Abstract
The peak rate of fat oxidation (PFO) achieved during a graded exercise test is an important indicator of metabolic health. In healthy individuals, there is a significant positive association between PFO and total daily fat oxidation (FO). However, conditions resulting in metabolic dysfunction may cause a disconnect between PFO and non-exercise FO. Ten adult men with chronic thoracic spinal cord injury (SCI) completed a graded arm exercise test. On a separate day following an overnight fast (≥ 10 h), they rested for 60 min before ingesting a liquid mixed meal (600 kcal; 35% fat, 50% carbohydrate, 15% protein). Expired gases were collected and indirect calorimetry data used to determine FO at rest, before and after feeding, and during the graded exercise test. Participants had “good” cardiorespiratory fitness (VO2peak: 19.2 ± 5.2 ml/kg/min) based on normative reference values for SCI. There was a strong positive correlation between PFO (0.30 ± 0.08 g/min) and VO2peak (r = 0.86, p = 0.002). Additionally, postabsorptive FO at rest was significantly and positively correlated with postprandial peak FO (r = 0.77, p = 0.01). However, PFO was not significantly associated with postabsorptive FO at rest (0.08 ± 0.02 g/min; p = 0.97), postprandial peak FO (0.10 ± 0.03 g/min; p = 0.43), or incremental area under the curve postprandial FO (p = 0.22). It may be advantageous to assess both postabsorptive FO at rest and PFO in those with SCI to gain a more complete picture of their metabolic flexibility and long-term metabolic health.
Highlights
Spinal cord injury (SCI) incites persistent metabolic derangement, readily observed through the interaction of decreases in the mass of skeletal muscle [1] and bone [2] and increases in fat mass [3]
The peak rate of fat oxidation (PFO) was defined as the highest rate of fat oxidation (FO) achieved in 20-s averages of data collected during the graded exercise test
The participants had “good” cardiorespiratory fitness based on normative data for paraplegic men [31]
Summary
Spinal cord injury (SCI) incites persistent metabolic derangement, readily observed through the interaction of decreases in the mass of skeletal muscle [1] and bone [2] and increases in fat mass [3]. It was shown that poor metabolic flexibility in the face of 24-h high-fat overfeeding predicted future weight gain [11] While these studies are intriguing, the 24-h measurements rely on whole-room calorimeters, limiting the implementation of this resource-intensive method by practitioners to identify those most at risk for poor metabolic health outcomes. More recent work has shown that postabsorptive fat oxidation (FO) at rest [14, 15], 24-h FO, and insulin sensitivity [16] in healthy men are positively related to PFO These relationships have important health implications as they provide evidence identifying PFO as an accessible and affordable means of assessing metabolic flexibility and long-term metabolic health. The degree to which these variables are related may determine whether PFO can be used to predict the future metabolic health of those with SCI and to target effective interventions to those most in need
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