Passive Ankle Stiffness Research Articles

Achilles tendon morphology, plantar flexors torque and passive ankle stiffness in spastic hemiparetic stroke survivors

BackgroundThe present study compared the Achilles tendon morphological characteristics, plantar flexor toque and passive ankle stiffness between hemiparetic spastic stroke survivors and healthy subjects. MethodsThe Achilles tendon length was measured at the affected and contralateral limbs of twelve hemiparetic stroke survivors with ankle spasticity and twelve healthy subjects. The ankle was held at three different angles (20° plantar flexion, 0° and maximum dorsiflexion) while an ultrasound system was used to capture images from the Achilles tendon. Active and passive plantar flexor torque production was measured using an isokinetic dynamometer. FindingsThere was no significant difference in tendon length and Achilles tendon complacency between stroke survivors [affected limb: 20.8 (1.59) cm at 0° and 0.11 (0.09) cm/N; contralateral limb: 20.8 (1.7) cm at 0° and 0.12 (0.08) cm/N] and healthy subjects [20 (2.78) cm at 0° and 0.15 (0.1) cm/N]. The contralateral limb was stronger than the affected limb, while healthy participants presented larger active torque in relation to stroke survivors. There was no significant difference in passive ankle stiffness between the affected [0.43 (0.08) N/°] and the contralateral limb [0.40 (0.11) N/°], but affected limb was significantly stiffer than the healthy subjects [0.32 (0.07) N/°]. InterpretationThe larger passive torque and ankle joint stiffness from stroke survivors with similar Achilles tendon length compared to healthy subjects seem to be unrelated to tendon extensibility.

Postinjury biomechanics of Achilles tendon vary by sex and hormone status.

Achilles tendon ruptures are common injuries. Sex differences are present in mechanical properties of uninjured Achilles tendon, but it remains unknown if these differences extend to tendon healing. We hypothesized that ovariectomized females (OVX) and males would exhibit inferior postinjury tendon properties compared with females. Male, female, and OVX Sprague-Dawley rats (n = 32/group) underwent acclimation and treadmill training before blunt transection of the Achilles tendon midsubstance. Injured hindlimbs were immobilized for 1 wk, followed by gradual return to activity and assessment of active and passive hindlimb function. Animals were euthanized at 3 or 6 wk postinjury to assess tendon structure, mechanics, and composition. Passive ankle stiffness and range of motion were superior in females at 3 wk; however, by 6 wk, passive and active function were similar in males and females but remained inferior in OVX. At 6 wk, female tendons had greater normalized secant modulus, viscoelastic behavior, and laxity compared with males. Normalized secant modulus, cross-sectional area and tendon glycosaminoglycan composition were inferior in OVX compared with females at 6 wk. Total fatigue cycles until tendon failure were similar among groups. Postinjury muscle fiber size was better preserved in females compared with males, and females had greater collagen III at the tendon injury site compared with males at 6 wk. Despite male and female Achilles tendons withstanding similar durations of fatigue loading, early passive hindlimb function and tendon mechanical properties, including secant modulus, suggest superior healing in females. Ovarian hormone loss was associated with inferior Achilles tendon healing.

Measurement of the passive stiffness of ankle joint in 3 DOF using stewart platform type ankle foot device.

This paper presents a method to measure the passive stiffness of an ankle joint in three degrees of freedom (DOF) under two motion speeds (1 Hz and 5 degree/s) using a developed Stewart platform-type device. The developed device can reproduce input motions of the foot in 6 DOF by controlling six pneumatic linear motion actuators. We used the device to measure the passive stiffness of an ankle joint undergoing three kinds of motion, namely dorsi-plantar flexion, inversion-eversion, and adduction-abduction. The measured values of the passive stiffness of the ankle joint in dorsiflexion that we obtained agreed well with that obtained in a previous study, indicating that the developed device is useful for measuring the passive stiffness of ankle joint. In addition, the developed device can be used to measure the stiffness in inversion-eversion and adduction-abduction motions as well, parameters that have never been measured. The results we obtained demonstrated certain interesting features as we varied both the direction and pace of motion (e.g., there were significant differences in the stiffness not only between adduction and abduction during the faster pace, but also between these and the other motions).

Treadmill training with an incline reduces ankle joint stiffness and improves active range of movement during gait in adults with cerebral palsy

Purpose: We investigated if 30 min of daily treadmill training with an incline for 6 weeks would reduce ankle joint stiffness and improve active range of movement in adults with cerebral palsy (CP).Methods: The study was designed as a randomized controlled clinical trial including 32 adults with CP (GMFCS 1–3) aged 38.1 SD 12 years. The training group (n = 16) performed uphill treadmill training at home daily for 30 min for 6 weeks in addition to their usual activities. Passive and reflex mediated stiffness and range of motion (ROM) of the ankle joint, kinematic and functional measures of gait were obtained before and after the intervention/control period. Intervention subjects trained 31.4 SD 10.1 days for 29.0 SD 2.3 min (total) 15.2 h.Results: Passive ankle joint stiffness was reduced (F = 5.1; p = 0.031), maximal gait speed increased (F = 42.8, p < 0.001), amplitude of toe lift prior to heel strike increased (F = 5.3, p < 0.03) and ankle angle at heel strike was decreased (F = 12.5; p < 0.001) significant in the training group as compared to controls.Conclusion: Daily treadmill training with an incline for 6 weeks reduces ankle joint stiffness and increases active ROM during gait in adults with CP. Intensive gait training may thus be beneficial in preventing and reducing contractures and help to maintain functional gait ability in adults with CP.Implications for rehabilitationUphill gait training is an effective way to reduce ankle joint stiffness in adult with contractures.6 weeks of daily uphill gait training improves functional gait parameters such as gait speed and dorsal flexion during gait in adults with cerebral palsy.

Four Weeks of Balance Training does not Affect Ankle Joint Stiffness in Subjects with Unilateral Chronic Ankle Instability.

Balance training has been shown to be effective in preventing ankle sprain recurrences in subjects with chronic ankle instability (CAI) but the biomechanical pathways underlying the clinical outcomes are still unknown. This study was conducted to determine if a 4-week balance training intervention can alter the mechanical characteristics in ankles with CAI. Twenty-two recreationally active subjects with unilateral CAI were randomized to either a control (n = 11, 35.1 ± 9.3 years) or intervention (n = 11, 33.5 ± 6.6 years) group. Subjects in the intervention group were trained on the affected limb with static and dynamic components using a Biodex balance stability system for 4-weeks. The ankle joint stiffness and neutral zone in inversion and eversion directions on the involved and uninvolved limbs was measured at baseline and post-intervention using a dynamometer. At baseline, the mean values of the inversion stiffness (0.69 ± 0.37 Nm/degree) in the involved ankle was significantly lower (p < 0.011, 95% CI [0.563, 0.544]) than that of uninvolved contralateral ankle (0.99 ± 0.41 Nm/degree). With the available sample size, the eversion stiffness, inversion neutral zone, and eversion neutral zone were not found to be significantly different between the involved and uninvolved contralateral ankles. The 4-week balance training intervention failed to show any significant effect on the passive ankle stiffness and neutral zones in inversion and eversion. Decreased inversion stiffness in the involved chronic unstable ankle was found that of uninvolved contralateral ankle. The 4-week balance training program intervention was ineffective in altering the mechanical characteristics of ankles with CAI. Randomized controlled clinical trial; Level of evidence, 1.

Measurement of gastrocnemius muscle elasticity by shear wave elastography: association with passive ankle joint stiffness and sex differences.

Passive joint stiffness is an important quantitative measure of flexibility, but is affected by muscle volume and all of the anatomical structures located within and over the joint. Shear wave elastography can assess muscle elasticity independent of the influences of muscle volume and the other nearby anatomical structures. We determined how muscle elasticity, as measured using shear wave elastography, is associated with passive joint stiffness and patient sex. Twenty-six healthy men (24.4 ± 5.9 years) and 26 healthy women (25.2 ± 4.8 years) participated in this study. The passive ankle joint stiffness and tissue elasticity of the medial gastrocnemius (MG) were quantified with the ankle in 30° plantar flexion (PF), a neutral anatomical position (NE), and 20° dorsiflexion (DF). No significant difference in passive joint stiffness by sex was observed with the ankle in PF, but significantly greater passive ankle joint stiffness in men than in women was observed in NE and DF. The MG elasticity was not significantly associated with joint stiffness in PF or NE, but it was significantly associated with joint stiffness in DF. There were no significant differences in MG elasticity by sex at any ankle position. Muscle elasticity, measured independent of the confounding effects of muscle volume and the other nearby anatomical structures, is associated with passive joint stiffness in the joint position where the muscle is sufficiently lengthened, but does not vary by sex in any joint position tested.

Sway-dependent changes in standing ankle stiffness caused by muscle thixotropy.

Key points The passive stiffness of the calf muscles contributes to standing balance, although the properties of muscle tissue are highly labile.We investigated the effect of sway history upon intrinsic ankle stiffness and demonstrated reductions in stiffness of up to 43% during conditions of increased baseline sway.This sway dependence was most apparent when using low amplitude stiffness‐measuring perturbations, and the short‐range stiffness component was smaller during periods of high sway.These characteristics are consistent with the thixotropic properties of the calf muscles causing the observed changes in ankle stiffness.Periods of increased sway impair the passive stabilization of standing, demanding more active neural control of balance. Quiet standing is achieved through a combination of active and passive mechanisms, consisting of neural control and intrinsic mechanical stiffness of the ankle joint, respectively. The mechanical stiffness is partly determined by the calf muscles. However, the viscoelastic properties of muscle are highly labile, exhibiting a strong dependence on movement history. By measuring the effect of sway history upon ankle stiffness, the present study determines whether this lability has consequences for the passive stabilization of human standing. Ten subjects stood quietly on a rotating platform whose axis was collinear with the ankle joint. Ankle sway was increased by slowly tilting this platform in a random fashion, or decreased by fixing the body to a board. Ankle stiffness was measured by using the same platform to simultaneously apply small, brief perturbations (<0.6 deg; 140 ms) at the same time as the resulting torque response was recorded. The results show that increasing sway reduces ankle stiffness by up to 43% compared to the body‐fixed condition. Normal quiet stance was associated with intermediate values. The effect was most apparent when using smaller perturbation amplitudes to measure stiffness (0.1 vs. 0.6 deg). Furthermore, torque responses exhibited a biphasic pattern, consisting of an initial steep rise followed by a shallower increase. This transition occurred earlier during increased levels of ankle sway. These results are consistent with a movement‐dependent change in passive ankle stiffness caused by thixotropic properties of the calf muscle. The consequence is to place increased reliance upon active neural control during times when increased sway renders ankle stiffness low.

A new method to assess passive and active ankle stiffness during quiet upright stance

Both passive and active ankle torque contribute to postural stability during quiet upright stance, yet directly measuring their relative contributions is difficult. Here, a new method was developed to estimate passive and active ankle stiffness (ST) and damping (DA). In contrast to earlier approaches, the proposed method does not require external mechanical or sensory perturbations. Instead, the method is based on the assumption that upright stance is intermittently controlled, and that active ankle torque is in-phase coherent with ankle angular acceleration. Thus, identifying the local maxima of ankle angular accelerations facilitates the identification of time windows that include substantial active ankle torque. After identifying these local maxima and associated windows, estimates of passive and active ankle ST and DA were obtained using linear regression analyses. Consistent with earlier work, passive ankle torque was estimated to account for 94–97% of the total ankle torque, and to have linear relationships with ankle angle and angular velocity. Predicted values of passive and active ankle stiffness were also consistent with earlier reports. This new approach may be a useful tool to efficiently investigate passive and active joint stiffness during quiet upright stance.

The association of muscle and tendon elasticity with passive joint stiffness: In vivo measurements using ultrasound shear wave elastography

BackgroundPassive joint stiffness is associated with various tissues, including muscles, tendons, ligaments, and joint capsules. The specific elasticity of muscles or tendons can be measured using ultrasound shear wave elastography. To examine the association of muscle and tendon elasticity with passive joint stiffness, in vivo measurements of muscle and tendon elasticity were performed using ultrasound shear wave elastography. MethodsIn 25 subjects, passive ankle joint stiffness was determined using the joint angle–passive torque relationship. The stiffness index of the muscle belly of the medial gastrocnemius (MG)—influenced by the muscle fascicles, its aponeuroses, and the proximal tendon—was quantified by the displacement of the muscle-tendon junction, which was visualized using B-mode ultrasonography during passive dorsiflexion. The stiffness index of the Achilles tendon—influenced by the tendon and the ligaments and joint capsule of the ankle—was similarly determined. The MG and Achilles tendon elasticity was measured using ultrasound shear wave elastography. FindingsSimple regression indicated a significant correlation between passive joint stiffness and stiffness index of the MG muscle belly (r=0.80) and Achilles tendon (r=0.60), but no correlation with elasticity of the MG (r=−0.37) or Achilles tendon (r=−0.39). InterpretationIndividual variations in the elasticity of either the MG or Achilles tendon are not associated with variations in passive ankle joint stiffness; however, variations in the elasticity of other tissues, including MG aponeuroses or the ligaments and joint capsule of the ankle, would be associated with the variations in joint stiffness.

Can balance training affect the ankle joint stiffness in subjects with unilateral chronic ankle instability?

Background: Lateral ankle sprain is one of the most frequent sports-related injuries, accounting for up to 60% of all athletic injuries. The development of repetitive ankle sprains and persistent residual symptoms such as repeated episodes of ankle giving way, pain, weakness, loss of function, and feeling of ankle instability after injury has been termed chronic ankle instability (CAI). The signs and symptoms of initial injury often resolve with time but mechanical joint laxity may last longer leading to residual symptoms. Balance training has been shown to be effective in preventing ankle sprain recurrences in subjects with CAI but the biomechanical and/or neurophysiological pathways underlying the clinical outcomes are still unknown. Balance training is routinely used in clinical practice for sprained ankles, however to our knowledge, only one study has examined the effects of balance training intervention on flexibility characteristics of the ankle joint in patients with CAI. Purpose: This study was conducted to determine if a 4week balance training intervention can alter the mechanical characteristics in ankles with CAI. Methods: Twenty-two recreationally active subjects with unilateral CAI were randomized to either a control (n= 11, 35.1± 9.3 years) or intervention (n= 11, 33.5± 6.6 years) group. Subjects in the intervention group were trained on the affected limb with static and dynamic components using a Biodex balance stability system for 4-weeks. The ankle joint stiffness and neutral zone in inversion and eversion directions on the involved and uninvolved limbs was measured at baseline and post-intervention using a dynamometer. Results:Atbaseline, themeanvalues of the inversion stiffness (0.69± 0.37Nm/degree) in the involved ankle was significantly lower (p< 0.011, 95% CI [0.563, 0.544]) than that of uninvolved contralateral ankle (0.99± 0.41Nm/degree). With the available sample size, the eversion stiffness, inversion neutral zone, and eversion neutral zone were not found to be significantly different between the involved and uninvolved contralateral ankles. The 4-week balance training intervention failed to show any significant effect on the passive ankle stiffness and neutral zones in inversion and eversion. Conclusion(s): Decreased inversion stiffness in the involved chronic unstable ankle was found that of uninvolved contralateral ankle. The 4-week balance training program intervention was ineffective in altering the mechanical characteristics of ankles with CAI. Implications:Traditionally, taping and bracing have been used to improve stability and prevent recurrent ankle injury in patients with CAI. However, the beneficial effects of ankle taping have been attributed to enhanced proprioception and mechanical restriction, but there is no indication of restoring ligamentous stability. Further research with additional stiffness measures along with functional tests, larger sample size, and progressive balance training exercises is needed to identify if the mechanical characteristics of chronic unstable ankles can be altered.

The influence of ankle muscle activation on postural sway during quiet stance

Although balance during quiet standing is postulated to be influenced by multiple factors, including ankle stiffness, it is unclear how different mechanisms underlying increases in stiffness affect balance control. Accordingly, this study examined the influence of muscle activation and passive ankle stiffness increases on the magnitude and frequency of postural sway. Sixteen young adults participated in six quiet stance conditions including: relaxed standing, four muscle active conditions (10%, 20%, 30% and 40% maximum voluntary contraction (MVC)), and one passive condition wearing an ankle foot orthotic (AFO). Kinetics were collected from a force plate, while whole-body kinematics were collected with a 12-sensor motion capture system. Bilateral electromyographic signals were recorded from the tibialis anterior and medial gastrocnemius muscles. Quiet stance sway amplitude (range and root mean square) and frequency (mean frequency and velocity) in the sagittal plane were calculated from time-varying centre of gravity (COG) and centre of pressure (COP) data. Compared to the relaxed standing condition, metrics of sway amplitude were significantly increased (between 37.5 and 63.2%) at muscle activation levels of 30% and 40% MVC. Similarly, frequency measures increased between 30.5 and 154.2% in the 20–40% MVC conditions. In contrast, passive ankle stiffness, induced through the AFO, significantly decreased sway amplitude (by 23–26%), decreased COG velocity by 13.8%, and increased mean COP frequency by 24.9%. These results demonstrate that active co-contraction of ankle musculature (common in Parkinson’s Disease patients) may have differential effects on quiet stance balance control compared to the use of an ankle foot orthotic (common for those recovering from stroke).

The Effects of Ankle Kinesio® Taping on Ankle Stiffness and Dynamic Balance

The purpose of this study was to determine the effects of Kinesio® taping on static restraint and dynamic postural control of the ankle joint. Thirty female subjects with no history of ankle injury participated in this study. Subjects were tested for passive ankle laxity and stiffness, and time to stabilization following forward, backward, medial, and lateral hops. Subjects were tested prior to tape application, immediately following application, and following 24 hours of use. Differences between taping conditions were investigated using analyses of variance and pairwise comparisons. Stiffness increased following initial application and 24 hours of Kinesio® tape use (F = 6.99, p = .003), despite no observed changes in ankle laxity (F = 0.77, p = .49); however, no changes were observed in time-to-stabilization (F = 0.03, p = .97). Our results suggest that Kinesio® tape may improve static restraint in the ankle joint without altering peak motion or dynamic postural control. A future investigation into Kinesio® tape efficacy in injury prevention or rehabilitation is warranted.

Neuromechanical assessment of lidocaine test block in spastic lower limbs

The objective of this study was to quantify in spastic lower limbs the changes in reflex EMGs and in ankle stiffness after a lidocaine block of the soleus nerve to better understand physiological effects of lidocaine. Twenty patients were prospectively included and assessed before and after lidocaine block of the soleus nerve. We studied clinical and neuromechanical parameters of the triceps surae, including quantification of the maximum Hoffmann's reflex (Hmax) and tendinous reflex (T) normalized to the maximum direct motor response (Mmax), and passive ankle stiffness assessed by sinusoidal length perturbations. All patients whatever the aetiology of spasticity were improved in clinical parameters of spasticity after the block (62% reduction of the Ashworth score, 85% reduction of stretch reflex scores, increased score on the Physicians' Rating Scale). All patients presented a reduction of the Hmax-Mmax ratio (mean reduction of 67%) and the T-Mmax ratio (82%). Ankle stiffness was decreased by an average of 23%. Measured stiffness was correlated with the Ashworth score and the T-Mmax ratio. Relatively greater change in the T reflex than in the H reflex suggests that lidocaine block reduces hyperreflexia not only by interfering with generation of afferent volleys in the injected nerve, but also probably by altering generation of the volleys at the level of muscle spindles in the affected spastic muscles, presumably by blocking the transmission along gamma-efferent fibers.

Changes in passive ankle stiffness and its effects on gait function in people with chronic stroke

Mechanical impedance of the ankle is known to influence key aspects of ankle function. We investigated the effects of robot-assisted ankle training in people with chronic stroke on the paretic ankle's passive stiffness and its relationship to overground gait function. Over 6 wk, eight participants with residual hemiparetic deficits engaged in a visuomotor task while seated that required dorsiflexion (DF) or plantar flexion (PF) of their paretic ankle with an ankle robot ("anklebot") assisting as needed. Passive ankle stiffness (PAS) was measured in both the trained sagittal and untrained frontal planes. After 6 wk, the PAS decreased in both DF and PF and reverted into the variability of age-matched controls in DF. Changes in PF PAS correlated strongly with gains in paretic step lengths (Spearman rho = -0.88, p = 0.03) and paretic stride lengths (Spearman rho = -0.82, p = 0.05) during independent floor walking. Moreover, baseline PF PAS were correlated with gains in paretic step lengths (Spearman rho = 0.94, p = 0.01), paretic stride lengths (Spearman rho = 0.83, p = 0.05), and single-support stance duration (Spearman rho = 0.94, p = 0.01); and baseline eversion PAS were correlated with gains in cadence (Spearman rho = -0.88, p = 0.03). These findings suggest that ankle robot-assisted, visuomotor-based, isolated ankle training has a positive effect on paretic ankle PAS that strongly influences key measures of gait function.

Sex differences in relationship between passive ankle stiffness and leg stiffness during hopping

The goal of this study was to examine the hypothesis that the relationships between passive ankle stiffness and leg stiffness would be different between males and females. 10 males and 10 females performed hopping in place on two legs at three frequencies of 2.0, 2.5, and 3.0Hz. Based on a spring-mass model, leg stiffness, which is defined as the ratio of maximum ground reaction force to maximum center of mass displacement at the middle of the stance phase, was calculated using the vertical ground reaction force. Further, passive ankle stiffness was calculated as the slope of the passive ankle torque-angle relationship, which results from controlled passive ankle dorsiflexion. There was no significant difference in the leg stiffness between males and females at three hopping frequencies; however, females displayed less passive ankle stiffness than males. Further, significant positive linear relationships were found between the passive ankle stiffness and the leg stiffness for females at all hopping frequencies; however, there were no significant correlations between the passive ankle stiffness and the leg stiffness in males for all hopping frequencies. These results suggest that the relationship between the passive ankle stiffness and the leg stiffness are not the same between males and females, which may lead to a greater risk of anterior cruciate ligament injuries in females.

Validity and reliability of clinical tests for assessing passive ankle stiffness

The presence of inadequate levels of passive ankle stiffness have been associated with the occurrence of movement disorders, the development of pathological conditions and the reduction in the performance of functional activities such as walking, running and jumping. Therefore, clinical tests to evaluate ankle stiffness may be useful for the physical therapy assessment. To investigate the concurrent validity and the intra- and inter-examiner reliability of clinical measures developed to assess passive stiffness of the ankle joint during dorsiflexion movement. Fifteen healthy participants underwent to test-retest evaluations of their ankles by two examiners. Two clinical measures were performed: 'position of first detectable resistance' and 'change in passive resistance torque'. The results of these tests were compared to the passive stiffness measured with an isokinetic dynamometer, in which the electromyography activity of specific muscles was monitored to ensure that the test was performed passively (gold standard measure). Pearson correlation coefficients ranged from r=-0.81 to -0.88 (p<0.001) for the correlation between the passive ankle stiffness measured with the isokinetic dynamometer and the results of the clinical measure 'position of the first detectable resistance'. For the measure of 'change in passive resistance torque', these coefficients ranged from r=0.72 to 0.83 (p<0.004). The Intraclass Correlation Coefficients (ICCs) for the intra- and inter-examiner reliability ranged from 0.75 to 0.98. The clinical measures presented satisfactory validity and reliability to be used in clinical practice.

Possible Factors Related to Functional Ankle Instability

Case control study. To classify individuals with functional ankle instability (FAI) into deficit and non-deficit categories based on the evaluation of the most common factors that have been proposed to be related to FAI. Recent studies have suggested that FAI may be secondary to a combination of factors including ankle proprioceptive deficit, muscular weakness, impaired balance, delayed neuromuscular reaction time, and joint laxity. However, only a few authors have investigated the prevalence and association among these factors in a single group of individuals. The above 5 factors were tested bilaterally in 21 individuals with FAI and in 16 healthy control subjects. Data were analyzed for (1) within- and between-group comparison, (2) classification of subjects with FAI into deficit and no-deficit categories, and (3) magnitude of association between factors in the subjects with FAI using Pearson bivariate correlation. Balance control and evertors' strength were significantly less on the affected side in comparison to the unaffected side in subjects with FAI. The evertors' strength was also significantly different between the side difference of the FAI group and the side difference of the control group. Passive ankle stiffness was significantly correlated to balance control, ankle proprioception, and evertor peak torque. Individuals with FAI demonstrated a large variation in the deficit categories ranging from multiple deficits to no noticeable deficits. Mechanical alterations in the ankle joint may influence several aspects of the ankle's functional ability. Alterations in the afferent processes, represented in this study by ankle proprioception, may effect the evertors' strength or vice versa. More importantly, individuals with FAI might exhibit high variability in ankle deficits.

Are passive ankle stiffness and ROM modified during the menstrual cycle?

Are passive ankle stiffness and ROM modified during the menstrual cycle?

Passive stiffness of the plantar flexion in relation to age and functional performance

Passive stiffness (Nm/ ◦ ) of the plantar flexors was measured during a passive stretch into dorsiflexion (DF) in 18 healthy female subjects (range 18-60 years old) using an isokinetic dynamometer. Passive stiffness of the ankle joint was measured at a short range of motion (from 10 ◦ of plantar flexion (PF) to 10 ◦ of DF), and at a full range of motion (from 10 ◦ PF to maximal DF for each individual) with a neutral EMG from a subset of four legs. The purpose of the study was to assess the variances in the measurements of passive stiffness of the calf muscle and to correlate passive stiffness to age and jumping ability. There was a significant correlation (r = 0.76) between the FRS and FRS test-retest. The methodological error for duplicate determinations was 7.7% for the SRS and 5.5% for the FRS. There was a significant correlation between age and the (FRS) full-range stiffness (r = 0.83). There was a significant negative correlation between age and jumping (r = �0.54). We conclude that the test model of passive stiffness used in the present study is a useful method with good reliability. The passive elastic properties of muscles and tendons might explain part of the muscle performance in functional tests with ageing. However, other qualities may influence performance as well.

Ankle ROM and stiffness measured at rest and during gait in individuals with and without diabetic sensory neuropathy.

The purpose of our study was to examine the relationship between ankle dorsiflexion (DF) range of motion (ROM) and stiffness measured at rest (passively) and plantar loading during gait in individuals with and without diabetes mellitus (DM) and sensory neuropathy. Specifically, we sought to address three questions for this at-risk patient population: (1) Does peak passive DF ROM predict ankle DF ROM used during gait? (2) Does passive ankle stiffness predict ankle stiffness used during gait? (3) Are any of the passive or gait-related ankle measures associated with plantar loading? Ten subjects with DM and 10 age and gender matched non-diabetic control subjects participated in this study. Passive ankle DF ROM and stiffness were measured with the Iowa Ankle ROM device. Kinematic, kinetic and plantar pressure data were collected as subjects walked at 0.89 m/s. We found that subjects with DM have reduced passive ankle DF ROM and increased stiffness compared to non-diabetic control subjects, however, subjects with DM demonstrated ankle motion, stiffness and plantar pressures, similar to control subjects, while walking at the identical speed, 0.89 m/s (2 mph). These data indicate that clinical measures of heel cord tightness and stiffness do not represent ankle motion or stiffness utilized during gait. Our findings suggest that subjects with DM utilize strategies such as shortening their stride length and reducing their push-off power to modulate plantar loading.