Paradoxical adaptation of successful movements: The crucial role of internal error signals

Steadiness training improves the quadriceps strength and self-reported outcomes in persistent quadriceps weakness following nine months of anterior cruciate ligament reconstruction and failed conventional physiotherapy

Background Persistent quadriceps weakness may occur after anterior cruciate ligament reconstruction, limiting the strength gain. However, steadiness strengthening might change the inability to gain strength. Hence, we determined whether strength training with force steadiness and visual biofeedback can improve knee quadriceps torque, self-reported pain and knee stability in patients with persistent quadriceps weakness after knee anterior cruciate ligament reconstruction. Methods Twenty-five patients (aged 43.7 ± 12.2 years) with persistent quadriceps weakness following knee anterior cruciate ligament reconstruction and 34-weeks of physiotherapy performed unilateral strength training for both lower limbs. Four-weeks of conventional physiotherapy at week-30 were given, confirming the inability to gain torque. Then, steadiness training (isometric knee extension with visual biofeedback) was given for 7-weeks. Knee quadriceps peak torque, strength improvement, determination of responders to the intervention, coherence of strength gain between limbs, and self-reported outcomes (pain and knee stability) were obtained. Descriptive statistics and data inference using mixed-ANOVA, McNemar test, and χ² test were described. Findings Quadriceps torque in the reconstructed knee improved (98.2 ± 47.2-155.2 ± 78.9 Nm; p = 0.031) for most patients (84%). Nevertheless, the torque was lower than the healthy side maintaining asymmetry (155.2 ± 78.9 vs. 209.5 ± 101.8 Nm; p = 0.026). There was high (20%) and medium coherence (80%) between limbs. Knee stability and pain improved in 72% of the patients (p < 0.001). Interpretations Steadiness training after anterior cruciate ligament reconstruction followed 9 months of surgery and failed conventional physiotherapy, improves the persistent weakness and self-reported outcomes, but gain strength was dissimilar between limbs.

Acoustic stimulation increases implicit adaptation in sensorimotor adaptation

Sensorimotor adaptation is an important part of our ability to perform novel motor tasks (i.e., learning of motor skills). Efforts to improve adaptation in healthy and clinical patients using non-invasive brain stimulation methods have been hindered by inter-individual and intra-individual variability in brain susceptibility to stimulation. Here, we explore unpredictable loud acoustic stimulation as an alternative method of modulating brain excitability to improve sensorimotor adaptation. In two experiments, participants moved a cursor towards targets, and adapted to a 30º rotation of cursor feedback, either with or without unpredictable acoustic stimulation. Acoustic stimulation improved initial adaptation to sensory prediction errors in Study 1, and improved overnight retention of adaptation in Study 2. Unpredictable loud acoustic stimulation might thus be a potent method of modulating sensorimotor adaptation in healthy adults.

Prism Adaptation in M1

During prism adaptation (PA), active exposure to an optical shift results in sustained modifications of the sensorimotor system, which have been shown to expand to the cognitive level and serve as a rehabilitation technique for spatial cognition disorders. Several models based on evidence from clinical and neuroimaging studies offered a description of the cognitive and the neural correlates of PA. However, recent findings using noninvasive neurostimulation call for a reexamination of the role of the primary motor cortex (M1) in PA. Specifically, recent studies demonstrated that M1 stimulation reactivates previously vanished sensorimotor changes 1 day after PA, induces after-effect strengthening, and boosts therapeutic effects up to the point of reversing treatment-resistant unilateral neglect. Here, we articulate findings from clinical, neuroimaging, and noninvasive brain stimulation studies to show that M1 contributes to acquiring and storing PA, by means of persisting latent changes after the behavioral training is terminated, consistent with studies on other sensorimotor adaptation procedures. Moreover, we describe the hierarchical organization as well as the timing of PA mechanisms and their anatomical correlates, and identify M1 as an anatomo-functional interface between low- and high-order PA-related mechanisms.

Intrasession Real-time Ultrasonography Feedback Improves the Quality of Transverse Abdominis Contraction

OBJECTIVE

The purpose of this study was to compare changes in thickness of the transverse abdominis during performance of the hollowing exercise guided by feedback using ultrasonography images together with verbal guidance and using verbal guidance alone. We also determined the minimal detectable change and agreement between normalized pressures and muscle thickness.

METHODS

Twenty participants without lumbar pain performed the hollowing exercises with or without ultrasonography feedback: 7 men and 13 women, mean (SD) age = 25 (5) years, height = 166 (10) cm, body mass = 64 (6) kg, body mass index = 22.2 (5.8) kg/m². The thickness of the transverse abdominis was quantified during the exercise using musculoskeletal ultrasonography. Basal and 3 repetitions guided by an evaluator were performed. Pressure was determined using a lumbar cushion. Data were compared with a mixed-model analysis of variance and Bonferroni post hoc test (P < .05). Minimal detectable changes were identified and Bland-Altman analysis performed considering normalized thickness and pressure.

RESULTS

Ultrasonography feedback resulted in larger thickness changes (P < .05). The lowest minimal detectable changes were achieved using ultrasonography feedback. Nonagreement was found between normalized thickness and pressure.

CONCLUSION

Contraction of the transverse abdominis is improved using real-time ultrasonography together with verbal feedback. Low changes in muscle contraction estimated by thickness showed nonagreement with a pressure cushion.