Investigating the birth-related caudal maternal pelvic floor muscle injury: The consequences of low cycle fatigue damage.

BACKGROUND: One of the major causes of pelvic organ prolapse is pelvic muscle injury sustained during a vaginal delivery. The most common site of this injury is where the pubovisceral muscle takes origin from the pubic bone. We hypothesized that it is possible for low-cycle material fatigue to occur at the origin of the pubovisceral muscle under the large repetitive loads associated with pushing during the second stage of a difficult labor. PURPOSE: The main goal was to test if the origin of the pubovisceral muscle accumulates material damage under sub-maximal cyclic tensile loading and identify any microscopic evidence of such damage. METHODS: Twenty origins of the ishiococcygeous muscle (homologous to the pubovisceral muscle in women) were dissected from female sheep pelvises. Four specimens were stretched to failure to characterize the failure properties of the specimens. Thirteen specimens were then subjected to relaxation and subsequent fatigue tests, while three specimens remained as untested controls. Histology was performed to check for microscopic damage accumulation. RESULTS: The fatigue stress-time curves showed continuous stress softening, a sign of material damage accumulation. Histology confirmed the presence of accumulated microdamage in the form of kinked muscle fibers and muscle fiber disruption in the areas with higher deformation, namely in the muscle near the musculotendinous junction. CONCLUSIONS: The origin of ovine ishiococcygeous muscle can accumulate damage under sub-maximal repetitive loading. The damage appears in the muscle near the musculotendinous junction and was sufficient to negatively affect the macroscopic mechanical properties of the specimens.

Relationship between intra-abdominal pressure and vaginal wall movements during Valsalva in women with and without pelvic organ prolapse: technique development and early observations.

OBJECTIVES: To develop and test a method for measuring the relationship between the rise in intra-abdominal pressure and sagittal plane movements of the anterior and posterior vaginal walls during Valsalva in a pilot sample of women with and without prolapse. METHODS: Mid-sagittal MRI images were obtained during Valsalva while changes in intra-abdominal pressure were measured via a bladder catheter in 5 women with cystocele, 5 women with rectocele, and 5 controls. The regional compliance of the anterior and posterior vagina wall support systems were estimated from the ratio of displacement (mm) of equidistant points along the anterior and posterior vaginal walls to intra-abdominal pressure rise (mmHg). RESULTS: The compliance of both anterior and posterior vaginal wall support systems varied along different regions of vaginal wall for all three groups, with the highest compliance found near the vaginal apex and the lowest near the introitus. Women with cystocele had more compliant anterior and posterior vaginal wall support systems than women with rectocele. The movement direction differs between cystocele and rectocele. In cystocele, the anterior vaginal wall moves mostly toward the vaginal orifice in the upper vagina, but in a ventral direction in the lower vagina. In rectocele, the direction of the posterior vaginal wall movement is generally toward the vaginal orifice. CONCLUSIONS: Movement of the vaginal wall and compliance of its support is quantifiable and was found to vary along the length of the vagina. Compliance was greatest in the upper vagina of all groups. Women with cystocele demonstrated the most compliant vaginal wall support.

On pelvic reference lines and the MR evaluation of genital prolapse: a proposal for standardization using the Pelvic Inclination Correction System.

Five midsagittal pelvic reference lines have been employed to quantify prolapse using MRI. However, the lack of standardization makes study results difficult to compare. Using MRI scans from 149 women, we demonstrate how use of existing reference lines can systematically affect measurements in three distinct ways: in oblique line systems, distances measured to the reference line vary with antero-posterior location; soft issue-based reference lines can underestimate organ movement relative to the pelvic bones; and systems defined relative to the MR scanner are affected by intra- and interindividual differences in the pelvic inclination angle at rest and strain. Thus, we propose a standardized approach called the Pelvic Inclination Correction System (PICS). Based on bony structures and the body axis, the PICS system corrects for variation in pelvic inclination, at rest of straining, and allows for the standardized measurement of organ displacement in the direction of prolapse.

Effect of pre-impact movement strategies on the impact forces resulting from a lateral fall.

Approximately 90% of hip fractures in older adults result from falls, mostly from landing on or near the hip. A three-dimensional, 11-segment, forward dynamic biomechanical model was developed to investigate whether segment movement strategies prior to impact can affect the impact forces resulting from a lateral fall. Four different pre-impact movement strategies, with and without using the ipsilateral arm to break the fall, were implemented using paired actuators representing the agonist and antagonist muscles acting about each joint. Proportional-derivative feedback controller controlled joint angles and velocities so as to minimize risk of fracture at any of the impact sites. It was hypothesized that (a) the use of active knee, hip and arm joint torques during the pre-contact phase affects neither the whole body kinetic energy at impact nor the peak impact forces on the knee, hip or shoulder and (b) muscle strength and reaction time do not substantially affect peak impact forces. The results demonstrate that, compared with falling laterally as a rigid body, an arrest strategy that combines flexion of the lower extremities, ground contact with the side of the lower leg along with an axial rotation to progressively present the posterolateral aspects of the thigh, pelvis and then torso, can reduce the peak hip impact force by up to 56%. A 30% decline in muscle strength did not markedly affect the effectiveness of that fall strategy. However, a 300-ms delay in implementing the movement strategy inevitably caused hip impact forces consistent with fracture unless the arm was used to break the fall prior to the hip impact.

Test-retest reliability of an instrumented speculum for measuring vaginal closure force.

AIMS: The study aimed to: a) determine reliability of an instrumented speculum designed for measuring intravaginal closure pressure, and b) compare findings with a comparable device reported in the literature. The goal of these new devices is to reduce subjectivity, improve precision, and acknowledge reliability issues in quantifying levator ani closure force acting on the vagina. METHODS: The instrumented speculum consisted of two parallel aluminum bills, similar in size to a Peterson speculum. Strain gages located near the root of each bill measure the magnitude of force exerted in the distal vagina. A contraction of the "U-shaped" levator ani muscle closes the levator hiatus with resultant reaction force measured by the speculum in the mid-sagittal plane. We tested the device in twelve nulliparous women making repeated measures within and across 3 different visit days. All measures were made by the same investigator. RESULTS: Same day measures were repeatable within +/-3.8 N by the third visit, with lesser repeatability on the 1st and 2nd visit days. Across days, repeatability was improved by Visits 2 and 3 with a coefficient of repeatability between those days of +/-5.5 N. Better repeatability was obtained using averaged scores rather than 'best effort' ; but average scores can underestimate best effort. CONCLUSION: Reasonable within-visit repeatability was found. Across-visit repeatability is consistent with the known difficulty that women have in maximally isolating and activating their levator ani muscles. The results corroborate the repeatability results of Dumoulin et al. [2004] using a similar type of dynamometer.

Servo-controlled stepped and ramped mechanical tissue algometry.

A hand-held, servo-controlled tissue palpation device (SCPD) was developed to measure the pressure-pain characteristics of human tissue for disease states linked to altered pressure-pain sensitivity. The design was based on an adaptive controller using force feedback to reach and maintain a desired force in spite of movements of the operator's hand holding the device or positional changes of the subject.

Measurement of the pubic portion of the levator ani muscle in women with unilateral defects in 3-D models from MR images.

OBJECTIVE: Develop a method to quantify the cross-sectional area of the pubic portion of the levator ani muscle, validate the method in women with unilateral muscle defects, and report preliminary findings in those women. METHOD: Multi-planar proton density magnetic resonance images of 12 women with a unilateral defect in the pubic portion of their levator ani were selected from a larger study of levator ani muscle anatomy in women with and without genital prolapse. Three-dimensional bilateral models of the levator ani were reconstructed (using 3-D Slicer, version 2.1b1) and divided into iliococcygeal and pubic portions. Muscle cross-sectional areas were calculated at four equally spaced locations perpendicular to a line drawn from the pubic origin to the visceral insertion using the I-DEAS computer modeling software. RESULTS: The cross-sectional area of the muscle on the side with the defect was smaller than the normal side at all the four locations. The average bilateral difference was up to 81% at location 1 (nearest pubic origin). Almost all of the volume difference (13.7%, P=0.0004) was attributable to a reduction in the pubic portion (24.6%, P<0.0001), not the iliococcygeal portion (P=0.64), of the muscle. CONCLUSIONS: A method was developed to quantify cross-sectional area of the pubic portion of the levator ani perpendicular to the intact muscle direction. Significant bilateral cross-sectional area differences were found between intact and defective muscles in women with a unilateral defect.

On reducing hand impact force in forward falls: results of a brief intervention in young males.

OBJECTIVE: To test the working hypotheses that after a brief (10 min) intervention, (a) young adults can volitionally reduce fall-related wrist impact forces, and (b) no difference in impact force would exist between intervention and control groups at 3-weeks or 3-months follow-up. BACKGROUND: The wrist is the most commonly fractured site in the body at any age, most often as a result of impact with the ground while arresting a forward fall.Methods. Twenty-nine healthy young male volunteers participated. A 3-month intervention group (n=10) performed five standardized forward falls before and after a 10-min instructional intervention aimed at reducing wrist impact forces during the baseline visit. They, along with a 3-month control group (n=11) who did not receive the intervention, were remeasured in five trials at 3-weeks and 3-months follow-up, without intervening practice. A baseline control group (n=8) performed the five trials, then repeated them at the baseline visit without receiving the intervention. Unilateral body segment kinematics and bilateral hand-ground impact forces were measured and the hypotheses were tested using repeated measures analysis of variance. RESULTS: At the baseline visit, a significant group-by-trial-block interaction was found (P=0.02): the 3-month intervention group reduced their average maximum impact forces by 18% from initial values (P=0.002); the baseline control group did not do so (0.5% increase, P=0.91). The 3-month intervention (20 falls) and control (15 falls) groups did not differ at the 3-month follow-up (P=0.62); however, when the groups were combined their maximum impact force had decreased significantly (8.9%, P=0.04) over that time. CONCLUSIONS: Healthy young males learned in 10 min to significantly reduce wrist impact forces in forward falls, but retention was poor at 3-weeks follow-up. Irrespective of group, however, after the 5 falls at 3-weeks subjects had taught themselves to reduce their impact forces at the 3-months follow-up. RELEVANCE: A brief educational intervention can significantly reduce forward fall-related impact forces in the short term. However, with or without the brief intervention, the experience of performing between 5-10 forward falls 3 weeks apart apparently resulted in decreased impact forces over the next 2 months, thereby reducing the risk of injury in these forward falls.

Fall-related upper body injuries in the older adult: a review of the biomechanical issues.

Although the epidemiology of fall-related injuries is well established for the elderly population over 65 years of age, the biomechanics of how, when and why injuries do and do not occur when arresting a fall have received relatively little attention. This paper reviews the epidemiological literature in the MEDLINE data base pertinent to the biomechanics of fall-related injuries, including data on fall rates, fall-related injury rates, fall directions and types of injuries available. It also covers primary sources not listed on MEDLINE, along with the pertinent biomechanics literature. Many falls in older adults are in a forward direction, and as a result the upper extremities are one of the most commonly injured structures, presumably in protecting the head and torso. In this review emphasis is placed on what is, and what is not, known of the biomechanical factors that determine the impact forces and injury risk associated with upper extremity injuries in forward falls. While decreased bone mineral density may be contributory, it is not a reliable predictor of fracture risk. Evidence is presented that fall-related impact forces can be reduced by appropriate volitional arrest strategies. Further theoretical and experimental research is needed to identify appropriate fall-arrest strategies for the elderly, as well as the physical capacities and skills required to do so. Inexpensive interventions might then be developed to teach safe fall-arrest techniques to older individuals.

The effect of age and movement speed on maximum forward reach from an elevated surface: a study in healthy women.

OBJECTIVE: To test the hypotheses (1) that the maximum distance reached by young or older women when standing on a raised platform is independent of movement speed, and (2) the maximum forward momentum generated at comfortable and fast reaching speeds is independent of age. DESIGN: Repeated measures case-control study in a university laboratory setting.Background. Maximum forward reach distance is often part of a geriatric mobility assessment. The effect of movement speed, and hence momentum, on forward reaching behavior is unknown in young or older subjects, despite the fact that excess momentum might increase the risk of fall-related injuries, especially from an elevated surface. METHODS: Ten healthy young women (mean age 23.7 years) and 10 healthy older women (mean age 70.5 years) participated. Subjects stood on an instrumented force platform and forward reach body segment kinematics were measured optoelectronically. Whole-body center of reaction and center of mass trajectories were calculated during six maximum forward reach trials: three performed "at a comfortable speed", and three performed "as fast as possible". RESULTS: Subjects reached slightly further at a comfortable speed than when reaching as fast as possible (P=0.016). Fast reaches were associated with a 25% increase in momentum (P<0.001; however, under both speed conditions, older women developed less whole-body momentum than did young controls (for example, 4.1 vs. 6.1 kgm/s at comfortable speed, P<0.05). Three young and one older women lost their balance in at least one trial. CONCLUSIONS: Independent of age, these women reached further when reaching slowly than when reaching rapidly, and older women restricted peak forward momentum under both speed conditions when standing on the elevated surface. RELEVANCE: Interventions designed to reduce falls from raised surfaces might utilize the insights gained from these women that (1) at any age, one cannot expect to reach as far when reaching fast as one can when reaching slowly; and (2) comfortable reaching speed is reduced in older individuals.

Differences in pelvic floor area between African American and European American women.

OBJECTIVE: This study tests the null hypothesis that the size of the pelvic opening spanned by the pelvic floor is the same in African American and European American women. STUDY DESIGN: Forty African American female pelvises were age matched with 40 European American female pelvises from the Hamann-Todd collection at the Cleveland Museum of Natural History. The distances between the anchoring points of the pelvic floor to the bony pelvis (pubis anteriorly, ischial spines laterally, and inferior lateral angle of the sacrum posteriorly) were measured on each half of the pelvis. Measurements from left and right halves were averaged. The cross-sectional area of the pelvic floor was calculated from these dimensions. The bi-ischial line divided the total area into anterior and posterior pelvic floor areas. Analyses taking into account differences in stature by dividing individual dimensions by height were also performed. Group differences were compared with the Student t test and the Mann-Whitney rank sum test. RESULTS: African American women had a 5.1% smaller pelvic floor area than European American women (889.6 cm(2) vs 937.0 cm(2), 5.1% P =.037). This was attributable to a 10.4% smaller posterior area (365.3 cm(2) vs 407.6 cm(2), 10.4% P =.016), whereas the anterior areas were similar (524.3 cm(2) vs 529.3 cm(2), P =.61). The following measured distances were smaller in African American women: ischial spine to inferior sacral angle (5.4 cm vs 5.9 cm, P =.016) and bi-ischial diameter (10.0 cm vs 10.6 cm, P =.004). These distances remained significant after height was controlled. CONCLUSIONS: In African American women, the posterior pelvic floor area is 10.4% smaller than in European American women, resulting in a 5.1% smaller total pelvic floor area.

Fall arrest strategy affects peak hand impact force in a forward fall.

We measured the peak hand impact force involved in bimanually arresting a forward fall to the ground from a 1-m shoulder height in five healthy young males. The effects of three different subject instruction sets: "arrest the fall naturally"; "keep the head as far from the ground as possible"; and "minimize the peak hand forces" were studied by measuring body segment kinematics, ground reaction forces, and upper-extremity myoelectric activity. The hypotheses were tested that the (a) arrest strategy did not influence peak impact force, (b) arm configuration, impact velocity and upper-extremity electromyography (EMG) levels correlate to the peak impact force (c) and impacting the ground with one hand leading the other does not increase the impact force over that obtained with simultaneous hand use. The results show that these subjects were able to volitionally decrease the peak impact force at the wrist by an average of 27% compared with a "natural landing" (p=0.014) and 40% compared with a "stiff-arm landing" (p<0.0005). The magnitude of the peak unilateral wrist force varied from 0.65 to 1.7 body weight for these moderate falls onto a padded surface. Peak force correlated with the elbow angle at impact, wrist velocity at impact and with pre-EMG triceps activity. The force was not significantly higher for non-simultaneous hand impacts. We conclude that fall arrest strategy can substantially alter the peak impact forces applied to the distal forearm during a fall arrest. Therefore, the fall arrest strategy likely influences wrist injury risk independent of bone strength.

Gender differences in knee angle when landing from a drop-jump.

Twenty (10 men and 10 women) healthy, height-matched patients (mean patient age: 28+/-5 years) participated in a study testing the (null) hypothesis that no significant gender differences would be found in the knee flexion angle upon impact from a drop-landing. Patients performed three unconstrained jumps from three vertical heights (20, 40, and 60 cm) onto a concrete floor. Reflective markers were placed on the right side of the body at six sites: the head of the fifth metatarsal, the lateral malleolus, the lateral femoral condyle, the greater trochanter, the posterosuperior iliac spine, and the anterosuperior iliac spine. Ankle, knee, and hip angles in the sagittal plane were then measured at 120 Hz using a two-dimensional motion analysis system. Significant gender differences in knee flexion angles were found at ground impact during the drop-landing (P<.05). The largest gender difference in knee angle occurred when landing from a height of 60 cm: men landed with 16 degrees of knee flexion, whereas women landed with a significantly straighter knee flexion angle of 7 degrees (P<.05). A similar gender difference was found when landing from the medium jump height (40 cm). In this sample, women landed with a straighter knee than did age- and height-matched men.

How quickly can healthy adults move their hands to intercept an approaching object? Age and gender effects.

BACKGROUND: The upper extremities are often used to protect the head and torso from impact with an object or with the ground. We tested the null hypotheses that neither age nor gender would affect the time required for healthy adults to move their upper extremities into a protective posture. METHODS: Twenty young (mean age 25 years) and twenty older (mean age 70 years) volunteers, with equal gender representation, performed a seated arm-movement task under three conditions: Condition 1, in which subjects were instructed to raise the hands upon cue as quickly as possible from thigh level to a shoulder height target; Condition 2, in which subjects were instructed as in Condition 1 with the addition of intercepting a swinging pendulum at the prescribed hand target; and Condition 3, in which subjects were instructed as in Condition 2 but were asked to wait as long as possible before initiating hand movement to intercept the pendulum. Arm movements were quantified using standard kinematic techniques. RESULTS: Age (p <.01) and gender (p <.05) affected hand movement times. In Conditions 1 and 2, the older women required 20% longer movement times than the other subject groups (335 vs 279 milliseconds; p <.01). In Condition 3, shorter movement times were achieved by young men (20%; p =.002) and older women (10%; p =.056) as compared with their respective performance in Conditions 1 and 2 because they did not fully decelerate their hands. The other groups slowed their movements in Condition 3. CONCLUSIONS: Age, gender, and perceived threat significantly affected movement times. However, even the slowest movement times were well within the time available to deploy the hands in a forward fall to the ground.

On-screen vector-based ultrasound assessment of vesical neck movement.

OBJECTIVE: We sought to develop a vector-based assessment to determine the magnitude and direction of bladder neck movements, as well as to assess whether probe movement relative to the pubis needs to be taken into account. STUDY DESIGN: Ten nulliparous continent, 10 primiparous continent, and 10 primiparous stress-incontinent women were recruited. Perineal ultrasound scanning was performed in standing women while they were resting, performing the Valsalva maneuver, coughing, and performing Kegel exercises. A direct on-screen assessment of bladder neck displacement from rest to the peak of dynamic activity relative to the pubic axis was made. Transducer movement was assessed by measuring the displacement of the pubic bone. RESULTS: The method was feasible because measurements were possible in all 30 subjects. Vesical neck and pubic point movement in millimeters (+/- SD) and the percentage error if pubic point movement is not accounted for are as follow: strain, vesical neck 16.9 +/- 6.1 and pubic point 4.8 +/- 3.9, 28%; cough, vesical neck 10.2 +/- 5.4, pubic point 2.9 +/- 3.4, 33%; Kegel exercise, vesical neck 7.0 +/- 3.6 and pubic point 0.7 +/- 1.4, 37%. Similar discrepancies in angle were found and are presented. Uncorrected direction of vesical neck and pubic point movement in degrees and the percentage error if pubic point movement is not accounted for are as follow: strain, vesical neck 169.4 +/- 18.5 and pubic point 214.0 +/- 56.7, 18%; cough, vesical neck 162.0 +/- 12.8, pubic point 238.4 +/- 27.4, 22%; Kegel exercise, vesical neck -0.9 +/- 12.7 and pubic point -4.8 +/- 20.6, 87%. Test-retest reliability correlations were more than an r value of 0.7 in all measures and 86% of the measurements greater than 0.8. CONCLUSION: The vector-based system provides a simple method for quantifying distance and direction of vesical neck motion, as well as localizing the resting vesical neck position.

Can proprioception really be improved by exercises?

There is little question that ankle disc training can improve ankle muscle motor performance in a unipedal balance task, most likely through improved strength and coordination [62] and possibly endurance. How much of the observed improvement in motor performance is due to improved ankle proprioception remains unknown. We have reviewed a number of theoretical ways in which training might improve proprioception for moderately challenging weight-bearing situations such as balancing on one leg. Although the relevant experiments have yet to be performed to test this hypothesis, any improvement would theoretically help to reduce injuries at these moderate levels of challenge. We question, however, whether these exercises can ever improve the reactive response required to prevent injury under the most challenging time-critical situations. If confirmed, this limitation needs to be acknowledged by authors and practitioners alike. Alternative protective strategies for the most challenging time-critical situations should be sought. We conclude that, despite their widespread acceptance, current exercises aimed at "improving proprioception" have not been demonstrated to achieve that goal. We have outlined theoretical scenarios by which proprioception might be improved, but these are speculative. The relevant experiments remain to be conducted. We argue that even if they were proven to improve proprioception, under the best circumstances such exercises could only prevent injury under slow to intermediate rate provocations to the joint musculoligamentous complex in question.

Age and gender differences in peak lower extremity joint torques and ranges of motion used during single-step balance recovery from a forward fall.

Previous studies have found substantial age and gender group differences in the ability of healthy adults to regain balance with a single step after a forward fall. It was hypothesized that differences in lower extremity joint strengths and ranges of motion (ROM) may have contributed to these observed differences. Kinematic and forceplate data were therefore used with a rigid-link biomechanical model simulating stepped leg dynamics to examine the joint torques and ROM used by subjects during successful single-step balance recoveries after release from a forward lean. The peak ROM and torques used by subjects in the study were compared to published estimates or measured values of the available maxima. No significant age or gender group differences were found in the mean ROM used by the subjects for any given initial lean angle. As initial lean angle increased, larger knee ROM and significantly larger hip ROM were used in the successful recoveries. There were substantial gender differences and some age group differences in peak lower extremity joint torques used in successful recoveries. Both young and older females often used nearly maximal joint torques to recover balance. Subjects' maximum joint strengths in plantarflexion and hip flexion were not good predictors of single-step balance recovery ability, particularly among the female subjects.

Mild diabetic neuropathy affects ankle motor function.

OBJECTIVE: To evaluate the effect of age and diabetic neuropathy on ankle motor function in the frontal plane in terms of rate of torque development and capability for balance recovery. DESIGN: Case control study. Six older women with diabetic neuropathy compared to six women without neuropathy, matched for age and presence of diabetes mellitus; and nine healthy young women. BACKGROUND: Neuropathy causes a distal impairment in lower extremity sensory function which increases fall risk. Impairments in ankle inversion/eversion proprioceptive thresholds have been identified, but the effect of neuropathy on ankle motor strength in the frontal plane is unknown. METHODS: Subjects' abilities to recover from a lateral lean (with center of gravity offset as percentage of foot width) while standing on one foot, and to rapidly generate inversion torque about the ankle, were quantified. RESULTS: All nine of the young, but only one of six older, control subjects recovered from a 10% lean (P=0.0052). Three of six older controls, but no neuropathy subject, recovered from a 5% lean (P=0.083). Neuropathy subjects demonstrated half the ankle rate of torque development [78.2 (50.8) N m/s; P=0.016] of the young and older controls [162.0 (54.6) and 152.7 (22.2) N m/s, respectively]. CONCLUSIONS: Diabetic neuropathy leads to a decrease in rapidly available ankle strength which impairs balance recovery among older women. Younger women demonstrate similar ankle strength but superior balance recovery compared to older women without neuropathy.

The functional anatomy of the female pelvic floor and stress continence control system.

This paper provides an overview of the functional anatomy of the structures responsible for controlling urinary continence under stress. The stress continence control system can be divided into two parts: the system responsible for bladder neck support, and the system responsible for sphincteric closure. Age- and injury-related changes in each of these systems are discussed. Understanding the pathophysiology of incontinence on the anatomical level will help to lead to identification of specific defects, thereby allowing better individualized treatment for the incontinent patient.

Inversion and eversion strengths in the weightbearing ankle of young women. Effects of plantar flexion and basketball shoe height.

Maximum isometric ankle inversion and eversion muscle strengths were measured under full unipedal weightbearing in 20 healthy young adult women. When the women wore a low-top shoe, the mean (standard deviation) maximum external eversion moments resisted with the foot in 0 degrees and 32 degrees of ankle plantar flexion were 24.1 (7.6) and 24.1 (8.1) N x m, respectively, while the corresponding values for maximum inversion moments resisted were 14.7 (6.8) and 17.4 (6.4) N x m, respectively. Both shoe height and ankle plantar flexion affected the overall inversion moment resisted by 17% (P = 0.03) at 0 degrees of ankle plantar flexion to 11.9% (P = 0.003) at 32 degrees of ankle plantar flexion. However, neither shoe height nor ankle plantar flexion significantly affected the maximum eversion moment resisted. Although eversion muscle strength of the young women averaged 39% less than the corresponding value found in young men, the sex difference was not significant when ankle strengths were normalized by body size (body weight x height). Thus, when data from healthy young men and women were averaged, eversion and inversion strengths averaged 1.6% and 2.7%, respectively, of body weight x height.