Aerobic metabolism and cardioventilatory responses in paraplegic athletes during an incremental wheelchair exercise

Abstract

The aims of the present study were: (1) to assess aerobic metabolism in paraplegic (P) athletes (spinal lesion level, T4-L3) by means of peak oxygen uptake (VO2peak) and ventilatory threshold (VT), and (2) to determine the nature of exercise limitation in these athletes by means of cardioventilatory responses at peak exercise. Eight P athletes underwent conventional spirographic measurements and then performed an incremental wheelchair exercise on an adapted treadmill. Ventilatory data were collected every minute using an automated metabolic system: ventilation (l x min[-1]), oxygen uptake (VO2, l x min[-1], ml x min[-1] x kg[-1]), carbon dioxide production (VCO2, ml x min[-1]), respiratory exchange ratio, breathing frequency and tidal volume. Heart rate (HR, beats x min[-1]) was collected with the aid of a standard electrocardiogram. VO2peak was determined using conventional criteria. VT was determined by the breakpoint in the VCO2 - VO2 relationship, and is expressed as the absolute VT (VO2, ml x min[-1] x kg[-1]) and relative VT (percentage of VO2peak). Spirometric values and cardioventilatory responses at rest and at peak exercise allowed the measurement of ventilatory reserve (VR), heart rate reserve (HRr), heart rate response (HRR), and O2 pulse (O2 P). Results showed a VO2peak value of 40.6 (2.5) ml x min(-1) x kg(-1), an absolute VT detected at 23.1 (1.5) ml x min(-1) x kg(-1) VO2 and a relative VT at 56.4 (2.2)% VO2peak. HRr [15.8 (3.2) beats min(-1)], HRR [48.6 (4.3) beat x l(-1)], and O2 P [0.23 (0.02) ml x kg(-1) x beat(-1)] were normal, whereas VR at peak exercise [42.7 (2.4)%] was increased. As wheelchair exercise excluded the use of an able-bodied (AB) control group, we compared our VO2peak and VT results with those for other P subjects and AB controls reported in the literature, and we compared our cardioventilatory responses with those for respiratory and cardiac patients. The low VO2peak values obtained compared with subject values obtained during an arm-crank exercise may be due to a reduced active muscle mass. Absolute VT was somewhat comparable to that of AB subjects, mainly due to the similar muscle mass involved in wheelchair and arm-crank exercise by P and AB subjects, respectively. The increased VR, as reported in patients with chronic heart failure, suggested that P athletes exhibited cardiac limitation at peak exercise, and this contributed to the lower VO2peak measured in these subjects.