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Substrate Utilization during and after Exercise in Mild Cystic Fibrosis


Medicine & Science in Sports & Exercise: February 2009 - Volume 41 - Issue 2 - p 270-278
doi: 10.1249/MSS.0b013e318188449b
Clinical Sciences

Purpose: To determine substrate utilization and energy expenditure during maximal and submaximal exercise and recovery in adolescents with cystic fibrosis (CF) and healthy age-matched controls (C).

Methods: Ten clinically stable CF patients (four girls, six boys; age = 10-22 yr) were matched by body mass index, age, gender, and Tanner stage to healthy controls. Subjects completed V˙O2peak testing and submaximal exercise (20 min) on a cycle ergometer at a relative intensity of 50% V˙O2peak and at an absolute power output (PO). Metabolic parameters were assessed during exercise and recovery (20 min).

Results: Similar respiratory quotient (RQ) values occurred in both groups during maximal exercise and recovery, despite differences in the maximal PO [CF = 114 (60-180) W and C = 171 (105-280) W, P = 0.006], the total work completed [CF = 27 (9.0-54.3) kJ and C = 55 (25.3-126.5) kJ, P = 0.008], or the V˙O2peak value attained [CF = 30.6 (8.5-45.2) mL·kg−1·min−1 and C = 40.6 (29-64.5) mL·kg−1·min−1, P = 0.027]. Submaximal exercise at the same absolute PO resulted in similar RQ values during exercise and recovery despite higher heart rates and average V˙O2 [CF = 18.8 (9.3-28.7) mL·kg−1·min−1 and C = 15.2 (6.5-20.1) mL·kg−1·min−1, P = 0.031] values in CF adolescents, and submaximal exercise at the same relative intensity also resulted in similar RQ values despite significantly greater average PO in the C group [CF = 38.7 (12.3-80) W and C = 67.8 (25.5-140) W, P = 0.039]. Excess postexercise oxygen consumption (EPOC) was greater in CF [2.79 (1.14-5.24) L O2] than C [1.46 (0.56-2.80) L O2] after submaximal exercise at a fixed PO (P = 0.036) but not after the relative exercise bout.

Conclusions: Habitual physical activity participation does not warrant adjustment of macronutrient intake ratios in adolescents with mild to moderate CF, but total caloric intake may need to be increased based on the level of EPOC and upon the intensity and the duration of the habitual activity.

1Department of Exercise and Sport Science, University of North Carolina at Greensboro, NC; 2School of Nursing, University of North Carolina at Greensboro, NC; 3Division of Public Health Sciences, Department of Biostatistical Sciences, Wake Forest University School of Medicine, Winston-Salem, NC; and 4Department of Medicine, Wake Forest University School of Medicine, Winston-Salem, NC

Address for correspondence: Laurie Wideman, Ph.D., Department of Exercise and Sport Science, University of North Carolina at Greensboro, Rm 270 HHP Building, 1408 Walker Ave, Greensboro, NC 27412; E-mail:

Submitted for publication March 2008.

Accepted for publication July 2008.

©2009The American College of Sports Medicine