Factor(s) & Author(s)

Sedentary Activity(ies)/Subjects

Effect(s)/Test(s) Outcome

Metabolic Dysfunction

Humburg et al. [30]

5 days of complete bed rest in 22 volunteers who remained in bed for 23.5 hours/day

*No change in body weight
*Significant ↑ total cholesterol, plasma triglycerides, glucose, and insulin resistance

Yanagibori et al. [31] and Bauman and Spungen [32]

20 days of bed rest

*Significant ↑ in plasma triglycerides
*Significant ↓ HDL (good) cholesterol levels
*↑ risk of cardiovascular disease

Bone Health

Garland et al. [33], Caillot-Augusseau et al. [34], Morey-Holton and Globus [35], Zerwekh et al. [36] and Kim et al. [37]

(1) Humans and animals spending long periods of time in space

(2) Spinal cord injured patients

(3) Long-term bed rest

*Significant ↓ in bone mass
*↓ in lone mineral density of 1% to 4% in the (1) lumbar spine, (2) femoral neck, and (3) greater trochanter in healthy subjects following 12 weeks of bed rest

Sedentary lifestyle leads to a reduction in bone mass, which is a result in an imbalance between bone resorption and deposition.

Cardiovascular Health

Purdy et al. [38], Bleeker et al. [39], Demiot et al. [40], and Hamburg et al. [30]

*5 days of bed rest of 20 healthy individuals

*56 days of bed rest of head-down position (Women and International Space Simulation for Exploration Program [WISE]) of health women

*Peripheral vascular function (reactive hyperemia) resulted in (1) ↓ by 20% in the legs and (2) ↓ by 30% in the arms
*Significant ↑ blood pressure and significant ↓ in brachial (arm) artery diameter
*↓vasodilatation (endothelium-dependant) and ↑ endothelial cell damage

**All detrimental changes in vascular function were reversed by aerobic and resistance training.

Inactivity seems to have a direct negative influence on vascular health.