Enhancing performance during inclined loaded walking with a powered ankle–foot exoskeleton

Abstract

PURPOSE. A simple ankle-foot exoskeleton that assists plantarflexion during push-off can reduce the metabolic power during walking. This suggests that walking performance during a maximal incremental exercise could be improved with an exoskeleton if the exoskeleton is still efficient during maximal exercise intensities. Therefore, we quantified the walking performance during a maximal incremental exercise test with a powered and unpowered exoskeleton: uphill walking with progressively higher weights.METHODS. Nine female subjects performed two incremental exercise tests with an exoskeleton: one day with (powered condition) and another day without (unpowered condition) plantarflexion assistance.Subjects walked on an inclined treadmill (15%) at 5 km•h -1 and 5% of body weight was added every 3 min until exhaustion.RESULTS. At volitional termination no significant differences were found between the powered and unpowered condition for blood lactate concentration (respectively 7.93±2.49; 8.14±2.24mmol•L -1 ), heart rate (respectively 190.00±6.50; 191.78±6.50bpm), Borg score (respectively 18.57±0.79; 18.93±0.73) and 2 peak (respectively 40.55±2.78; 40.55±3.05ml•min -1 •kg -1 ). Thus, subjects were able to reach the same (near) maximal effort in both conditions. However, subjects continued the exercise test longer in the powered condition and carried 7.07±3.34kg more weight because of the assistance of the exoskeleton.

Reducing the metabolic cost of walking with an ankle exoskeleton: interaction between actuation timing and power

“…1) consisted of an ankle-foot orthosis at each leg with a hinge at the ankle joint and pneumatic muscles [3, 17–19]. The pneumatic muscles were 0.27 m in length and were connected between the foot segment and the shank segment.…”

“…Based on footswitch signals from the previous stride, exoskeleton actuation for the next stride was controlled using fixed percentages of stride time with a feedforward algorithm in Labview (National Instruments, Austin, TX, USA) [3, 17–19]. To control the amount of exoskeleton mechanical power, air pressure in the pneumatic muscles was adjusted using an iterative learning algorithm [9, 21].…”

Varying negative work assistance at the ankle with a soft exosuit during loaded walking

“…While early studies with rigid full-leg exoskeletons demonstrated the ability to unload a backpack load from a wearer [4], these systems caused an increase in metabolic effort compared to normal walking [5, 6]. However, over the past years, a number of labs successfully developed early prototype devices that achieved reductions in metabolic rate of unloaded [7–9] and loaded [10, 11] walking, and increase in maximal load-carrying performance [12] in controlled treadmill experiments. One explanation as to why reductions in metabolic rate were achieved only recently could be that earlier exoskeletons were too heavy [10, 13], with rigid structures over the length of the whole leg that caused wearers to deviate significantly from their natural gait.…”

Human Factors Considerations for Enabling Functional Use of Exosystems in Operational Environments

“…As previously mentioned, the less the user must directly input and control, the better for synergy and ability to engage with the surroundings. However, the selection of the underlying controller impacts the kinematics and metabolic consumption (e.g., [40], [58]- [60]). The actuation timings are important for enabling efficient mode transitions such that systems do not have a sluggish response or disturb the desired biomechanics.…”