Bradley Bowser

Movement variability during single leg jump landings in individuals with and without chronic ankle instability

BACKGROUND Repeated episodes of giving way at the ankle may be related to alterations in movement variability. METHODS Eighty-eight recreational athletes (39 males, 49 females) were placed in 4 groups: mechanically unstable, functionally unstable, copers, and controls based on ankle injury history, episodes of giving way, and joint laxity. Lower extremity kinematics and ground reaction forces were measured during single leg landings from a 50% maximum vertical jump in the anterior, lateral, and medial directions. Ensemble curves of 10 trials were averaged and coefficients of variation were identified for ankle, knee, hip, and trunk motion in 3 planes. A log(e) (ln) transformation was performed on the data. Mixed model analyses of variance (ANOVAs) with Tukey post-hoc tests were utilized with Bonferroni corrections to α ≤ 0.008. FINDINGS At the knee, controls were more variable than functionally unstable and copers for knee rotation before initial contact, and were more variable during stance than functionally unstable in knee rotation (P ≤ 0.008). Interactions during stance revealed controls were more variable than functionally unstable in lateral jumps for hip flexion, and than mechanically and functionally unstable in hip abduction in the anterior direction (P≤0.008). Controls were more variable than all other groups in hip flexion and than mechanically unstable in hip abduction (P ≤0 .008). INTERPRETATION Individuals with ankle instability demonstrated less variability at the hip and knee compared to controls during single leg jump landings. Inability to effectively utilize proximal joints to perform landing strategies may influence episodes of instability.

Dynamic Postural Stability in Females with Chronic Ankle Instability

PURPOSE To determine whether females with chronic ankle instability (CAI) demonstrated decreased dynamic postural stability compared with controls in the anterior, lateral, and medial jump directions. METHODS Individuals with CAI (n = 24) reported a history of moderate to severe ankle sprain, two or more episodes of giving way in the past year, and decreased ankle function. The control group (n = 24) reported one or no previous mild to moderate ankle sprain, no episodes of giving way, and no decrease in ankle function. Maximum vertical jump height was measured in the anterior, lateral, and medial directions. Participants jumped at 50% maximum height in the three directions, landed on the involved limb, and balanced for 10 s. Ground reaction forces were collected at 1200 Hz and filtered. Stability indices for anterior-posterior, medial-lateral, and vertical and a composite index were calculated. Independent-samples t-tests compared groups on demographic data and stability indices in three jump directions, with α = 0.05. RESULTS The CAI group demonstrated significantly higher vertical (0.34 ± 0.04 vs 0.32 ± 0.03) and composite stability index scores (0.36 ± 0.04 vs 0.34 ± 0.03) in the anterior jump direction compared with the control group. Lateral jumps had similar results for vertical (0.33 ± 0.05 vs 0.30 ± 0.03) and composite scores (0.36 ± 0.04 vs 0.33 ± 0.03). CONCLUSIONS Females with CAI demonstrated stability deficits compared with control group in the anterior and lateral jump directions. Multiple jump directions may be necessary to adequately capture dynamic stability measures.

Greater vertical impact loading in female runners with medically diagnosed injuries: a prospective investigation

Background Running has been critical to human survival. Therefore, the high rate of injuries experienced by modern day runners is puzzling. Landing on the heel, as most modern day shod runners do, results in a distinct vertical impact force that has been shown to be associated with running-related injuries. However, these injury studies were retrospective in nature and do not establish cause and effect. Objective To determine whether runners with high impacts are at greater risk for developing medically diagnosed injuries. Methods 249 female runners underwent a gait analysis to measure vertical instantaneous loading rate, vertical average loading rate (VALR), vertical impact peak (VIP) and peak vertical force. Participants then recorded their mileage and any running-related injuries monthly in a web-based, database programme. Variables were first compared between the entire injured (INJ; n=144) and uninjured (n=105) groups. However, the focus of this study was on those injured runners seeking medical attention (n=103) and those who had never injured (n=21). Results There were no differences between the entire group of injured and uninjured groups. However, all impact-related variables were higher in those with medically diagnosed injuries compared with those who had never been injured. (effect size (ES) 0.4–0.59). When VALR was >66.0 body weight (BW)/s, the odds of being DX_INJ were 2.72 (95% CI 1.0 to 7.4). Impact loading was associated with bony and soft-tissue injuries. Conclusions Vertical average loading rate was lower in female runners classified as ‘never injured’ compared with those who had been injured and sought medical attention.

Sit-to-stand biomechanics of individuals with multiple sclerosis.

BACKGROUND It is unclear how people with multiple sclerosis, who often have compromised strength and balance, compare to healthy controls during sit-to-stand movements. The purpose of this study was to compare sit-to-stand biomechanics among three groups: people with multiple sclerosis who exhibit leg weakness, people with multiple sclerosis who have comparable strength to controls, and healthy controls. METHODS Twenty-one individuals with multiple sclerosis (n=10 exhibiting leg weakness: n=11 exhibiting comparable strength to controls), and 12 controls performed five sit-to-stand trials while kinematic data and ground reaction forces were captured. ANOVAs followed by Tukeys post-hoc tests (α=0.05) were used to determine group and limb differences for leg strength, movement time, and sagittal-plane joint kinematics and kinetics. FINDINGS Persons with multiple sclerosis exhibiting leg weakness displayed decreased leg strength, greater trunk flexion, faster trunk flexion velocity and decreased knee extensor power compared to the other two groups (p<0.05; d≥0.87), and slower rise times compared to controls(p<0.03; d≥1.17). No differences were found between controls and the multiple sclerosis-comparable strength group. Across all 3 groups, leg strength was moderately correlated with trunk kinematics and knee extensor velocities, moments and powers of the sit-to-stand (p≤0.05). INTERPRETATION Participants with multiple sclerosis exhibiting leg weakness took longer to stand and appeared to use a trunk-flexion movement strategy when performing the sit-to-stand. The majority of group differences appear to be a result of leg extension weakness. Treatment that includes leg strengthening may be necessary to improve sit-to-stand performance for people with multiple sclerosis.

Effect of Footwear on Dynamic Stability during Single-leg Jump Landings

Barefoot and minimal footwear running has led to greater interest in the biomechanical effects of different types of footwear. The effect of running footwear on dynamic stability is not well understood. The purpose of this study was to compare dynamic stability and impact loading across 3 footwear conditions; barefoot, minimal footwear and standard running shoes. 25 injury free runners (21 male, 4 female) completed 5 single-leg jump landings in each footwear condition. Dynamic stability was assessed using the dynamic postural stability index and its directional components (mediolateral, anteroposterior, vertical). Peak vertical ground reaction force and vertical loadrates were also compared across footwear conditions. Dynamic stability was dependent on footwear type for all stability indices (ANOVA, p<0.05). Post-hoc tests showed dynamic stability was greater when barefoot than in running shoes for each stability index (p<0.02) and greater than minimal footwear for the anteroposterior stability index (p<0.01). Peak vertical force and average loadrates were both dependent on footwear (p≤0.05). Dynamic stability, peak vertical force, and average loadrates during single-leg jump landings appear to be affected by footwear type. The results suggest greater dynamic stability and lower impact loading when landing barefoot or in minimal footwear.