Article

Cross-sectional study comparing trained spinal cord injured (SCI) subjects (lesion level: L1 similar to T6) with healthy young subjects (CONT). Objective: To investigate the kinetics of response in oxygen uptake ((V)over dotO(2)) in human upper-body skeletal muscles, nine trained SCI subjects underwent submaximal supine arm exercises. Method: The SCI subjects underwent an incremental arm exercise test until exhaustion. The days after this first round of testing, breath-by-breath (V)over dotO(2) and beat-by-beat heart rate (HR) on- and off-kinetics were determined during three repetitions of constant exercise at 50% of (V)over dotO(2peak). The overall time course of response was determined from the half time (t(1/2)). Increased capillary blood lactate production (Delta[La]b) at the onset of exercise was defined as the difference between at rest and at the end of exercise. Cardiac output ((Q)over dot) was measured using the acetylene rebreathing method during the steady state of exercise. In accordance with the Fick principle, the difference in arterial-venous O-2 content (Ca-(v) over barO(2)) was defined as (V)over dotO(2)/(Q)over dot. Results: During the steady state of the submaximal arm exercise, a more significant increase in the steady state of 0 was obtained in the CONT subjects than in the trained SCI subjects: respectively, 14.9 +/- 1.4 l/min versus (12.7 +/- 0.8 l/min). There was no difference in the steady state of (V)over dotO(2) between the two groups; as a result, SCI subjects had the greater Ca-(v) over barO(2). Meanwhile,(V)over dotO(2), on- and off-kinetics became much faster in the trained SCI subjects than in the CONT subjects. In addition, t(1/2) FIR on-kinetics was not significantly different between the SCI and CONT groups. Increased A[La]b was closely related to larger t(1/2) (V)over dotO(2) on-kinetics (r=0.624, P<0.05). Conclusion: It is concluded that the acceleration of (V)over dotO(2) on- and off-kinetics in the trained SCI subjects was observed even though there was no difference in HR on- and off-kinetics between the SCI and CONT groups and a lower steady state of (Q)over dot in the trained SCI subjects. (V)over dotO(2) kinetics would therefore be the limiting factor in oxidative phosphorylation in the upper skeletal muscles, thereby providing a lower lactic O-2-deficit (ie Delta[La]b). Sponsorship: This study was partly supported by the grant from Frontier Science Promotion in Kumamoto, Japan (1997, 1998).

Langue : ANGLAIS

Identifiant basis : 2003225557