A biologically-inspired multi-joint soft exosuit that can reduce the energy cost of loaded walking - PubMed (original) (raw)
A biologically-inspired multi-joint soft exosuit that can reduce the energy cost of loaded walking
Fausto A Panizzolo et al. J Neuroeng Rehabil. 2016.
Abstract
Background: Carrying load alters normal walking, imposes additional stress to the musculoskeletal system, and results in an increase in energy consumption and a consequent earlier onset of fatigue. This phenomenon is largely due to increased work requirements in lower extremity joints, in turn requiring higher muscle activation. The aim of this work was to assess the biomechanical and physiological effects of a multi-joint soft exosuit that applies assistive torques to the biological hip and ankle joints during loaded walking.
Methods: The exosuit was evaluated under three conditions: powered (EXO_ON), unpowered (EXO_OFF) and unpowered removing the equivalent mass of the device (EXO_OFF_EMR). Seven participants walked on an instrumented split-belt treadmill and carried a load equivalent to 30 % their body mass. We assessed their metabolic cost of walking, kinetics, kinematics, and lower limb muscle activation using a portable gas analysis system, motion capture system, and surface electromyography.
Results: Our results showed that the exosuit could deliver controlled forces to a wearer. Net metabolic power in the EXO_ON condition (7.5 ± 0.6 W kg(-1)) was 7.3 ± 5.0 % and 14.2 ± 6.1 % lower than in the EXO_OFF_EMR condition (7.9 ± 0.8 W kg(-1); p = 0.027) and in the EXO_OFF condition (8.5 ± 0.9 W kg(-1); p = 0.005), respectively. The exosuit also reduced the total joint positive biological work (sum of hip, knee and ankle) when comparing the EXO_ON condition (1.06 ± 0.16 J kg(-1)) with respect to the EXO_OFF condition (1.28 ± 0.26 J kg(-1); p = 0.020) and to the EXO_OFF_EMR condition (1.22 ± 0.21 J kg(-1); p = 0.007).
Conclusions: The results of the present work demonstrate for the first time that a soft wearable robot can improve walking economy. These findings pave the way for future assistive devices that may enhance or restore gait in other applications.
Keywords: Loaded walking; Lower limb exoskeleton; Metabolic power; Soft exosuit.
Figures
Fig. 1
Soft exosuit components. a and b Back and side view of a participant wearing the soft exosuit. The two actuator units were mounted on an empty backpack and the exosuit was worn from the waist down. c Schematic drawing highlighting the two load paths of the soft exosuit, namely a monoarticular path assisting hip extension (green) and a multiarticular path assisting both hip flexion and ankle plantarflexion (_blu_e). Both load paths share the waist belt (grey). Numbers correspond to the actuation and suit components in (d) and (e). d Mechanics and electronic elements composing the actuator system. Motor (1), battery module (2) and multi-wrap pulley (3). e Textiles elements composing the soft exosuit. Waist belt (5), thigh brace (6) and calf strap (7)
Fig. 2
Suit-human series stiffness. This schematic illustrates the mapping between the cable position and the applied external force at the ankle [24]. The three panels on the left describe the effect of the suit-human series stiffness on force generation. The motor pulls on a Bowden cable thus regulating its position across the gait cycle (top panel). This position is transformed into a force on the wearer through the suit-human series stiffness, a non-linear relationship between the force measured at the ankle and the cable position of the motor (middle panel) that is due to the presence of series elastic elements. These elements include cable stretch, soft tissue compression and textile stretch. A force-based feedback loop in the control system ensures the application of a consistent force profile (bottom panel) accounting for the little variations applied by the suit-human series stiffness [24]. The description of the present schematic is relative to the multiarticular load path but an analogous behavior is present in the monoarticular load path
Fig. 3
Experimental methods. a Data collection representing an instrumented participant carrying a loaded backpack and wearing the soft exosuit while walking on a split-belt treadmill (Bertec, Columbus, OH, USA). b-c An instrumented participant, front and side view. Metabolic cost is measured by means of portable gas analysis system (K4b2, Cosmed, Roma, Italy) and participant’s kinematics are measured by means of a 3D motion capture system (VICON, Oxford Metrics, UK; 120 Hz) tracking the position of 50 reflective markers placed on the participant. d Placement of surface electrodes (Delsys, Natick, MA, USA) on the lower limb muscles investigated, back and front view: rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), gluteus maximus (GM), biceps femoris (BF), soleus (SOL), medial gastrocnemius (MG) and tibialis anterior (TA)
Fig. 4
Assistance applied by the soft exosuit to the wearer. a Side view of the soft exosuit highlighting the load cells at the hip and at the ankle used to quantify the level of mechanical assistance provided by the soft exosuit. b Experimental setup highlighting the load cells inserted in the soft exosuit to assess contribution of the hip extension external force during the exosuit characterization experiment. c Peak force at the waist (light blue) and peak force at the ankle (blue) recorded during the exosuit characterization experiment. The waist peak force is the sum of the peak forces collected by the two load cells placed at the front of the thigh and the ankle peak force was collected directly by the load cell placed on the ankle. Data are relative to one representative participant. d Torque profiles at the ankle (blue) and at hip flexion (green) recorded during the testing sessions across all the participants involved in the study; estimated torque profile at the hip extension (light blue) calculated during the exosuit characterization experiment. The schematic drawing illustrates the assistance provided by the exosuit during the phases of the gait cycle. The multiarticular load path is displayed in blue and the monoarticular path is displayed in green. e Joint power (black) and biological joint power (dashed black) calculated for hip and ankle during the EXO_ON condition. The shaded area represents the power provided by the exosuit. Data are group means
Fig. 5
Metabolic power and biological power. a Metabolic power reported in the three conditions of testing: EXO_OFF_EMR (black), EXO_OFF (grey) and EXO_ON (red). b Biological negative and positive power across the lower limb joints and for each single joint reported in the three conditions of testing: EXO_OFF_EMR (black), EXO_OFF (grey) and EXO_ON (red). Data are means ± SD. * and § indicate significant difference (p < 0.05) with respect to the EXO_OFF_EMR condition, # indicates a significant difference (p < 0.05) with respect to the EXO_OFF condition
Fig. 6
Muscle activation. Normalized EMG linear envelope as a percent of gait cycle (heel-strike to heel-strike) for the eight muscles examined. The curves represent the three different conditions: EXO_OFF_EMR (dashed black), EXO_OFF (solid grey) and EXO_ON (dashed red). The dotted vertical lines represent toe off of each testing condition. # indicates a significant difference (p < 0.05) with respect to the EXO_OFF condition, § indicates a significant difference (p < 0.05) between the EXO_OFF_EMR and the EXO_OFF condition
Fig. 7
Joint kinematics and kinetics. Comparison of joint angles, moments and powers (top to bottom) for the three different conditions of testing across the gait cycle. The curves represent the three different conditions: EXO_OFF_EMR (dashed black), EXO_OFF (solid grey) and EXO_ON (dashed red). Ankle, knee and hip joints are displayed from left to right. Data are group means. The dotted vertical lines represent toe off. Positive joint angles represent flexion (dorsi-flexion at the ankle) and negative angles represent extension (plantarflexion at the ankle). Positive moments represent net extension joint moments (plantarflexion at ankle) and negative moments represent net flexion joint moments (dorsi-flexion at ankle). Positive powers represent instantaneous joint power generation and negative powers represent instantaneous joint power absorption. * Indicates significant difference (p < 0.05) with respect to the EXO_OFF_EMR condition, # indicates a significant difference (p < 0.05) with respect to the EXO_OFF condition
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