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

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 ((V) over dot O-2peak) 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.min(-1)), oxygen uptake ((V) over dot O-2, ml.min(-1), ml.min(-1).kg(-1)), carbon dioxide production ((V) over dot CO2, ml.min(-1)), respiratory exchange ratio, breathing frequency and tidal volume. Heart rate (HR, beats.min(-1)) was collected with the aid of a standard electrocardiogram. (V) over dot O-2peak was determined using conventional criteria. VT was determined by the breakpoint in the (V) over dot CO2-(V) over dot O-2 relationship, and is expressed as the absolute VT ((V) over dot O-2, ml.min(-1).kg(-1)) and relative VT (percentage of (V) over dot O-2peak) 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 O-2 pulse (O-2 P). Results showed a (V) over dot O-2peak value of 40.6 (2.5) ml.min(-1).kg(-1), an absolute VT detected at 23.1 (1.5) ml.min(-1).kg(-1) (V) over dot O-2 and a relative VT at 56.4 (2.2)% (V) over dot O-2peak. HRr [15.8 (3.2) beats .min(-1)], HRR [48.6 (4.3) beat.1(-1)], and O-2 P [0.23 (0.02) ml.kg(-1).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 (V) over dot O-2peak 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 (V) over dot O-2peak 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 (V) over dot O-2peak measured in these subjects.