Cardiorespiratory fitness in highly active versus inactive paraplegics

Maximum and submaximum arm crank exercise performances 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 VO2 peak during arm cranking 2.24 l.min-1) demonstrated a significantly higher maximal cardiorespiratory fitness compared to I subjects (average VO2 peak 1.56 l.min-1). During graded arm exertion, at exercise intensities approximating 45%, 57%, and 70% of VO2 peak, the active subjects developed cardiac outputs (assessed via CO2-rebreathing) ranging from 9.07 to 11.21 l.min-1; a 34-44% advantage relative to their inactive counterparts (6.30-8.36 l.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.