed plantar flexion exercise on three separate occasions with the only variable altered for each exercise bout being the FI_O2 (either 0.1, 0.21, or 1.00 O₂ in balance N₂). Work rate was increased (1-W increments starting at 0 W) every 2 min until exhaustion. Time to exhaustion (and thereby workload achieved) was significantly (P < 0.05) greater as FI_O2 was increased. Muscle phosphocreatine (PCr) concentration, P_i concentration, and pH at exhaustion were not significantly different among the three FI_O2 conditions. However, muscle PCr concentration and pH were significantly reduced at identical submaximal workloads (and thereby equivalent rates of respiration) above 4-5 W during the lowest FI_O2 condition compared with the other two FI_O2 conditions. These results demonstrate that exhaustion during all FI_O2 occurred when a particular intracellular environment was acheived and suggest that during the lowest FI_O2 condition, the greater PCr hydrolysis and intracellular acidosis at submaximal workloads may have contributed to the significantly earlier time to exhaustion.

skeletal muscle; fatigue; oxygen uptake; muscle bioenergetics; exercise; adenosine 5'-triphosphate; adenosine 5'-diphosphate; pH; inorganic phosphate; glycolysis; mitochondrial respiration; fraction of inspired oxygen; phosphocreatine; magnetic resonance spectroscopy

This article has been cited by other articles:

				H. J. Green, M. E. Burnett, I. C. Smith, S. M. Tupling, and D. A. Ranney Failure of hypoxia to exaggerate the metabolic stress in working muscle following short-term training Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2009; 297(3): R593 - R604. [Abstract] [Full Text] [PDF]

				R. C. I. Wust, R. T. Jaspers, A. F. van Heijst, M. T. E. Hopman, L. J. C. Hoofd, W. J. van der Laarse, and H. Degens Region-specific adaptations in determinants of rat skeletal muscle oxygenation to chronic hypoxia Am J Physiol Heart Circ Physiol, July 1, 2009; 297(1): H364 - H374. [Abstract] [Full Text] [PDF]

				M. Amann, L. T. Proctor, J. J. Sebranek, D. F. Pegelow, and J. A. Dempsey Opioid-mediated muscle afferents inhibit central motor drive and limit peripheral muscle fatigue development in humans J. Physiol., January 1, 2009; 587(1): 271 - 283. [Abstract] [Full Text] [PDF]

				M. Amann, L. T. Proctor, J. J. Sebranek, M. W. Eldridge, D. F. Pegelow, and J. A. Dempsey Somatosensory feedback from the limbs exerts inhibitory influences on central neural drive during whole body endurance exercise J Appl Physiol, December 1, 2008; 105(6): 1714 - 1724. [Abstract] [Full Text] [PDF]

				B. Walsh, C. M. Stary, R. A. Howlett, K. M. Kelley, and M. C. Hogan Glycolytic activation at the onset of contractions in isolated Xenopus laevis single myofibres Exp Physiol, September 1, 2008; 93(9): 1076 - 1084. [Abstract] [Full Text] [PDF]

				M. Amann and J. A. Dempsey Reply from Markus Amann and Jerome A. Dempsey J. Physiol., April 1, 2008; 586(7): 2029 - 2030. [Full Text] [PDF]

				M. Amann and J. A. L. Calbet Convective oxygen transport and fatigue J Appl Physiol, March 1, 2008; 104(3): 861 - 870. [Abstract] [Full Text] [PDF]

				D. G. Allen, G. D. Lamb, and H. Westerblad Skeletal Muscle Fatigue: Cellular Mechanisms Physiol Rev, January 1, 2008; 88(1): 287 - 332. [Abstract] [Full Text] [PDF]

				A. W. Subudhi, M. C. Lorenz, C. S. Fulco, and R. C. Roach Cerebrovascular responses to incremental exercise during hypobaric hypoxia: effect of oxygenation on maximal performance Am J Physiol Heart Circ Physiol, January 1, 2008; 294(1): H164 - H171. [Abstract] [Full Text] [PDF]

				M. Amann, L. M. Romer, and J. A. Dempsey Reply from Markus Amann, Lee M. Romer and Jerome A. Dempsey J. Physiol., December 15, 2007; 585(3): 923 - 924. [Full Text] [PDF]

				M. Amann, D. F. Pegelow, A. J. Jacques, and J. A. Dempsey Inspiratory muscle work in acute hypoxia influences locomotor muscle fatigue and exercise performance of healthy humans Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2007; 293(5): R2036 - R2045. [Abstract] [Full Text] [PDF]

				A. M. Jones, D. P. Wilkerson, N. J. Berger, and J. Fulford Influence of endurance training on muscle [PCr] kinetics during high-intensity exercise Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2007; 293(1): R392 - R401. [Abstract] [Full Text] [PDF]

				C. G. R. Perry, J. L. Talanian, G. J. F. Heigenhauser, and L. L. Spriet The effects of training in hyperoxia vs. normoxia on skeletal muscle enzyme activities and exercise performance J Appl Physiol, March 1, 2007; 102(3): 1022 - 1027. [Abstract] [Full Text] [PDF]

				K. Katayama, M. Amann, D. F. Pegelow, A. J. Jacques, and J. A. Dempsey Effect of arterial oxygenation on quadriceps fatigability during isolated muscle exercise Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2007; 292(3): R1279 - R1286. [Abstract] [Full Text] [PDF]

				L. M. Romer, H. C. Haverkamp, M. Amann, A. T. Lovering, D. F. Pegelow, and J. A. Dempsey Effect of acute severe hypoxia on peripheral fatigue and endurance capacity in healthy humans Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2007; 292(1): R598 - R606. [Abstract] [Full Text] [PDF]

				I. R. Lanza, D. M. Wigmore, D. E. Befroy, and J. A. Kent-Braun In vivo ATP production during free-flow and ischaemic muscle contractions in humans J. Physiol., November 15, 2006; 577(1): 353 - 367. [Abstract] [Full Text] [PDF]

				M. Amann, M. W. Eldridge, A. T. Lovering, M. K. Stickland, D. F. Pegelow, and J. A. Dempsey Arterial oxygenation influences central motor output and exercise performance via effects on peripheral locomotor muscle fatigue in humans J. Physiol., September 15, 2006; 575(3): 937 - 952. [Abstract] [Full Text] [PDF]

				M. Amann, L. M. Romer, D. F. Pegelow, A. J. Jacques, C. J. Hess, and J. A. Dempsey Effects of arterial oxygen content on peripheral locomotor muscle fatigue J Appl Physiol, July 1, 2006; 101(1): 119 - 127. [Abstract] [Full Text] [PDF]

				J P Weir, T W Beck, J T Cramer, T J Housh, T D Noakes, A St Clair Gibson, and E V Lambert Is fatigue all in your head? A critical review of the central governor model * Commentary. Br. J. Sports Med., July 1, 2006; 40(7): 573 - 586. [Abstract] [Full Text] [PDF]

				T. Stellingwerff, P. J. LeBlanc, M. G. Hollidge, G. J. F. Heigenhauser, and L. L. Spriet Hyperoxia decreases muscle glycogenolysis, lactate production, and lactate efflux during steady-state exercise Am J Physiol Endocrinol Metab, June 1, 2006; 290(6): E1180 - E1190. [Abstract] [Full Text] [PDF]

				M. Burnley, C. L. Roberts, R. Thatcher, J. H. Doust, and A. M. Jones Influence of blood donation on O2 uptake on-kinetics, peak O2 uptake and time to exhaustion during severe-intensity cycle exercise in humans Exp Physiol, May 1, 2006; 91(3): 499 - 509. [Abstract] [Full Text] [PDF]

				L. M. Romer, H. C. Haverkamp, A. T. Lovering, D. F. Pegelow, and J. A. Dempsey Effect of exercise-induced arterial hypoxemia on quadriceps muscle fatigue in healthy humans Am J Physiol Regulatory Integrative Comp Physiol, February 1, 2006; 290(2): R365 - R375. [Abstract] [Full Text] [PDF]

				C. M. Stary and M. C. Hogan Intracellular pH during sequential, fatiguing contractile periods in isolated single Xenopus skeletal muscle fibers J Appl Physiol, July 1, 2005; 99(1): 308 - 312. [Abstract] [Full Text] [PDF]

				M. C. Hogan, C. M. Stary, R. S. Balaban, and C. A. Combs NAD(P)H fluorescence imaging of mitochondrial metabolism in contracting Xenopus skeletal muscle fibers: effect of oxygen availability J Appl Physiol, April 1, 2005; 98(4): 1420 - 1426. [Abstract] [Full Text] [PDF]

				K. K. McCully, S. Smith, S. Rajaei, J. S. Leigh Jr., and B. H. Natelson Muscle metabolism with blood flow restriction in chronic fatigue syndrome J Appl Physiol, March 1, 2004; 96(3): 871 - 878. [Abstract] [Full Text] [PDF]

				D. J. Marcinek, W. A. Ciesielski, K. E. Conley, and K. A. Schenkman Oxygen regulation and limitation to cellular respiration in mouse skeletal muscle in vivo Am J Physiol Heart Circ Physiol, November 1, 2003; 285(5): H1900 - H1908. [Abstract] [Full Text] [PDF]

				R. T. Hepple, D. J. Krause, J. L. Hagen, and C. C. Jackson VO2 max is unaffected by altering the temporal pattern of stimulation frequency in rat hindlimb in situ J Appl Physiol, August 1, 2003; 95(2): 705 - 711. [Abstract] [Full Text] [PDF]

				J. L. Olive, J. M. Slade, G. A. Dudley, and K. K. McCully Blood flow and muscle fatigue in SCI individuals during electrical stimulation J Appl Physiol, February 1, 2003; 94(2): 701 - 708. [Abstract] [Full Text] [PDF]

				R. S. Richardson, E. A. Noyszewski, B. Saltin, and J. Gonzalez-Alonso Effect of mild carboxy-hemoglobin on exercising skeletal muscle: intravascular and intracellular evidence Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2002; 283(5): R1131 - R1139. [Abstract] [Full Text] [PDF]

				M. K. Evans, I. Savasi, G. J. F. Heigenhauser, and L. L. Spriet Effects of acetate infusion and hyperoxia on muscle substrate phosphorylation after onset of moderate exercise Am J Physiol Endocrinol Metab, December 1, 2001; 281(6): E1144 - E1150. [Abstract] [Full Text] [PDF]

				R. S. Richardson, L. J. Haseler, A. T. Nygren, S. Bluml, and L. R. Frank Local perfusion and metabolic demand during exercise: a noninvasive MRI method of assessment J Appl Physiol, October 1, 2001; 91(4): 1845 - 1853. [Abstract] [Full Text] [PDF]

				C. M. Stary and M. C. Hogan Impairment of Ca2+ release in single Xenopus muscle fibers fatigued at varied extracellular PO2 J Appl Physiol, May 1, 2000; 88(5): 1743 - 1748. [Abstract] [Full Text] [PDF]

				S. E. Bearden and R. J. Moffatt VO2 kinetics and the O2 deficit in heavy exercise J Appl Physiol, April 1, 2000; 88(4): 1407 - 1412. [Abstract] [Full Text] [PDF]

				R. S. Richardson; and T. Jue Intracellular PO2 and bioenergetic measurements in skeletal muscle: the role of exercise paradigm Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2000; 278(4): R1111 - R1113. [Full Text] [PDF]

				P. J. Radell, S. M. Eleff, and D. G. Nichols Effects of loaded breathing and hypoxia on diaphragm metabolism as measured by 31P-NMR spectroscopy J Appl Physiol, March 1, 2000; 88(3): 933 - 938. [Abstract] [Full Text] [PDF]

				M. L. Parolin, L. L. Spriet, E. Hultman, M. G. Hollidge-Horvat, N. L. Jones, and G. J. F. Heigenhauser Regulation of glycogen phosphorylase and PDH during exercise in human skeletal muscle during hypoxia Am J Physiol Endocrinol Metab, March 1, 2000; 278(3): E522 - E534. [Abstract] [Full Text] [PDF]

				R. S. Richardson, H. Wagner, S. R. D. Mudaliar, R. Henry, E. A. Noyszewski, and P. D. Wagner Human VEGF gene expression in skeletal muscle: effect of acute normoxic and hypoxic exercise Am J Physiol Heart Circ Physiol, December 1, 1999; 277(6): H2247 - H2252. [Abstract] [Full Text] [PDF]

				P. W. Hochachka The metabolic implications of intracellular circulation PNAS, October 26, 1999; 96(22): 12233 - 12239. [Abstract] [Full Text] [PDF]

				C. M. Stary and M. C. Hogan Effect of varied extracellular PO2 on muscle performance in Xenopus single skeletal muscle fibers J Appl Physiol, June 1, 1999; 86(6): 1812 - 1816. [Abstract] [Full Text] [PDF]