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Evidence-based prescriptions for balance training in youth have recently been established. However, there is currently no standardized means available to assess and quantify balance task difficulty (BTD). Therefore, the objectives of this study were to examine the effects of graded BTD on postural sway, lower limb muscle activity and coactivation in adolescents. Thirteen healthy high-school students aged 16 to 17 volunteered to participate in this cross-sectional study. Testing involved participants to stand on a commercially available balance board with an adjustable pivot that allowed six levels of increasing task difficulty. Postural sway [i.e., total center of pressure (CoP) displacements] and lower limb muscle activity were recorded simultaneously during each trial. Surface electromyography (EMG) was applied in muscles encompassing the ankle (m. tibialis anterior, medial gastrocnemius, peroneus longus) and knee joint (m. vastus medialis, biceps femoris). The coactivation index (CAI) was calculated for ankle and thigh muscles. Repeated measures analyses of variance revealed a significant main effect of BTD with increasing task difficulty for postural sway (p < 0.001; d = 6.36), muscle activity (p < 0.001; 2.19 < d < 4.88), and CAI (p < 0.001; 1.32 < d < 1.41). Multiple regression analyses showed that m. tibialis anterior activity best explained overall CoP displacements with 32.5% explained variance (p < 0.001). The observed increases in postural sway, lower limb muscle activity, and coactivation indicate increasing postural demands while standing on the balance board. Thus, the examined board can be implemented in balance training to progressively increase BTD in healthy adolescents.
Background
In the past, plyometric training (PT) has been predominantly performed on stable surfaces. The purpose of this pilot study was to examine effects of a 7-week lower body PT on stable vs. unstable surfaces. This type of exercise condition may be denoted as metastable equilibrium.
Methods
Thirty-three physically active male sport science students (age: 24.1 ± 3.8 years) were randomly assigned to a PT group (n = 13) exercising on stable (STAB) and a PT group (n = 20) on unstable surfaces (INST). Both groups trained countermovement jumps, drop jumps, and practiced a hurdle jump course. In addition, high bar squats were performed. Physical fitness tests on stable surfaces (hexagonal obstacle test, countermovement jump, hurdle drop jump, left-right hop, dynamic and static balance tests, and leg extension strength) were used to examine the training effects.
Results
Significant main effects of time (ANOVA) were found for the countermovement jump, hurdle drop jump, hexagonal test, dynamic balance, and leg extension strength. A significant interaction of time and training mode was detected for the countermovement jump in favor of the INST group. No significant improvements were evident for either group in the left-right hop and in the static balance test.
Conclusions
These results show that lower body PT on unstable surfaces is a safe and efficient way to improve physical performance on stable surfaces.
Background and objectives: Age-related losses of lower extremity muscle strength/power and deficits in static and particularly dynamic balance are associated with impaired functional performance and the occurrence of falls. It has been shown that balance and resistance training have the potential to improve balance and muscle strength in healthy older adults. However, it is still open to debate how the effectiveness of balance and resistance training in older adults is influenced by different factors. This includes the role of trunk muscle strength, the comprehensive effects of combined balance and resistance training, and the role of exercise supervision. Therefore, the primary objectives of this doctoral thesis are to investigate the relationship between trunk muscle strength and balance performance and to examine the effects of an expert-based balance and resistance training protocol on various measures of balance and lower extremity muscle strength/power in older adults. Furthermore, the impact of supervised versus unsupervised balance and/or resistance training interventions in the elderly will be evaluated.
Methods: Healthy older adults aged 63-80 years were included in a cross-sectional study, a longitudinal study, and a meta-analysis (range group means meta-analysis: 65.3-81.1 years) registering balance and muscle strength/power performance. Different measures of balance (i.e., static/dynamic, proactive, reactive) were examined using clinical (e.g., Romberg test) and instrumented tests (e.g., 10 meter walking test on a sensor-equipped walkway). Isometric strength of the trunk muscles was assessed using instrumented trunk muscle strength apparatus and lower extremity dynamic muscle strength/power was examined using clinical tests (e.g., Chair Stand Test). Further, a combined balance and resistance training protocol was applied to examine training-induced effects on balance and muscle strength/power as well as the role of supervision in older adults.
Results: Findings revealed that measures of trunk muscle strength and static steady-state balance as well as specific measures of dynamic steady-state balance were significantly associated in the elderly (0.42 ≤ r ≤ 0.57). Combined balance and resistance training significantly improved older adults' static/dynamic steady-state (e.g., Romberg test; habitual gait speed), pro-active (e.g., Timed Up and Go Test), and reactive balance (e.g., Push and Release Test) as well as muscle strength/power (e.g., Chair Stand Test) (0.62 ≤ Cohen’s d ≤ 2.86; all p < 0.05). Supervised compared to unsupervised balance and/or resistance training was superior in enhancing older adults' balance and muscle strength/power performance regarding all observed outcome categories [longitudinal study: effects for the supervised group 0.26 ≤ d ≤ 2.86, effects for the unsupervised group 0.06 ≤ d ≤ 2.30; meta-analysis: all between-subject standardized mean differences (SMDbs) in favor of the supervised training programs 0.24-0.53]. The meta-analysis additionally showed larger effects in favor of supervised interventions when compared to completely unsupervised interventions (0.28 ≤ SMDbs ≤ 1.24). These effects in favor of the supervised programs faded when compared with studies that implemented a small amount of supervised sessions in their unsupervised interventions (−0.06 ≤ SMDbs ≤ 0.41).
Conclusions: Trunk muscle strength is associated with steady-state balance performance and may therefore be integrated in fall-preventive exercise interventions for older adults. The examined positive effects on a large number of important intrinsic fall risk factors (e.g., balance deficits, muscle weakness) imply that particularly the combination of balance and resistance training appears to be a feasible and effective exercise intervention for fall prevention. Owing to the beneficial effects of supervised compared to unsupervised interventions, supervised sessions should be integrated in fall-preventive balance and/or resistance training programs for older adults.