Friday, November 18, 2011

What is metabolic fitness (MF)?


In previous years, fitness was commonly defined as the capacity to carry out the day’s activities without undue fatigue. These days, physical fitness (PF) is considered a measure of the body’s ability to function efficiently and effectively in work and leisure activities, to be healthy, to resist hypokinetic diseases, and to meet emergency situations.

Physical fitness comprises two related concepts: general fitness (for the purpose of health), and specific fitness (a task-oriented definition based on the ability to perform specific aspects of sports or occupations). Physical fitness is generally achieved through correct nutrition, exercise, and enough rest.

PF can be measured as an out come of physical activity and also as a moderator on morbidity and mortality. Physical fitness for purposes of health, is best defined by the specific components that relate to improved health or reduced disease. The components of Health-Related Fitness are:
–    Morphological
–    Muscular
–    Motor
–    Cardiorespiratory
–    Metabolic
For the discussion of our topic metabolic fitness is more important. Metabolic fitness is the newest component if fitness.

Metabolic fitness:

Physical inactivity is strongly associated with an increased risk of premature disease and death, and the falling level of physical activity. Both aerobic fitness (maximum oxygen uptake) and metabolic capacity of the muscles are important in this matter. The role of the metabolic capacity/fitness of muscle, appears to be especially critical for the development of metabolic-related diseases and thus for the health of the individual.

Definition: A definition of metabolic fitness is proposed as the ratio between mitochondrial capacity for substrate utilisation and maximum oxygen uptake of the muscle.
Indirect means of determining metabolic fitness is Glucose tolerance, blood lipid & cholesterol profiles (especially HDL & triglyerisdes) & finally lipid oxidation.

Skeletal muscle is an extraordinarily plastic tissue and metabolic capacity/fitness changes quickly when the level of physical activity is altered. High metabolic fitness includes an elevated use of fat at rest and during exercise. The capacity for glucose metabolism is also enhanced in trained muscle.

There are many adaptations to physical activity. Exercise-induced activation of genes coding for proteins involved in metabolism is described as an underlying mechanism for some of these adaptations. The increased gene expression is of relatively short duration, which implies that a certain regularity of physical activity is required to maintain high metabolic fitness. Thus, metabolic fitness is directly related to how much the muscle is used, but even low levels of physical activity have a beneficial effect on metabolic fitness and the overall health of the individual.
Subcomponents of metabolic fitness include:
–    Glucose Tolerance
–    Blood Lipid and Cholesterol Profiles
–    Lipid Oxidation

Glucose Tolerance
1. Regular exercise can be used to treat glucose intolerance in Type II diabetics.
2. Effects of exercise include normalizing insulin and glucagon production by the liver, increasing insulin sensitivity by the exercising muscle, thus enhancing glucose uptake.

Blood Lipid and Cholesterol Profiles
1. Exercise decreases total blood cholesterol, increases HDL-Cholesterol, and decreases blood triglycerides.

Lipid Oxidation
1. High lipid oxidation alters cholesterol metabolism and reduces body fat to reduce risk of cardiovascular disease. Thus, chronic aerobic exercise spares glucose stores and uses more fat oxidation for fuel.

Assessment of metabolic fitness:
The direct measurement of metabolic fitness and/or aerobic demand is the means that can be used as an index of the efficacy of an exercise training program or other therapeutic intervention; as medical risk factor for predicting the risk of cardiovascular disease, diabetes, death or other health outcome; or as an aid to pharmaceutical companies for drug discovery in the area of metabolic fitness, deconditioning, and oxidative biology.

References:
1. Ugeskr Laeger. 2002 Apr 15;164(16):2156-62.
2. Kennedy RA et al; Journal of Sports Science and Medicine (2007) 6, 448-454

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