Sliding machines composed of F-actin and myosin or microtubules and ki
nesin or dynein convert the free energy of ATP hydrolysis into sliding
movements and mechanical work. Development of optical microscopy with
micromanipulation techniques has made possible direct observation of
single events of sliding exhibited by single sliding machines. The exp
erimental data and theoretical consideration suggest that the influx-e
fflux coupling in these machines may be loose, Specific characters of
sliding machines are summarized and the problems we have for understan
ding of the coupling mechanism are discussed.