Michael T. Gross

Balance measures for discriminating between functionally unstable and stable ankles.

PURPOSE To identify force plate measures that discriminate between ankles with functional instability and stable ankles and to determine the most accurate force plate measure for enabling this distinction. METHODS Twenty-two subjects (177 +/- 10 cm, 77 +/- 16 kg, 21 +/- 2 yr) without a history of ankle injury and 22 subjects (177 +/- 10 cm, 77 +/- 16 kg, 20 +/- 2 yr) with functional ankle instability (FAI) performed a single-leg static balance test and a single-leg jump-landing dynamic balance test. Static force plate measures analyzed in both anterior/posterior (A/P) and medial/lateral (M/L) directions included the following: ground reaction force (GRF) SD; center-of-pressure (COP) SD; mean, maximum, and total COP excursion; and mean and maximum COP velocity. COP area was also analyzed for static balance. A/P and M/L time to stabilization quantified dynamic balance. Greater values of force plate measures indicated impaired balance. A stepwise discriminant function analysis examined group differences, group classification, and accuracy of force plate measures for discriminating between ankle groups. RESULTS The FAI group had greater values than the stable ankle group for A/P GRF SD (P = 0.027), M/L GRF SD (P = 0.006), M/L COP SD (P = 0.046), A/P mean COP velocity (P = 0.015), M/L mean COP velocity (P = 0.016), A/P maximum COP velocity (P = 0.037), M/L mean COP excursion (P = 0.014), M/L total COP excursion (P = 0.016), A/P time to stabilization (P = 0.011), and M/L time to stabilization (P = 0.040). M/L GRF SD and A/P time to stabilization had the greatest accuracy scores of 0.73 and 0.72, respectively. CONCLUSION Although 10 measures identified group differences, M/L GRF SD and A/P time to stabilization were the most accurate in discriminating between ankle groups. These results provide evidence for choosing these GRF measures for evaluating static and dynamic balance deficits associated with FAI.

A stochastic biomechanical model for risk and risk factors of non-contact anterior cruciate ligament injuries

Gender has been identified as a risk factor for non-contact anterior cruciate ligament (ACL) injuries. Although some possible biomechanical risk factors underlying the gender differences in the risk for non-contact ACL injuries have been identified, they have not been quantitatively confirmed yet because of the descriptive nature of the traditional epidemiological methods. The purpose of this study was to validate a stochastic biomechanical model for the risk and risk factors for non-contact ACL injuries. An ACL loading model was developed and instrumented to a Monte Carlo simulation to estimate the ACL injury rate for a stop-jump task in which non-contact ACL injuries frequently occur. Density distributions of independent variables of the ACL loading model were determined from in-vivo data of 40 male and 40 female athletes when performing the stop-jump task. A non-contact ACL injury was defined as the peak ACL loading being greater than 2250N for males and 1800N for females. The female-to-male non-contact ACL injury rate ratio was determined as the ratio of the probability of ACL ruptures of females to that of males. The female-to-male non-contact ACL injury rate ratio predicted by the stochastic biomechanical model was 4.96 (SD=0.22). The predicted knee flexion angle at the peak ACL loading in the simulated injury trials was 22.0 (SD=8.0) degrees for males and 24.9 (SD=5.6) degrees for females. The stochastic biomechanical model for non-contact ACL injuries developed in the present study accurately predicted the female-to-male injury rate ratio for non-contact ACL injuries and one of the kinematic characteristics of the injury.

The Effects of 2 Landing Techniques on Knee Kinematics, Kinetics, and Performance During Stop-Jump and Side-Cutting Tasks

Background: Anterior cruciate ligament injuries (ACL) commonly occur during jump landing and cutting tasks. Attempts to land softly and land with greater knee flexion are associated with decreased ACL loading. However, their effects on performance are unclear. Hypothesis: Attempts to land softly will decrease peak posterior ground-reaction force (PPGRF) and knee extension moment at PPGRF compared with a natural landing during stop-jump and side-cutting tasks. Attempts to land with greater knee flexion at initial ground contact will increase knee flexion at PPGRF compared with a natural landing during both tasks. In addition, both landing techniques will increase stance time and lower extremity mechanical work as well as decrease jump height and movement speed compared with a natural landing during both tasks. Study Design: Controlled laboratory study. Methods: A total of 18 male and 18 female recreational athletes participated in the study. Three-dimensional kinematic and kinetic data were collected during stop-jump and side-cutting tasks under 3 conditions: natural landing, soft landing, and landing with greater knee flexion at initial ground contact. Results: Attempts to land softly decreased PPGRF and knee extension moment at PPGRF compared with a natural landing during stop-jump tasks. Attempts to land softly decreased PPGRF compared with a natural landing during side-cutting tasks. Attempts to land with greater knee flexion at initial ground contact increased knee flexion angle at PPGRF compared with a natural landing during both stop-jump and side-cutting tasks. Attempts to land softly and land with greater knee flexion at initial ground contact increased stance time and lower extremity mechanical work, as well as decreased jump height and movement speed during both stop-jump and side-cutting tasks. Conclusion: Although landing softly and landing with greater knee flexion at initial ground contact may reduce ACL loading during stop-jump and side-cutting tasks, the performance of these tasks decreased, as indicated by increased stance time and mechanical work as well as decreased jump height and movement speed. Clinical Relevance: Training effects tested in laboratory environments with the focus on reducing ACL loading may be reduced in actual competition environments when the focus is on athlete performance. The effects of training programs for ACL injury prevention on lower extremity biomechanics in athletic tasks may need to be evaluated in laboratories as well as in actual competitions.

Effects of Foot Orthoses on Balance in Older Adults

STUDY DESIGN Controlled laboratory study using a single-cohort design. OBJECTIVES To determine if balance in older adults could be significantly improved with foot-orthotic intervention. BACKGROUND Poor balance has been associated with risk for falls. Limited evidence exists indicating that foot orthoses influence balance. METHODS Thirteen individuals older than 65 years, who reported at least 1 unexplained fall during the past year and demonstrated poor balance, participated in the study. Subjects were tested for 1-leg stance, tandem stance, tandem gait, and alternating step tests during the first (SCREEN) and second (PRE) sessions prior to foot-orthotic intervention. Tests were repeated during the second testing session immediately after custom foot-orthotic intervention (POST) and 2 weeks following foot-orthotic use (FU). SCREEN and PRE measures were compared for stability using absolute difference computations and the Friedman rank test. PRE, POST, and FU data were analyzed using the Friedman rank test (α = .05), with Bonferroni correction for multiple post hoc comparisons. RESULTS Each balance measure was statistically equivalent between the SCREEN and PRE measurements. One-leg stance times for PRE were significantly less than POST (P = .002) and FU (P = .013) measurements. Tandem stance times for PRE were significantly less than POST (P = .013) and FU (P = .013) measurements. Steps taken for the tandem gait test during the PRE measurements were significantly fewer than steps taken for the FU test (P = .007). Steps taken during the alternating step test for the PRE test were significantly fewer than steps taken during the POST (P = .002) and FU (P =.001) tests. POST and FU measurements were not significantly different for any of the 4 outcome measures. CONCLUSIONS The results provide preliminary evidence that foot orthoses can effect improvement in balance measures for older adults.

The repeatability of scapular rotations across three planes of humeral elevation

Measurement of scapular kinematics is an important component in the assessment of shoulder function; however, repeatability of these measurements has not been established. The purpose of this study, therefore, was to determine the repeatability of scapular rotation measures for different humeral elevation planes between trials, sessions, and days. Three-dimensional scapular rotations were collected using an electromagnetic tracking system in three planes of humeral elevation. Coefficient of multiple correlation (CMC) values were calculated between trials, sessions, and days for curves of scapular rotations. CMC values were compared with repeated measures analysis of variance (ANOVAs) and Tukeys post-hoc procedures. Tests of simple main effects were performed for significant interaction effects. Our results suggest that scapular rotation measures are repeatable between trials within the same testing session, but less repeatable between testing sessions and days. Sagittal plane elevation consistently yielded the highest CMC values for all scapular rotations. These results suggest sagittal plane elevation should be considered to evaluate differences in scapular rotations.

A Comparison of Negative Joint Work and Vertical Ground Reaction Force Loading Rates in Chi Runners and Rearfoot-Striking Runners

STUDY DESIGN Observational. OBJECTIVES To compare lower extremity negative joint work and vertical ground reaction force loading rates in rearfoot-striking (RS) and Chi runners. BACKGROUND Alternative running styles such as Chi running have become a popular alternative to RS running. Proponents assert that this running style reduces knee joint loading and ground reaction force loading rates. METHODS Twenty-two RS and 12 Chi runners ran for 5 minutes at a self-selected speed on an instrumented treadmill. A 3-D motion analysis system was used to obtain kinematic data. Average vertical ground reaction force loading rate and negative work of the ankle dorsiflexors, ankle plantar flexors, and knee extensors were computed during the stance phase. Groups were compared using a 1-way analysis of covariance for each variable, with running speed and age as covariates. RESULTS On average, RS runners demonstrated greater knee extensor negative work (RS, -0.332 J/body height × body weight [BH·BW]; Chi, -0.144 J/BH·BW; P<.001), whereas Chi runners demonstrated more ankle plantar flexor negative work (Chi, -0.467 J/BH·BW; RS, -0.315 J/BH·BW; P<.001). RS runners demonstrated greater average vertical ground reaction force loading rates than Chi runners (RS, 68.6 BW/s; Chi, 43.1 BW/s; P<.001). CONCLUSION Chi running may reduce vertical loading rates and knee extensor work, but may increase work of the ankle plantar flexors.

Comparison of Gluteus Medius Muscle Electromyographic Activity During Forward and Lateral Step-up Exercises in Older Adults

Background Step-up exercises often are suggested for strengthening the hip abductor muscles and improving balance in older adults. Little is known, however, about whether the forward or lateral version of these exercises is best for activating the hip abductor muscles. Objective The purpose of this study was to examine the electromyographic (EMG) amplitude of the gluteus medius (GM) muscles bilaterally during forward and lateral step-up exercises. Design The study design involved single-occasion repeated measures. Methods Twenty-seven community-dwelling adults (7 men and 20 women) with a mean (SD) age of 79.4 (8.0) years performed forward and lateral step-up exercises while the surface EMG activity of the GM muscles was recorded bilaterally. Pressure switches and dual forceplates were used to identify the ascent and descent phases. Subjects were instructed to lead with the right lower extremity during ascent and the left lower extremity during descent. Differences in normalized root-mean-square EMG amplitudes with exercise direction (forward versus lateral) and phase (ascent versus descent) were examined by use of separate repeated-measures analyses of variance for the right and left lower extremities. The alpha level was set at .05. Results Gluteus medius muscle EMG activity was significantly greater for lateral than for forward step-up exercises for the left lower extremity during the ascent phase and for both lower extremities during the descent phase. In addition, right GM muscle EMG activity was significantly greater during ascent than during descent for both exercise directions. Limitations Study limitations include use of a convenience sample and collection of limited information about participants. Conclusions Step-up exercises are effective in activating the GM muscle, with lateral step-up exercises requiring greater GM muscle activation than forward step-up exercises. Further study is needed to determine whether exercise programs for hip abductor muscle strengthening in older adults should preferentially include lateral over forward step-up exercises.

Lower Extremity Biomechanics and Self-Reported Foot-Strike Patterns Among Runners in Traditional and Minimalist Shoes

CONTEXT The injury incidence rate among runners is approximately 50%. Some individuals have advocated using an anterior-foot-strike pattern to reduce ground reaction forces and injury rates that they attribute to a rear-foot-strike pattern. The proportion of minimalist shoe wearers who adopt an anterior-foot-strike pattern remains unclear. OBJECTIVE To evaluate the accuracy of self-reported foot-strike patterns, compare negative ankle- and knee-joint angular work among runners using different foot-strike patterns and wearing traditional or minimalist shoes, and describe average vertical-loading rates. DESIGN Descriptive laboratory study. SETTING Research laboratory. PATIENTS OR OTHER PARTICIPANTS A total of 60 healthy volunteers (37 men, 23 women; age = 34.9 ± 8.9 years, height = 1.74 ± 0.08 m, mass = 70.9 ± 13.4 kg) with more than 6 months of experience wearing traditional or minimalist shoes were instructed to classify their foot-strike patterns. INTERVENTION(S) Participants ran in their preferred shoes on an instrumented treadmill with 3-dimensional motion capture. MAIN OUTCOME MEASURE(S) Self-reported foot-strike patterns were compared with 2-dimensional video assessments. Runners were classified into 3 groups based on video assessment: traditional-shoe rear-foot strikers (TSR; n = 22), minimalist-shoe anterior-foot strikers (MSA; n = 21), and minimalist-shoe rear-foot strikers (MSR; n = 17). Ankle and knee negative angular work and average vertical-loading rates during stance phase were compared among groups. RESULTS Only 41 (68.3%) runners reported foot-strike patterns that agreed with the video assessment (κ = 0.42, P < .001). The TSR runners demonstrated greater ankle-dorsiflexion and knee-extension negative work than MSA and MSR runners (P < .05). The MSA (P < .001) and MSR (P = .01) runners demonstrated greater ankle plantar-flexion negative work than TSR runners. The MSR runners demonstrated a greater average vertical-loading rate than MSA and TSR runners (P < .001). CONCLUSIONS Runners often cannot report their foot-strike patterns accurately and may not automatically adopt an anterior-foot-strike pattern after transitioning to minimalist running shoes.

Ergonomics-related risk identification and pain analysis for farmers involved in rice field preparation

BACKGROUND A previous ergonomic screening of rice field preparation revealed farmer exposure to high risks of musculoskeletal disorders at the shoulders, hands, wrists and back. The screening method was not applied to muddy soil farming in which analysts could not observe farmer legs and feet. This study analyzed farmer pain in all stages of field preparation. OBJECTIVE To examine the relationship of farmer experience and demographics to perceptions of pain and to identify body areas exposed to ergonomics risks, unknown to farmers. Results were expected to support interventions and guidelines for famers on physical behaviors towards minimizing risk of injury as well as validation of the screening approach. METHODS Comparison of analyst screening results and farmer pain ratings using self-ratings and interviews. RESULTS Farmer experience and age were significantly correlated with occurrence of pain and cramping. Less experienced farmers reported less pain in high-risk body parts (e.g., neck and lower back). More experienced farmers reported more pain in the legs, as compared with analyst risk ratings. CONCLUSIONS Results demonstrated less experienced farmers to be unaware of critical areas of exposure to ergonomics risks. Correlation of farmer ratings of pain with analyst risk assessments support validity of the screening method for hazard identification and control.

Relationship between Multiple Predictor Variables and Normal Biodex Eversion-Inversion Peak Torque and Angular Work

Normative data should help in the development of treatment goals. The purpose of this study was to generate predictive models relating isokinetic ankle testing performance to anthropometric and demographic variables. The subjects were 44 healthy females (age = 40.48, s = 11.98) and 43 healthy males (age = 39.83, s = 10.31) between the ages of 19 and 62. For each subject the investigators measured concentric peak torque and angular work at 60 and 120 degrees /sec for Biodex eversion and inversion. Stepwise regression analyses were used to examine the relationship between each isokinetic variable and the following predictor variables: age, side of lower extremity dominance, height, weight, percentage of body fat, leg girth, and shoe size. Separate analyses were conducted for females and males. The results indicate a significant relationship (p < 0.001) between multiple variable models and the isokinetic performance variables. The magnitude of the relationships may be explained, in part, by the restricted range of Biodex eversion and inversion measurements of peak torque and angular work. The models generated in this study can be used to establish muscle performance goals for patient rehabilitation programs. J Orthop Sports Phys Ther 1992;15(1):24-31.