The Dangers of Inactivity; Exercise and Inactivity Physiology for the manual therapist
Wittink H, et al. The Dangers of Inactivity; Exercise and Inactivity Physiology for the manual therapist. Manual Therapy 2011; 16:209-216.
This paper defines deconditioning as the physiological response of the body to a reduction in metabolic rate; that is, how the body reacts to a reduction in energy use or exercise levels, as in sitting or bed rest. Deconditioning is associated with a host of physiological changes:
1. Muscle mass decreases with loss of muscle strength.
2. Muscle capillary density declines along with mitochondrial enzyme activity & ATP production leading to loss of muscle oxidative potential & increased fatigability of muscle.
3. Decline of cardiac output.
4. Decrease of aerobic capacity (VO2 max).
5. Bone strength decreases through increased bone resorption & decreased bone formation in response to unloading. Bone loss occurs most at weight-bearing skeletal sites.
6. Disuse decreases the collagen turn-over in tendons & muscles, weakens attachments of ligaments to bone & causes a disorganization of collagenous fibers.
7. Proprioceptive mechanisms within muscle & muscle-tendon junctions degenerate & become less responsive, increasing risk of injury.
8. Metabolic changes lead to increased risk of cardiovascular disease (CVD)
9. Metabolic changes lead to increased risk of type II Diabetes and a decline in sensitivity to insulin-mediated glucose uptake (insulin resistance).
10. There is a shift towards increased reliance on carbohydrate for energy at submaximal & maximal exercise intensities in muscle & a decrease in the contribution from lipid metabolism.
11. Blood lactate concentration with exercise increases at submaximal intensities & the lactate threshold is apparent at a lower percentage of VO2 max so exercise performed at the same intensity after disuse results in a higher heart rate, higher blood lactate accumulation, an increase in muscle glycogen utilization & carbohydrate oxidation, a reduction in exercise time to fatigue & increased dyspnea.
12. Activities demand a higher relative percentage of VO2max & this may cause shortness of breath & fatigue.
13. Activities, therefore, may be reduced or avoided, causing physical functioning to decline.
14. A vicious cycle develops where activity is reduced, walking speed is lowered, fitness levels decline.