All this happened, more or less.

Reduced variation of physical exertion, environmental stressors, and thermal gradients that characterize modern lifestyles may reduce the autonomic dynamic range resulting in lowered heart rate variability and a myriad of systemic dysfunctions. The health benefits of activities such as exercise, meditation, acupuncture, coitus, and laughter may operate through increasing autonomic variability. Reduced physical exertion also accounts for declining dynamic range of musculoskeletal function. The resulting muscle atrophy, fat infiltration, and sarcomere shortening may not only have deleterious local effects, but may also be involved in systemic metabolic dysfunctions such as insulin resistance. The extent to which our endogenous systems rely on environmental variation for self-tuning and the impact that under-utilization of compensatory mechanisms has on biologic function are not well understood. Modern therapeutic approaches generally result in reversion to the mean of physiologic functions and may buffer against variation.
The dynamic range of biologic functions and variation of many environmental cues may be declining in the modern age: implications for diseases and therapeutics. Anthony J. Yun, et all.
Medical Hypotheses. Volume 65, Issue 1, 2005, Pages 173-178