Spinal cord injury level influences acute plasma caffeine responses

Purpose. To investigate the absorption curve and acute effects of caffeine at rest in individuals with no spinal cord injury (SCI), paraplegia (PARA) and tetraplegia (TETRA). Methods. Twenty-four healthy males (8 able-bodied (AB), 8 PARA and 8 TETRA) consumed 3 mg∙kg-1 caffeine anhydrous (CAF) in a fasted state. Plasma caffeine [CAF], glucose, lactate, free-fatty acid [FFA] and catecholamine concentrations were measured during a 150 min rest period. Results. Peak [CAF] was greater in TETRA (21.5 µM) compared to AB (12.2 µM) and PARA (15.1 µM), and mean peak [CAF] occurred at 70, 80 and 80 min, respectively. Moderate and large ES were revealed for TETRA compared to PARA and AB (-0.55 and -1.14, respectively) for the total area under the [CAF] versus time curve. Large inter-individual responses were apparent in SCI groups. The change in plasma catecholamine concentrations following CAF did not reach significance (p>0.05) however both adrenaline and noradrenaline concentrations were lowest in TETRA. Significant increases in [FFA] were seen over time (p<0.0005) but there was no significant influence of SCI level. Blood lactate concentration reduced over time (p=0.022) whereas blood glucose concentration decreased modestly (p=0.695), and no difference between groups was seen (p>0.05). Conclusion. Level of SCI influenced the caffeine absorption curve and there was large inter-individual variation within and between groups. Individual curves should be considered when using caffeine as an ergogenic aid in athletes with an SCI. The results indicate TETRA should trial low doses in training and PARA may consider consuming caffeine greater than 60 min prior to exercise performance. The study also supports caffeine’s direct effect on adipose tissue, which is not secondary to catecholamine release.