About the Authors

Ji-Guo Yu

Affiliation Department of Surgical and Perioperative Sciences, Sports Medicine Unit and School of Sport Sciences, Umeå University, Umeå, Sweden

Patrik Bonnerud

Affiliation Department of Health Sciences, Luleå University of Technology, Luleå, Sweden

Anders Eriksson

Affiliation Department of Health Sciences, Luleå University of Technology, Luleå, Sweden

Per S. Stål

Affiliation Department of Integrative Medical Biology, Section for Anatomy, Umeå University, Umeå, Sweden

Yelverton Tegner

Affiliation Department of Health Sciences, Luleå University of Technology, Luleå, Sweden

Christer Malm

Christer.malm@idrott.umu.se

Affiliations Department of Surgical and Perioperative Sciences, Sports Medicine Unit and School of Sport Sciences, Umeå University, Umeå, Sweden, Winternet, Boden, Sweden

Competing Interests

Christer Malm has part-time employment at the non-profit organization (an economical union) Winternet, Boden, Sweden since 2001. Some of the work for the manuscript was executed using equipment at Winternet. All data, ethical permission, potential patents etc. are filed under Sports Medicine Unit, Umeå University (EPN nr 08–145M). Thus, all past and present data belong to Umeå University. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Author Contributions

Conceived and designed the experiments: CM AE YT PB. Performed the experiments: CM PS AE YT PB. Analyzed the data: JGY CM PS AE YT PB. Contributed reagents/materials/analysis tools: CM PS. Contributed to the writing of the manuscript: JGY CM PS AE YT PB.