A system for inflating e.g. a pair of lumbar support bags of a vehicle seat comprises two pumps (4) each connected to a respective bag and controlled by a common electronic control system (7). The control system causes each bag to be inflated over a period of between 1 and 10 minutes, the inflation of one bag taking place whilst the other bag is deflated and vice versa to produce alternating pressure zones in the lumbar region. Inflation of each bag is produced by a multiplicity of individual spaced apart energizations of the associated pump. The duration and spacing of the energizations is variable to produce the desired complete inflation of a bag within the required period. In the preferred embodiment the duration of each energization is preset during manufacture of the system but the spacing of the energizations is under the control of the user of the seat to vary the duration of the inflate/deflate cycle.