Biomedical subjects

Sandra J Shultz

Publications and source records attributed to Sandra J Shultz.

At least 19 recordsLinked to original sources

PubMed2006

Absolute serum hormone levels predict the magnitude of change in anterior knee laxity across the menstrual cycle.

This study aimed to determine whether absolute sex hormone concentrations predict the magnitude of knee joint laxity changes across the menstrual cycle. Twenty-two females (18-30 years, body mass index <or=30), who reported normal menstrual cycles for the previous 6 months were tested daily across one complete menstrual cycle for serum levels of estradiol (E=pg/mL), progesterone (P=ng/mL), and testosterone (T=ng/dL), and knee joint laxity (K(Lax)=mm displacement at 134N) measured with a standard knee arthrometer. The change in K(Lax) across the cycle (maximum-minimum), and minimum (early follicular) and peak (postovulatory) hormone concentrations were recorded for each subject. A stepwise linear regression determined if the minimum, peak, or absolute change in hormone concentrations would predict the magnitude of change in K(Lax) across the cycle. K(Lax) changed on average 3.2+/-1.1 mm across the menstrual cycle (range, 1.5-5.3 mm). Minimum levels of E (39.9+/-11.8 pg/mL) and P (0.61+/-0.27 ng/mL), coupled with peak concentrations of E (199.6+/-54.9 pg/mL) and T (22.5+/-10.5 ng/dL) explained 57.6% of the change in K(Lax) across the cycle. Greater absolute changes in K(Lax) were observed in response to peak E and T levels when minimum E concentrations were lower and minimum P concentrations were higher in the early follicular phase. The absolute minimum concentrations of E and P in the early follicular phase appear to be important factors in determining the sensitivity of the knee joint's response to changing hormone levels.

Adolescent↗

PubMed2006

Nonweight-bearing anterior knee laxity is related to anterior tibial translation during transition from nonweight bearing to weight bearing.

We examined the relationship between anterior knee laxity (AKL), evaluated while the knee was nonweight bearing, and anterior translation of the tibia relative to the femur (ATT), evaluated when the knee transitioned from nonweight-bearing to weight-bearing conditions in response to an applied compressive load at the foot. Twenty subjects with normal knees (10 M, 10 F; 25.2 +/- 4.1 years, 169.8 +/- 11.5 cm, 71.6 +/- 16.9 kg) underwent measurements of AKL and ATT of the right knee on 2 days. AKL was measured at 133N with the KT-2000. ATT was measured with the Vermont Knee Laxity Device and electromagnetic position sensors attached to the patella and the anteromedial aspect of the proximal tibia. Three trials for each measure were averaged and analyzed. Measurement consistency was high for both AKL (ICC = 0.97; SEM = 0.44 mm) and ATT (ICC = 0.88; SEM = 0.84 mm). Linear regression revealed that AKL predicted 35.5% of the variance in ATT (p = 0.006), with a prediction equation of Y(ATT) = 3.20 + 0.543(X(AKL)). Our findings suggest that increased AKL is associated with increased ATT as the knee transitions from nonweight-bearing to weight-bearing conditions. The potential for increased knee joint laxity to disrupt normal knee biomechanics during activities such as landing from a jump, or the foot strike phase of gait deserves further study.

Adult↗

PubMed2006

Intratester and intertester reliability of clinical measures of lower extremity anatomic characteristics: implications for multicenter studies.

OBJECTIVE: To determine whether multiple examiners could be trained to measure lower extremity anatomic characteristics with acceptable reliability and precision, both within (intratester) and between (intertester) testers. We also determined whether testers trained 18 months apart could perform these measurements with good agreement. SETTING: University's Applied Neuromechanics Research Laboratory. PARTICIPANTS: Sixteen, healthy participants (7 men, 9 women). ASSESSMENT OF RISK FACTORS: Six investigators measured 12 anatomic characteristics on the right lower extremity in the Fall of 2004. Four testers underwent training immediately preceding the study, and measured subjects on 2 separate days to examine intratester reliability. Two testers trained 18 months before the study (Spring 2002) measured each subject on day 1 to examine the consistency of intertester reliability when testers are trained at different times. MAIN OUTCOME MEASUREMENTS: Knee laxity, genu recurvatum, quadriceps angle, tibial torsion, tibiofemoral angle, hamstring extensibility, pelvic angle, navicular drop, femur length, tibial length, and hip anteversion. RESULTS: With few exceptions, all testers consistently measured each variable between test days (intraclass correlation coefficient>or=0.80). Intraclass correlation coefficient values were lower for intertester reliability (0.48 to 0.97), and improved from day 1 to day 2. Intertester reliability was similar when comparing testers trained 18 months before those trained immediately before the study. Absolute measurement error varied considerably across individual testers. CONCLUSIONS: Multiple investigators can be trained at different times to measure anatomic characteristics with good to excellent intratester reliability. Intratester reliability did not always ensure acceptable intertester reliability or measurement precision, suggesting more training (or more experience) may be required to achieve acceptable measurement reliability and precision between multiple testers.

Adult↗

PubMed2006

Postural control deficits in participants with functional ankle instability as measured by the balance error scoring system.

OBJECTIVE: To determine if postural control deficits are present in participants with functional ankle instability (FAI) as measured by the Balance Error Scoring System (BESS). DESIGN AND SETTING: We used a between-groups design to assess postural control. All testing was conducted in a university athletic training facility. PARTICIPANTS: Sixty collegiate Division I athletes were included in this study. Thirty participants had functional ankle instability and thirty participants had no history of ankle injuries. MAIN OUTCOME MEASUREMENTS: Postural control was measured using the BESS. The BESS test battery requires participants to stand unsupported on two different surfaces (firm and foam) in three different stances (double, single, and in tandem). Each condition lasted 20 seconds. The number of errors were calculated for each individual condition and then summed to produce a total BESS score. RESULTS: We found a significant group by condition interaction (F5,290 = 5.12, P < 0.001) and significant main effects for group (F1,58 = 16.01, P < 0.001) and condition (F5,290 = 228.88, P < 0.001). Post hoc analyses revealed that subjects with functional ankle instability scored more errors (poorer balance) on the single stancefirm condition (2.9 +/- 2.1 versus 1.6 +/- 1.3 errors), tandem stancefoam condition (4.3 +/- 2.4 versus 2.7 +/- 1.6 errors), single stancefoam condition (7.0+/-1.6 versus 5.6 +/- 1.8 errors), and total BESS score (15.7 +/- 6.0 versus 10.7 +/- 3.2). CONCLUSIONS: Postural control deficits were identified in participants with functional ankle instability using the BESS. These deficits could be a contributing factor to the repeated episodes of instability and giving way that often occurs following an inversion ankle sprain. These results suggest the BESS, traditionally used for monitoring recovery from mild head injury, may also be useful in screening athletes for postural deficits following lower extremity injury.

Adolescent↗

PubMed2006

Understanding and preventing noncontact anterior cruciate ligament injuries: a review of the Hunt Valley II meeting, January 2005.

The incidence of noncontact anterior cruciate ligament injuries in young to middle-aged athletes remains high. Despite early diagnosis and appropriate operative and nonoperative treatments, posttraumatic degenerative arthritis may develop. In a meeting in Atlanta, Georgia (January 2005), sponsored by the American Orthopaedic Society for Sports Medicine, a group of physicians, physical therapists, athletic trainers, biomechanists, epidemiologists, and other scientists interested in this area of research met to review current knowledge on risk factors associated with noncontact anterior cruciate ligament injuries, anterior cruciate ligament injury biomechanics, and existing anterior cruciate ligament prevention programs. This article reports on the presentations, discussions, and recommendations of this group.

Anterior Cruciate Ligament↗

PubMed2005

Females recruit quadriceps faster than males at multiple knee flexion angles following a weight-bearing rotary perturbation.

OBJECTIVE: To compare the effect of knee angle on muscle response times and neuromuscular recruitment patterns between sexes following a perturbation in single leg stance at 10 degrees, 20 degrees, and 30 degrees. We hypothesized that response times would be faster at lesser knee flexion angles and that females would recruit their quadriceps faster than males at all angles. DESIGN: A repeated-measures design. SETTING: Motion analysis laboratory. PARTICIPANTS: Twenty (10 female; 10 male) healthy, recreationally active volunteers. INTERVENTIONS: A rotary perturbation in single leg stance. OUTCOME MEASUREMENTS: Response times of the medial and lateral quadriceps, hamstrings, and gastrocnemius. RESULTS: There was a trend toward faster response times for all muscles closer toward extension. A consistent neuromuscular recruitment pattern for both males and females was evident for each knee angle tested. Females, however, contracted their quadriceps faster than males at all knee flexion angles. CONCLUSIONS: Small changes in knee angle near extension do not alter muscle response times and hence neuromuscular recruitment patterns in males and females. Regardless of knee flexion angle, following a perturbation in single leg stance, females contract their quadriceps faster than males. CLINICAL RELEVANCE: Earlier contraction of the quadriceps in females may increase anterior tibial translation and hence anterior cruciate ligament strain, thereby heightening injury risk.

Adult↗

PubMed2005

Effects of Pronated and Supinated Foot Postures on Static and Dynamic Postural Stability.

Context: The foot is the most distal segment in the lower extremity chain and represents a relatively small base of support on which the body maintains balance (particularly in single-leg stance). Although it seems reasonable that even minor biomechanical alterations in the support surface may influence postural-control strategies, the implications of a hypermobile or hypomobile foot on balance have received little attention to date.Objective: To determine if supinated and pronated foot types influence measures of static and dynamic balance.Design: Participants were assigned to 1 of 3 groups depending on foot type, as defined by navicular-drop measures: pronated (>/=10 mm), neutral (5-9 mm), or supinated (</=4 mm). Measures of static and dynamic balance were obtained for each participant and compared across groups.Setting: Sports medicine and athletic training research laboratory.Patients or Other Participants: Sixteen individuals with pronated (navicular drop = 13.0 +/- 3.7 mm), neutral (navicular drop = 6.2 +/- 1.1 mm), or supinated (navicular drop = 2.2 +/- 1.7 mm) foot postures volunteered to participate in the study.Main Outcome Measure(s): We used the Chattecx Balance System to measure center of balance, stability index, and postural sway during static single-limb stance under eyes-open and eyes-closed conditions. Center of balance was defined as the point on the foot at which the body weight was equally distributed between the medial-lateral and anterior-posterior quadrants and was recorded in centimeters. Stability index was defined as the mean deviation in sway around the center of balance. Postural sway was expressed as the maximum sway distance recorded (cm) in the medial-lateral and anterior-posterior directions. The Star Excursion Balance Test was used to measure dynamic balance, which was reported as the reach distance (cm) in each of the 8 directions tested. The average of 3 trials of each measure was calculated and normalized to the subject's height.Results: We found no difference in center of balance or postural sway as a function of foot type. The stability index was greater in pronators than in supinators, but neither group was different from those with neutral foot types. Dynamic reach differed among groups but only in some directions. Generally, pronators reached farther in the anterior and anterior medial directions and supinators reached farther in the posterior and posterio-lateral directions. In the lateral direction, supinators reached farther than pronators but not farther than neutrals.Conclusions: Our results suggest that postural stability is affected by foot type under both static and dynamic conditions. These differences appear to be related to structural differences as opposed to differences in peripheral input. These effects should be considered when clinicians use such balance measures to assess injury deficits and recovery.

Journal Article↗

PubMed2004

Low levels of anterior tibial loading enhance knee extensor reflex response characteristics.

We examined whether neuromuscular reflexes were altered with anterior loads applied to the tibio-femoral joint. A ligament testing device was modified by attaching a reflex hammer to a steel mounted frame to illicit a patellar tendon tap, while anterior directed loads displaced the tibia on the femur. Five trials were acquired while anterior-directed loads (20, 50, 100 N; counterbalanced) were applied to the posterior tibia between 20 N pre (20 N(Pre)) and post (20 N(Post)) baseline conditions on two different days. Surface electromyography (sEMG) recorded mean quadriceps (Q) and hamstring (H) reflex time (R(Time)=ms) and reflex amplitude (R(Amp)=%MVIC). A load cell on the anterior tibia measured the timing (KE(Time)=ms) and amplitude (KE(Amp)=N) of the knee extension force, and was used to calculate electromechanical delay (EMD=ms) and peak knee extension moment (KE(Mom)=Nm/kg). Data from 19 recreationally active subjects revealed good to excellent response consistency between test days and between baseline conditions for R(Time), R(Amp), KE(Time) and KE(Amp). With anterior tibial loading, R(Time) was faster at 50 N vs. 20 N(Post), and R(Amp) was greater at 20 N(Pre) vs. 20 N(Post) (Q and H) and at 50 N vs. 100 N (Q only). KE(Mom) was greater at 20 N(Pre) and 50 N vs. 20 N(Post), and EMD was shorter at 50 N vs. 20 N, 20 N(Pre) and 20 N(Post). These results suggest that knee extensor reflex responses are enhanced with low (50 N) but not moderate (100 N) anterior loading of the knee.

Adult↗

PubMed2004

Knee ligament behavior following a controlled loading protocol does not differ by menstrual cycle day.

BACKGROUND: Females experience a disproportionate number of anterior cruciate ligament injuries compared to males. Increased estradiol concentration has been suggested to alter ligament properties and strength. Determining whether the knee responds differently to an external load at various hormonal levels may be helpful in further explaining the gender disparity. METHODS: Estradiol, progesterone and testosterone were quantified at menses, near ovulation and at the mid-luteal phase. With one knee serving as the control limb and the other as the experimental limb, displacement at 134N and stiffness between 90 and 134N were recorded with a knee ligament arthrometer on both knees before and after a loading protocol. The protocol consisted of three, 3-min, posterior to anterior normalized loads directed to the posterior calf with a ligament testing device. FINDINGS: The loading protocol produced a measurable increase in displacement but not stiffness. Neither displacement nor stiffness measures however were affected by day of the menstrual cycle. No consistent relationships between hormonal concentrations and displacement or stiffness were evident. INTERPRETATION: Following a controlled, static external load, displacement and stiffness were not affected differently by day of the menstrual cycle.

Adolescent↗

PubMed2004

Kinematic analysis of functional lower body perturbations.

BACKGROUND: Sudden changes in direction on a single weight-bearing-limb are commonly associated with injury to the lower extremity. The purposes of this study were to assess the between day reliability of hip, knee, and ankle kinematic displacements achieved with internal and external femur-on-weight-bearing-tibia rotation perturbations and to determine the effect of these perturbations on three dimensional hip, knee and ankle kinematics. METHODS: Twenty recreationally active, healthy college students with no history of significant orthopedic injury (10 male, 10 female) were subjected to a forward and either internal or external rotary perturbation of the trunk and thigh on the weight-bearing-tibia while three dimensional kinematics were simultaneously collected. The protocol was repeated 24-48 h later to assess reliability. FINDINGS: External perturbations resulted in significant internal rotation (IR) of the tibia on the femur (mean 7.3 (SD 3.9 degrees)) and IR of the femur on the pelvis (mean 6.8 (SD 5.4 degrees)) (P<0.05). Internal perturbations resulted in significant external rotation (ER) of the tibia on the femur (mean 6.8 (5.9 degrees)) and ER of the femur on the pelvis (mean 10.7 (SD 96.1 degrees)) (P<0.05). Additionally the external perturbation results in a significantly greater knee valgus (mean 3.6 (SD 2.2 degrees)) position while the internal perturbation results in a significantly greater knee varus position (mean 2.3 (SD 3.5 degrees)) (P<0.05). External perturbation hip and knee total joint displacements revealed moderate to strong reliability (Intraclass Correlation Coefficient(2,k)=0.67-0.94) while internal perturbations revealed slightly higher Intraclass Correlation Coefficients(2,k)(0.80-0.96). INTERPRETATION: The lower extremity perturbation device provides a consistent external and internal perturbation of the femur on the weight-bearing-tibia. The observed transverse and frontal plane kinematics are similar to motions observed during cross-over and side-stepping tasks.

Adult↗

PubMed2004

Knee joint laxity affects muscle activation patterns in the healthy knee.

This study investigated the effects of anterior knee joint laxity on muscle activation patterns prior to and following a lower extremity perturbation. Participants were subjected to a forward and either internal (IR) or external (ER) rotation perturbation of the trunk and thigh on the weight-bearing shank. Pre-activity (%MVIC) before the perturbation, and reflex time (ms) and mean reflex amplitude (%MVIC) following the perturbation were recorded via surface electromyography (sEMG) in the medial and lateral gastrocnemius, hamstring and quadriceps muscles. Twenty-one NCAA DI intercollegiate female athletes with below average anterior knee laxity (3-5 mm) were compared to 21 with above average anterior knee laxity (7-14 mm) as measured by a standard knee arthrometer. Groups differed in reflex timing by muscle (P = 0.013), with females with above average knee laxity (KT((>7 mm))) demonstrating a 16 ms greater delay in biceps femoris reflex timing compared to females with below average knee laxity (KT((<5 mm))). Groups also differed in muscle activation amplitude by response, muscle and direction of rotation (i.e. a 4-way interaction; P = 0.027). The magnitude of change from pre to post perturbation was significantly less in KT((>7 mm)) vs. KT((<5 mm)) for the medial (MG) and lateral (LG) gastrocnemius muscles, primarily due to higher levels of muscle preactivity while awaiting the perturbation (MG = 20% vs. 12% MVIC, P = 0.05; LG = 33% vs. 21% MVIC, P = 0.11). Further, KT((>7 mm)) demonstrated higher activation levels in the biceps femoris than KT((<5 mm)) (47% vs. 27% MVIC; P = 0.025) regardless of response (pre vs. post perturbation) or direction of rotation. These findings suggest females with increased knee laxity may be less sensitive to joint displacement or loading (delayed reflex), and are more reliant on active control of the gastrocnemius and biceps femoris muscles to potentially compensate for reduced passive joint stability.

Adult↗

PubMed2004

Serial administration of clinical concussion assessments and learning effects in healthy young athletes.

OBJECTIVE: To determine if serial administration of the Standardized Assessment of Concussion (SAC) and Balance Error Scoring System (BESS) would elicit a learning effect in young athletes and to determine the intratester reliability of scoring the BESS. DESIGN: A prospective study of 50 healthy young athletes who were assigned to either the control or practice group. All subjects were administered the assessments on 2 occasions, 60 days apart. In addition, subjects in the practice group received serial administration of the assessments on 3 occasions in the week following the initial assessment. SETTING: University Sports Medicine/Athletic Training Research Laboratory. SUBJECTS: Fifty uninjured young athletes between 9 and 14 years of age. MAIN OUTCOME MEASURED: Scores on 2 clinical concussion assessments, the SAC and the BESS. RESULTS: We found a significant learning effect upon serial BESS testing in the practice group. BESS error scores were significantly lower than baseline (15.0 +/- 4.6) on days 5 (11.3 +/- 5.33), 7 (12.4 +/- 6.2), and 60 (12.6 +/- 6.2). We also found a significant learning effect upon the day 60 BESS administration across all subjects. We did not find a practice or learning effect with serial SAC test administration. The intratester reliability of the investigator's ability to score repeated observations of the same BESS test ranged from 0.87 to 0.98. CONCLUSIONS: Our results demonstrated that serial administration of the BESS elicited a learning effect, which was more prominent during the tandem conditions. Clinicians utilizing the BESS as a measure of postural stability should be aware of the potential for improvement with repeated testing. Clinicians should not expect improvement with the SAC, as scores remained relatively stable across all trials.

Adolescent↗

PubMed2004

Relationship between sex hormones and anterior knee laxity across the menstrual cycle.

PURPOSE: To comprehensively quantify through daily, serial measures changes in knee laxity as a function of changing sex-hormone levels across one complete menstrual cycle. METHODS: Twenty-five females, 18 - 30 yr, body mass index < or = 30, who reported normal menstrual cycles (28-32 d) over the past 6 months participated. Participants were tested daily across one complete menstrual cycle; 5-7 cc of venous blood were withdrawn to assay serum levels of estradiol, progesterone, and testosterone. Knee laxity was measured as the amount of anterior tibial displacement at 133 N, using a standard knee arthrometer. To evaluate the relationship of knee laxity to changes in sex hormone concentrations, a multiple linear regression model with the possibility of a time delay was performed on each individual subject and the group as a whole. RESULTS: Individual regression equations revealed an average of 63% of the variance in knee laxity was explained by the three hormones and their interactions. All three hormones significantly contributed to the prediction equation, and the amount of variance explained was substantially greater when a time delay was considered. On average, knee laxity changed approximately 3, 4, and 4.5 d after changes in estradiol, progesterone, and testosterone, respectively. When females were analyzed as a group, only 8% of the variance in knee laxity was explained by sex-hormones levels. CONCLUSION: Changes in sex hormones mediate changes in knee laxity across the menstrual cycle. However, the strength of this relationship, the relative contribution of each hormone, and the associated time delay are highly variable between women. This individual variability is consistent with the variability in menstrual cycle characteristics among women.

Adolescent↗

PubMed2004

Rate of force application during knee arthrometer testing affects stiffness but not displacement measurements.

STUDY DESIGN: Repeated-measures counterbalanced design. OBJECTIVES: To determine the effect of rate of force application on anterior tibial displacement and anterior tibial stiffness when measured with the KT-2000 knee arthrometer. BACKGROUND: Clinicians and researchers frequently use the KT-2000 to quantify anterior tibial displacement and stiffness. While many factors (ie, tibial rotation, alignment of the arthrometer, etc) have been identified to affect KT-2000 measurements, the effect of the rate of force application has not been studied. METHODS AND MEASURES: Seventeen recreationally active males between the ages of 19 and 36 years (mean age +/- SD, 27.8 +/- 5.3 years) with no previous history of knee injury participated. With the knee in 25 degrees of flexion, the KT-2000 was applied to the participants' anterior tibia. While the distal femur was stabilized, the first author applied a posterior-to-anterior force at a fast and slow rate. Three trials for the slow and fast rates of force application were averaged and used for statistical analysis. Anterior tibial displacement (mm) was measured at 133 N and the related anterior tibial stiffness (N/mm) values were calculated between 89 and 133 N. Separate paired t tests with Bonferroni adjustment were used to determine if differences in displacement and stiffness between rates of force application were present. RESULTS: Stiffness was significantly greater in the slow (mean +/- SD, 58 +/- 22 N/mm) as compared to the fast trials (mean +/- SD, 47 +/- 19 N/mm) (P = .005). Differences in displacement, however, were small and not significant (P = .132) between the slow (mean +/- SD, 3.9 +/- 1.5 mm) and fast (mean +/- SD, 4.0 +/- 1.6 mm) trials. CONCLUSION: The rate of force application affects anterior tibial stiffness but not anterior tibial displacement when measured with the KT-2000. This suggests that to ensure reliable results when using the KT-2000, the rate of force application must be controlled when measuring stiffness between 89 and 133 N, but not when measuring anterior tibial displacement at 133 N.

Adult↗

PubMed2004

Balance Recovers Within 20 Minutes After Exertion as Measured by the Balance Error Scoring System.

OBJECTIVE: To determine a balance recovery timeline after a functional exertion protocol using the Balance Error Scoring System (BESS). DESIGN AND SETTING: Five subject groups (4 test, 1 control) were tested 3 times during 1 session: once before the exertion protocol (pretest) and twice after the exertion protocol (posttest I and posttest II). Posttest I occurred at staggered intervals of 0, 5, 10, and 15 minutes, depending on experimental group assignment, and posttest II occurred at 20 minutes. SUBJECTS: One hundred subjects (80 test, 20 control) volunteered to participate in this study. None of the subjects had a balance disorder, mild head injury, or lower extremity injury in the 6 months before testing. MEASUREMENTS: We assessed balance using the BESS, assigning a score for each stance-surface condition. RESULTS: We found a significant decrease in BESS performance after the exertion protocol in all test groups, with exertion having the greatest effect on the tandem and single-leg stance conditions. All subjects recovered by posttest II, which was administered 20 minutes after cessation of the exertion protocol. CONCLUSIONS: Athletic trainers need to be aware of the effect of exertion when administering the BESS after physical activity. Athletic trainers can expect the BESS performance of healthy athletes to return to baseline levels within 20 minutes of rest.

Journal Article↗

PubMed2004

Functional Fatigue Decreases 3-Dimensional Multijoint Position Reproduction Acuity in the Overhead-Throwing Athlete.

OBJECTIVE: To determine the effects of functional fatigue on active multijoint position reproduction in overhead-throwing athletes. DESIGN AND SETTING: A standard, repeated-measures, randomized-ordered, counterbalanced, 2-period (crossover) design was used. During the first test session, we randomly assigned subjects to either the nonfatigue or fatigue condition. Subjects underwent pretest measurements and then either a functional fatigue protocol or rest period, followed by posttest measurements. After a recovery period, subjects crossed over to the opposing condition for the second testing session. SUBJECTS: Thirteen overhead-throwing athletes competing in National Collegiate Athletic Association Division I or club baseball, with no history of upper extremity or central nervous system disorders, volunteered for this study. MEASUREMENTS: We measured active multijoint position reproduction accuracy in 3 dimensions using an electromagnetic tracking device. We noted each subject's ability to reproduce 3 positions corresponding with distinct moments of his throwing motion. A variable error score was calculated to compare the locations of the reproduced points with reference to the target point. RESULTS: A significant difference occurred between the pretest and posttest error scores in the fatigue condition. Comparisons between positions indicated that more errors were seen in the arm-cocked position than in the follow-through position under both fatigue and nonfatigue conditions. CONCLUSIONS: Functional fatigue decreased joint position sense acuity in overhead-throwing athletes. Our findings using this novel testing measurement method are in agreement with past research, with one exception. The trend toward higher error scores in the arm-cocked position would appear to contradict findings that sensorimotor system acuity increases toward end ranges of motion.

Journal Article↗

PubMed2003

Reliability and validity of the Biodex system 3 pro isokinetic dynamometer velocity, torque and position measurements.

This study quantitatively assessed the mechanical reliability and validity of position, torque and velocity measurements of the Biodex System 3 isokinetic dynamometer. Trial-to-trial and day-to-day reliability were assessed during three trials on two separate days. To assess instrument validity, measurement of each variable using the Biodex System 3 dynamometer was compared to a criterion measure of position, torque and velocity. Position was assessed at 5 degrees increments across the available range of motion of the dynamometer. Torque measures were assessed isometrically by hanging six different calibrated weights from the lever arm. Velocity was assessed (30 degrees/s to 500 degrees/s) across a 70 degrees arc of motion by manually accelerating the weighted lever arm. With the exception of a systematic decrease in velocity at speeds of 300 degrees/s and higher, the Biodex System 3 performed with acceptable mechanical reliability and validity on all variables tested.

Humans↗

PubMed2002

The differential effects of fatigue on reflex response timing and amplitude in males and females.

We examined the effects of fatigue on patellar tendon reflex responses in males and females. A spring-loaded reflex hammer elicited a standardized tendon tap with the knee positioned in an isokinetic dynamometer and flexed to 85 degrees. We recorded vastus lateralis activity (SEMG) and knee extension force production at the distal tibia (force transducer). Reflex trials were performed before and after (immediate, 2, 4, and 6 min) an isokinetic fatigue protocol to 50% MVC (90 degrees /s). For each event, pre-motor time (PMT), electromechanical delay (EMD), and total motor time (TMT) were obtained, as well as EMG amplitude (EMG(amp)), time to peak EMG (EMG(tpk)), peak force amplitude (F(amp)), time to peak force (F(tpk)), EMG:force ratio (E:F), and rate of force production (F(rate)=N/ms). TMT increased significantly in females following fatigue, while males showed no change. The increased TMT was due to an increased EMD with fatigue, while PMT was unaffected. EMG(amp) and F(amp) were somewhat diminished in females yet significantly augmented in males following fatigue, likely accounting for the differential changes in EMD noted. Results suggest males and females may respond differently to isokinetic fatigue, with males having a greater capacity to compensate for contraction force failure when responding to mechanical perturbations.

Adult↗