Table 1.

Biological mechanisms by which physical activity may enhance glucose homeostasis and confer protection against diabetes

Structural changes in skeletal muscle
    • ↑ fiber size
    • ↑ percentage of Type IIa fibers (possibly Type I fibers)
    • ↑ capillary density and blood flow
Biochemical changes in skeletal muscle
    • ↑ insulin signaling kinetics (↑ phosphatidylinositol 3-kinase and GLUT4 activity)
    • ↑ non-insulin signaling kinetics (↑ 5′-AMP-activated protein kinase activity)
    • ↑ enzymes related to glucose metabolism [hexokinase, glycogen synthase, and key oxidative enzymes (e.g., citrate synthase, aconitase, succinate dehydrogenase)]
    • ↑ myoglobin
Systemic influences of physical activity
    • ↑ oxygen uptake and functional capacity at submaximal and maximal workloads
    • ↑ lipoprotein lipase and other key enzymes to improve lipemic control
    • ↓ excessive hepatic secretion of glucose and VLDL
    • Improvements in counter-regulatory hormone levels/activity (e.g., cortisol, IGF-I)
    • Improvements in comorbid conditions (e.g., hypertension, visceral obesity, systemic inflammation, dyslipidemia)