Participants

Two recently published studies investigating the effect of different knee joint angles on voluntary activation of the knee extensors did not provide sufficient information to allow for effect size calculation for the present study (Doguet et al., 2017b; Lanza et al., 2017). Therefore, a sample size calculation was performed assuming a medium effect size (f = 0.25) for the change in voluntary activation between joint angles, with an α level of 0.05, a power (1–β) of 0.8, and a correlation among repeated measures of 0.7 (G^*Power, version 3.1.9.2, University of Kiel, Kiel, Germany). Sample size calculation indicated that 17 participants would be required. To account for potential drop outs, 18 recreationally active, right-handed males (age: 26.8 ± 3.8 years, height: 183.7 ± 8.0 cm, body mass: 84.8 ± 7.7 kg, exercise involving the upper body per week: 3.1 ± 3.9 h) without known neurological and/or orthopedic disorders of the left arm were recruited. Handedness of the participants was determined by the Edinburgh handedness inventory (Oldfield, 1971). Participants were informed about the experimental procedures as well as the discomfort and possible risks associated with the experiment before giving their written informed consent. In addition, the participants were asked to refrain from strenuous exercise involving the upper body as well as alcohol and caffeine consumption 48 h prior to the experiment. The study was conducted according to the declaration of Helsinki and was approved by the local ethics committee.