1. Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
2. Department of Clinical Science, Intervention and Technology (CLINTEC), Karolinska Institutet, Huddinge 14186, Sweden.
3. Department of Anaesthesia and Intensive Care, Karolinska University Hospital, Huddinge 14186, Sweden.
4. Department of Human Movement Sciences, Medical Centre+, PO Box 616, 6200 MD Maastricht, the Netherlands.