In the past decade, significant focus has been on electromyography (EMG) control of prostheses in transtibial amputees (TTAs). Reliable signal acquisition requires accurate EMG electrode placement. Conventional electrode placement methods are challenging due to altered post-surgical anatomy. This study investigated the application of ultrasound imaging for placement of EMG electrodes in TTAs. Four residual limb muscles, Tibialis Anterior (TA), Peroneus Longus (PL), Gastrocnemius Medial (GM), and Gastrocnemius Lateral (GL), were examined in 9 unilateral TTAs. Ultrasound was used to identify each muscle belly’s thickest part and fiber orientation. A Certified Prosthetist Orthotist (CPO) then performed palpation to identify muscle bellies, blinded to ultrasound findings. Distances between ultrasound- and palpation-identified spots were measured. EMG data were contrasted between methods in terms of root mean square (RMS) amplitude and signal-to-noise ratio (SNR). The results indicated that Ultrasound-guided placement produced slightly higher, though non-significant, signal amplitudes (p = 0.06) and significantly higher SNR (p = 0.04). Moreover, palpation misidentified muscles in four cases. In 72.2% of cases, the distance between ultrasound- and palpation-identified spots was more than 10 mm. The mean distance was the greatest for PL and GL. Relying on palpation to identify PL and TA in TTAs may provide irrelevant EMG due to erroneous placement. Using ultrasound imaging can avoid this and, in addition to accurate muscle identification, may improve signal amplitude and SNR. In conclusion, ultrasound imaging is a valuable tool for enhancing the accuracy of EMG electrode placement in TTAs, which may lead to better prosthetic control outcomes.

This study investigates the structural and functional characteristics of residual muscles in transtibial amputees (TTAs) to improve electromyography (EMG)-based prosthetic control. Using ultrasonography, we measured the thickness of the Tibialis Anterior (TA), Peroneus Longus (PL), Gastrocnemius Medialis (GM), and Lateralis (GL) at rest and during contraction. Surface EMG was employed to assess muscle activation patterns, co-contraction levels, and accuracy in modulating submaximal contractions at 25%, 50%, and 75% of maximum voluntary contraction (MVC). Results revealed that muscle thickness on the amputated side was significantly lower than on the sound side (p < 0.0001), with the TA and PL exhibiting the greatest atrophy. Despite this, all muscles demonstrated significant increases in thickness during contraction (p<0.0001), indicating preserved neuromuscular activity. GL showed the highest percentage increase in thickness (23.7%), followed by PL (20.5%) and GM (15.4%). EMG analysis demonstrated high co-contraction, particularly between TA and PL, which may complicate selective muscle activation for prosthetic control. During dorsiflexion, PL activation was nearly as high as TA, while TA also exhibited unintended activation during eversion, suggesting poor muscle differentiation. During plantarflexion, GM and GL exhibited dominant activation, while the PL showed substantial co-contraction. Accuracy in controlling submaximal contractions was inconsistent, with TA showing the lowest absolute error (0.17), while GM and GL exhibited the highest errors (0.26 and 0.27, respectively). These findings suggest that TTAs retain the ability to activate residual muscles but struggle with selective activation and intensity modulation, emphasizing the need for targeted training and prosthetic control strategies to optimize functional outcomes.

Lower limb amputation greatly affects quality of life by restricting functional mobility. Despite advancements in prosthetic design, powered transtibial prostheses still have limitations in user control and adaptability to dynamic environments. This research presents a comparative analysis between a novel electromyography (EMG)-driven variable impedance controller (VIC) and a hybrid controller (HC) that integrates a volitional EMG-driven musculoskeletal model with a finite-state machine impedance controller. A Hill-type muscle model was used to model the gastrocnemius and tibialis anterior muscles. Biomechanical testing was conducted with a transtibial amputee to assess the controllers’ performance across various tasks, including ambulation on level ground, stairs, and ramps, using EMG signals from the residual limb. Results demonstrated that the VIC provided more repeatable performance, perceived control, and power output. Notable effect sizes for peak power, observed in ramp ascent (Cohen’s d = -1.04) and high-speed level ground walking (Cohen’s d = -2.92), illustrate robust differences in joint-level output even when walking speeds and cadences were comparable. The greater predictability of the VIC led the user to feel more in control and comfortable throughout the various activities. On the other hand, the HC controller performed better in enabling more seamless transitions between gait subphases, particularly during stair ascent, which led to a significantly higher ROM (18.63 ± 1.53 deg vs. 12.43 ± 1.86 deg) and nearly double peak power compared to the VIC. This comparison lays the groundwork for future research into optimizing EMG-based control strategies that adapt to both biomechanical demands and user preferences.

Background: Myoelectric control of lower-limb prostheses is challenging due to residual muscle co-contraction, inconsistent activation, and signal variability. Evidence regarding the efficacy of training interventions targeting residual muscle activation in transtibial amputees (TTAs) to enhance prosthetic control remains limited. This study investigated whether a 4-week structured training could improve residual muscle control in TTAs. Methods: Nine male unilateral TTAs were assigned to either (A) biofeedback training with daily home exercises or (B) home exercises alone. Biofeedback sessions provided real-time surface electromyography (EMG) feedback on Tibialis Anterior, Gastrocnemius, and Peroneus Longus activity. Performance was evaluated at baseline and post-intervention using contraction accuracy (root mean square error), signal stability (time outside bounds), and selective muscle activation (co-contraction index). Results: Despite substantial inter-individual variability, participants demonstrated overall improvements in accuracy, stability, and selective muscle activation, irrespective of group. These findings suggest that consistent home-based training alone can induce rapid neuromuscular adaptation with measurable improvements in residual muscle control. However, this study was exploratory in nature and not powered to detect small between-group differences. Inter-individual variability highlighted the influence of baseline control and amputation etiology on outcomes, and one participant reported adverse neuropathic pain, underscoring the need to screening for neuropathic susceptibility, especially in individuals with prior neuroma or chronic phantom limb pain. Conclusions: Overall, structured EMG-based training improved residual muscle control in TTAs. These findings support the potential of EMG-guided interventions to foster more intuitive and reliable prosthetic use and to inform future rehabilitation protocols.

This study investigated the feasibility and biomechanical effects of volitional electromyography (EMG)-based control of a powered transtibial ankle prosthesis. Four male participants completed static and dynamic EMG assessments and gait analysis while using both their prescribed passive prosthesis and an EMG-controlled powered prototype during level walking at self-selected and fast speeds, as well as ramp ascent and descent. Selective activation of residual tibialis anterior and gastrocnemius muscles was quantified using a co-contraction index, and lower-limb kinematics and kinetics were compared between prosthetic conditions. Participants were able to generate task-dependent residual muscle activity, supporting the feasibility of EMG-based volitional control. However, muscle selectivity was reduced during dynamic tasks, with higher co-contraction during gait than during seated static contractions, and substantial inter-subject variability was observed. Compared to the prescribed passive prosthesis, the EMG-controlled prototype generally produced lower prosthetic-side ankle range of motion and ankle power, although ankle moments were sometimes slightly greater. These findings suggest that EMG control is feasible, but that future controller design must remain flexible to individual users’ neuromuscular abilities and dynamic control limitations. The results provide important guidance for the development and testing of more adaptive, personalized, and functionally effective EMG-controlled prosthetic ankle systems.