Variance components models for physical activity with age as modifier: a comparative twin study in seven countries

Jacqueline M Vink, Dorret I Boomsma, Sarah E Medland, Marleen H M de Moor, Janine H Stubbe, Belinda K Cornes, Nicholas G Martin, Axel Skytthea, Kirsten O Kyvik, Richard J Rose, Urho M Kujala, Jaakko Kaprio, Jennifer R Harris, Nancy L Pedersen, Lynn Cherkas, Tim D Spector, Eco J C de Geus