Even microorganisms, which lack a nervous system, have daily cycles of activity and inactivity driven by internal body clocks known as circadian clocks. (newscientist.com)
It's certainly reasonable to hypothesize that the combination of long flights, strange beds and time zone changes confuse internal body clocks and prevent players and teams from performing up to expectations. (sportsinsights.com)
Zeitgeber is a German word for «time giver» and is used to describe internal body clocks that become synchronized with the external environment, such as air temperatures, sunrises and sunsets. (aqnb.com)