Cardiorespiratory fitness in highly active versus inactive paraplegics

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Abstract
Maximum and submaximum arm crank exercise performance were assessed in male paraplegics (PARA) with the purpose of comparing cardiovascular responses among individuals of highly active (A, N = 15) vs inactive (I, N = 15) lifestyles. The A PARAs (average V̇O2 peak during arm cranking 2.241·min-1) demonstrated a significantly higher maximal cardiorespiratory fitness compared to I subjects (average V̇O2 peak 1.56 1·min-1). During graded arm exertion, at exercise intensities approximating 45%, 57%, and 70% of V̇O2 peak, the active subjects developed cardiac outputs (assessed via CO2-rebreathing) ranging from 9.07 to 11.21 1·min-1; a 34–44% advantage relative to their inactive counterparts (6.30–8.36 1·min-1). Similarly, exercise stroke volumes for A (76–80 ml) were 38–45% higher than for I paraplegics (55–56 ml). Although both groups demonstrated a distinctive circulatory hypokinesis during arm cranking, the immediate pattern of cardiovascular response was dissimilar for the highly active versus inactive subjects. The former demonstrated a predominantly “central” adaptation to steady-state arm exercise (exhibiting normal stroke volumes and arteriovenous O2 extractions for spinal cord-injured subjects), while the latter displayed markedly reduced stroke volumes concomitant with abnormally large peripheral arteriovenous oxygen extractions for a given oxygen uptake.