1. Escuela de Ciencias de la Salud, Universidad Viña del Mar , Viña del Mar 2520000 , Chile
2. School of Public Health, University of Alberta , Edmonton, Alberta T6G 1C9 , Canada
3. Public Health Research Group, University of Alicante , San Vicente del Raspeig, Alicante 03690 , Spain
4. Physiotherapy Service, Department of Health Care, Medical and Health Care Services Division, MC Mutual Barcelona 08037 , Spain
5. CIBERESP , Madrid 28029 , Spain