Stability During Stairmill Ascent With Upward and Downward Applied Forces on the Pelvis.

This study investigates how external vertical forces on the pelvis change the stability of stairmill climbing and other gait parameters such as kinematics and muscle activity. We use a Tethered Pelvic Assist Device (TPAD) to apply forces on the pelvis during continuous ascent on a stairmill. Ten young healthy subjects participated in three one-minute stair ascent with no force, a 10% body weight (BW) downward force, and a 10% BW upward force applied on the pelvis. The stability is determined by evaluating the base of support (BoS) and margin of stability (MoS). Kinematics and muscle activities were used to characterize the biomechanical changes. The results show that the upward forces applied on the pelvis decreased the (i) MoS by 1.84cm in the lateral direction, 2.07cm in the anterior direction, (ii) double stance phase by 1.85%, and (iii) the knee flexion by 5°. Furthermore, the peak activation levels of the muscles rectus femoris (RF), vastus lateralis (VL), and left gastrocnemius decreased. In contrast, the downward forces applied on the pelvis increased (i) the MOS by 1.5cm in the anterior direction and (ii) mean activation levels of RF and VL muscles. This study provides insights into the effects of applied vertical forces on the pelvis during stair ascent. These findings contribute to the understanding of the gait parameter changes and their relation with stability. Results could be used as a basis for designing training protocols to improve balance during stair ascent.

A novel neck brace to characterize neck mobility impairments following neck dissection in head and neck cancer patients.

Objective: This article introduces a dynamic neck brace to measure the full range of motion (RoM) of the head-neck. This easy-to-wear brace was used, along with surface electromyography (EMG), to study changes in movement characteristics after neck dissection (ND) in a clinical setting. Methods: The brace was inspired by the head-neck anatomy and was designed based on the head-neck movement of 10 healthy individuals. A 6 degrees-of-freedom open-chain structure was adopted to allow full RoM of the head-neck with respect to the shoulders. The physical model was realized by 3D printed materials and inexpensive sensors. Five subjects, who underwent unilateral selective ND, were assessed preoperative and postoperative using this prototype during the head-neck motions. Concurrent EMG measurements of their sternocleidomastoid, splenius capitis, and trapezius muscles were made. Results: Reduced RoM during lateral bending on both sides of the neck was observed after surgery, with a mean angle change of 8.03° on the dissected side (95% confidence intervals [CI], 3.11-12.94) and 9.29° on the nondissected side (95% CI, 4.88-13.69), where CI denotes the confidence interval. Axial rotation showed a reduction in the RoM by 5.37° (95% CI, 2.34-8.39) on the nondissection side. Neck extension showed a slight increase in the RoM by 3.15° (95% CI, 0.81-5.49) postoperatively. Conclusions: This brace may serve as a simple but useful tool in the clinic to document head-neck RoM changes in patients undergoing ND. Such a characterization may help clinicians evaluate the surgical procedure and guide the recovery of patients.

Passive knee exoskeletons in functional tasks: Biomechanical effects of a SpringExo coil-spring on squats.

Passive wearable exoskeletons are desirable as they can provide assistance during user movements while still maintaining a simple and low-profile design. These can be useful in industrial tasks where an ergonomic device could aid in load lifting without inconveniencing them and reducing fatigue and stress in the lower limbs. The SpringExo is a coil-spring design that aids in knee extension. In this paper, we describe the muscle activation of the knee flexors and extensors from seven healthy participants during repeated squats. The outcome measures are the timings of the key events during squat, flexion angle, muscle activation of rectus femoris and bicep femoris, and foot pressure characteristics of the participants. These outcome measures assess the possible effects of the device during lifting operations where reduced effort in the muscles is desired during ascent phase of the squat, without changing the knee and foot kinematics. The results show that the SpringExo significantly decreased rectus femoris activation during ascent (-2%) without significantly affecting either the bicep femoris or rectus femoris muscle activations in descent. This implies that the user could perform a descent without added effort and ascent with reduced effort. The exoskeleton showed other effects on the biomechanics of the user, increasing average squat time (+0.02 s) and maximum squat time (+0.1 s), and decreasing average knee flexion angle (-4°). The exoskeleton has no effect on foot loading or placement, that is, the user did not have to revise their stance while using the device.

Biomechanical differences during ascent on regular stairs and on a stairmill.

Stair climbing is an intense physical activity and requires large range of motion at the joints, adequate muscle strength, and balance control. A powered stairmill, integrated with a gait rehabilitation device, can potentially be used for training those who have difficulty climbing stairs. In order to assess the effectiveness of such an approach, it is necessary to understand the similarities and differences in walking on regular stairs and on a stairmill. We have conducted an experiment to compare the differences in kinematics and muscle activations during climbing on regular stairs and a stairmill. Twelve subjects participated in this study. They first walked on regular stairs five times and then performed a one-minute continuous walking on a stairmill. The results showed several important differences. During continuous walking on a stairmill, when compared to regular stairs, there was (i) an increase in the percentage of stance phase during a walking cycle, (ii) a higher angle of plantarflexion of the ankle during the transition from stance phase to swing phase, and (iii) a decrease in muscle activation of the tibialis anterior during swing phase. These differences would provide additional insights into the design of future rehabilitation systems and to interpret human data obtained from stairmills.

A robotic neck brace to characterize head-neck motion and muscle electromyography in subjects with amyotrophic lateral sclerosis.

OBJECTIVE: This paper presents the first study where a dynamic neck brace was used to characterize the head motion of ALS patients while concurrently recording the surface electromyography (EMG) of the neck muscles. METHODS: Eleven ALS patients and 10 age-matched healthy controls consented and participated in an experiment. Each participant was asked to perform three single-plane motions of the head-neck that included flexion-extension in the sagittal plane, lateral bending in the coronal plane, and axial rotation in the transverse plane. Each motion was performed in a cycle and was repeated five times at self-selected speeds. RESULTS: During single-plane flexion-extension under gravity, compared to healthy peers, ALS patients showed a shorter duration to reach the maximum flexion and an earlier EMG onset in the neck extensors starting from the neutral. The brace measures in activation of the neck muscles in ALS patients were well correlated with clinically measured scores, such as the ALSFRS-r and the FVC. The activation duration of sternocleidomastoid, used to rotate the head, correlated well with the ALSFRS-r and FVC in ALS patients during axial rotation. INTERPRETATION: The ability to synchronously activate a pair of muscles to execute single-plane motions in ALS patients seems to have been compromised due to the disease and potentially results in head drop. The neck brace measures can be adapted in the clinic to complement self-reporting in ALS patients and used to assess the head drop and progress of the disease.

Using the Motion of the Head-Neck as a Joystick for Orientation Control.

Head-neck interfaces have the potential to command and control orientation tasks when the hand-wrist is not available for use as a joystick. We pose the question in this paper-How well can the head-neck be used to perform orientation tasks when compared to the hand-wrist? Anatomically, the motion of the head-neck is similar to that of the hand-wrist. We hypothesize that the head-neck motion can be as effective as the motion of the hand-wrist to control orientation tasks. A study was designed to characterize the ability of head-neck to command and control general orientation tasks. Fourteen healthy participants were asked to control the head orientation of an avatar on a computer screen using the motion of their head-neck and hand-wrist, measured by a robotic neck brace and a conventional joystick, respectively. Visual feedback was given to the participants with the display of the target and the actual head orientations of the avatar. The outcomes were defined for comparison between the head-neck and hand-wrist motions as follows: 1) mean absolute error; 2) time delay in tracking continuous orientation trajectories; and 3) settling time to reach target orientations. The results showed that the performance outcomes were significantly better with the hand-wrist than that of the head-neck when used as a joystick. However, all participants successfully completed the tasks with the head-neck. This demonstrates that the head-neck can be used as a joystick for controlling three dimensional object orientations, even though it may not be as dexterous as the hand-wrist. These results have fundamental implications in the design of devices and interfaces with the human head-neck.