Dynamic stability in cerebral palsy during walking and running: Predictors and regulation strategies.

BACKGROUND: The postural control in cerebral palsy (CP) is often deficient and manifests in a variety of impairments. Consequently, maintaining balance and controlling posture is impeded and results in an increased cost of locomotion and higher risk of falls. The margin of stability is an established measure to quantify dynamic stability during gait. It can be facilitated to analyze impaired control mechanisms, but it is unknown if and how people with CP manage to control the margin of stability during a more demanding motor task, such as running. RESEARCH QUESTION: How do people with cerebral palsy regulate dynamic stability during walking and running? METHODS: Children and adolescents with bilateral cerebral palsy (N = 117; 50 female, 67 male; age 11.0 ± 3.2) were retrospectively included. All underwent instrumented 3D gait analysis, walking and running barefoot at a self-selected gait speed. People with CP were compared to a control group of N = 25 typically developed (TD). Repeated measures ANOVAs were computed to analyze group differences and multiple linear regressions to identify predictors for the medio-lateral margin of stability. RESULTS: The medio-lateral margin of stability was significantly higher in the CP group and was statistically unchanged during running. Different adaptions when running were particularly observed in the lateral trunk lean and step width, which remained high in CP, whereas the TD increased the trunk lean and reduced their step width. Step width was the main predictor for the medio-lateral margin of stability in both gait conditions. SIGNIFICANCE: Young people with cerebral palsy manage to maintain their medio-lateral margin of stability during walking and running, however, with significantly higher safety margins compared to typically developed. This conservative strategy may reflect an adaption to motor and postural control impairments.

Acute effects of whole-body vibration on trunk and neck muscle activity in consideration of different vibration loads.

The intention of this study was to systematically analyze the impact of biomechanical parameters in terms of different peak-to-peak displacements and knee angles on trunk and neck muscle activity during whole-body vibration (WBV). 28 healthy men and women (age 23 ± 3 years) performed four static squat positions (2 peak-to-peak displacements x 2 knee angles) on a side alternating vibration platform with and without vibration stimulus. Surface electromyography (EMG) was used to record the neuromuscular activity of the erector spinae muscle, the rectus abdominis muscle, and of the splenius muscle. EMG levels normalized to maximal voluntary contractions ranged between 3.2 - 27.2 % MVC during WBV. The increase in muscle activity caused by WBV was significant, particularly for the back muscles, which was up to 19.0 % MVC. The impact of the factor 'condition' (F-values ranged from 13.4 to 132.0, p ≤ 0.001) and of the factor 'peak-to-peak displacement' (F-values ranged from 6.4 to 69.0 and p-values from < 0.001 to 0.01) were statistically significant for each muscle tested. However, the factor 'knee angle' only affected the back muscles (F-value 10.3 and 7.3, p ≤ 0.01). The results of this study should give more information for developing effective and safe training protocols for WBV treatment of the upper body. Key pointsThe maximum levels of muscle activity were significantly reached at high amplitudes at a vibration frequency of 30 Hz.WBV leads to a higher muscle activation of the lower back muscles than of the abdominal muscles.Both knee angles of 30° and 45° have similar effects on the vibration load and represent safe positions to prevent any actual harm.Certain combinations of the biomechanical variables have similar effects on the level of muscle activity.

Evaluation of a six-week whole-body vibration intervention on neuromuscular performance in older adults.

Research in the field of whole-body vibration (WBV) for the enhancement of neuromuscular performance is becoming increasingly popular. However, additional understanding of optimal WBV training protocols is still necessary to develop optimal and effective training and prevention concepts, especially for elderly people. The intention of this study was to evaluate a 6-week WBV intervention program based on optimal vibration loads adapted from the literature on lower-limb strength parameters and performance, as well as on perceived exertion according to a subjective rating. A total of 21 older adults were allocated randomly into either a WBV training or control group (CO). Before and after the intervention period, jump height was measured during a countermovement jump. In addition, isolated isokinetic maximal knee extension and flexion strength, mean power, and work were recorded using a motor-driven dynamometer. Borg's scale for rating of perceived exertion was used to evaluate the intensity of WBV exercises within each training session. After the intervention period, jump height increased by 18.55% (p < 0.001) in the WBV group, whereas values of the CO remained unchanged. There were no statistically significant differences in isokinetic maximal strength, mean power, or work values in knee extension or flexion (all p > 0.05). Finally, the subjective perceived exertion of the WBV exercises and respective training parameters ranged between moderate rating levels of 7 and 13 of Borg's scale. Our data show that WBV is a feasible and safe training program for elderly people to increase multijoint strength performance of the lower limbs during a countermovement jump. This could help to determine the potential of WBV programs in training of the elderly to prevent age-related reduction of neuromuscular performance.

Variations in neuromuscular activity of thigh muscles during whole-body vibration in consideration of different biomechanical variables.

The intention of this study was to systematically analyze the impact of biomechanical variables in terms of different vibration frequencies, amplitudes and knee angles on quadriceps femoris and hamstring activity during exposure to whole-body vibration (WBV). 51 healthy men and women (age 55 ± 8 years) voluntary participated in the study and were randomly allocated to five different vibration-frequency groups. Each subject performed 9 static squat positions (3 amplitudes x 3 knee angles) on a side alternating vibration platform. Surface electromyography (EMG) was used to record the neuromuscular activity of the quadriceps femoris and hamstring muscles. Maximal voluntary contractions (MVCs) were performed prior to the measurements to normalize the EMG signals. A three-way mixed ANOVA was performed to analyze the different effects of the biomechanical variables on muscle activity. Depending on the biomechanical variables, EMG muscle activity ranged between 18.2 and 74.1 % MVC in the quadriceps femoris and between 5.2 and 27. 3 % MVC in the hamstrings during WBV. The highest levels of muscle activation were found at high frequencies and large amplitudes. Especially in the quadriceps femoris muscle, a WBV frequency of 30 Hz led to a significant increase in muscle activity compared to the other tested frequencies. However, it seems that knee angle is only relevant for the quadriceps femoris muscle. The results of this study should give more information for developing individual training protocols for WBV treatment in different practical applications. Key PointsWBV leads to a higher muscle activity of the quadriceps femoris than of the hamstrings.The maximum levels of muscle activity were significantly reached at high amplitude and high frequency.The knee angle only significantly affects the quadriceps femoris.Certain combinations of the biomechanical variables have similar effects on the level of muscle activity.