1. Department of Kinesiology, McMaster University, Hamilton, ON L8S 4L8, Canada.
2. Department of Pediatrics, McMaster University, Hamilton, ON L8S 4L8, Canada.
3. School of Medicine, Virginia Commonwealth University, Richmond, VA 23284, USA.
4. Department of Human Biology, Maastricht University, Maastricht, P.O. Box 616, 6200 MD, the Netherlands.
5. Department of Medicine, McMaster University, Hamilton, ON L8S 4L8, Canada.