Aging, fat oxidation and exercise

Immediate Effects of Aerobic Exercise and Whole-Body Vibration on Fat Oxidation, Lipid Mobilization, and Cardiovascular Response in Individuals with Obesity

Among obesity, cumulative fat and poor physical activity are risk factors for cardiovascular disease. Due to the limit in performing aerobic exercise (AER), whole-body vibration (WBV) as a passive form of exercise is an alternative therapeutic strategy. Herein, this study aimed to compare the immediate effects of AER and WBV on metabolic and cardiovascular responses, and dyspnea level in obesity. Forty-nine eligible obesities performed both AER and WBV, with a random order assignment (age = 28.94 ± 11.39 years). Fat oxidation, cardiovascular parameters (i.e., heart rate (HR) and blood pressure (BP)), and dyspnea level (i.e., rating perceived exertion (RPE)) were measured during exercise, while lipid mobilization (i.e., triglycerides) was collected pre- and post-exercise. Fat oxidation rate in AER was significantly higher than in WBV. Significantly increased fat oxidation rates were shown in both groups (within-group analyses) (also shown in females aged 20-45). Triglyceride levels between AER and WBV were similar. A significant decrease in triglyceride levels was only observed in WBV (within-group change). HR and RPE in AER were significantly higher than in WBV (p < 0.05). HR and RPE were significantly increased throughout both AER and WBV, while systolic blood pressure was only significantly elevated in AER (whining-group analyses). WBV may facilitate fat oxidation (particularly in females aged below 45), induce lipid mobilization, and reduce interference on cardiovascular parameters in obesity.

The effects of age and muscle contraction on AMPK activity and heterotrimer composition

Sarcopenia is characterized by increased skeletal muscle atrophy due in part to alterations in muscle metabolism. AMP-activated protein kinase (AMPK) is a master regulator of skeletal muscle metabolic pathways which regulate many cellular processes that are disrupted in old-age. Functional AMPK is a heterotrimer composed of α, β and γ subunits, and each subunit can be represented in the heterotrimer by one of two (α1/α2, β1/β2) or three (γ1/γ2/γ3) isoforms. Altered isoform composition affects AMPK localization and function. Previous work has shown that overall AMPK activation with endurance-type exercise is blunted in old vs. young skeletal muscle. However, details regarding the activation of the specific isoforms of AMPK, as well as the heterotrimeric composition of AMPK in old skeletal muscle, are unknown. Our purpose here, therefore, was to determine the effect of old-age on 1) the activation of the α1 and α2 catalytic subunits of AMPK in skeletal muscle by a continuous contraction bout, and 2) the heterotrimeric composition of skeletal muscle AMPK. We studied gastrocnemius (GAST) and tibialis anterior (TA) muscles from young adult (YA; 8months old) and old (O; 30months old) male Fischer344×Brown Norway F1 hybrid rats after an in situ bout of endurance-type contractions produced via electrical stimulation of the sciatic nerve (STIM). AMPKα phosphorylation and AMPKα1 and α2 activities were unaffected by age at rest. However, AMPKα phosphorylation and AMPKα2 protein content and activity were lower in O vs. YA after STIM. Conversely, AMPKα1 content was greater in O vs. YA muscle, and α1 activity increased with STIM in O but not YA muscles. AMPKγ3 overall concentration and its association with AMPKα1 and α2 were lower in O vs. YA GAST. We conclude that activation of AMPKα1 is enhanced, while activation of α2 is suppressed immediately after repeated skeletal muscle contractions in O vs. YA skeletal muscle. These changes are associated with changes in the AMPK heterotrimer composition. Given the known roles of AMPK α1, α2 and γ3, this may contribute to sarcopenia and associated muscle metabolic dysfunction.

Invited review: Aging and energy balance

Humans over 70 yr of age often lose weight. This appears to be due to a physiological anorexia of aging as well as a loss of lean mass (sarcopenia) and, to a lesser extent, fat mass. The causes of the physiological anorexia of aging include changes in taste and smell and a decrease in adaptive relaxation of the fundus of the stomach, which leads to more rapid antral filling and early satiation. In addition, basal and stimulated levels of the satiating hormone, cholecystokinin, are increased. In men, the decline in testosterone leads to an increase in leptin and a loss of lean mass. Although resting metabolic rate declines with aging, this is mainly due to the decline in lean body mass. Energy metabolism is also decreased due to a decline in Na+-K+-ATPase activity, decreased muscle protein turnover, and possibly changes in mitochondrial membrane protein permeability. Physical energy expenditure declines with aging. Meal-induced thermogenesis shows a delay to peak, possibly due to a delay in gastric emptying. Inadequate data are available on the effect of aging in humans on other energy-producing mechanisms such as adaptive thermogenesis. These physiological changes place older men and women at major risk of developing pathological weight loss when they develop disease states, especially those associated with cytokine elaboration.

Menopause, energy expenditure, and body composition

OBJECTIVES

The effects of menopause transition on metabolic and cardiovascular disease risk in women are unclear. It is unknown whether estrogen deficiency, aging, or a combination of both factors are independent contributors to a worsening health profile in women. We considered the effects of menopause transition and hormone replacement therapy on body composition, regional body fat, energy expenditure, and insulin sensitivity.

METHODS

A brief review of current literature that has considered the role of menopause transition and hormone replacement therapy on body composition, energy expenditure, and insulin sensitivity with an emphasis on longitudinal investigations.

RESULTS

Preliminary evidence suggests that natural menopause is associated with reduced energy expenditure during rest and physical activity, an accelerated loss of fat-free mass, and increased central adiposity and fasting insulin levels. Hormone replacement therapy has been shown to attenuate these changes. Longitudinal and longer intervention studies are needed to confirm these initial findings.

CONCLUSIONS

Menopause transition may represent a risky period in a woman's life, 'triggering' adverse metabolic and cardiovascular processes that predispose women to a greater incidence of obesity-related comorbidities. Dietary, exercise, and hormonal interventions specifically targeted at premenopausal women may help mitigate the worsening cardiovascular and metabolic risk profile associated with menopause.

Fuel oxidation during exercise in middle-aged men: role of training and glucose disposal

PURPOSE

The purpose of this study was to test the hypothesis that carbohydrate (CHO) utilization in middle-aged trained men is increased during hard-intensity exercise and decreased during moderate-intensity exercise in comparison with age-matched sedentary men. We also investigated whether a relationship between CHO utilization and glucose disposal exists.

METHODS

Seven trained cyclists (Tr) and seven age-matched sedentary men (Sed) underwent an intravenous glucose tolerance test after an overnight fast (minimal model method) to determine their glucose disposal; they also performed two 1-h trials on a cycle ergometer below and above their individual ventilatory threshold (VT). Substrate oxidation was evaluated by indirect calorimetry. Hormonal responses were investigated during exercise.

RESULTS

Insulin sensitivity (SI) and glucose effectiveness (Sg) were significantly higher in the Tr group than in the Sed group (P < 0.001, P < 0.03). CHO oxidation was significantly higher in the Tr group than in the Sed group when exercise was performed above VT, whereas CHO oxidation was higher in the Sed group when exercise was performed below VT (P < 0.05). Epinephrine (Epi) response during hard-intensity exercise was higher in the Tr group than in the Sed group (P < 0.01). SI was negatively correlated to CHO oxidation in the Tr group (r = -0.743, P < 0.05).

CONCLUSION

Endurance training results in increased CHO utilization during hard-intensity exercise and reduced CHO oxidation during moderate-intensity exercise in middle-aged men. During hard-intensity exercise, the increased CHO utilization in middle-aged trained men is associated with a greater response in Epi and is inversely related with SI.

Regulation of macronutrient balance in healthy young and older men

OBJECTIVE

To determine the influence of age on the ability to adjust macronutrient oxidation to changes in diet composition. Our hypothesis was that the ability to adjust macronutrient oxidation to changes in diet composition would be impaired with age.

DESIGN

Cross-sectional, randomized to three different isocaloric diets containing a constant percentage protein but varying in percentage fat and percentage carbohydrate: mixed diet (M; 15/30/55); high-fat diet (HF; 15/60/25), and high-carbohydrate (HC; 15/15/70).

SUBJECTS

Six young (YM; age=25+/-1 y) and five middle-aged and older men (OM; age=63+/-3 y).

MEASUREMENTS

Each subject underwent 24 h whole-room calorimetry on day 4 of each diet to determine 24 h macronutrient oxidation rates. Macronutrient balance was calculated from the individual macronutrient oxidation rates and the corresponding macronutrient intake.

RESULTS

Body mass, percentage fat, and fat-free mass were similar in the two groups. Twenty-four-hour energy expenditure (EE) and energy balance did not differ across diets or between groups; 24 h EE was approximately 7% lower (NS) in the OM. Macronutrient oxidation rates were not significantly different in YM vs OM during M. Protein oxidation was similar across diets, but higher (P<0.05) in OM. Fat oxidation contributed 28.8+/-7.0% vs 37.8+/-4.7% to 24 h EE on M (NS) in the OM vs YM, respectively. This increased to 58.4+/-6.7 vs 51.9+/-5.3% of 24 h EE (NS) in the OM vs YM, respectively, during HF and decreased to 25.4+/-9.7 vs 20.2+/-14.3% (NS) during HC (diet effect, both P<0.05). Carbohydrate oxidation contributed 54.3+/-10.5% vs 56.6+/-2.4% of 24 h EE (NS) on M in the OM vs YM, respectively. This decreased to 19.5+/-10.6 vs 29.9+/-12.6% (NS) during HF and increased to 53.6+/-12.3 vs 64.7+/-14.3% (NS) in the OM vs YM, respectively during HC (diet effect, P<0.05).

CONCLUSION

Taken together, these results suggest that the ability to adjust macronutrient oxidation to changes in diet composition is maintained in OM and, thus, is unlikely to contribute to the increased susceptibility to weight gain and obesity development that accompanies aging.