The effects of leg preference and leg dominance on static and dynamic balance performance in highly-trained tennis players

In this study, 90 (51 males, 39 females) tennis players performed single-leg quiet stance and single-leg landing tasks. For the static standing task, center-of pressure (CoP) velocities, amplitudes, frequency and area were calculated. For the landing tasks, time to stabilization as well as dynamic postural stability index were considered. The analysis of differences between the legs was done based on two methods for a priori determination of leg preference, one based on the preference of kicking a ball and one based on the preference for single-leg jumping. An additional analysis was done based on the leg dominance (determined post hoc), based on the observed performance of the tasks. In case of the classification based on kicking a ball, there was a statistically significantly lower CoP anterior-posterior velocity and anterior-posterior amplitude in static balance task (p ≤ 0.017; 0.17 ≤ d ≤ 0.28) for the preferred leg. The CoP frequency was higher in the preferred leg for both directions (p ≤ 0.002; 0.10 ≤ d ≤ 0.22). For the landing task, CoP medial-lateral time to stabilization was statistically significantly shorter for the preferred leg (0.28 ± 0.38 s) compared to the non-preferred leg (0.47 ± 0.60 s) (p = 0.012; d = 0.38). There were no differences between the legs for the landing task. Moreover, there were no differences between the legs when we used the preference based on jumping for either of the tasks (d ≤ 0.14). The differences between legs in terms of observed dominance were larger than the differences based on the preference, which stresses the need for clear distinction of limb preference and limb dominance in research and practice. Regarding the effect of leg preference, small differences in static balance may exist between the legs (when the preference is based on kicking a ball).

The Effect of External Focus Attention Exercise On the Kinetic Risk Factors Associated With ACL Injury

Background and Aims One of the most common and dangerous injuries in sports is an Anterior Cruciate Ligament (ACL) injury. Today, despite the ACL injury prevention programs, the prevalence of this injury remains high. Most of the instructions used in injury prevention programs are based on internal focus, while studies have shown that using external focus can improve performance in individuals. The purpose of this study was to investigate the effect of focus of attention on eight weeks of anterior cruciate ligament injury prevention training on landing skill kinetic variables in soccer players. Methods The current methodology included 35 players from 3 premier league teams in Tehran province. The teams were randomly divided into three groups of Prevent injury and Enhance Performance (PEP) exercises based on the External Focus (EF) (12 people), Internal Focus (IF) (12 people), and control group (11 people). In the pretest of ground reaction force, rate of loading, and time to stabilization during landing skill. The training groups performed pep injury prevention exercises for eight weeks and related instructions instead of warm-up exercises. Control group players were performing the regular activities. ANOVA with repeated measures and one-way ANOVA and Tukey post hoc tests were used to evaluate changes Results The test results showed significant changes in vertical, anterior-posterior ground reaction force and rate of loading in the external focus group (P≤0.05). But there was no critical difference in time to stabilization and internal-external ground reaction force. Conclusion According to the results, external focus instruction has positive effects on kinetic components. Therefore, it is recommended that exercises based on these instructions be used to reduce the risk of ACL injury and to repair this injury.

Prophylactic ankle supports effects on time to stabilization, perceived stability and ground reaction force during lateral landing in female collegiate athletes with chronic ankle instability

Background This study was designed to investigate effects of Kinesiotape (KT) with closed basket weave method and lace-up braces (LB) on the vertical time to stabilization, peak vertical ground reaction force (PvGRF), and time to PvGRF as well as perceived stability during lateral landing of participants with chronic ankle instability before and after fatigue. Methods Thirty female college athletes with chronic ankle instability of three conditions (control, KT, and LB) performed lateral landing from a 30 cm high step on the plantar pressure platform pre and post fatigue. Results The pre-test findings on the rearfoot, of LB indicated negatively increased the PvGRF force (F2,58=3.63, P = 0.04) and decreased the time to PvGRF (F2,58=4.67, P = 0.01). The Bonferroni post-hoc testing revealed LB condition increased the PvGRF than the control (P = 0.002) and KT (P = 0.038). Also, the post-hoc testing showed LB condition decreased the time to PvGRF force than the control (P = 0.05) and KT (P = 0.01). The LB negatively prolonged vertical time to stabilization in the forefoot (F2,58=6.74, P = 0.002) and rearfoot (F2,58=6.13, P = 0.004) after fatigue. The post-hoc testing revealed LB condition generated a slower vertical time to stabilization than the control and KT conditions (P ≤ 0.05). The use of KT had no positive effects as elevated the PvGRF in the forefoot post fatigue (F2,58=7.11, P = 0.002). The post-hoc test uncovered that KT augmented the PvGRF than control (P = 0.01) and LB (P < 0.001). On the other hand, using KT had psychological effects at pre-fatigue which resulting significantly greater in perceived stability compared to other conditions (F2,58=9.65, P < 0.001). The post-hoc test showed that using KT increased perceived stability than LB (P = 0.004) and control (P < 0.001). Moreover, perceived stability improved significantly in KT and LB compared to the control condition at the post-fatigue (P ≤ 0.001). Conclusions Despite the positive psychological impact of the prophylactic ankle supports, there were no positive effect on the vertical time to stabilization, PvGRF, and time to PvGRF. Further studies are needed to distinguish the psychological and actual effects of prophylactic ankle supports on athletes with chronic ankle instability.

Effect of aeration on fresh and aged municipal solid waste

Under the anaerobic conditions of conventional sanitary landfill, entombed municipal solid waste (MSW) is slow to stabilize necessitating long-term monitoring and pollution control. Although anaerobic conditions can provide revenue through energy generation, aerobic stabilization may offer several advantages including reduced fugitive greenhouse gas emissions, accelerated landfill stabilization, and increased landfill airspace recovery. Air injection was applied to bench-scale bioreactor landfills in order to determine the potential for active aeration to accelerate municipal solid waste stabilization and settlement in both new and pre-existing landfills. Fresh and aged wastes were used to represent newly constructed and existing landfill matrices over 130 days. In the fresh MSW bioreactors, aeration reduced the time to stabilization of leachate pH by 44%, TSS by 25%, TDS by 54%, BOD5 by 38% and COD by 59%. Ammonia concentrations stabilized after 129 days of aeration, but remained problematic in the anaerobic bioreactors at the study conclusion. Final leachate concentrations were consistently lower in the aerobic bioreactors than in their anaerobic counterparts. Physical settlement also improved, resulting in a 21.5% recovery of landfill airspace in the aerobic fresh waste bioreactors. Aeration had a similar but reduced influence in the aged waste bioreactors since they were near stabilization at the study inception. The results of this study indicate that aeration significantly accelerates stabilization of MSW with greatest influence on fresh waste with a high biodegradable organic fraction.

Effect of aeration on fresh and aged municipal solid waste

Under the anaerobic conditions of conventional sanitary landfill, entombed municipal solid waste (MSW) is slow to stabilize necessitating long-term monitoring and pollution control. Although anaerobic conditions can provide revenue through energy generation, aerobic stabilization may offer several advantages including reduced fugitive greenhouse gas emissions, accelerated landfill stabilization, and increased landfill airspace recovery. Air injection was applied to bench-scale bioreactor landfills in order to determine the potential for active aeration to accelerate municipal solid waste stabilization and settlement in both new and pre-existing landfills. Fresh and aged wastes were used to represent newly constructed and existing landfill matrices over 130 days. In the fresh MSW bioreactors, aeration reduced the time to stabilization of leachate pH by 44%, TSS by 25%, TDS by 54%, BOD5 by 38% and COD by 59%. Ammonia concentrations stabilized after 129 days of aeration, but remained problematic in the anaerobic bioreactors at the study conclusion. Final leachate concentrations were consistently lower in the aerobic bioreactors than in their anaerobic counterparts. Physical settlement also improved, resulting in a 21.5% recovery of landfill airspace in the aerobic fresh waste bioreactors. Aeration had a similar but reduced influence in the aged waste bioreactors since they were near stabilization at the study inception. The results of this study indicate that aeration significantly accelerates stabilization of MSW with greatest influence on fresh waste with a high biodegradable organic fraction.

Test–Retest Reliability of Single-Leg Time to Stabilization Following a Drop-Landing Task in Healthy Individuals

Context: Single-leg stability has been associated with injury risk and is a key component of many injury prevention interventions. Methods of measuring single-leg stability are varied yet often unreliable. Objective: To establish within- and between-day test–retest reliability for single-leg time to stabilization (SL-TTS) following a drop-landing maneuver of 20 cm in height among a healthy cohort. Design: Test–retest reliability study. Setting: Healthy cohort from a third-level educational institution. Participants: Nineteen (11 females and 8 males) healthy individuals. Main Outcome Measures: The SL-TTS in the vertical plane. Results: The SL-TTS showed good within-day (intraclass correlation coefficient = .715) and excellent between-day (intraclass correlation coefficient = .83) test–retest reliability. The minimal detectable change was calculated as 171.6 ms for within-day contexts and 123.8 ms for between-day contexts. Conclusions: This method of measuring SL-TTS is reliable and could be used to detect changes over time in a healthy cohort. This could be of value to clinicians in injury risk factor identification or assessing the effectiveness of single-leg stability training. However, further research is needed to investigate its reliability in pathological populations.

Bilateral Differences in Dancers' Dynamic Postural Stability During Jump Landings

Although traditional dance training aims to train dancers' legs equally, the recognized practice of predominately starting and repeating exercises on one side more than the other has led to suggestions that technique classes may cause lateral bias. Such an imbalance could lead to a greater risk of injury; however, despite this potential risk, little is known about the effects of bilateral differences on dancers' postural stability during jump landings, a key dynamic action in dance. Therefore, the aim of this study was to examine the effects of possible bilateral differences on dynamic postural stability during single-leg landing using a time-to-stabilization protocol. Thirty-two injury-free female university undergraduate dancers (19 ± 1.9 years; 164.8 ± 6.7 cm; 62.6 ± 13.6 kg) volunteered for the study. They completed a two-foot to one-foot jump over a bar onto a force platform while stabilizing as quickly as possible. The landing leg was randomly assigned, and participants completed three trials for each leg. No significant differences in dynamic postural stability between right and left legs were revealed, and poor effect size was noted (p > 0.05): MLSI: t = -.04, df = 190, p = 0.940 (CI = -.04, .04, r2 = 0); APSI: t = .65, df = 190, p = 0.519 (CI = -.06-, .12, r2 = .09); VSI: t = 1.85, df = 190, p = 0.066 (CI = -.02, .68, r2 = .27); DPSI: t = 1.88, df = 190, p = 0.061 (CI = -.02, .70, r2 = .27). The results of this study do not support the notion that dance training may cause lateral bias with its associated risk of injury. Furthermore, dancers' self-perceptions of leg dominance did not correlate with their ability to balance in single-leg landings or to absorb the ground reaction forces often associated with injury. Even when biased training exists, it may not have detrimental effects on the dancer's postural stability.

Single-Legged Hop and Single-Legged Squat Balance Performance in Recreational Athletes With a History of Concussion

Context Researchers have suggested that balance deficiencies may linger during functional activities after concussion recovery. Objective To determine whether participants with a history of concussion demonstrated dynamic balance deficits as compared with control participants during single-legged hops and single-legged squats. Design Cross-sectional study. Setting Laboratory. Patients or Other Participants A total of 15 previously concussed participants (6 men, 9 women; age = 19.7 ± 0.9 years, height = 169.2 ± 9.4 cm, mass = 66.0 ± 12.8 kg, median time since concussion = 126 days [range = 28–432 days]) were matched with 15 control participants (6 men, 9 women; age = 19.7 ± 1.6 years, height = 172.3 ± 10.8 cm, mass = 71.0 ± 10.4 kg). Intervention(s) During single-legged hops, participants jumped off a 30-cm box placed at 50% of their height behind a force plate, landed on a single limb, and attempted to achieve a stable position as quickly as possible. Participants performed single-legged squats while standing on a force plate. Main Outcome Measure(s) Time to stabilization (TTS; time for the normalized ground reaction force to stabilize after landing) was calculated during the single-legged hop, and center-of-pressure path and speed were calculated during single-legged squats. Groups were compared using analysis of covariance, controlling for average days since concussion. Results The concussion group demonstrated a longer TTS than the control group during the single-legged hop on the nondominant leg (mean difference = 0.35 seconds [95% confidence interval = 0.04, 0.64]; F2,27 = 5.69, P = .02). No TTS differences were observed for the dominant leg (F2,27 = 0.64, P = .43). No group differences were present for the single-legged squat on either leg (P ≥ .11). Conclusions Dynamic balance-control deficits after concussion may contribute to an increased musculoskeletal injury risk. Given our findings, we suggest that neuromuscular deficits currently not assessed after concussion may linger. Time to stabilization is a clinically applicable measure that has been used to distinguish patients with various pathologic conditions, such as chronic ankle instability and anterior cruciate ligament reconstruction, from healthy control participants. Whereas the single-legged squat may not sufficiently challenge balance control, future study of the more dynamic single-legged hop is needed to determine its potential diagnostic and prognostic value after concussion.

Does a six-weeks of Hip-focused exercises has the effects on Time to Stabilization after Anterior Cruciate Ligament Reconstruction?

Background: The investigation of hip muscles on knee functions has been broadly published. The deficits in proximal neuromuscular control has been identified as a contributor to valgus knee which is compromise to knee injuries. The aim of study was to determine the relationship between muscle strength and time taking to maintain the stability. Methods: Thirteen male underwent Anterior Cruciate Ligament Reconstruction (ACLR) participated in the six week of hip-focused exercise program. Single leg jump-landing test were performed to determine the Time to Stabilization (TTS). Concentric hip abduction-adduction and knee extension-flexion strength was evaluated muscle peak torques at 60 degree/second. Results: The study demonstrated that there was a strength improvement on both hip and knee muscles. Moreover, the IKDC score was significantly increased (82.71±15.21 to 90.80±8.44) after completed the exercise. We found no correlation between muscle peak torques and TTS. However, there was a moderate relationship between hip abduction and knee extension strength (r=0.624, p =0.023). Conclusion: The main findings suggesting that rehabilitation program targets on strengthen the hip muscles demonstrate an improvement of knee functions in individual with ACLR.

Dynamic Balance Measures in Healthy and Chronic Ankle Instability Participants While Wearing Ankle Braces: Systematic Review With Meta-Analysis

Context: Ankle braces have been theorized to augment dynamic balance. Objectives: To complete a systematic review with meta-analysis of the available literature assessing the effect of ankle braces on dynamic balance in individuals with and without chronic ankle instability (CAI). Evidence Acquisition: Electronic databases (PubMed, MEDLINE, CINAHL, and SPORTDiscus) were searched from inception to October 2019 using combinations of keywords related to dynamic balance, ankle braces, Star Excursion Balance Test (SEBT), Y-Balance Test (YBT), and Time to Stabilization. Inclusion criteria required that studies examined the effects of ankle braces on dynamic balance. Studies were excluded if they evaluated other conditions besides CAI, did not access dynamic balance, or did not use an ankle brace. Methodological quality was assessed using the Physiotherapy Evidence Database scale. The level of evidence was assessed using the Strength of Recommendation Taxonomy. The magnitude of brace effects on dynamic balance was examined using Hedges g effect sizes (ESs) and 95% confidence intervals (CIs). Random-effects meta-analysis was performed to synthesize SEBT/YBT and Time to Stabilization data separately. Data Synthesis: Seven studies were included with a median Physiotherapy Evidence Database score of 60% (range 50%–60%), and 4 were classified as high quality. Overall meta-analysis indicated a weak to no effect of braces on SEBT/YBT (ES = 0.117; 95% CI, −0.080 to 0.433; P = .177) and Time to Stabilization (ES = −0.064; 95% CI, −0.211 to 0.083, P = .083). Subanalysis of SEBT/YBT measures indicated a weak negative effect in healthy participants (ES = −0.116; 95% CI, −0.209 to −0.022, P = .015) and a strong positive effect in individuals with CAI (ES = 0.777; 95% CI, 0.418 to 1.136; P < .001). Conclusion: The current literature supports a strong effect of ankle braces on the SEBT/YBT in those with CAI. However, little to no dynamic balance changes were noted in healthy participants. Future research should include consistent ankle brace types, pathologic populations, and the examination of dynamic balance changes contribution to injury risk reduction.