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Table 4 Overview of the evaluation measurements and related results

From: EMG-driven control in lower limb prostheses: a topic-based systematic review

Ref. Perform-based measurements Biomechanical measurements Averaged results Control delay Subjects number Reported limitations
[64] QA on locomotion performance NI NI 50–100 ms > 1 TFA NS
[29] Cadence, Swing and Stance duration Joint angles and moments, maximum knee flexion Results in figures only NS 1 TFA Sensitive to movement artifacts
[24,25,26,27] Error events analysis Joint angle NRME, CC Max error events amplitude = 42 (11 SD); NRME < 6.56 (1.85 SD)%; CC = 0.59 (0.9 SD) NS 4 ABS High maximum error amplitudes
[56] Joint flexion/extension CA Joint angle RMSE CA = 92 (7 SD)%; RMSE = 6.2 (0.71 SD)\(^{\circ }\) NS 2 TFA, 1 BTFA NS
[14, 23, 62, 63] \(t_{STRIDE}\); \(v_{WALKING}\) Joint angle and joint stiffness; RMSE in joint angle trajectory tracking \(t_{STRIDE}\) = 1.96s; \(v_{WALKING}\) = 2.9 km/h; able-bodied resemblance joint trajectories (figures only); RMSE statistical different only with haptic feedback and no-visual 1 ms 1 TFA; 2 ABS Not appropriate swing control; lack of somatosensory feedback; sensitive to movement artifacts and skin perspiration
[57] Motor task CA, MCT and MCP NI CA = 90.7 (5.0 SD)%; MCT = 1.26 (0.1 SD)s; CP = 96.3 (4.3 SD)% < 700 ms 6 TFA Sensitive to electrode shifts and impedance; extensive training necessary
[37] NI VAF, RMSE joint angle VAF > 83%; RMSE < 5.4 (1.2 SD)\(^{\circ }\) − 100 ms 3 TTA Performance being tested only in constant velocity walking task
[16] MCT NI MCT = 1.9 s NS 5 ABS Position controller unsatisfactorily during stance phase
[67, 68] NP Joint peak power and work respect to state-base controller Statistical difference of evaluated parameters only with visual feedback (p-val = 0.02) 33 ms 5 TTA Short training session, experienced high muscular fatigue
[76] NI Joint angle trajectories Results in figures only NS 10 ABS No walking speed adaptation, no real-time
[11] NI Joint trajectory r-value and SNR r-value = 0.64 (0.22SD); SNR = 7.42 (2.88SD) 3.3 ms 6 ABS Position controller unsatisfactorily for limb dynamics
[39, 40] Number of falling Joint angle RMSE, EMG contraction level, mean joint torque during balance task Falling events and applied torque decrease with training; final RMSE = 0.19 (8.78)\(^{\circ }\); no significant changes in muscle activation with training 10 ms 6 ABS; 6 TTA Small sample population; study used visual feedback
[98] NI QA of EMG signals and joint angle Figures only NS 1 TFA Sensitive to movement artifacts; sensitive to muscular mass changes
[70] Locomotion classification accuracy QA of ankle joint position and shank angular orientation CA = 86.53 (8.5 SD)%; biomechanical measurements (figures only) NS > 1 ABS, > 1 TFA NS
[5] Stance time; gait symmetry Toe-off angle; peak torque; joint trajectories Qualitatively similar to biological ankle trajectories (figures only) NS 1 BTTA Asymmetry on knee flexion during late stance
[65, 66, 141, 144] Locomotion and transitions CA NI Locomotion CA = 91.79–100%; transition CA = 100% 12 ms 5 TFA Sensor fusion and sound leg instrumentation is necessary to increase accuracy
[53] Locomotion CA NI CA \(\approx\) 80–100% (figures only) NS 5 ABS NS
[85] Locomotion CA NI CA = 91.46% NS 100 ms NS
[15, 110] Locomotion CA NI CA = 91.23% NS 3 ABS Tested only healthy subjects
[32, 33, 143] Locomotion and transitions CA NI Locomotion CA \(\approx\) 98%; transitions CA > 99% < 45.2 ms 4 TFA Real-time test only on non-powered prosthesis; mechanical sensor feature are necessary
[86, 87] Locomotion CA NI CA = 97.9 (1.39 SD)% NS 5 ABS, 5 TFA Only limited number of locomotions; major misclassification during gait transitions
[120] Joint DoF motion CA NI 1-DoF CA = 93.3 (0.5 SD)%; 3-DoF CA = 84.4 (0.8 SD)%; 50ms 5 ABS, 12 TTA Best results only combining both tibia and thigh muscles
[58, 111] Locomotion CA, NWB CA, falls occurrences NI with TMR: locomotion CA = 8.9%, NWB CA = 91.0 (4.7SD)%, falls occurrence = 0%; no-TMR: locomotion CA = 10.2%, NWB CA = 86.8 (3.0SD)%, falls occurrence = 2% NS 4 TFA, 1 TMR Control degradation over time due to fatigue, electrode shift and skin perspiration; necessity of mechanical sensors for high accuracy; small number of subjects
[59, 113, 114, 139, 140] Locomotion and transitional CA, effects on classification errors NI Locomotion CA < 99%; transition CA = 87%; classification errors during stairs were more disruptive < 20 ms 7 TFA Control degradation over time due to fatigue, electrode shift and skin perspiration; testing is performed in only one sessions
[17] Questioner on control comfort Inclination CA CA > 95%; comfort higher when no classification error (accepted error \(\le 5^\circ\)) NS 2 TFA Experienced high muscular fatigue; lack of sensory feedback
[106] NI QA of EMG signals Results in figures only NS 1 ABS Not tested on amputee; only walking activity control
[54, 55] Locomotion CA NI CA = 99.06 (0.87SD)% 32 ms 5 ABS Not tested on-line
[6] NI Joint angle trajectory frequency content mean frequency = 5.4 (0.3 SD) Hz, qualitatively similar to biological ankle NS 1 TTA Temporal variation of the EMG signals are not accounted for
[61] Subject qualitative report QA of knee joint position and torque Control interface did not feel natural; able-bodied resemblance joint trajectories (figures only) NS 1 ABS with ABA Experimental tuning of the parameters is necessary
[135, 136] QA of joint trajectories with respect to ABS Joint angle trajectory RMSE Results in figures only NS 1 ABS with ABA Model parameters are tuned manually; control instable with biarticular muscles
[71, 72, 130] NI Toe-off angle, joint net work, peak power, joint torque vs angle Net work performed higher than the biological norms; not substantial difference in joint moments between intrinsic controller and EMG-driven 2 ms 1 BTTA; 3 TTA, 3 ABS Further studies on the real metabolic cost benefits are required
[19] NI Joint torque NRMSD with respect ABS NRMSD \(\le\) 0.24 (0.11 SD) < 50 ms 1 ABS Complex subject-specific calibration; required validation on more subjects and hardware
  1. Fields include: paper reference; performance-based measurements (e.g. cadence, stance/swing time, stumble rates, etc.); biomechanical measurements (e.g. joint trajectory deviations, peak angles, net work, etc.); averaged results (averaged or worst subject-case results); control delay (time required for the generation of the high-level control output from the acquired relevant signals, including processing); subjects (number of subjects); reported limitations (limitations reported by the authors)
  2. NP not present, NI not implemented, NS not specified, QA qualitative analysis, CA classification accuracy, RMSE root mean squared error, NRMSD normalized root mean squared deviation, \(t_{STRIDE}\) time stride, \(v_{WALKING}\) walking self selected velocity, VAF variance accounted for, MCT motion completion time, MCP motion compilation percentage, DoF Degree of Freedom, TFA transfemoral amputee, BTFA bilateral transfemoral amputee, TTA transtibial amputee, BTTA bilateral transtibial amputee, ABS able-bodied subjects, ABA able-body adaptor