Plantar Flexor Stiffness Research Articles

Effects of short-duration constant torque and constant angle stretching on the musculotendinous stiffness of ankle plantar flexors

Effects of short-duration constant torque and constant angle stretching on the musculotendinous stiffness of ankle plantar flexors

Quantifying Active and Passive Stiffness in Plantar Flexor Muscles Following Intermittent Maximal Isometric Contractions Using Shear Wave Elastography

ObjectiveThis study aimed: (i) to investigate the impact of fatigue, triggered by maximal isometric contraction exercises, on the active and passive stiffness of plantar flexors (PF), and (ii) to examine the relationship between changes in mechanical parameters and neuromuscular alterations after fatigue. MethodsA healthy cohort (n = 12; age = 27.3 ± 5.5 y; BMI = 24.4 ± 2.35 kg/m²) was instructed to perform 60 isometric contractions, each lasting 4 s with a 1-s rest interval, using an ergometer. Several measures were taken before and after the fatigue protocol. First, the stiffness of the PF-tendon complex (PFC) was quantified during passive ankle mobilization both during and after the fatigue protocol using the ergometer. Additionally, from shear wave elastography, the active and passive stiffness of the gastrocnemius medialis (GM) were measured during passive ankle mobilization and isometric maximal voluntary contraction (MVC), respectively. Finally, the peak torque and the rate of torque development (RFD) of PF were assessed during the MVC using the ergometer. Ankle muscle activities (surface electromyograph [SEMG]) were recorded during all evaluations using electromyography. ResultsAfter the fatigue protocol, the results revealed a decline in active stiffness, peak torque of PF, RFD and SEMG activity of the GM (p < 0.001). Furthermore, significant correlation was identified between the decrease of the peak torque of PF and the active stiffness of the GM (r = 0.6; p < 0.05). A decrease in the PFC stiffness (p < 0.001) and a decrease in the shear modulus of the GM at 20° (p < 0.001) were also observed. ConclusionIsometric fatiguing exercises modify the mechanical properties of both the contractile and elastic components. Notably, decreases in both passive and active stiffness may be critical for athletes, as these changes could potentially increase the risk of injury.

The interaction between muscle pathophysiology, body mass, walking speed and ankle foot orthosis stiffness on walking energy cost: a predictive simulation study

BackgroundThe stiffness of a dorsal leaf AFO that minimizes walking energy cost in people with plantarflexor weakness varies between individuals. Using predictive simulations, we studied the effects of plantarflexor weakness, passive plantarflexor stiffness, body mass, and walking speed on the optimal AFO stiffness for energy cost reduction.MethodsWe employed a planar, nine degrees-of-freedom musculoskeletal model, in which for validation maximal strength of the plantar flexors was reduced by 80%. Walking simulations, driven by minimizing a comprehensive cost function of which energy cost was the main contributor, were generated using a reflex-based controller. Simulations of walking without and with an AFO with stiffnesses between 0.9 and 8.7 Nm/degree were generated. After validation against experimental data of 11 people with plantarflexor weakness using the Root-mean-square error (RMSE), we systematically changed plantarflexor weakness (range 40–90% weakness), passive plantarflexor stiffness (range: 20–200% of normal), body mass (+ 30%) and walking speed (range: 0.8–1.2 m/s) in our baseline model to evaluate their effect on the optimal AFO stiffness for energy cost minimization.ResultsOur simulations had a RMSE < 2 for all lower limb joint kinetics and kinematics except the knee and hip power for walking without AFO. When systematically varying model parameters, more severe plantarflexor weakness, lower passive plantarflexor stiffness, higher body mass and walking speed increased the optimal AFO stiffness for energy cost minimization, with the largest effects for severity of plantarflexor weakness.ConclusionsOur forward simulations demonstrate that in individuals with bilateral plantarflexor the necessary AFO stiffness for walking energy cost minimization is largely affected by severity of plantarflexor weakness, while variation in walking speed, passive muscle stiffness and body mass influence the optimal stiffness to a lesser extent. That gait deviations without AFO are overestimated may have exaggerated the required support of the AFO to minimize walking energy cost. Future research should focus on improving predictive simulations in order to implement personalized predictions in usual care.Trial Registration Nederlands Trial Register 5170. Registration date: May 7th 2015. http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=5170

Characteristics of the static muscle stiffness of ankle plantar flexors in individuals with chronic ankle instability.

Individuals with chronic ankle instability (CAI) have deficits in closed kinetic chain dorsiflexion that may perpetuate injury. Determining the characteristics of muscle stiffness in the plantar flexors of individuals with CAI may help in developing appropriate treatments. We aimed to highlight the characteristics of static muscle stiffness in ankle plantar flexor muscles during the passive dorsiflexion of the ankle joint in individuals with CAI. A total of 30 patients were included in the study based on the International Ankle Consortium criteria. The patients were categorized evenly into healthy, coper, and CAI groups (i.e., 10 patients in each group). After measuring the dorsiflexion range of motion (non-weight-bearing/weight-bearing) of the ankle joint, the static muscle stiffness measurements of the medial gastrocnemius, lateral gastrocnemius, soleus, and peroneus longus were obtained. The measurements were performed during the knee joint's extension and 50° flexion and passive dorsiflexion between the range of 40° plantar flexion and 20° dorsiflexion. The dorsiflexion range of motion of the CAI group was significantly smaller than that of the healthy and coper groups in the weight-bearing position. No interaction was observed for muscle stiffness in both the knee flexion and extension positions, and no significant differences were identified among the three groups. The shear modulus of the soleus at 20° ankle dorsiflexion with knee flexion had a significant negative correlation with the weight-bearing range of motion of the ankle. The limitation in the weight-bearing dorsiflexion range of motion in CAI was largely due to factors other than the increased elasticity of the ankle plantar flexor muscles.

Relationship Between Drop Jump Training–Induced Changes in Passive Plantar Flexor Stiffness and Explosive Performance

Passive muscle stiffness is positively associated with explosive performance. Drop jump training may be a strategy to increase passive muscle stiffness in the lower limb muscles. Therefore, the purpose of this study was to examine the effect of 8-week drop jump training on the passive stiffness in the plantar flexor muscles and the association between training-induced changes in passive muscle stiffness and explosive performance. This study was a randomized controlled trial. Twenty-four healthy young men were divided into two groups, control and training. The participants in the training group performed drop jumps (five sets of 20 repetitions each) 3days per week for 8weeks. As an index of passive muscle stiffness, the shear moduli of the medial gastrocnemius and soleus were measured by shear wave elastography before and after the intervention. The participants performed maximal voluntary isometric plantar flexion at an ankle joint angle of 0° and maximal drop jumps from a 15cm high box. The rate of torque development during isometric contraction was calculated. The shear modulus of the medial gastrocnemius decreased for the training group (before: 13.5±2.1kPa, after: 10.6±2.1kPa); however, such a reduction was not observed in the control group. There was no significant group (control and training groups)×time (before and after the intervention) interaction for the shear modulus of the soleus. The drop jump performance for the training group improved, while the rate of torque development did not change. Relative changes in these measurements were not correlated with each other in the training group. These results suggest that drop jump training decreases the passive stiffness in the medial gastrocnemius, and training-induced improvement in explosive performance cannot be attributed to change in passive muscle stiffness.

Effects of Intermittent and Continuous Static Stretching on Range of Motion and Musculotendinous Viscoelastic Properties Based on a Duration-Matched Protocol.

The different effects of intermittent and continuous stretching on the mechanical properties of the musculotendinous complex have been unclear. This study aimed to compare the effects of intermittent and continuous stretching for the same duration on the range of motion (ROM), passive resistive torque (PRT), and musculotendinous stiffness (MTS) of ankle plantar flexors. Eighteen healthy young men participated in the study. Intermittent (four sets × 30 s) and continuous stretching (one set × 120 s) were performed in random orders on two separate days. Both stretching protocols were conducted using a dynamometer with a constant torque applied. ROM and PRT were determined using a dynamometer, and MTS was calculated using the torque–angle relationship measured before and after stretching. Two-way repeated measures analysis of variance was performed for all parameters. Both intermittent and continuous stretching significantly increased ROM and decreased PRT and MTS (p < 0.05). Intermittent stretching led to greater changes in ROM and PRT than continuous stretching. However, the reduction in MTS did not differ between the two conditions. These results suggest that intermittent stretching is more effective in increasing ROM and changing the mechanical properties of the musculotendinous complex.

Increased Ankle Plantar Flexor Stiffness Is Associated With Reduced Mechanical Response to Stretch in Adults With CP

Hyperexcitable stretch reflexes are often not present despite of other signs of spasticity in people with brain lesion. Here we looked for evidence that increased resistance to length change of the plantar flexor muscle-fascicles may contribute to a reduction in the stretch reflex response in adults with cerebral palsy (CP). A total of 17 neurologically intact (NI) adults (mean age 36.1; 12 female) and 13 ambulant adults with CP (7 unilateral; mean age 33.1; 5 female) participated in the study. Subjects were seated in a chair with the examined foot attached to a foot plate, which could be moved by a computer-controlled electromotor. An ultrasound probe was placed over the medial aspect of the leg to measure the length of medial gastrocnemius muscle fascicles. Slow (7 deg/s) and fast (200 deg/s) stretches with amplitude 6 deg of the plantar flexors were applied over an ankle range of 70 deg at 10 deg intervals between 60 and 130 deg plantarflexion. It was checked by EMG electrodes that the slow stretches were sufficiently slow not to elicit any activity and that the fast stretches were sufficiently quick to elicit a maximal stretch reflex in both groups. The torque elicited by the stretches was measured together with changes in the length of medial gastrocnemius muscle fascicles. Muscle fascicles increased significantly in length with increasing dorsiflexion position in both populations (p < 0.001), but the fascicles were shorter in the CP population at all positions. Slow stretches elicited significantly larger torque and significantly smaller length change of muscle fascicles as the ankle joint position was moved more towards dorsiflexion in CP than in NI (p < 0.001). Fast stretches elicited larger torque responses at ankle joint positions of 80–100 deg in the NI than in the CP group (p < 0.01). A significant negative correlation was observed between the torque response and muscle fascicle length change to slow stretch in CP (p < 0.05), but not in NI. These findings support that increased passive resistance of the ankle plantar flexor muscle-tendon unit and development of contractures may conceal stretch reflex response in adults with CP. We argue that this should be taken into account in the neurological examination of spasticity.

Use of an Instrumented Ankle Arthrometer and External Strain Gauge to Assess Ankle Dorsiflexion Motion and Plantarflexor Stiffness.

Ankle dorsiflexion motion and plantarflexor stiffness measurement offer clinical insight into the assessment and treatment of musculoskeletal and neurologic disorders. We aimed to determine reliability and concurrent validity of an ankle arthrometer in quantifying dorsiflexion motion and plantarflexor stiffness. Ten healthy individuals were assessed for dorsiflexion motion and plantarflexor stiffness using an ankle arthrometer with a 6 degree-of-freedom kinematic linkage system and external strain gauge to apply dorsiflexion torque. Two investigators each performed five loads to the ankle at different combinations of loads (10 or 20 Nm), rates (2.5 or 5 Nm/sec), and knee angles (10° or 20°). Anteroposterior displacement and inversion-eversion rotation were also assessed with arthrometry, and functional dorsiflexion motion was assessed with the weightbearing lunge (WBL) test. Good-to-excellent intrarater reliability was observed for peak dorsiflexion (intraclass correlation coefficient [ICC][2,k] = 0.949-0.988) and plantarflexor stiffness (ICC[2,k] = 0.761-0.984). Interrater reliability was good to excellent for peak dorsiflexion (ICC[2,1] = 0.766-0.910) and poor to excellent for plantarflexor stiffness (ICC[2,1] = 0.275-0.914). Reliability was best for 20-Nm loads at 5 Nm/sec. Strong correlations were observed between peak dorsiflexion and anteroposterior displacement (r = 0.666; P = 0.035) and WBL distance (r = -0.681; P = 0.036). Using an ankle arthrometer to assess peak dorsiflexion and plantarflexor stiffness seems reliable when performed to greater torques with faster speeds; and offers consistency with functional measures. Use of this readily available tool may benefit clinicians attempting to quantify equinus and dorsiflexion deficits in pathological populations.

Influence of Constant Torque Stretching at Different Stretching Intensities on Flexibility and Mechanical Properties of Plantar Flexors.

Oba, K, Samukawa, M, Nakamura, K, Mikami, K, Suzumori, Y, Ishida, Y, Keeler, N, Saitoh, H, Yamanaka, M, and Tohyama, H. Influence of constant torque stretching at different stretching intensities on flexibility and mechanical properties of plantar flexors. J Strength Cond Res 35(3): 709-714, 2021-The purpose of this study was to examine the effects of constant torque stretching (CTS) at different stretching intensities on the maximal range of motion (ROM) and muscle-tendon unit (MTU) stiffness of plantar flexors. Fourteen healthy men performed 4 trials of differing stretch intensities: no stretching (control), 50, 75, and 100%. Stretch intensity was defined as maximum passive resistive torque predetermined at a familiarization trial. Each stretch trial consisted of 5 sets of 60-second CTS at the designated stretch intensity. Both maximal ROM and passive resistive torque were assessed during passive dorsiflexion, and MTU stiffness was calculated using the torque-angle curves measured before and after CTS. There were no significant differences in maximal ROM or MTU stiffness at the baseline condition. After the intervention, significantly greater maximal ROM and significantly lower MTU stiffness were observed in the 100% CTS condition than the control condition, whereas there were no significant differences between the submaximal intensity condition (i.e., 50 or 75% intensity) and the control condition. Therefore, our findings suggest that maximal intensity stretching is the most effective approach for improving both flexibility and MTU stiffness with CTS.

Associations of passive muscle stiffness, muscle stretch tolerance, and muscle slack angle with range of motion: individual and sex differences

Joint range of motion (ROM) is an important parameter for athletic performance and muscular injury risk. Nonetheless, a complete description of muscular factors influencing ROM among individuals and between men and women is lacking. We examined whether passive muscle stiffness (evaluated by angle-specific muscle shear modulus), tolerance to muscle stretch (evaluated by muscle shear modulus at end-ROM), and muscle slack angle of the triceps surae are associated with the individual variability and sex difference in dorsiflexion ROM, using ultrasound shear wave elastography. For men, ROM was negatively correlated to passive muscle stiffness of the medial and lateral gastrocnemius in a tensioned state and positively to tolerance to muscle stretch in the medial gastrocnemius. For women, ROM was only positively correlated to tolerance to muscle stretch in all muscles but not correlated to passive muscle stiffness. Muscle slack angle was not correlated to ROM in men and women. Significant sex differences were observed only for dorsiflexion ROM and passive muscle stiffness in a tensioned state. These findings suggest that muscular factors associated with ROM are different between men and women. Furthermore, the sex difference in dorsiflexion ROM might be attributed partly to that in passive muscle stiffness of plantar flexors.

Potential relationship between passive plantar flexor stiffness and sprint performance in sprinters

ObjectiveTo investigate the relationship between passive planter flexor stiffness and sprint performance in sprinters. DesignCross-sectional study. ParticipantsFifty well-trained male sprinters (age: 20.7 ± 1.9 years, height: 175.6 ± 4.9 cm, weight: 66.7 ± 5.1 kg) were participated in this study. Their best personal times in a 100-m sprint ranged from 10.22 to 11.86 s (mean, 11.12 ± 0.43 s). MethodsPassive stiffness of the plantar flexors measured using a dynamometer system. Passive stiffness during passive dorsiflexion was calculated from the slope of the linear portion of the torque-angle curve. ResultsPlantar flexor passive stiffness was significantly correlated with personal best 100-m sprint time (r = −0.334, P = 0.018). ConclusionThe present findings suggest that although the relationship between plantar flexor passive stiffness and personal best 100-m sprint time was relatively minimal, a higher plantar flexor passive stiffness may be a potential factor for achieving superior sprint performance in sprinters. Therefore, in the clinical setting, measurement of passive planter flexor stiffness may be useful for assessing sprint performance.

Potential Relationship between Passive Plantar Flexor Stiffness and Running Performance.

The present study aimed to determine the relationship between passive stiffness of the plantar flexors and running performance in endurance runners. Forty-eight well-trained male endurance runners and 24 untrained male control subjects participated in this study. Plantar flexor stiffness during passive dorsiflexion was calculated from the slope of the linear portion of the torque-angle curve. Of the endurance runners included in the present study, running economy in 28 endurance runners was evaluated by measuring energy cost during three 4-min trials (14, 16, and 18 km/h) of submaximal treadmill running. Passive stiffness of the plantar flexors was significantly higher in endurance runners than in untrained subjects. Moreover, passive plantar flexor stiffness in endurance runners was significantly correlated with a personal best 5000-m race time. Furthermore, passive plantar flexor stiffness in endurance runners was significantly correlated with energy cost during submaximal running at 16 km/h and 18 km/h, and a trend towards such significance was observed at 14 km/h. The present findings suggest that stiffer plantar flexors may help achieve better running performance, with greater running economy, in endurance runners. Therefore, in the clinical setting, passive stiffness of the plantar flexors may be a potential parameter for assessing running performance.

Contribution of sensory feedback to plantar flexor muscle activation during push-off in adults with cerebral palsy.

Exaggerated sensory activity has been assumed to contribute to functional impairment following lesion of the central motor pathway. However, recent studies have suggested that sensory contribution to muscle activity during gait is reduced in stroke patients and children with cerebral palsy (CP). We investigated whether this also occurs in CP adults and whether daily treadmill training is accompanied by alterations in sensory contribution to muscle activity. Seventeen adults with CP and 12 uninjured individuals participated. The participants walked on a treadmill while a robotized ankle-foot orthosis applied unload perturbations at the ankle, thereby removing sensory feedback naturally activated during push-off. Reduction of electromyographic (EMG) activity in the soleus muscle caused by unloads was compared and related to kinematics and ankle joint stiffness measurements. Similar measures were obtained after 6 wk of gait training. We found that sensory contribution to soleus EMG activation was reduced in CP adults compared with uninjured adults. The lowest contribution of sensory feedback was found in participants with lowest maximal gait speed. This was related to increased ankle plantar flexor stiffness. Six weeks of gait training did not alter the contribution of sensory feedback. We conclude that exaggerated sensory activity is unlikely to contribute to impaired gait in CP adults, because sensory contribution to muscle activity during gait was reduced compared with in uninjured individuals. Increased passive stiffness around the ankle joint is likely to diminish sensory feedback during gait so that a larger part of plantar flexor muscle activity must be generated by descending motor commands.NEW & NOTEWORTHY Findings suggest that adults with cerebral palsy have less contribution of sensory feedback to ongoing soleus muscle activation during push-off than uninjured individuals. Increased passive stiffness around the ankle joint is likely to diminish sensory feedback during gait, and/or sensory feedback is less integrated with central motor commands in the activation of spinal motor neurons. Consequently, muscle activation must to a larger extent rely on descending drive, which is already decreased because of the cerebral lesion.

Plantarflexor passive-elastic properties related to BMI and walking performance in older women

The objective of this study was to examine the influence of BMI on the passive-elastic properties of the ankle plantarflexors in older women. Twenty-three women, 65–80 yr, were separated into normal weight (NW, BMI <25.0kgm−2, n=11) and overweight-obese (OW, BMI≥25.0kgm−2, n=12) groups. Resistive torque of the ankle plantarflexors was recorded on an isokinetic dynamometer by passively moving the ankle into dorsiflexion. Stiffness, work absorption, and hysteresis were calculated across an ankle dorsiflexion angle of 10–15°. Maximal plantarflexor strength was assessed, then participants walked at maximal speed on an instrumented gait analysis treadmill while muscle activation (EMG) was recorded. Plantarflexor stiffness was 34% lower in OW (26.4±12.7Nmrad−1) than NW (40.0±15.7Nmrad−1, p=0.032). Neither work absorption nor hysteresis were different between OW and NW. Stiffness per kg was positively correlated to strength (r=0.66, p<0.001), peak vertical ground reaction force during walking (r=0.72, p<0.001), weight acceptance rate of force (r=0.51, p=0.007), push-off rate of force (r=0.41, p=0.026), maximal speed (r=0.61, p=0.001), and inversely correlated to BMI (r=−0.61, p=0.001), and peak plantarflexor EMG (r=−0.40, p=0.046). Older women who are OW have low plantarflexor stiffness, which may limit propulsive forces during walking and necessitate greater muscle activation for active force generation.

Active muscle and tendon stiffness of plantar flexors in sprinters

ABSTRACTThe aim of the present study was to investigate and compare muscle and tendon stiffness under active conditions in sprinters and untrained participants. In total, 14 sprinters and 24 untrained men participated in this study. Active muscle stiffness in the medial gastrocnemius muscle was calculated based on changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Tendon stiffness was determined during isometric plantar flexion using ultrasonography. No significant differences were observed in active muscle stiffness between sprinters and untrained men at any torque levels. Furthermore, no significant difference was noted in tendon stiffness between the two groups. These results suggest that muscle and tendon mechanical properties in the plantar flexors under active conditions are similar in sprinters and untrained participants.

Balance decrements are associated with age-related muscle property changes.

In this study, a comprehensive evaluation of static and dynamic balance abilities was performed in young and older adults and regression analysis was used to test whether age-related variations in individual ankle muscle mechanical properties could explain differences in balance performance. The mechanical properties included estimates of the maximal isometric force capability, force-length, force-velocity, and series elastic properties of the dorsiflexors and individual plantarflexor muscles (gastrocnemius and soleus). As expected, the older adults performed more poorly on most balance tasks. Muscular maximal isometric force, optimal fiber length, tendon slack length, and velocity-dependent force capabilities accounted for up to 60% of the age-related variation in performance on the static and dynamic balance tests. In general, the plantarflexors had a stronger predictive role than the dorsiflexors. Plantarflexor stiffness was strongly related to general balance performance, particularly in quiet stance; but this effect did not depend on age. Together, these results suggest that age-related differences in balance performance are explained in part by alterations in muscular mechanical properties.

Benefits of repetitive transcranial magnetic stimulation (rTMS) for spastic subjects: clinical, functional, and biomechanical parameters for lower limb and walking in five hemiparetic patients.

Introduction. Spasticity is a disabling symptom resulting from reorganization of spinal reflexes no longer inhibited by supraspinal control. Several studies have demonstrated interest in repetitive transcranial magnetic stimulation in spastic patients. We conducted a prospective, randomized, double-blind crossover study on five spastic hemiparetic patients to determine whether this type of stimulation of the premotor cortex can provide a clinical benefit. Material and Methods. Two stimulation frequencies (1 Hz and 10 Hz) were tested versus placebo. Patients were assessed clinically, by quantitative analysis of walking and measurement of neuromechanical parameters (H and T reflexes, musculoarticular stiffness of the ankle). Results. No change was observed after placebo and 10 Hz protocols. Clinical parameters were not significantly modified after 1 Hz stimulation, apart from a tendency towards improved recruitment of antagonist muscles on the Fügl-Meyer scale. Only cadence and recurvatum were significantly modified on quantitative analysis of walking. Neuromechanical parameters were modified with significant decreases in H max⁡ /M max⁡ and T/M max⁡ ratios and stiffness indices 9 days or 31 days after initiation of TMS. Conclusion. This preliminary study supports the efficacy of low-frequency TMS to reduce reflex excitability and stiffness of ankle plantar flexors, while clinical signs of spasticity were not significantly modified.

Long-term neuromechanical results of selective tibial neurotomy in patients with spastic equinus foot

The neuromechanical consequences of tibial neurotomy have not been extensively studied. Fifteen patients were evaluated before and after selective tibial neurotomy (after 2 months and after 15 months) by means of clinical, neurophysiological [tendon (T) reflexes, Hoffmann (H) reflexes and maximum motor response, Mmax] and mechanical parameters (passive stiffness of plantar flexors at the ankle). The neurotomy concerned the soleus (100 % of cases), gastrocnemius (20 % of cases), posterior tibial (60 % of cases) and flexor digitorum longus (47 % of cases) nerves. Neurotomy provided more than 90 % improvement of clinical spasticity scores, 20 % improvement of walking scores and the angle of passive dorsiflexion (APDF) of the ankle (mean angle: 7°), temporary reduction of the soleus Mmax (18 % at 2 months with return to the preoperative value at 15 months), and lasting reduction of the soleus Hmax/Mmax (68 % at 2 months, 78 % at 15 months) and T/Mmax (84 % at 2 months, 80 % at 15 months). M and H responses of the gastrocnemius (whether or not they were included in the neurotomy) were not modified, while T/Mmax decreased to the same degree as for soleus. Passive stiffness was lastingly decreased from 64.0 Nm/rad to 49.0 Nm/rad (2 months) and 49.5 Nm/rad (15 months). Selective tibial neurotomy of the soleus nerve induces long-term reduction of reflex hyperexcitability and passive stiffness of plantar flexors in spastic patients, with no lasting impairment of motor efferents. In parallel, it modifies the tendon reflexes of synergistic muscles (gastrocnemius) not concerned by the neurotomy.

The Effects of Functional Electrical Stimulation on Walking in Hereditary and Spontaneous Spastic Paraparesis

To investigate in people with spastic paraparesis (SP): 1) the factors contributing to foot drop and reduced toe clearance while walking; 2) short-term effects of bilateral functional electrical stimulation (FES) of the common peroneal nerve. Long term (>0.5 years) users of FES with SP were compared to matched controls (N = 11 per group). Ankle strength and plantarflexor stiffness and walking kinematics were objectively recorded. The effects of FES on: 1) perceived efficacy; 2) muscle torque and ankle motion; 3) clinical outcome measures and walking kinematics were assessed. Results were compared using an analysis of covariance. Ankle weakness and stiffness is higher among people with SP. Higher plantarflexor stiffness is associated with reduced swing phase dorsiflexion; higher toe clearance while walking is associated with increased hip flexion. FES increases dorsiflexor torque, improves toe clearance and dorsiflexion in swing phase, and significantly improves walking speed (p < 0.05). There are multiple causes of tripping in people with SP; FES reduces foot drop and improves walking speed.

Comparison of 3 Different Methods to Analyze Ankle Plantarflexor Stiffness in Children With Spastic Diplegia Cerebral Palsy

Ross SA, Foreman M, Engsberg JR. Comparison of 3 different methods to analyze ankle plantarflexor stiffness in children with spastic diplegia cerebral palsy. Objective To compare 3 different methods of measuring plantarflexor stiffness in children with spastic diplegia cerebral palsy (CP) and children without disability. Design Case-control study. Setting Human performance laboratory. Participants A retrospective analysis was conducted with children with spastic diplegia (n=121; mean age, 8.4y) and children with typical development (TD) (n=48; mean age, 9.7y). Interventions Not applicable. Main Outcome Measures An isokinetic dynamometer was used to measure ankle plantarflexor stiffness at 10°/s using 3 methods: (1) end-range method, which applied a linear slope to the end of the torque-angle curve; (2) set-range method, which applied a linear slope from 30° to 10° plantarflexion; and (3) a linear method, which applied a slope only to the linear portion of the curve. Results Two-way analysis of variance revealed significant main effects for group and stiffness method. The end-range method showed no significant difference between groups for plantarflexor stiffness ( P=.62), the set-range method showed the CP group with 120% greater stiffness than the TD group ( P<.046), and the linear method showed the CP group with 35% greater stiffness than the TD group ( P<.001). Conclusions The linear method appeared to resolve the issues with the previous methods; applying a linear slope to a nonlinear curve or applying a linear slope to the same range of motion for each child regardless of their range limitations. It is clear that children with CP have limited range of motion; therefore, stiffness occurs earlier in the range than would be expected for a typically developing child. Using the linear method, children with CP were 35% stiffer in the ankle plantarflexors than typically developing peers.