Sport Sciences - Performance and Technology, Department of Health Science and Technology, Aalborg University, DK-9220, Aalborg, Denmark. Electronic address: torben@hst.aau.dk. Sport Sciences - Performance and Technology, Department of Health Science and Technology, Aalborg University, DK-9220, Aalborg, Denmark. Respiratory and Critical Care Group, Department of Health Science and Technology, Aalborg University, DK-9220, Aalborg, Denmark. Department of Physiology and Pharmacology, Karolinska Institutet, 171 77, Stockholm, Sweden. Center for Robotics Research, Department of Engineering, King's College London, London, United Kingdom.