Inspired substrate oxidation in healthy elderly men after eccentric exercise

• Published in: Journal of applied physiology (1985) Vol. 94; no. 2; p. 716
• Main Authors: Krishnan, Raj K, Evans, William J, Kirwan, John P
• Format: Journal Article
• Language: English
• Published: Bethesda American Physiological Society 01-02-2003
• Subjects: Exercise; Men; Older people; Oxidation
• ISSN: 8750-7587; 1522-1601

The metabolic response to eccentric exercise in healthy older adults is unknown. Therefore, substrate metabolism was examined in the basal state and after sustained hyperglycemia (180 min, 10 mM) in eight healthy, sedentary older [66 ± 2 yr; body mass index (BMI) of 25.5 ± 1.2 kg/m] and nine younger (23 ± 1 yr; BMI of 23.6 ± 1.7 kg/m) men, under control conditions and 48 h after eccentric exercise. Indirect calorimetry was performed to evaluate carbohydrate and lipid oxidation (Cox and Lox, respectively). Eccentric exercise caused muscle soreness and increased plasma creatine kinase in both groups of men (P < 0.02). Although a similar level of hyperglycemia was maintained in the two groups, glucose infusion rates were lower (P < 0.001) in the older men. Compared with basal levels, hyperglycemia stimulated an increase in Cox and a decrease in Lox during the control and exercise trials in the younger group (P < 0.03), but only during the control trial in the older subjects (P < 0.007). Cox was unchanged after eccentric exercise in the younger men [4.00 ± 0.30 vs. 3.54 ± 0.44 mg kg fat-free mass (FFM)1 min1; exercise vs. control] but was suppressed by 20% in the older group (3.37 ± 0.37 vs. 4.21 ± 0.23 mg kg FFM1 min1; P < 0.04). Moreover, Lox was reduced by 38% in the younger subjects (0.47 ± 0.09 vs. 0.76 ± 0.10 mg kg FFM1 min1; P< 0.03) but was augmented by 89% in the older group (0.68 ± 0.11 vs. 0.36 ± 0.08 mg kg FFM1 min1; P < 0.04). In addition, hyperglycemia-stimulated Cox, Lox, and respiratory exchange ratio responses to eccentric exercise were related to abdominal adiposity (r = 0.57, P < 0.04, r = 0.68, P < 0.02 and r = 0.60, P < 0.02, respectively). Despite normal glucose tolerance and the absence of obesity per se, older men experience a reduction in carbohydrate oxidation in response to hyperglycemia after eccentric exercise.