Sex efficiency through exercises : special physical culture for women / by Th. H. van de Velde ; [photos, by E. Steinemann].
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The image contains the following text:
FILM 3.
VERTICAL
PELVIC ROTA-
T I O N ON
HANDS AND
KNEES. " The
Machine"
Exercise (Second
Phase).
The head and
face are directly
above the sup-
porting hands.
The back must
not be pushed
further forwards.