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- postural sway (2) (entfernen)
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- Department Sport- und Gesundheitswissenschaften (2) (entfernen)
Non-local or crossover (contralateral and non-stretched muscles) increases in range-of-motion (ROM) and balance have been reported following rolling of quadriceps, hamstrings and plantar flexors. Since there is limited information regarding plantar sole (foot) rolling effects, the objectives of this study were to determine if unilateral foot rolling would affect ipsilateral and contralateral measures of ROM and balance in young healthy adults. A randomized within-subject design was to examine non-local effects of unilateral foot rolling on ipsilateral and contralateral limb ankle dorsiflexion ROM and a modified sit-and-reachtest (SRT). Static balance was also tested during a 30 s single leg stance test. Twelve participants performed three bouts of 60 s unilateral plantar sole rolling using a roller on the dominant foot with 60 s rest intervals between sets. ROM and balance measures were assessed in separate sessions at pre-intervention, immediately and 10 minutes post-intervention. To evaluate repeated measures effects, two SRT pre-tests were implemented. Results demonstrated that the second pre-test SRT was 6.6% higher than the first pre-test (p = 0.009, d = 1.91). There were no statistically significant effects of foot rolling on any measures immediately or 10 min post-test. To conclude, unilateral foot rolling did not produce statistically significant increases in ipsilateral or contralateral dorsiflexion or SRT ROM nor did it affect postural sway. Our statistically non-significant findings might be attributed to a lower degree of roller-induced afferent stimulation due to the smaller volume of myofascia and muscle compared to prior studies. Furthermore, ROM results from studies utilizing a single pre-test without a sufficient warm-up should be viewed critically.
Background and objectives: The intricate interdependencies between the musculoskeletal and neural systems build the foundation for postural control in humans, which is a prerequisite for successful performance of daily and sports-specific activities. Balance training (BT) is a well-established training method to improve postural control and its components (i.e., static/dynamic steady-state, reactive, proactive balance). The effects of BT have been studied in adult and youth populations, but were systematically and comprehensively assessed only in young and old adults. Additionally, when taking a closer look at established recommendations for BT modalities (e.g., training period, frequency, volume), standardized means to assess and control the progressive increase in exercise intensity are missing. Considering that postural control is primarily neuronally driven, intensity is not easy to quantify. In this context, a measure of balance task difficulty (BTD) appears to be an auspicious alternative as a training modality to monitor BT and control training progression. However, it remains unclear how a systematic increase in BTD affects balance performance and neurophysiological outcomes. Therefore, the primary objectives of the present thesis were to systematically and comprehensively assess the effects of BT on balance performance in healthy youth and establish dose-response relationships for an adolescent population. Additionally, this thesis aimed to investigate the effects of a graded increase in BTD on balance performance (i.e., postural sway) and neurophysiological outcomes (i.e, leg muscle activity, leg muscle coactivation, cortical activity) in adolescents.
Methods: Initially, a systematic review and meta-analysis on the effects of BT on balance performance in youth was conducted per the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statement guidelines. Following this complementary analysis, thirteen healthy adolescents (3 female/ 10 male) aged 16-17 years were enrolled for two cross-sectional studies. The participants executed bipedal balance tasks on a multidirectional balance board that allowed six gradually increasing levels of BTD by narrowing the balance boards’ base of support. During task performance, two pressure sensitive mats fixed on the balance board recorded postural sway. Leg muscle activity and leg muscle coactivation were assessed via electromyography while electroencephalography was used to monitor cortical activity.
Results: Findings from the systematic review and meta-analysis indicated moderate-to-large effects of BT on static and dynamic balance performance in youth (static: weighted mean standardized mean differences [SMDwm] = 0.71; dynamic: SMDwm = 1.03). In adolescents, training-induced effects were moderate and large for static (SMDwm = 0.61) and dynamic (SMDwm = 0.86) balance performance, respectively. Independently (i.e. modality-specific) calculated dose-response relationships identified a training period of 12 weeks, a frequency of two training sessions per week, a total of 24-36 sessions, a duration of 4-15 minutes, and a total duration of 31-60 minutes as the training modalities with the largest effect on overall balance performance in adolescents. However, the implemented meta-regression indicated that none of these training modalities (R² = 0%) could predict the observed performance-increasing effects of BT.
Results from the first cross-sectional study revealed that a gradually increasing level of BTD caused increases in postural sway (p < 0.001; d = 6.36), higher leg muscle activity (p < 0.001; 2.19 < d < 4.88), and higher leg muscle coactivation (p < 0.001; 1.32 < d < 1.41). Increases in postural sway and leg muscle activity were mainly observed during low and high levels of task difficulty during continuous performance of the respective balance task. Results from the second cross-sectional study indicated frequency-specific increases/decreases in cortical activity of different brain areas (p < 0.005; 0.92 < d < 1.80) as a function of BTD. Higher cortical activity within the theta frequency band in the frontal and central right brain areas was observed with increasing postural demands. Concomitantly, activity in the alpha-2 frequency band was attenuated in parietal brain areas.
Conclusion: BT is an effective method to increase static and dynamic balance performance and, thus, improve postural control in healthy youth populations. However, none of the reported training modalities (i.e., training period, frequency, volume) could explain the effects on balance performance. Furthermore, a gradually increasing level of task difficulty resulted in increases in postural sway, leg muscle activity, and coactivation. Frequency and brain area-specific increases/decreases in cortical activity emphasize the involvement of frontoparietal brain areas in regulatory processes of postural control dependent on BTD. Overall, it appears that increasing BTD can be easily accomplished by narrowing the base of support. Since valid methods to assess and quantify BT intensity do not exist, increasing BTD appears to be a very useful candidate to implement and monitor progression in BT programs in healthy adolescents.