B. Experimental Testing
Once constructed, the prototype lift walker was tested on three able bodied subjects (mass = 85.3 ± 15.8 kg) to verify the design and assure the walker could safely lift and support the specified loads. During these tests, the subjects used the lift walker to transition from a seated to standing posture. The subjects also loaded the walker with their full body weight in the standing position by removing their legs from the floor with their arms on the platform.
After the design and safety of the walker was verified in able bodied subjects, one subject with incomplete spinal cord injury (SCI) was recruited to test the ability of the walker to assist in sit-to-stand transition. The male volunteer (age 40, 6 years post injury, mass = 64.5 kg) with motor incomplete SCI (C6/7 level, ASIA D) was able to rise from a seated to standing posture on his own through the use of his upper extremities on a walker. Experiments were performed to compare the prototype lift walker with a standard walker during the sit-to-stand transition.
In all experiments, a Vicon® MX40 motion capture system (Vicon Motion Systems, Oxford, UK) was used to track the lower and upper extremity kinematics of the subject, as well as the kinematics of the lift walker. During sit-to-stand transition, the vertical motion of the torso was monitored as the motion of the plane defined by four markers placed on the right shoulder, left shoulder, seventh cervical vertebra, and the clavicular notch. Force plates (AMTI, Watertown, MA) under each foot were used to measure lower extremity force data. The standard walker was outfitted with two load cells (AMTI, Watertown, MA) mounted below the handles of the walker to measure upper extremity lift force. The vertical lift force provided by the prototype walker was computed using inverse dynamics from the measured kinematics and lower extremity forces.
All data were sampled at 100 Hz and filtered offline with a third order, low pass, digital Butterworth filter with a cutoff frequency of 5 Hz. Five trials of sit-to-stand transition were performed under each experimental condition. An analysis of variance (ANOVA) was used to compare measured quantities across experimental conditions, with p < 0.05 considered significant.
B. Experimental TestingOnce constructed, the prototype lift walker was tested on three able bodied subjects (mass = 85.3 ± 15.8 kg) to verify the design and assure the walker could safely lift and support the specified loads. During these tests, the subjects used the lift walker to transition from a seated to standing posture. The subjects also loaded the walker with their full body weight in the standing position by removing their legs from the floor with their arms on the platform.After the design and safety of the walker was verified in able bodied subjects, one subject with incomplete spinal cord injury (SCI) was recruited to test the ability of the walker to assist in sit-to-stand transition. The male volunteer (age 40, 6 years post injury, mass = 64.5 kg) with motor incomplete SCI (C6/7 level, ASIA D) was able to rise from a seated to standing posture on his own through the use of his upper extremities on a walker. Experiments were performed to compare the prototype lift walker with a standard walker during the sit-to-stand transition.In all experiments, a Vicon® MX40 motion capture system (Vicon Motion Systems, Oxford, UK) was used to track the lower and upper extremity kinematics of the subject, as well as the kinematics of the lift walker. During sit-to-stand transition, the vertical motion of the torso was monitored as the motion of the plane defined by four markers placed on the right shoulder, left shoulder, seventh cervical vertebra, and the clavicular notch. Force plates (AMTI, Watertown, MA) under each foot were used to measure lower extremity force data. The standard walker was outfitted with two load cells (AMTI, Watertown, MA) mounted below the handles of the walker to measure upper extremity lift force. The vertical lift force provided by the prototype walker was computed using inverse dynamics from the measured kinematics and lower extremity forces.
All data were sampled at 100 Hz and filtered offline with a third order, low pass, digital Butterworth filter with a cutoff frequency of 5 Hz. Five trials of sit-to-stand transition were performed under each experimental condition. An analysis of variance (ANOVA) was used to compare measured quantities across experimental conditions, with p < 0.05 considered significant.
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