Plantar Flexor Stiffness Research Articles

Morphological and Mechanical Properties of Muscle and Tendon in Highly Trained Sprinters

The purpose of this study was to investigate muscle and tendon properties in highly trained sprinters and their relations to running performance. Fifteen sprinters and 15 untrained subjects participated in this study. Muscle thickness and tendon stiffness of knee extensors and plantar flexors were measured. Sprinter muscle thickness was significantly greater than that of the untrained subjects for plantar flexors, but not for knee extensors (except for the medial side). Sprinter tendon stiffness was significantly lower than that of the untrained subjects for knee extensors, but not for plantar flexors. The best official record of a 100-m race was significantly correlated to the muscle thickness of the medial side for knee extensors. In conclusion, the tendon structures of highly trained sprinters are more compliant than those of untrained subjects for knee extensors, but not for plantar flexors. Furthermore, a thicker medial side of knee extensors was associated with greater sprinting performance.

Distinguishing active from passive components of ankle plantar flexor stiffness in stroke, spinal cord injury and multiple sclerosis

Objective Spasticity is a common manifestation of lesion of central motor pathways. It is essential for correct anti-spastic treatment that passive and active contributions to increased muscle stiffness are distinguished. Here, we combined biomechanical and electrophysiological evaluation to distinguish the contribution of active reflex mechanisms from passive muscle properties to ankle joint stiffness in 31 healthy, 10 stroke, 30 multiple sclerosis and 16 spinal cord injured participants. The results were compared to routine clinical evaluation of spasticity. Methods A computer-controlled robotic device applied stretches to the ankle plantar flexor muscles at different velocities (8–200 deg/s; amplitude 6°). The reflex threshold was determined by soleus EMG. Torque and EMG data were normalized to the maximal torque and EMG evoked by supramaximal stimulation of the tibial nerve. Passive resistance (the torque response to stretches) was confirmed to be a good representation of the passive stiffness also at higher velocities when transmission in the tibial nerve was blocked by ischemia. Results Passive torque tended to be larger in the neurological than in the healthy participants, but it did not reach statistical significance, except in the stroke group ( p < 0.05). Following normalization to the maximal stimulus-evoked torque, the passive torque was found to be significantly larger in neurological participants identified with spasticity than in non-spastic participants ( p < 0.01). There was no significant difference in the reflex threshold between the healthy and the neurological participants. The reflex evoked torque and EMG were significantly larger in all neurological groups than in the healthy group ( p < 0.001). Twenty three participants with evidence of hypertonia in the plantar flexors (Ashworth score ⩾ 1) showed normal reflex torque without normalization. With normalization this was only the case in 11 participants. Increased reflex mediated stiffness was detected in only 64% participants during clinical examination. Conclusion The findings confirm that the clinical diagnosis of spasticity includes changes in both active and passive muscle properties and the two can hardly be distinguished based on routine clinical examination. Significance The data suggest that evaluation techniques which are more efficient in distinguishing active and passive contributions to muscle stiffness than routine clinical examination should be considered before anti-spastic treatment is initiated.

Simulated force–length curves as a tool to enhance clinical interpretation of gait data

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 < 25.0 kg m−2, n = 11) and overweight-obese (OW, BMI ≥ 25.0 kg m−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 ± 12.7 Nm rad−1) than NW (40.0 ± 15.7 Nm rad−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.

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.

Relationships between plantar flexor muscle stiffness, strength, and range of motion in subjects with diabetes-peripheral neuropathy compared to age-matched controls.

Descriptive study to compare relationships between muscle performance measures in 2 subject groups. To determine the relationships between plantar flexor (PF) muscle stiffness, strength (concentric peak torque), and dorsiflexion (DF) range of motion (ROM) in subjects with diabetes who have peripheral neuropathy (n = 17, 10 men, 7 women; age = 58 +/- 11 years) and age-matched controls (n = 17, 10 men, 7 women; age = 62 +/- 6 years). The relationships between muscle stiffness, strength, and joint ROM have not been clearly established. Furthermore, the effect of neuromuscular pathology on these relationships is unknown. PF stiffness and strength measurements were obtained with an isokinetic dynamometer. DF ROM was measured with a goniometer. A Pearson correlation matrix was constructed for each subject group using stiffness, strength, and ROM variables. The percent contribution of passive torque to total torque was computed at 2 joint angles. In subjects with diabetes and peripheral neuropathy (DM-PN) peak concentric PF torque was positively correlated with passive torque at 5 degrees DF (r = 0.77), Stiffness #1 (r = 0.58), and Stiffness #2 (r = 0.50). The percentage of passive PF torque at 5 degrees DF was greater in subjects with DM-PN, compared to control subjects (29.3 +/- 9.4% versus 12.6 +/- 5.9%). The positive correlation between PF stiffness and strength, and the greater percentage of passive PF torque in subjects with DM-PN suggest that patients with decreased strength may use passive torque to maximize total torque. Therefore, treatment methods designed to decrease stiffness should be used cautiously.

Effect of plantar flexor muscle stiffness on selected gait characteristics.

Although plantar flexor muscle strength is known to affect gait characteristics, the effect of plantar flexor (PF) muscle stiffness on gait is unknown. The purpose of this study was to determine the effect of PF muscle stiffness, in addition to PF strength, on the gait characteristics of subjects with diabetes and peripheral neuropathy (DM & PN) and age-matched controls. Thirty-four subjects were tested (17 DM & PN, 17 controls), 10 males and seven females in each group. PF muscle strength (concentric peak torque) explained a significant amount of variance in all gait variables (20-37%). Passive stiffness added a unique contribution to plantar flexor peak moment and walking speed (10-11%). Plantar flexor stiffness, in addition to strength, may be an important factor contributing to gait characteristics. Treatment techniques designed to preserve or increase stiffness may be indicated for patients with limited PF strength.

Contribution of passive stiffness to ankle plantarflexor moment during gait after stroke

<h2>Abstract</h2> Lamontagne A, Malouin F, Richards CL. Contribution of passive stiffness to ankle plantarflexor moment during gait after stroke. Arch Phys Med Rehabil 2000;81:351-8. <b>Objective:</b> To measure the contribution of passive stiffness to the ankle plantarflexor moment during gait in subjects with hemiparesis early after stroke. The relationship of passive stiffness with gait speed was also examined. <b>Design:</b> Cross-sectional, descriptive. <b>Patients and Other Participants:</b> A sample of convenience of 14 patients (54.7 ± 10.9yrs) with a hemiparesis for less than 5 months and 11 healthy controls (50.6 ± 11.6yrs). <b>Main Outcome Measures:</b> The contribution of passive stiffness to the plantarflexor moment during gait was obtained using moment-angle slope (stiffness) values. Total plantarflexor stiffness was measured during gait, and passive stiffness was measured during passive dorsiflexion imposed by an isokinetic dynamometer at velocities and ranges of movement matched with values recorded during the plantarflexor lengthening period of the stance phase. The contribution of passive stiffness was obtained by dividing the passive stiffness (dynamometer) by the total plantarflexor stiffness (gait). <b>Results:</b> On the paretic side, passive stiffness contributed more (16.8%; range 2.9% to 49.6%) to total plantarflexor stiffness during gait compared (<i>p</i> <.01) with both the nonparetic side (7.3%) and control values (5.9%). This increased contribution on the paretic side resulted from a large muscle-tendon passive stiffness, a decreased active muscle contribution, or both. Although in some patients the increased passive component led to the development of a total plantarflexor stiffness that was within normal values, it did not in others either because the active component was very small or because limited dorsiflexion during the stance phase prevented the passive component tension to develop. The contribution of passive stiffness was not significantly (<i>p</i> >.05) related to gait speed in both the patients and the controls. <b>Conclusions:</b> The increased contribution of passive stiffness to total plantarflexor moment during gait likely acts as an adaptation for a defective muscle active component, helping ankle push-off at the end of the stance phase. Although this mechanism is effective in most of the patients, it cannot come into action if the dorsiflexion movement during the stance phase is prevented, for instance, by enhanced stretch reflexes. <i>© 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation</i>

Contribution of passive stiffness to ankle plantarflexor moment during gait after stroke

Objective: To measure the contribution of passive stiffness to the ankle plantarflexor moment during gait in subjects with hemiparesis early after stroke. The relationship of passive stiffness with gait speed was also examined.Design: Cross-sectional, descriptive.Patients and Other Participants: A sample of convenience of 14 patients (54.7 ± 10.9yrs) with a hemiparesis for less than 5 months and 11 healthy controls (50.6 ± 11.6yrs).Main Outcome Measures: The contribution of passive stiffness to the plantarflexor moment during gait was obtained using moment-angle slope (stiffness) values. Total plantarflexor stiffness was measured during gait, and passive stiffness was measured during passive dorsiflexion imposed by an isokinetic dynamometer at velocities and ranges of movement matched with values recorded during the plantarflexor lenghtening period of the stance phase. The contribution of passive stiffness was obtained by dividing the passive stiffness (dynamometer) by the total plantarflexor stiffness (gait).Results: On the paretic side, passive stiffness contributed more (16.8%; tange 2.9% to 49.6%) to total plantarflexor stiffness during gait compared (p < .01) with both the nonparetic side (7.3%) and control values (5.9%). This increased contribution on the paretic side resulted from a large muscletendon passive stiffness, a decreased active muscle contribution, or both. Although in some patients the increased passive component led to the development of a total plantarflexor stiffness that was within normal values, it did not in others either because the active component was very small or because limited dorsiflexion during the stance phase prevented the passive component tension to develop. The contribution of passive stiffness was not significantly (p > .05) related to gait speed in both the patients and the controls.Conclusions: The increased contribution of passive stiffness to total plantarflexor moment during gait likely acts as an adaptation for a defective muscle active component, helping ankle push-off at the end of the stance phase. Although this mechanism is effective in most of the patients, it cannot come into action if the dorsiflexion movement during the stance phase is prevented, for instance, by enhanced stretch reflexes.

Passive stiffness characteristics of ankle plantar flexors in hemiplegia

Objective. To assess the feasibility and reliability of ankle plantar flexor stiffness measurements in hemiplegia. Design. Repeated measurements in five consecutive weeks. Background. In hemiplegia, an equinovarus positioning of the foot might be caused by an increased stiffness of the m. triceps surae. Methods. In eight hemiplegic patients the net joint torque of passive muscle stretch was measured as a function of ankle-angle by a dynamometer, at both sides. Ankle-stiffness was characterised and also a biomechanical model of the passive muscle was fitted. Results. In the vast majority of measurements it was possible to obtain measurements that were not distorted by involuntary muscle contraction. These measurements showed for the angle at which a passive plantar moment of 10 N m was reached a standard error of measurement of less than 2.7°. The muscle model showed the increased stiffness as a shortening of the muscle-fibre-length. Conclusion. The feasibility of this method to measure muscle stiffness was fair to good in hemiplegic patients. Provided the abandoning of involuntary muscle activity, the reproducibility warrants application in clinical practice at an individual level. The use of the model relates this changes to a shortened m. soleus and/or m. gastrocnemius. Relevance Effective clinical decisions for treatment of equinovarus positioning of the foot in the hemiplegic individual, should consider excessive involuntary contractions of the m. triceps surae complex (i.e., spasticity), as well as shortened muscle tissue resulting in high stiffness. Despite the importance of increased stiffness there have been no validated methods of measurement.

Human plantarflexor stiffness to multiple single-stretch trials

The purpose of this investigation was to determine the influence of different stretch velocities, different rates of pre-stretch force development, and different pre-stretch muscle lengths on the intrinsic stiffness exhibited by the quasi-statically contracting active human plantarflexors during multiple single-stretch trials at 20–60% of maximum isometric contraction. Subjects were positioned prone, with the knee flexed 1.57 rad (90°), shank stabilized, and foot secured in a hard plastic orthotic. Slowly increasing isometric plantarflexion force was produced until the plantarflexors were stretched by a rapid 0.2 rad (12°) dorsiflexion movement. Plantarflexion forces and ankle positions were determined during these stretches as well as during resting stretches when the muscle was inactive. Resting forces were subtracted from the active trials, forces converted to torques, and stiffnesses determined for the first 62 ms of the stretch. The slope of the stiffness vs pre-stretch torque relationship averaged 4.30±0.34 Nm rad −1 Nm −1. Little difference was found between stiffness determined through the single-stretch method and the results of previous studies employing different mechanical inputs. Differences in stiffnesses with different stretching velocities were caused by computational artifact rather than by differences in intrinsic muscular reaction. Faster rates of pre-stretch force increase prior to the stretch resulted in slightly lower stiffnesses. Different pre-stretch muscle lengths apparently did not result in different stiffnesses. The shape of the torque vs displacement curve was remarkably insensitive to the planned manipulations of the testing conditions, responding in a stereotypical manner.