Impact of reduced nicotine content on behavioral economic measures of cigarette reinforcement in adolescents who smoke cigarettes.

BACKGROUND: Public health officials in the U.S. and New Zealand are considering a reduced nicotine standard for cigarettes to reduce their addictive potential. This study's aim was to evaluate the effects of nicotine reduction on the reinforcing efficacy of cigarettes in adolescents who smoke, which has implications for this policy's potential for success. METHODS: Adolescents who smoked cigarettes daily (n = 66; mean age: 18.6) participated in a randomized clinical trial assessing effects of assignment to very low nicotine content (VLNC; 0.4 mg/g nicotine) or normal nicotine content (NNC; 15.8 mg/g nicotine) cigarettes. Hypothetical cigarette purchase tasks were completed at baseline and the end of Week 3 and demand curves fit to the data. Linear regressions estimated effects of nicotine content on demand for study cigarettes at baseline and Week 3 and associations between baseline demand for cigarette consumption at Week 3. RESULTS: An extra sum of squares F-test of fitted demand curves indicated that demand (α) was more elastic among VLNC participants at baseline and Week 3 (F(2, 1016)= 35.72, p < 0.001). Adjusted linear regressions indicated demand was more elastic (ß= 1.45, p < 0.01) and maximum expenditure (Omax) lower (ß= -1.42, p-0.03) among VLNC participants at Week 3. More elastic demand for study cigarettes at baseline predicted lower consumption of cigarettes at Week 3 (p's < 0.01). CONCLUSIONS: A nicotine reduction policy may reduce the reinforcing value of combustible cigarettes among adolescents. Future work should investigate likely responses to such a policy among youth with other vulnerabilities and evaluate the potential for substitution to other nicotine containing products.

Associations Between Nicotine Knowledge and Smoking Cessation Behaviors Among US Adults Who Smoke.

INTRODUCTION: Misperceptions about nicotine's contribution to smoking-related health harms could complicate efforts to reduce the public health burden of smoking. Study goals were to describe nicotine knowledge among adults who smoke and investigate whether misperceiving nicotine as a source of health harm was associated with beneficial health behaviors, or lower uptake of using less harmful sources of nicotine to support smoking cessation attempts. METHOD: This study used longitudinal data from 9140 adults who participated in four waves of the Population Assessment of Tobacco and Health Study and were current smokers during the first wave. Logistic regressions estimated odds ratios for correct responses across six aspects of nicotine knowledge assessed in Wave 4. Longitudinal models estimated associations between misperceptions and cigarette consumption, and odds of making a quit attempt; self-reported cessation; e-cigarette use; and use of NRT or e-cigarettes to support quit attempts. RESULTS: Participants who were non-White, older, and had lower educational attainment or income tended to be least knowledgeable about nicotine. Misperceiving nicotine as harmful to health was associated with increased odds of quit attempts (AOR: 1.12, 95% CI: 1.03, 1.23), lower odds of cessation success (AOR: 0.84, 95% CI: 0.73, 0.98) and e-cigarette use (AOR: 0.79, 95% CI: 0.72, 0.86), and lower odds of using NRT (AOR: 0.84, 95% CI: 0.71, 0.99) or e-cigarettes to support quit attempts (AOR: 0.59, 95% CI: 0.49, 0.71). CONCLUSION: Harm reduction efforts may be impeded by misperceptions about nicotine. Further work should evaluate the effects of correcting such misperceptions through public education. IMPLICATIONS: This study provides longitudinal evidence that among adult smokers, misperceiving nicotine as a primary cause of smoking-related diseases may be associated with reduced cessation success and lower likelihood of using less harmful nicotine products. These misperceptions may therefore impede efforts to encourage smokers ready to quit to use evidence-based cessation support such as nicotine replacement during quit attempts and limit the success of policies designed to shift smokers to less harmful sources of nicotine. Further work should evaluate the longitudinal effects of correcting nicotine misperceptions through public education targeted toward adults who smoke.

Computational fluid dynamics modeling of Bacillus anthracis spore deposition in rabbit and human respiratory airways.

Three-dimensional computational fluid dynamics and Lagrangian particle deposition models were developed to compare the deposition of aerosolized Bacillus anthracis spores in the respiratory airways of a human with that of the rabbit, a species commonly used in the study of anthrax disease. The respiratory airway geometries for each species were derived respectively from computed tomography (CT) and µCT images. Both models encompassed airways that extended from the external nose to the lung with a total of 272 outlets in the human model and 2878 outlets in the rabbit model. All simulations of spore deposition were conducted under transient, inhalation-exhalation breathing conditions using average species-specific minute volumes. Two different exposure scenarios were modeled in the rabbit based upon experimental inhalation studies. For comparison, human simulations were conducted at the highest exposure concentration used during the rabbit experimental exposures. Results demonstrated that regional spore deposition patterns were sensitive to airway geometry and ventilation profiles. Due to the complex airway geometries in the rabbit nose, higher spore deposition efficiency was predicted in the nasal sinus compared to the human at the same air concentration of anthrax spores. In contrast, higher spore deposition was predicted in the lower conducting airways of the human compared to the rabbit lung due to differences in airway branching pattern. This information can be used to refine published and ongoing biokinetic models of inhalation anthrax spore exposures, which currently estimate deposited spore concentrations based solely upon exposure concentrations and inhaled doses that do not factor in species-specific anatomy and physiology for deposition.

Validation of the Marijuana Effect Expectancy Questionnaire-Brief.

The purpose of this study was to evaluate a brief version of the Marijuana Effect Expectancy Questionnaire (MEEQ; Schafer & Brown, 1991). The original MEEQ was reduced to 6 items (MEEQ-B). Principal component analysis (PCA) was performed and two factors were identified (positive effects and negative effects) accounting for 52.3% of the variance. Internal consistencies (0.42 to 0.60) were slightly lower than those of the original MEEQ. The negative effect expectancy scale correlated with criterion variables that assess marijuana use (p ≤ .05). This measure is a helpful tool for clinicians to use when assessing youth expectancies. Replication across different samples of adjudicated youth is recommended.

Naltrexone and cue exposure with coping and communication skills training for alcoholics: treatment process and 1-year outcomes.

BACKGROUND: Promising treatments for alcoholics include naltrexone (NTX), cue exposure combined with urge-specific coping skills training (CET), and communication skills training (CST). This study investigated the effects of combining these elements as treatment adjuncts. METHODS: A 2 x 2 design investigated the effects of CET combined with CST, as compared with an education and relaxation control treatment, during a 2-week partial hospital program (n = 165) followed by 12 weeks of NTX (50 mg/day) or placebo during aftercare (n = 128). Drinking outcomes were assessed at 3, 6, and 12 months after discharge from the partial hospital. Process measures included urge, self-efficacy (confidence about staying abstinent in risky situations), and self-reported coping skills. Medically eligible alcohol-dependent patients were recruited. RESULTS: Among those compliant with medication on at least 70% of days, those who received NTX had significantly fewer heavy drinking days and fewer drinks on days that they drank than those receiving placebo during the medication phase but not during the subsequent 9 months. CET/CST-condition patients were significantly less likely to report a relapse day and reported fewer heavy drinking days at the 6- and 12-month follow-ups than patients in the control treatment. Interactions of medication with behavioral treatments were not significant. Process measures showed that NTX resulted in lower weekly urge ratings, and those in CET/CST used more of the prescribed coping skills after treatment, reported fewer cue-elicited urges, and reported more self-efficacy in a posttest role-play test. Drinking reductions at 3, 6, and 12 months correlated with more use of coping skills, lower urge, and higher self-efficacy. CONCLUSIONS: The results suggest the probable value of keeping alcoholics on NTX for longer periods of time and the importance of increasing compliance with NTX. They also support the earlier promising effects of CET and CST as adjuncts to treatment programs for alcoholics by maintaining treatment gains over at least a year. The value of the urge-specific and general coping skills and of self-efficacy and urge constructs was demonstrated in their association with drinking outcomes.

Risks associated with alcohol-positive status among adolescents in the emergency department: a matched case-control study.

OBJECTIVE: The purpose of this study was to examine alcohol use, alcohol-related problems, other risk-taking behaviors, and parental monitoring in adolescents who tested positive for alcohol in an emergency department. STUDY DESIGN: A matched case-control design was implemented for adolescents presenting to a pediatric emergency department who were screened for alcohol use. An alcohol-positive sample (N = 150) was compared with a matched alcohol-negative sample (N = 150) for alcohol use, alcohol problems, depression, smoking, risk-taking behavior, and parental monitoring. RESULTS: The alcohol-positive group reported significantly higher drinking frequency, drinking problems, prior alcohol-related injuries, and episodes of driving after drinking and riding with a drinking driver than the alcohol-negative adolescents. The same pattern was true for depressed mood, reckless behaviors, poor grades in school, and daily smoking. The parents of alcohol-positive teens reported their teens had come home intoxicated more often than parents of alcohol-negative teens. There were no differences between parent groups in monitoring of teens. CONCLUSION: Adolescents who test positive for alcohol in an emergency department are a high-risk group who meet the criteria for indicated prevention. Screening for alcohol abuse is recommended.

Concurrent versus delayed smoking cessation treatment for persons in early alcohol recovery. A pilot study.

This pilot study investigated the efficacy of initiating a smoking cessation intervention early in inpatient treatment for alcohol dependence versus shortly after an inpatient stay. Thirty-six male smokers recruited from an inpatient substance abuse treatment program were randomly assigned to begin smoking cessation either two weeks (concurrent treatment) or six weeks (delayed treatment) after admission to the substance abuse program. Smoking cessation treatment involved three sessions of individual smoking cessation treatment plus eight weeks of transdermal nicotine replacement. Significantly fewer participants began the delayed treatment than the concurrent treatment. Few participants were smoking-abstinent at follow-up, and the timing of treatment onset did not have an impact on smoking outcome. Clinical trials with larger samples may be needed to better evaluate the efficacy of concurrent versus delayed treatment and to test the efficacy of more aggressive interventions with smokers in early alcohol recovery.

Cue exposure with coping skills training and communication skills training for alcohol dependence: 6- and 12-month outcomes.

AIMS: Cue exposure treatment (CET) has shown promise in preliminary studies with alcoholics, and Communication Skills Training (CST) has been found beneficial, especially in intensive treatment programs. The aim of the present study was to investigate the effects of CET and CST in a larger controlled study when both were added to intensive treatment programs. DESIGN AND INTERVENTIONS: A 2 x 2 design investigated the effects of CET with urge coping skills training compared to a meditation-relaxation control, and CST compared to an education control when all were added to intensive treatment programs for alcoholics. SETTING: The sites were the inpatient or partial hospital substance abuse treatment programs at a private psychiatric hospital, a state-funded residential facility and a VA medical center. PARTICIPANTS: Patients diagnosed with alcohol dependence without active psychosis were eligible. MEASUREMENTS: Participants were assessed for quantity and frequency of drinking, alcohol cue-reactivity, responses to high risk simulations and urge specific coping skills. FINDINGS: Of 100 treated patients, 86% provided 6-month and 84% provided 12-month follow-up data. Patients who received either CET or CST had fewer heavy drinking days in the first 6 months than control patients. In the second 6 months, CET continued to result in fewer heavy drinking days among lapsers and interacted with CST to decrease quantity of alcohol consumed. CST resulted in fewer alcohol-related problems reported at 12 months. CET resulted in greater reductions in urge to drink in a measure of simulated high-risk situations. CET also resulted in greater reports of use of coping strategies during the follow-up, and many of the urge-specific strategies taught in CET were associated with reduced drinking. CONCLUSIONS: Both CET and CST continue to show promise as elements of comprehensive alcohol treatment programs. Limitations and directions for future research are discussed.

A comparison of knee joint motion patterns between men and women in selected athletic tasks.

BACKGROUND: Women have higher non-contact anterior cruciate ligament injury rate than men do in sport activities. Non-contact anterior cruciate ligament injuries frequently occur in sports requiring cutting tasks. Alternated motor control strategies have identified as a potential risk factor for the non-contact anterior cruciate ligament injuries. The purpose of this study was to compare the patterns of knee kinematics and electromyographic activities in running, side-cutting, and cross-cutting between men and women recreational athletes. METHODS: Three-dimensional kinematic data of the knee and electromyographic data of selected muscles across the knee joint were collected for 11 men and 9 women recreational athletes in running, side-cutting, and cross-cutting. Regression analyses with dummy variables for comparison of knee motion patterns between men and women. RESULTS: Women tend to have less knee flexion angles, more knee valgus angles, greater quadriceps activation, and lower hamstring activation in comparison to men during the stance phase of each of the three athletic tasks. Literatures suggest these alternated knee motion patterns of women tend to increase the load on the anterior cruciate ligament. CONCLUSION: Women on average may have certain motor control strategies that may alter their knee motion patterns. Women's altered knee motion patterns may tend to increase the load on the anterior cruciate ligament in the selected athletic tasks, which may contribute to the increased anterior cruciate ligament injury rate among women. RELEVANCE: Non-contact anterior cruciate ligament injuries frequently occur in sports. Altered motor control strategies and lower extremity motion patterns are likely to play an important role in non-contact anterior cruciate ligament injuries. Non-contact anterior cruciate ligament injuries may be prevented by correcting altered motor control strategies and associated lower extremity motion patterns through certain training programs.

Predictors of compliance with naltrexone among alcoholics.

OBJECTIVE: Naltrexone has been found to be an effective adjunct to treatment to reduce the rate of drinking among alcoholics. However, adherence to the medication has been of considerable concern; the high rates of noncompliance with the medication limits the benefits that could potentially be realized from this pharmacotherapy. Knowledge of predictors of noncompliance could result in interventions targeted at these variables. METHOD: Participants were 128 alcohol-dependent patients who participated in a clinical placebo-controlled trial of naltrexone. Upon discharge from a 1- to 2-week partial hospital program, patients were randomly placed into 12 weeks of naltrexone (50 mg/day) or placebo (n = 64 per condition). Patients met with a physician and a research assistant weekly for 4 weeks then biweekly for 8 weeks. RESULTS: Compliance (number of days taking medication) was not predicted by demographic or pretreatment alcohol use variables. Number and severity of side effects in the first week, particularly nausea and fatigue, predicted early termination. Compliance was not predicted by commitment to abstinence or self-efficacy about abstinence, but was greater among patients who believed more strongly that the medication would help them stay sober. Compliance was not predicted by general level of urge to drink during the first week on medication but compliance was greater among those with a higher urge to drink in response to alcohol stimuli in the laboratory. CONCLUSIONS: Implications for approaches to increase compliance include reducing side effects and increasing patients' beliefs in the efficacy of naltrexone.

Screening adolescents for problem drinking: performance of brief screens against DSM-IV alcohol diagnoses.

OBJECTIVE: The performance of three brief screens, the CAGE, TWEAK and Alcohol Use Disorders Identification Test (AUDIT), was evaluated against a DSM-IV diagnosis of alcohol abuse or dependence in an adolescent sample. METHOD: Adolescents (13-19 years old) who presented to an emergency department for treatment of an injury, and who tested negative for blood alcohol concentration at time of admission, were administered a structured diagnostic interview and modified versions of the CAGE, TWEAK and AUDIT. RESULTS: Of the 415 adolescents for whom complete data were available, 18% met criteria for a DSM-IV alcohol use disorder according to the Diagnostic Interview Schedule for Children (version 2.3). Teens who reported alcohol use in the last year (n = 261, 58% male, 71% white) were included in analyses that compared the performance of the three screening instruments. Receiver Operating Characteristic analysis indicated that the AUDIT demonstrated the best performance across the range of its cut-scores, with optimal performance at a cut-score of 4. The TWEAK performed optimally at a cut-score of 2 and the CAGE at a cut-score of 1. CONCLUSIONS: Routine alcohol screening among adolescents seen in a hospital setting is indicated. Two important directions for future research include the identification of adolescent-specific alcohol screening items, and the validation of an adolescent-specific definition of problem drinking that addresses limitations of DSM-IV alcohol diagnoses when applied to adolescents.

The relationship between anxiety levels and outcome of cocaine abuse treatment.

Although a number of studies have examined the comorbidity of anxiety disorders and substance use disorders, much less is known about the impact of anxiety symptoms on substance use and on substance abuse treatment outcome. In the current study, we examined how self-reported anxiety levels, as measured by the Spielberger State-Trait Anxiety Inventory, were related to cocaine use variables and patterns following substance abuse treatment. There were 108 patients in substance abuse treatment who met DSM-III-R diagnostic criteria for cocaine abuse or dependence who completed an assessment battery at pretreatment, posttreatment, and 3-month follow-up. State anxiety scores significantly declined from pre- to posttreatment and remained stable into the 3-month follow-up period regardless of relapse status. Trait anxiety was correlated positively with negative consequences due to cocaine use and negatively correlated with days in treatment. State and trait anxiety both were correlated positively with the Alcohol Composite Index of the Addiction Severity Index (ASI). These findings suggest that elevated anxiety scores at pretreatment subside with time, do not require clinical management of associated anxiety symptoms, and may be a temporary by-product of experiencing negative consequences due to recent cocaine use.

Measuring nicotine dependence among youth: a review of available approaches and instruments.

This paper reviews issues and concepts related to the measurement of nicotine dependence among youth. The primary objectives of this review are to: (1) review the measures of nicotine dependence currently being used; and (2) delineate a future research agenda in an attempt to advance the quality of measurement and instrumentation for this important research endeavor. Existing measures of nicotine dependence, including formal diagnostic interviews, related withdrawal assessments, brief self-report measures, and single-item indicators, are described. While formal diagnostic systems have been considered the 'gold standard' for evaluating dependence clinically, their specific limitations related to use for research purposes are outlined. Each broad class of measure is evaluated in terms of its rationale for use, strengths and limitations, and the extent to which it has successfully been applied to adolescent populations. A research agenda follows in the second section of the paper. In this section, the need for identification and inclusion of a standard set of optimal dependence measures, for enhancement of current measures, and for the onset of a new and comprehensive measures development program is outlined.

Are adolescent smokers dependent on nicotine? A review of the evidence.

This paper reviews the empirical literature on adolescent nicotine dependence, withdrawal, and their associated features. Data documenting nicotine dependence scores, diagnoses, and individual features among adolescents are reviewed in detail and compared to observations based on adult smokers. These data are derived from a broad variety of sources, including national surveys, school-based surveys, and smoking cessation studies. Overall, results indicate that one to three out of five adolescent smokers is dependent on nicotine, with some adolescent groups clearly at higher risk for dependence (those who are incarcerated, in vocational schools, daily smokers, and/or heavy smokers). Across studies, data consistently indicate that a large majority (two-thirds or more) of adolescent smokers report experiencing withdrawal symptoms during attempts to quit or reduce their smoking. Craving or strong desire to smoke was the most commonly reported withdrawal symptom in every study reviewed. Although analyses of concurrent validity generally support the dependence and withdrawal findings among adolescents, data on the predictive validity of measures used are needed. Moreover, studies of adolescent tobacco withdrawal rely almost exclusively on retrospective self-report data. Recommendations for enhancing methodology and advancing our understanding of adolescent nicotine dependence and withdrawal are offered.

Smoking and drinking among alcoholics in treatment: cross-sectional and longitudinal relationships.

OBJECTIVE: The relationship between tobacco dependence and alcohol dependence has received considerable scrutiny in the past few years. The present study of alcoholics in treatment for alcoholism extended previous work by investigating the cross-sectional and longitudinal relationships between drinking and smoking variables. METHOD: Male and female alcoholics (N = 116) completed a standard assessment of smoking and drinking pretreatment followed by a laboratory assessment of reactivity to alcohol cues. Participants' drinking and smoking were evaluated again 6 months following treatment. RESULTS: (1) Pretreatment tobacco dependence, pretreatment alcohol dependence, urge to smoke and urge to drink were positively correlated; (2) smoking rates and drinking rates were not correlated either before or following treatment; (3) pretreatment smoking history did not predict posttreatment drinking; (4) the rate of smoking declined following treatment for alcoholism for 45% of the smoking patients who completed a 6-month follow-up, independent of relapse status; and (5) relapsers who smoked more heavily also drank less frequently during follow up. CONCLUSIONS: Consistent but modest cross-sectional relationships between drinking and smoking variables before alcohol treatment decrease after treatment for alcohol dependence. A spontaneous improvement in smoking rate occurs in many (45%), particularly among those who smoked more heavily pretreatment and thus benefit most by the reduction. Directions for future research are discussed.

Naltrexone's effects on reactivity to alcohol cues among alcoholic men.

The mechanisms of naltrexone's effects on urges to drink during abstinence are unclear. Naltrexone may suppress either urges to drink specifically or appetitive responses in general. The effects of naltrexone on cue reactivity to alcoholic and sweet nonalcoholic beverages were investigated. Alcohol-dependent men (N = 53) in treatment received naltrexone (50 mg) or placebo. Four hours later, they received baseline assessment, exposure to fruit juice, and exposure to their usual alcoholic beverage in 3-min trials. Naltrexone reduced urge to drink and self-reported attention to the alcohol cues, not at the initial exposure but after repeated exposures to alcohol cues. Naltrexone reduced negative affect across baseline and alcohol trials. No effects of naltrexone on responses to the nonalcoholic appetitive beverage cues were found, suggesting that general appetite suppression does not mediate the effects of naltrexone on urges.

Brief intervention for harm reduction with alcohol-positive older adolescents in a hospital emergency department.

This study evaluated the use of a brief motivational interview (MI) to reduce alcohol-related consequences and use among adolescents treated in an emergency room (ER) following an alcohol-related event. Patients aged 18 to 19 years (N = 94) were randomly assigned to receive either MI or standard care (SC). Assessment and intervention were conducted in the ER during or after the patient's treatment. Follow-up assessments showed that patients who received the MI had a significantly lower incidence of drinking and driving, traffic violations, alcohol-related injuries, and alcohol-related problems than patients who received SC. Both conditions showed reduced alcohol consumption. The harm-reduction focus of the MI was evident in that MI reduced negative outcomes related to drinking, beyond what was produced by the precipitating event plus SC alone.

Electromyographic analysis and energy expenditure of harness supported treadmill walking: implications for knee rehabilitation.

Harness supported treadmill ambulation has been recommended for patients as a way of decreasing loads on the healing tissues, conserving energy and reducing pain. We quantified muscle activation levels around the knee and metabolic responses during harness supported treadmill walking. Ten healthy recreational athletes (age 28.9+/-7.8 years) walked on the treadmill (1.34 m/s) for 5 min each at full weight bearing (FWB), 20 and 40% body weight support (BWS). Electromyography (EMG) was monitored for the vastus lateralis, vastus medialis, rectus femoris, biceps femoris, medial hamstrings and the gastrocnemius. Oxygen consumption was collected by open circuit spirometry and the heart rate was collected by a heartwatch. A statistically significant reduction in EMG was found at 40% BWS for the quadriceps. Oxygen consumption decreased by 6% (20% BWS) and by 12% (40% BWS) from FWB (P<0.05). The heart rate was unchanged. BWS ambulation reduces energy cost, but does not significantly alter muscle activation, except for the quadriceps at 40% BWS.

Naltrexone's effect on cue-elicited craving among alcoholics in treatment.

BACKGROUND: Advancing knowledge of biobehavioral effects of interventions can result in improved treatments. Thus, a standardized laboratory cue reactivity assessment has been developed and validated to assess the cognitive and psychophysiological responses to a simulated high-risk situation: alcohol cues. The present study investigates the effects of a pharmacotherapy (naltrexone) on a laboratory-based, cue-elicited urge to drink among abstinent alcoholics in treatment. METHODS: Alcohol-dependent subjects were randomized to 12 weeks of naltrexone or placebo after completing a partial hospital program. After approximately 1 week on medication, all received cue reactivity assessment. RESULTS: Significantly fewer patients taking naltrexone reported any urge to drink during alcohol exposure than did those on placebo. Those with any urges reported no decrement in level of the urges. Mean arterial pressure decreased significantly for those on placebo, but not for those on naltrexone, whereas cue-elicited decreases in heart rate were not affected by the medication. CONCLUSIONS: The results have implications for models of relapse and naltrexone's effects. Cue reactivity methodology has utility for investigating hypothesized mediators of therapeutic effects of pharmacotherapies as well as behavioral treatments.

Lower limb stability with ACL impairment.

STUDY DESIGN: Repeated measures (3 separate day sessions) to determine test reliability; single-session repeated measures to compare stability between limbs. OBJECTIVES: To develop a functional test measuring dynamic stability that is capable of differentiating between the injured and uninjured lower limb in 2 populations: (1) people with anterior cruciate ligament deficiency (ACLd) and (2) people with anterior cruciate ligament reconstruction (ACLr), and to establish the reliability of this test. BACKGROUND: Many functional tests of the lower limb used by clinicians, such as the 1-legged hop for distance, the 1-legged hop for time, the vertical jump, the triple hop for distance, shuttle run, and single-limb standing, do not allow the clinician to discern differences between function in the injured and uninjured limbs. METHODS AND MEASURES: Twenty-five nonimpaired subjects (14 men, 11 women, aged 31.2 +/- 9.1 years), 11 subjects with ACLr (9 men, 2 women, aged 26.3 +/- 10.4 years), and 13 subjects with ACLd (5 men, 8 women, aged 40.4 +/- 12.6 years) were tested. Twelve nonimpaired subjects participated in 3 testing sessions to determine the reliability of the force plate measures. Ground reaction forces (vertical, medial-lateral, and anterior-posterior) were measured while the subjects performed 1-legged hop and step-down tests onto a force plate. Stability was defined as the ability to transfer the vertical projection of the center of gravity to the supporting base and keep the knee still. A repeated-measures analysis of variance (2-factor; limbs by trials) was used to compare the stability between limbs. RESULTS: The majority of the measures used to calculate dynamic stability were reliable. Moreover, the data provide normal standards of functional knee stability for step-down and hop tests. In the step-down test, changes in vertical force did identify dysfunction in the injured limb (stabilization time = 1527 +/- 216 ms) compared to the uninjured limb (stabilization time = 892 +/- 498 ms) for subjects with ACLr. CONCLUSIONS: The normal standards may serve as a reference for comparing functional differences in ACLr or ACLd populations. The vertical force parameter during a step-down may be useful as an outcome measure to monitor progress during rehabilitation.