Healthy Volunteer Coordination Study

All participants in this study were healthy volunteers (students or teachers at the Radboud university medical center), recruited by personal contacts of the authors. They were unaware of the actual purpose of this study and were told that this study investigated their lower extremity coordination. The inclusion criteria were: age between 18 and 65 years old, practice of symmetrical sports (e.g. running, cycling, swimming, rowing) or sports which involve the lower extremities only (e.g. soccer) or people who do not practice any type of sport. Participants that practiced sports in which the upper extremity is predominantly used (e.g. handball, tennis, volleyball) were excluded, because of the introduction of a possible bias as stated by Peters, who mentioned that in athletics, the choice of arm usually influences the choice of the leg [9 (link)]. Other exclusion criteria were surgery to one or both legs in the past three years, a back or lower extremity injury at the moment of testing, the use of medication which influences balance, and the presence of any disease which affects balance or coordination.
Forty-one healthy adults were eligible for inclusion: 21 men aged 35.8 ± 16.5 years old and 20 women aged 36.1 ±15.2 years old. 90% of them were right-handed, which is comparable to the world population [14 (link)]. All participants agreed to take part in this study and gave their written informed consent to their inclusion in this study. This study was approved by the Medical Ethics Committee Arnhem/Nijmegen (registration number 2017–3373).