A Reappraisal of Ventilatory Thresholds in Wheelchair Athletes With a Spinal Cord Injury: Do They Really Exist?

The ventilatory threshold (VT) separates low- from moderate-intensity exercise, the respiratory compensation point (RCP) moderate- from high-intensity exercise. Both concepts assume breakpoints in respiratory data. However, the objective determination of the VT and RCP using breakpoint models during upper-body modality exercise in wheelchair athletes with spinal cord injury (SCI) has received little attention. Therefore, the aim of this study was to compare the fit of breakpoint models (i.e., two linear regression lines) with continuous no-breakpoint models (i.e., exponential curve/second-order polynomial) to respiratory data obtained during a graded wheelchair exercise test to exhaustion. These fits were compared employing adjusted R2, and blocked bootstrapping was used to derive estimates of a median and 95% confidence intervals (CI). V̇O2-V̇CO2 and V̇E/V̇O2-time data were assessed for the determination of the VT, and V̇CO2-V̇E and V̇E/V̇CO2-time data for the determination of the RCP. Data of 9 wheelchair athletes with tetraplegia and 8 with paraplegia were evaluated. On an overall group-level, there was an overlap in the adjusted R2 median ± 95% CI between the breakpoint and the no-breakpoint models for determining the VT (V̇O2-V̇CO2: 0.991 ± 0.003 vs. 0.990 ± 0.003; V̇E/V̇O2-time: 0.792 ± 0.101 vs. 0.782 ± 0.104, respectively) and RCP (V̇E-V̇CO2: 0.984 ± 0.004 vs. 0.984 ± 0.004; V̇E/V̇CO2-time: 0.729 ± 0.064 vs. 0.691 ± 0.063, respectively), indicating similar model fit. We offer two lines of reasoning: (1) breakpoints in these respiratory data exist but are too subtle to result in a significant difference in adjusted R2 between the investigated breakpoint and no-breakpoint models; (2) breakpoints do not exist, as has been argued previously.

Mucosal immune responses to treadmill exercise in elite wheelchair athletes.

PURPOSE: The study's purpose was to examine salivary secretory immunoglobulin A (sIgA) responses and α-amylase activity after constant load and intermittent exercise in elite wheelchair athletes. METHODS: Twenty-three wheelchair athletes divided into three groups (eight tetraplegic (TETRA), seven paraplegic, and eight non-spinal cord-injured) performed two randomized and counterbalanced 60-min sessions on a treadmill. These consisted of constant load (60% peak oxygen uptake) and intermittent (80% and 40% peak oxygen uptake) exercise blocks. Timed unstimulated saliva samples were obtained before, mid, after, and 30 min after exercise and analyzed for sIgA and α-amylase. Furthermore, oxygen uptake, blood lactate concentration, and RPE were measured during both sessions. RESULTS: SIgA secretion rate and α-amylase activity were increased during exercise in all groups (P < 0.05). However, the increase of sIgA secretion rate during exercise was greater in TETRA individuals (postexercise average data for both trials in comparison with preexercise data: TETRA = +60% ± 31%, paraplegic = +30% ± 35%, non-spinal cord-injured = +11% ± 25%; P < 0.05). Yet, groups were comparable with respect to blood lactate concentration and RPE for both exercise sessions. CONCLUSIONS: Despite the disruption of autonomic salivary gland innervation in TETRA athletes, their ability to increase sIgA secretion rate seems comparable to wheelchair athletes with intact autonomic salivary gland innervation. The similar responses between groups may stem from sympathetic reflex activity during exercise or a predominant contribution of parasympathetic activity, which are still intact systems in the TETRA population. The results of this study support the positive role of acute exercise on oral immune function in wheelchair athletes independent of disability type.