Impact of Aerobic Exercise Training on Age-Related Changes in Insulin Sensitivity and Muscle Oxidative Capacity

Abstract

1Insulin resistance increases and muscle oxidative capacity decreases during aging, but lifestyle changesespecially physical activity-may reverse these trends. Here we report the effect of a 16-week aerobic exercise program (n ‫؍‬ 65) or control activity (n ‫؍‬ 37) performed by men and women aged 21-87 years on insulin sensitivity and muscle mitochondria. Insulin sensitivity, measured by intravenous glucose tolerance test, decreased with age (r ‫؍‬ ؊0.32) and was related to abdominal fat content (r ‫؍‬ ؊0.65). Exercise increased peak oxygen uptake (VO 2peak ; 10%), activity of muscle mitochondrial enzymes (citrate synthase and cytochrome c oxidase, 45-76%) and mRNA levels of mitochondrial genes (COX4, ND4, both 66%) and genes involved in mitochondrial biogenesis (PGC-1␣, 55%; NRF-1, 15%; TFAM, 85%). Exercise also increased muscle GLUT4 mRNA and protein (30 -52%) and reduced abdominal fat (5%) and plasma triglycerides (25%). None of these changes were affected by age. In contrast, insulin sensitivity improved in younger people but not in middle-aged or older groups. Thus, the muscle mitochondrial response to 4 months of aerobic exercise training was similar in all age-groups, although the older people did not have an improvement in insulin sensitivity. Diabetes 52: 1888 -1896, 2003 T he number of people with type 2 diabetes and impaired glucose tolerance is rapidly increasing (1,2). Key factors contributing to this increase in diabetes include age, obesity, and sedentary lifestyle (3-8). Exercise is a readily available intervention that can increase insulin action (9 -14) and prevent the onset of diabetes (15-18). An important question is whether the effects of aerobic exercise on insulin action are diminished with advancing age. A recent study reported that a vigorous 7-day exercise program increased insulin sensitivity and muscle glucose transporter (GLUT4) content by a similar amount in younger (22 years) and older (61 years) people (12). However, current health and fitness guidelines for healthy adults recommend exercising at more moderate intensities at least 3 days per week over long periods (19). Thus, the first purpose of the current study was to determine whether a 4-month program of bicycle training that could be readily followed by most elderly individuals would lead to a similar improvement in insulin sensitivity in men and women across a wide age span.Skeletal muscle is the major site of insulin-mediated glucose disposal and is implicated in the pathogenesis of insulin resistance and diabetes (20,21). Several pieces of evidence suggest that insulin action may be related to the oxidative capacity of skeletal muscle. First, aerobic exercise training improves both insulin sensitivity and activity of oxidative enzymes in muscle (22,23). Second, people who are obese and insulin resistant or have type 2 diabetes tend to have lower activity of muscle oxidative enzymes (24,25). Third, insulin infusion preferentially stimulates the synthesis rate of mitochondrial proteins in skeletal muscle (26) and increa...

Influence of Pro12Ala peroxisome proliferator-activated receptor γ2 polymorphism on glucose response to exercise training in type 2 diabetes

“…Exercise training and the Ala allele must act either independently or in unison to modify glucose homeostasis through increasing glucose uptake or by decreasing hepatic glucose output. At the whole-body level, exercise training has been shown to increase insulin sensitivity [53][54][55] and has also been shown to decrease basal hepatic glucose production in patients with type 2 diabetes [56]. At baseline, the association of the Ala allele with lower fasting glucose or insulin is inconsistent [31,42,49,57,58].…”

Dietary protein and exercise training in ageing

“…In addition, endurance (97,98,(104)(105)(106)(107)(108)(109)(110) exercise was shown to enhance the skeletal muscle oxidative capacity, resulting in greater endurance capacity (5,120) . Although the muscle regenerative capacity seems to decline at a more advanced age, the reduced satellite cell pool size (119) does not compromise the capacity for muscle hypertrophy to occur even at an advanced age (121)(122)(123) and resistance exercise training was shown to increase muscle fibre size (124)(125)(126)(127) .…”

Lipotoxicity: the obese and endurance-trained paradox

“…10,11 Additionally, ETr, unlike obesity, also results in an increase in CPT-I, citrate synthase and cytochrome c oxidase gene expression and their respective enzyme activities. [12][13][14][15][16][17] Therefore, the mechanisms regulating IMTG storage in ETr subjects appear to differ to those from obese subjects. Endurance exercise has been shown to use both carbohydrate and lipids as a fuel source.…”