Effects of NMES-elicited versus voluntary low-level conditioning contractions on explosive knee extensions.

OBJECTIVES: Electrically-induced or voluntary conditioning-contractions (CC) can be used to affect contractile properties of a subsequent explosive contraction (EC). Here, we aimed at comparing the effect of neuromuscular-electrical-stimulation (NMES) vs voluntary CC performed prior to explosive contractions of the knee extensors. METHODS: A 10 sec NMES CC (100Hz, 1000µs, 10% MVC), or a voluntary contraction (VOL CC) mimicking the NMES CC, preceded an isometric EC of the knee extensors. Explosive contraction was performed with the goal to reach the target (70% MVC) as quickly as possible. RESULTS: All the parameters related with the explosive contractions' muscle-output were similar between protocols (difference ranging from 0.23%, Mean Torque; to 5.8%, Time to Target), except for the Time to Peak Torque, which was lower when preceded by NMES (11.1%, p=0.019). Interestingly, the RTD 0-50 ms_EC was 37.3% higher after the NMES compared with the VOL CC protocol. CONCLUSION: Explosive contraction was potentiated by an NMES CC as compared with a voluntary CC. This may be due to a reduction in descending drive following VOL CC, which has been shown to occur even with low-level voluntary efforts. These findings could be used to improve rehabilitation or training protocols that include conditioning contractions.

Novel Noninvasive Spinal Neuromodulation Strategy Facilitates Recovery of Stepping after Motor Complete Paraplegia.

It has been suggested that neuroplasticity-promoting neuromodulation can restore sensory-motor pathways after spinal cord injury (SCI), reactivating the dormant locomotor neuronal circuitry. We introduce a neuro-rehabilitative approach that leverages locomotor training with multi-segmental spinal cord transcutaneous electrical stimulation (scTS). We hypothesized that scTS neuromodulates spinal networks, complementing the neuroplastic effects of locomotor training, result in a functional progression toward recovery of locomotion. We conducted a case-study to test this approach on a 27-year-old male classified as AIS A with chronic SCI. The training regimen included task-driven non-weight-bearing training (1 month) followed by weight-bearing training (2 months). Training was paired with multi-level continuous and phase-dependent scTS targeting function-specific motor pools. Results suggest a convergence of cross-lesional networks, improving kinematics during voluntary non-weight-bearing locomotor-like stepping. After weight-bearing training, coordination during stepping improved, suggesting an important role of afferent feedback in further improvement of voluntary control and reorganization of the sensory-motor brain-spinal connectome.

Physical capacities and leisure activities are related with cognitive functions in older adults.

BACKGROUND: This study aimed to evaluate the relationship between physical activity habits, physical performance and cognitive capacity in older adults' population of Italy and Slovenia. METHODS: Anthropometric characteristics and body composition bioelectrical impedance analysis were evaluated in 892 older adults (60-80 y). Aerobic capacity was measured using the 2-km walk test and handgrip and flexibility tests were performed. Physical activity habits and cognitive functions were evaluated by the Global-Physical-Activity-Questionnaires (GPAQ) and by Montreal-Cognitive-Assessment (MoCA) questionnaires, respectively. RESULTS: GPAQ scores were associated with lower BMI (r=-0.096; P=0.005), lower percentage of fat-mass (r=-0.138; P=0.001), better results in the 2-km walk test (r=-0.175; P=0.001) and a higher percentage of fat-free mass (r=0.138; P=0.001). We also evaluated that a higher MoCA Score correlates with age (r=-0.208; P=0.001), 2-km walk test (r=-0.166; P=0.001), waist-hip ratio (r=-0.200; P=0.001), resting heart-rate (r=-0.087; P=0.025) and heart-rate at the end of 2-km walk test (r=0.189; P=0.001). CONCLUSIONS: Older adults with a higher level of daily physical activity showed reduction in fat-mass and BMI, and higher aerobic fitness; these characteristics have a protection effect on cognitive function.

Energy cost of walking and body composition changes during a 9-month multidisciplinary weight reduction program and 4-month follow-up in adolescents with obesity.

The purpose of the present study was to investigate changes in the energy cost of locomotion during walking (Cw) related to changes in body mass (BM, kg) and body composition in adolescents with obesity. Twenty-six (12 boys and 14 girls) obese adolescents (mean: body mass index, 33.6 ± 3.7 kg·m-2; 42.7 ± 4.5% fat mass (FM)) followed a 9-month multidisciplinary inpatient weight-reduction program consisting of lifestyle education, moderate energy restriction, and regular physical activity in a specialised institution. At baseline (M0), the end of the 9-month program (M9), and after the 4-month follow-up (M13), oxygen consumption and carbon dioxide production of the standardised activity program were assessed by whole-body indirect calorimetry over 24 hours, and body composition was assessed by dual-energy X-ray absorptiometry. At M9, adolescents showed an 18% reduction in BM (p < 0.001) and 40% in total FM, while fat-free mass (kg) remained stable in boys but decreased by ∼6% in girls (p = 0.001). Similarly, the mean Cw decreased by 20% (p < 0.001). At M13, BM, FM, and Cw were slightly higher compared with at M9. In conclusion, moderate energy restriction and regular moderate physical activities improved walking economy, improved exercise tolerance, and induced beneficial changes in the body composition of adolescents with obesity. Novelty: Reduction of FM in the trunk region, and consequently reducing the work carried out by respiratory muscles, contributes to reducing Cw in adolescents with obesity. A lower walking cost can be effective in improving exercise tolerance and quality of life in obese adolescents.

Effects of NMES pulse width and intensity on muscle mechanical output and oxygen extraction in able-bodied and paraplegic individuals.

PURPOSE: Neuromuscular Electrical Stimulation (NMES) is commonly used in neuromuscular rehabilitation protocols, and its parameters selection substantially affects the characteristics of muscle activation. Here, we investigated the effects of short pulse width (200 µs) and higher intensity (short-high) NMES or long pulse width (1000 µs) and lower intensity (long-low) NMES on muscle mechanical output and fractional oxygen extraction. Muscle contractions were elicited with 100 Hz stimulation frequency, and the initial torque output was matched by adjusting stimulation intensity. METHODS: Fourteen able-bodied and six spinal cord-injured (SCI) individuals participated in the study. The NMES protocol (75 isometric contractions, 1-s on-3-s off) targeting the knee extensors was performed with long-low or short-high NMES applied over the midline between anterior superior iliac spine and patella protrusion in two different days. Muscle work was estimated by torque-time integral, contractile properties by rate of torque development and half-relaxation time, and vastus lateralis fractional oxygen extraction was assessed by Near-Infrared Spectroscopy (NIRS). RESULTS: Torque-time integral elicited by the two NMES paradigms was similar throughout the stimulation protocol, with differences ranging between 1.4% (p = 0.877; able-bodied, mid-part of the protocol) and 9.9% (p = 0.147; SCI, mid-part of the protocol). Contractile properties were also comparable in the two NMES paradigms. However, long-low NMES resulted in higher fractional oxygen extraction in able-bodied (+ 36%; p = 0.006). CONCLUSION: Long-low and short-high NMES recruited quadriceps femoris motor units that demonstrated similar contractile and fatigability properties. However, long-low NMES conceivably resulted in the preferential recruitment of vastus lateralis muscle fibers as detected by NIRS.

Neurophysiological markers predicting recovery of standing in humans with chronic motor complete spinal cord injury.

The appropriate selection of individual-specific spinal cord epidural stimulation (scES) parameters is crucial to re-enable independent standing with self-assistance for balance in individuals with chronic, motor complete spinal cord injury, which is a key achievement toward the recovery of functional mobility. To date, there are no available algorithms that contribute to the selection of scES parameters for facilitating standing in this population. Here, we introduce a novel framework for EMG data processing that implements spectral analysis by continuous wavelet transform and machine learning methods for characterizing epidural stimulation-promoted EMG activity resulting in independent standing. Analysis of standing data collected from eleven motor complete research participants revealed that independent standing was promoted by EMG activity characterized by lower median frequency, lower variability of median frequency, lower variability of activation pattern, lower variability of instantaneous maximum power, and higher total power. Additionally, the high classification accuracy of assisted and independent standing allowed the development of a prediction algorithm that can provide feedback on the effectiveness of muscle-specific activation for standing promoted by the tested scES parameters. This framework can support researchers and clinicians during the process of selection of epidural stimulation parameters for standing motor rehabilitation.