A sex-specific relationship between capillary density and anaerobic threshold

1 Duke University Medical Center, Division of Cardiology, Durham, North Carolina; 2 Department of Internal Medicine, Harbor-UCLA Medical Center, Torrance, California; 3 Department of Exercise and Sports Science and Human Performance Laboratory, East Carolina University, Greenville, North Carolina; and 4 Department of Medicine, University of Virginia, Charlottesville, Virginia Submitted 8 July 2008 ; accepted in final form 19 January 2009 Although both capillary density and peak oxygen consumption ( O 2 ) improve with exercise training, it is difficult to find a relationship between these two measures. It has been suggested that peak O 2 may be more related to central hemodynamics than to the oxidative potential of skeletal muscle, which may account for this observation. We hypothesized that change in a measure of submaximal performance, anaerobic threshold, might be related to change in skeletal muscle capillary density, a marker of oxidative potential in muscle, with training. Due to baseline differences among these variables, we also hypothesized that relationships might be sex specific. A group of 21 subjects completed an inactive control period, whereas 28 subjects (17 men and 11 women) participated in a 6-mo high-intensity exercise program. All subjects were sedentary, overweight, and dyslipidemic. Potential relationships were assessed between change in capillary density with both change in O 2 at peak and at anaerobic threshold with exercise training. All variables and relationships were assessed for sex-specific effects. Change in peak O 2 was not related to change in capillary density after exercise training in either sex. Men had a positive correlation between change in O 2 at anaerobic threshold and change in capillary density with exercise training ( r = 0.635; P < 0.01), whereas women had an inverse relationship ( r = –0.636; P < 0.05) between the change in these variables. These findings suggest that, although enhanced capillary density is associated with training-induced improvements in submaximal performance in men, this relationship is different in women. skeletal muscle; exercise; studies of a targeted risk reduction intervention through defined exercise; peak oxygen consumption Address for reprint requests and other correspondence: J. L. Robbins, Div. of Cardiology, Duke Univ. Medical Center, 1300 Morreene Rd., DUMC 3022, Durham, NC 27710 (e-mail: j.robbins{at}duke.edu )