Introduction: A spinal cord injury (SCI) results in deconditioning of the cardiovascular system, including changes in both vascular function and structure (1), leading to an elevated risk of cardiovascular diseases (2). While exercise training (arms-only) for persons with SCI has been shown to increase the diameter of the peripheral conduit artery feeding the active limb, little is known about the effects of arm exercise on central artery diameter and wall thickness. Our main hypothesis was that peripheral, but not central, conduit artery diameter would be increased following 12 weeks of upper-body rowing exercise (UBROW) in SCI individuals.

Methods: Seventeen male and female adults with chronic (>1 yr) motor-complete and incomplete SCI (level of injury: C4-L3) were randomized to control (CON, n=9) or exercise (UBROW, n=8). Participants in UBROW performed 12 weeks of 3 weekly sessions of 30-min moderate-to-vigorous-intensity rowing (arms-only) on an ergometer adapted to wheelchair users. In supine resting position, common carotid artery (CCA) and brachial artery (BA) lumen diameters (M-line to M-line) were determined using high-resolution ultrasound at baseline, after 6 weeks (6W), and after the intervention (12W). CCA wall thickness was measured by near and far-wall carotid intima-media thickness (CIMT). Recordings of resting arterial diameters and CIMT were analyzed off-line frame-by-frame using semi-automated edge-detecting and wall-tracking software. Intra-observer coefficient of variation for CIMT and CCA diameter analyses was 1.6% and 0.95%, respectively. Linear mixed-effects model was used to determine main effects of group and time, and their interaction, with Holm-Sidak Post hoc tests in case of significant interaction effects.

Results: For BA diameter, there was a group-by-time interaction (P=0.016). UBROW increased BA diameter from baseline (4.80±0.72mm) to 12W (5.08±0.91mm; P<0.01), with no changes at 6W (4.96±0.91mm), and no changes in CON.
For CCA diameter, there was no interaction (P=0.478) or main effects of time or group (P≥0.102). For CIMT near-wall, there was no interaction (P=0.72) or main effects of time or group (P≥0.43). UBROW vs. CON: Baseline (0.69 mm vs. 0.73 mm); 6-week (0.70 mm vs. 0.72 mm); and 12-week (0.71 mm vs. 0.71 mm). For CIMT far-wall, there was a main effect of group (P≥0.02) but no interaction (P=0.06). UBROW vs. CON: Baseline (0.56 mm vs. 0.65 mm); 6-week (0.59 mm vs. 0.61 mm); and 12-week (0.55 mm vs. 0.60 mm).

Conclusions: 12 weeks of arms-only rowing significantly increased peripheral conduit artery diameter (BA) but did not change central artery diameter (CCA) or wall thickness (CIMT) in individuals with SCI. These results demonstrate localized, but not systemic, arterial adaptations in response to 12 weeks of arm exercise. While structural enlargement of the BA seems likely, it is possible that changes in sympathetic nervous system activity may have influenced BA resting diameter. Further research is needed to fully understand the underlying mechanism for the exercise-induced enlargement in peripheral arterial diameter and the possible influence of this adaptation on cardiovascular disease risk.