Tsa 110

Participants sat on a custom-made leg extension chair used previously [9 (link)], with hips flexed at approximately 70° (0°: trunk and femur aligned) and 90° of knee flexion. The leg was strapped to a force transducer (TSA-110, Takei Scientific Instruments Co., Ltd., Niigata City, Japan), with the hips and chest belted to the seat. The force transducer was linked to an analog interface (PowerLab/8sp, ADInstruments Pty, Ltd., Castle Hill, Australia), and data were collected via software (LabChart 6, ADInstruments NZ Limited, Dunedin, New Zealand) at a sampling rate of 1 kHz.
Two electrode pads were strapped to the quadriceps: 20 cm × 10 cm on the proximal part (middle of the upper third of the thigh) and 20 cm × 10 cm for male or 15 cm × 10 cm for female participants on the distal part (middle of the lower third of the thigh), to fully cover the quadriceps muscle belly without covering the knee flexors. The electrodes were connected to a high–voltage, constant–current stimulator (DS7AH, Digitimer, Hertfordshire, UK) linked to the same analog interface as the transducer and controlled via the same software.

A custom-made body suspension apparatus lifted the participant’s torso by an elastic rehabilitation harness (Fig. 1) that was installed around a motor-driven treadmill (Well Road 200E; Takei Scientific Instruments, Niigata, Japan). The same apparatus was used in our earlier studies^{21 (link),25} . The participant’s body weight (BW) was reduced by 0% (100% of his BW remained; 100%BW), 30% (70% of his BW: 70%BW), and 50% (50% of his BW: 50%BW) based on previous studies^{20 (link),21 (link),25 ,26 (link)}. A load cell (TSA-110; Takei Scientific Instruments) was positioned between a control box and a spring (with 30 cm free length and a spring constant of 5.7 kg cm⁻¹) to measure the actual delivered force. The participant’s BW was lifted by the spring system before he began the walking protocols, and he walked while wearing the harness even under the 100%BW condition (in which none of his BW was lifted). This BWS system allowed normal leg swing during walking^{21 (link),25} .Figure 1

The custom-made body weight support (BWS) apparatus. The participant’s body weight was reduced by 0%, 30%, and 50% without disturbing the normal leg-swing motion during walking.

BWS was established with a custom-made body suspension apparatus that lifted the participant’s torso via an elastic rehabilitation harness (Fig. 1). This was installed around a motor-driven treadmill (Well Load 200E; Takei Scientific Instruments Co. Ltd., Niigata, Japan). For the BWS condition, we chose a 30% decrement in the participant’s body weight (BW), equivalent to that used in some previous studies (Grabowski, 2010 (link); McGowan, Neptune & Kram, 2008 (link), 2009 (link); Raffalt, Hovgaard-Hansen & Jensen, 2013 (link); Teunissen, Grabowski & Kram, 2007 (link)). A force transducer (TSA-110; Takei Scientific Instruments Co. Ltd., Niigata, Japan) was located between a control box and spring (with 30 cm free length and a spring constant of 5.7 kg·cm⁻¹) to slide a rigid main frame (see Video S1). Before the participant walked or ran, he stood stationary on the treadmill while wearing the harness, and 30% of his BW was lifted by the spring system. The set-up allowed normal leg swing.