BackgroundRepetitive task practice is argued to drive neural plasticity following stroke. However, current evidence reveals that hemiparetic weakness impairs the capacity to perform, and practice, movements appropriately. Here we investigated how power training (i.e., high-intensity, dynamic resistance training) affects recovery of upper-extremity motor function post-stroke. We hypothesized that power training, as a component of upper-extremity rehabilitation, would promote greater functional gains than functional task practice without deleterious consequences.MethodNineteen chronic hemiparetic individuals were studied using a crossover design. All participants received both functional task practice (FTP) and HYBRID (combined FTP and power training) in random order. Blinded evaluations performed at baseline, following each intervention block and 6-months post-intervention included: Wolf Motor Function Test (WMFT-FAS, Primary Outcome), upper-extremity Fugl-Meyer Motor Assessment, Ashworth Scale, and Functional Independence Measure. Neuromechanical function was evaluated using isometric and dynamic joint torques and concurrent agonist EMG. Biceps stretch reflex responses were evaluated using passive elbow stretches ranging from 60 to 180º/s and determining: EMG onset position threshold, burst duration, burst intensity and passive torque at each speed.ResultsPrimary outcome: Improvements in WMFT-FAS were significantly greater following HYBRID vs. FTP (p = .049), regardless of treatment order. These functional improvements were retained 6-months post-intervention (p = .03).Secondary outcomes: A greater proportion of participants achieved minimally important differences (MID) following HYBRID vs. FTP (p = .03). MIDs were retained 6-months post-intervention. Ashworth scores were unchanged (p > .05).Increased maximal isometric joint torque, agonist EMG and peak power were significantly greater following HYBRID vs. FTP (p < .05) and effects were retained 6-months post-intervention (p’s < .05). EMG position threshold and burst duration were significantly reduced at fast speeds (≥120º/s) (p’s < 0.05) and passive torque was reduced post-washout (p < .05) following HYBRID.ConclusionsFunctional and neuromechanical gains were greater following HYBRID vs. FPT. Improved stretch reflex modulation and increased neuromuscular activation indicate potent neural adaptations. Importantly, no deleterious consequences, including exacerbation of spasticity or musculoskeletal complaints, were associated with HYBRID. These results contribute to an evolving body of contemporary evidence regarding the efficacy of high-intensity training in neurorehabilitation and the physiological mechanisms that mediate neural recovery.

With hemiplegia following stroke, a person's movement response to anti-gravity posture often appears rigid and inflexible, exacerbating the motor dysfunction. A major determinant of pathological movement in anti-gravity postures is the failure to adapt muscle-activity patterns automatically to changes in posture. The aim of the present study was to determine whether the impaired motor performance observed when persons with hemiplegia pedal in a horizontal position is exacerbated at more vertical anti-gravity body orientations. Twelve healthy elderly subjects and 17 subjects with chronic (> 6 months) post-stroke hemiplegia participated in the study. Subjects pedalled a modified ergometer at different body orientations (from horizontal to vertical), maintaining the same workload, cadence, and hip and knee kinematics. Pedal reaction forces, and crank and pedal kinematics, were measured and then used to calculate the work done by each leg and their net positive and negative components. The EMG was recorded from four leg muscles (tibialis anterior, medial gastrocnemius, rectus femoris and biceps femoris). The main result from this study was that impaired plegic leg performance, as measured by net negative work done by the plegic leg and abnormal early rectus femoris activity, was exacerbated at the most vertical body orientations. However, contrary to the belief that muscle activity cannot adapt to anti-gravity postures, net positive work increased appropriately and EMG activity in all muscles showed modulated levels of activity similar to those in elderly control subjects. These results support the hypothesis that increased verticality exacerbates the already impaired movement performance. Yet, much of the motor response to verticality was flexible and appropriate, given the mechanics of the task.

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Bicycle pedaling has been studied from both a motor control and an equipment setup and design perspective. In both cases, although the dynamics of the bicycle drive system may have an influence on the results, a thorough understanding of the dynamics has not been developed. This study pursued three objectives related to developing such an understanding. The first was to identify the limitations of the inertial/frictional drive system model commonly used in the literature. The second was to investigate the advantages of an inertial/frictional/compliant model. The final objective was to use these models to develop a methodology for configuring a laboratory ergometer to emulate the drive system dynamics of road riding. Experimental data collected from the resulting road-riding emulator and from a standard ergometer confirmed that the inertial/frictional model is adequate for most studies of road-riding mechanics or pedaling coordination. However, the compliant model was needed to reproduce the phase shift in crank angle variations observed experimentally when emulating the high inertia of road riding. This finding may be significant for equipment setup and design studies where crank kinematic variations are important or for motor control studies where fine control issues are of interest. [S0148-0731(00)02004-5]

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