Sex efficiency through exercises : special physical culture for women / by Th. H. van de Velde ; [photos, by E. Steinemann].

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FILM 3. VERTICAL PELVIC ROTA- T I O N ON HANDS AND KNEES. " The M a c h i n e " Exercise (Third Phase). Arch the lumbar vertebra?, draw the abdominal muscles tense and the pelvis backwards.