Biomechanical characterization and clinical implications of artificially induced crouch walking: Differences between pure iliopsoas, pure hamstrings and combination of iliopsoas and hamstrings contractures

The purpose of this study was to characterize biomechanically three different crouch walking patterns, artificially induced in eight neurologically intact subjects and to compare them to selected cases of pathological crouch walking. The subjects were equipped with a lightweight mechanical exoskeleton with artificial muscles that acted in parallel with hamstrings and iliopsoas muscles. They walked at a speed of approximately 1m/s along the walkway under four experimental conditions: normal walking (NW), hamstrings contracture emulation (HAM), iliopsoas contracture emulation (IPS) and emulation of both hamstrings and iliopsoas contractures (IPSHAM). Reflective markers and force platform data were collected and ankle, knee and hip-joint angles, moments and powers were calculated. HAM and IPSHAM shifted ankle-angle rotation profiles into dorsiflexion during midstance compared to IPS and NW where ankle-angle trajectories were similar. HAM, IPS and IPSHAM shifted the knee angle of rotation profiles into flexion during stance, compared to NW. IPS and IPSHAM shifted hip angle of rotation profiles toward pronounced flexion while HAM shifted hip angle of rotation profile toward extension, compared to NW. HAM and IPSHAM significantly increased ankle moment during midstance, compared to IPS and NW where ankle moment profiles were similar. All experimental conditions exhibited similar behavior in the knee-moment profiles during midstance while IPS and IPSHAM knee-moment profiles exhibited significantly higher knee-extension moment during terminal stance and pre-swing. In the hip joint all experimental conditions exhibited similar shape of hip moment profiles throughout the gait cycle. HAM and IPS kinematic and kinetic patterns were qualitatively compared to two selected clinical cases, showing considerable similarity. This implies that distinct differences in kinematics and kinetics between HAM, IPS and IPSHAM may be clinically relevant in helping determine the relative contribution of hamstrings and iliopsoas muscles contractures to particular crouch walking.     

Empirical evaluation of gastrocnemius and soleus function during walking

Distinguishing gastrocnemius and soleus muscle function is relevant for treating gait disorders in which abnormal plantarflexor activity may contribute to pathological movement patterns. Our objective was to use experimental and computational analysis to determine the influence of gastrocnemius and soleus activity on lower limb movement, and determine if anatomical variability of the gastrocnemius affected its function. Our hypothesis was that these muscles exhibit distinct functions, with the gastrocnemius inducing limb flexion and the soleus inducing limb extension. To test this hypothesis, the gastrocnemius or soleus of 20 healthy participants was electrically stimulated for brief periods (90 ms) during mid- or terminal stance of a random gait cycle. Muscle function was characterized by the induced change in sagittal pelvis, hip, knee, and ankle angles occurring during the 200 ms after stimulation onset. Results were corroborated with computational forward dynamic gait models, by perturbing gastrocnemius or soleus activity during similar portions of the gait cycle. Mid- and terminal stance gastrocnemius stimulation induced posterior pelvic tilt, hip flexion and knee flexion. Mid-stance gastrocnemius stimulation also induced ankle dorsiflexion. In contrast mid-stance soleus stimulation induced anterior pelvic tilt, knee extension and plantarflexion, while late-stance soleus stimulation induced relatively little change in motion. Model predictions of induced hip, knee, and ankle motion were generally in the same direction as those of the experiments, though the gastrocnemius? results were shown to be quite sensitive to its knee-to-ankle moment arm ratio.     

Gastrocnemius and soleus lengths in cerebral palsy equinus gait--differences between children with and without static contracture and effects of gastrocnemius recession

Equinus gait is one of the most common abnormalities in children with cerebral palsy. Although it is generally assumed that the calf muscles are abnormally short in equinus gait, no studies have been done to confirm that the muscles are short and that this shortness contributes to the equinus. This study used musculoskeletal modeling combined with computerized gait analysis to examine medial gastrocnemius (MGAS), lateral gastrocnemius (LGAS), and soleus (SOL) musculotendinous lengths during equinus gait in children with cerebral palsy. All three muscles were abnormally short during equinus gait whether or not the children had equinus contractures (P < or = 0.005). Children with static contractures had shorter maximum static MGAS and LGAS lengths than children with dynamic equinus (P < or = 0.002). The children with static contractures had ratios of peak dynamic length to maximum static length close to 1.0 for MGAS and LGAS (1.005 +/- 0.015) but lower ratios for SOL (0.984 +/- 0.024). For the children with static contracture, these ratios did not change significantly after gastrocnemius recession (P > or = 0.14) because both static and dynamic lengths increased postoperatively (P < or = 0.04). These results support the current clinical understanding of the role of calf "tightness" in equinus gait, including the appropriateness and effectiveness of gastrocnemius recession for children with equinus contracture.     

Passive knee movement-induced modulation of the soleus H-reflex and alteration in the fascicle length of the medial gastrocnemius muscle in humans

In humans, an inhibitory via Ia afferent pathway from the medial gastrocnemius (MG) to the soleus (SOL) motoneuron pool has been suggested. Herein, we examined the relation between MG fascicle length changes and the SOL H-reflex modulation during passive knee movement. Twelve subjects performed static and passive (5° s^?1) knee movement tasks with the ankle immobilized using an isokinetic dynamometer in sitting posture. The maximal H- and M-waves were measured at four target angles (20°, 40°, 60°, and 80° flexion from full knee extension). The MG fascicles length and velocity were measured using a B-mode ultrasonic apparatus. Results demonstrated that the SOL Hmax/Mmax; i.e., ratio of the maximal H- to M-waves, was attenuated with increasing MG fascicle length in static tasks. The SOL Hmax/Mmax at 20° was significantly attenuated compared with 60° and 80° with increasing MG fascicle length and lengthening velocity in passive knee extension. However, no significant differences in the SOL Hmax/Mmax were found across the target angles in the passive knee flexion task. In conclusion, as muscle spindles increase their discharge with lengthening fascicle velocity, but keep silent when fascicles shorten, our data suggest that lengthening the MG facilitates an inhibitory Ia pathway from MG to SOL, and modulates SOL motoneuron activity during movements.     

Myofascial force transmission between the human soleus and gastrocnemius muscles during passive knee motion

The plantarflexors of the lower limb are often assumed to act as independent actuators, but the validity of this assumption is the subject of considerable debate. This study aims to determine the degree to which passive changes in gastrocnemius muscle length, induced by knee motion, affect the tension in the adjacent soleus muscle. A second aim is to quantify the magnitude of myofascial passive force transmission between gastrocnemius and adjacent soleus. Fifteen healthy volunteers participated. Simultaneous ultrasound images of the gastrocnemius and soleus muscles were obtained during passive knee flexion (0-90°), while keeping the ankle angle fixed at either 70° or 115°. Image correlation analysis was used to quantify muscle fascicle lengths in both muscles. The data show that the soleus muscle fascicles elongate significantly during gastrocnemius shortening. The approximate change in passive soleus force as a result of the observed change in fascicle length was estimated and appears to be <5 N, but this estimate is sensitive to the assumed slack length of soleus.     

Lower extremity muscle activity during different types and speeds of underwater movement

To compare the activity of lower extremity muscles during land walking (LW), water walking (WW), and deep-water running (DWR), 9 healthy young subjects were tested at self-selected low, moderate, and high intensities for 8 sec with two repetitions. Surface EMG electrodes were placed on the tibialis anterior (TA), soleus (SOL), medial gastrocnemius (GAS), rectus femoris (RF), and biceps femoris (BF). During DWR, the SOL and GAS activities were lower than LW and WW. The BF activities were higher during DWR than LW and WW. It was considered that the lower activity of SOL and GAS depended on water depth, and higher activity of BF occurred by greater flexion of the knee joint or extension of the hip joint during exercise.     

Force-length properties and functional demands of cat gastrocnemius, soleus and plantaris muscles.

The purpose of this study was to measure isometric force-length properties of cat soleus, gastrocnemius and plantaris muscle-tendon units, and to relate these properties to the functional demands of these muscles during everyday locomotor activities. Isometric force-length properties were determined using an in situ preparation, where forces were measured using buckle-type tendon transducers, and muscle-tendon unit lengths were quantified through ankle and knee joint configurations. Functional demands of the muscles were assessed using direct muscle force measurements in freely moving animals. Force-length properties and functional demands were determined for soleus, gastrocnemius and plantaris muscles simultaneously in each animal. The results suggest that isometric force-length properties of cat soleus, gastrocnemius and plantaris muscles, as well as the region of the force-length relation that is used during everyday locomotor tasks, match the functional demands.     

In vivo passive mechanical properties of the human gastrocnemius muscle belly

The purpose of the present study was to determine the in vivo passive mechanical properties, including the length below the slack length, of the gastrocnemius muscle (GAS) belly in humans. Transverse ultrasound images of the medial head of the GAS were taken in 11 subjects during passive knee extension from 80 degrees to 5 degrees with a constant ankle joint angle of 10 degrees (0 degrees is the neutral ankle position: positive values for dorsiflexion). The change in passive ankle joint moment (Mp), which is produced only by the GAS length change, was also measured during passive knee extension. The onset of Mp during passive knee extension was found to be 43+/-8 degrees (mean+/-SD) when the baseline of the Mp was set at the average Mp in the range of 55-60 degrees where the Mp was almost constant (SD<0.03 Nm). At this onset, the muscle fascicle length of the GAS (Lf) was 46+/-7 mm (slack length; Lfs). Lf at 80 degrees was 6+/-4 mm (13+/-6%) less than the Lfs, and Lf at 5 degrees was 12+/-5 mm (27+/-11%) greater than the Lfs. The passive force-resisting compression of the GAS did not produce a dorsiflexion moment in the joint angle range adopted. The passive ankle joint moment increased linearly with Lf (coefficient of determination (R2)=0.85-0.96), and the slopes of the relationships between Lf and Mp, and between the relative Lf to Lfs and Mp were 0.093+/-0.038 Nm/mm and 0.043+/-0.021 Nm/%Lfs. The findings of the present study can be implemented in musculoskeletal modeling, which would provide a more accurate evaluation of the passive mechanical properties of muscle during movement.     

The function of gastrocnemius as a knee flexor at selected knee and ankle angles.

The gastrocnemius has been viewed as an important contributor at the knee joint as a joint flexor and stabilizer across all the knee and ankle joint angles. The purpose of this study was to investigate the influence of knee and ankle joint angles on the knee flexor function of the gastrocnemius. Seventeen participants were tested on a Biodex dynamometer with the gastrocnemius muscle selectively stimulated at a standardized level of electrical current. The results indicated that both ankle and knee joint angle influence the knee joint flexion moment produced by the gastrocnemius. Further analysis revealed that the flexion moment was greatest with the knee joint straight (180 degrees ) across all ankle joint angles. The greatest reduction in knee flexion moment occurred between 180 and 165 degrees of knee angle. No significant difference was observed in the knee flexion moment between 165 degrees and 115 degrees knee flexion, and little knee flexion moment was observed at knee angles of 90 degrees and 75 degrees. The dramatic reduction of moment between 180 degrees and 165 degrees knee angle is possibly due to the change of moment arm while the little moment production during extreme flexion (90 degrees and 75 degrees ) may be due to the reduction of muscle length.     

The effects of gastrocnemius–soleus muscle forces on ankle biomechanics during triple arthrodesis

This paper presents a finite element model of the ankle, taking into account the effects of muscle forces, determined by a musculoskeletal analysis, to investigate the contact stress distribution in the tibio-talar joint in patients with triple arthrodesis and in normal subjects. Forces of major ankle muscles were simulated and corresponded well with the trend of their EMG signals. These forces were applied to the finite element model to obtain stress distributions for patients with triple arthrodesis and normal subjects in three stages of the gait cycle, i.e. heel strike, midstance, and heel rise. The results demonstrated that the stress distribution patterns of the tibio-talar joint in patients with triple arthrodesis differ from those of normal subjects in investigated gait cycle stages. The mean and standard deviations for maximum stresses in the tibo-talar joint in the stance phase for patients and normal subjects were 9.398e7 ± 1.75e7 and 7.372e7 ± 4.43e6 Pa, respectively. The maximum von Mises stresses of the tibio-talar joint for all subjects in the stance phase found to be on the lateral side of the inferior surface of the joint. The results also indicate that, in patients with triple arthrodesis, increasing gastrocnemius–soleus muscle force reduces the stress on the medial malleolus compared with normal subjects. Most of stresses in this area are between 45 and 109 kPa, and will decrease to almost 32 kPa in patients after increasing of 40% in gastrocnemius–soleus muscle force.     

Contributions of the individual ankle plantar flexors to support, forward progression and swing initiation during walking.

Walking is a motor task requiring coordination of many muscles. Previous biomechanical studies, based primarily on analyses of the net ankle moment during stance, have concluded different functional roles for the plantar flexors. We hypothesize that some of the disparities in interpretation arise because of the effects of the uniarticular and biarticular muscles that comprise the plantar flexor group have not been separated. Furthermore, we believe that an accurate determination of muscle function requires quantification of the contributions of individual plantar flexor muscles to the energetics of individual body segments. In this study, we examined the individual contributions of the ankle plantar flexors (gastrocnemius (GAS); soleus (SOL)) to the body segment energetics using a musculoskeletal model and optimization framework to generate a forward dynamics simulation of normal walking at 1.5 m/s. At any instant in the gait cycle, the contribution of a muscle to support and forward progression was defined by its contribution to trunk vertical and horizontal acceleration, respectively, and its contribution to swing initiation by the mechanical energy it delivers to the leg in pre-swing (i.e., double-leg stance prior to toe-off). GAS and SOL were both found to provide trunk support during single-leg stance and pre-swing. In early single-leg stance, undergoing eccentric and isometric activity, they accelerate the trunk vertically but decelerate forward trunk progression. In mid single-leg stance, while isometric, GAS delivers energy to the leg while SOL decelerates it, and SOL delivers energy to the trunk while GAS decelerates it. In late single-leg stance through pre-swing, though GAS and SOL both undergo concentric activity and accelerate the trunk forward while decelerating the downward motion of the trunk (i.e., providing forward progression and support), they execute different energetic functions. The energy produced from SOL accelerates the trunk forward, whereas GAS delivers almost all its energy to accelerate the leg to initiate swing. Although GAS and SOL maintain or accelerate forward motion in mid single-leg stance through pre-swing, other muscles acting at the beginning of stance contribute comparably to forward progression. In summary, throughout single-leg stance both SOL and GAS provide vertical support, in mid single-leg stance SOL and GAS have opposite energetic effects on the leg and trunk to ensure support and forward progression of both the leg and trunk, and in pre-swing only GAS contributes to swing initiation.     

Selective activation of human soleus and medial gastrocnemius muscles during walking in water

During walking in water (WW) the vertical component of ground reaction forces decreases, while the greater propulsive force is required to move forward against the greater resistance of water. In such reduced gravity environment, Hutchison et al. (1989) have demonstrated that the relative activation of rat medial gastrocnemius (MGAS) increased compared to that of the soleus (SOL) during swimming, suggesting different effects of peripheral information on motoneuron excitability of these muscles. It is conceivable that both buoyancy and resistance of water have different effects on the activation patterns of triceps surae muscles during WW, since the reduced weight in water might decrease the peripheral inflow relating load information while greater volitional command might be needed to propel a body forward against the water resistance. The present study was designed to assess each peripheral inflow and efferent input by adjusting the load and walking speed voluntarily during WW. The aim of this study is to investigate the dissociative activation pattern between the SOL and the MGAS during WW.     

Recruitment of the Rhesus soleus and medial gastrocnemius before, during and after spaceflight

Electromyograms were recorded from the soleus and medial gastrocnemius muscles and tendon force from the medial gastrocnemius muscle of 2 juvenile Rhesus monkeys before, during and after Cosmos flight 2229 and of ground control animals. Recording sessions were made while the Rhesus were performing a foot pedal motor task. Preflight testing indicated normal patterns of recruitment between the soleus and medial gastrocnemius, i.e. a higher level of recruitment of the soleus compared to the medial gastrocnemius during the task. Recording began two days into the spaceflight and showed that the media gastrocnemius was recruited preferentially over the soleus. This observation persisted throughout the flight and for the 2 week period of postflight testing. These data indicate a significant change in the relative recruitment of slow and fast extensor muscles under microgravity conditions. The appearance of clonic-like activity in one muscle of each Rhesus during flight further suggests a reorganization in the neuromotor system in a microgravity environment.     

Gastrocnemius and soleus muscle length, velocity, and EMG responses to changes in pedalling cadence

Several authors have shown different excitation patterns for soleus and gastrocnemius muscles in response to cadence manipulation during cycling. The purpose of this study was to examine gastrocnemius and soleus length and velocity change as a function of pedalling cadence to consider mechanisms underlying these excitation differences. Ten male and two female cyclists rode at five randomly assigned cadences (50, 65, 80, 95, and 110 rpm) at a nominal 200 W power output while EMG of the gastrocnemius and soleus and sagittal plane video were recorded. Joint-coordinate data for the knee and ankle were used with equations of Grieve et al. [Grieve D, Pheasant S, Cavanagh PR. Prediction of gastrocnemius length from knee and ankle joint posture, in: E. Asmussen, K. Jorgensen, editors. International Series on Biomechanics, vol. 2A, Baltimore: University Park Press; 1978. p. 405–412] to compute gastrocnemius and soleus length and velocity. Consistent with previous publications, gastrocnemius displayed a significant (p < 0.05) increase in integrated EMG with increased cadence, whereas cadence had no significant effect on integrated EMG of the soleus. The ankle became significantly (p < 0.05) more plantar flexed and reflected a reduced range of motion with increased cadence while the knee became significantly (p < 0.05) less extended. Soleus decreased its range of motion by 29%, whereas gastrocnemius decreased its range of motion by 9%. In contrast, soleus increased its velocity range by 32% and gastrocnemius increased by 45%. These data show that with increased cadence gastrocnemius operated over a narrower range of operating lengths but at a higher range of shortening velocity than soleus. The higher range of velocity may have resulted in the need for a relatively higher excitation, as indicated by the integrated EMG, as the muscle was working at a different range on its force–velocity curve. During the recovery portion of the pedalling cycle, the soleus was acting eccentrically while the gastrocnemius acted concentrically indicating the triceps surae complex did not always act in unison.     

Muscle contracture emulating system for studying artificially induced pathological gait in intact individuals

When studying pathological gait it is important to correctly identify primary gait anomalies originating from damage to the central nervous and musculoskeletal system and separate them from compensatory changes of gait pattern, which is often challenging due to the lack of knowledge related to biomechanics of pathological gait. A mechanical system consisting of specially designed trousers, special shoe arrangement, and elastic ropes attached to selected locations on the trousers and shoes is proposed to allow emulation of muscle contractures of soleus (SOL) and gastrocnemius (GAS) muscles and both SOL-GAS. The main objective of this study was to evaluate and compare gait variability as recorded in normal gait and when being constrained with the proposed system. Six neurologically and orthopedically intact volunteers walked along a 7-m walkway while gait kinematics and kinetics were recorded using VICON motion analysis system and two AMTI forceplates. Statistical analysis of coefficient of variation of kinematics and kinetics as recorded in normal walking and during the most constrained SOL-GAS condition showed comparable gait variability. Inspection of resulting group averaged gait patterns revealed considerable resemblance to a selected clinical example of spastic diplegia, indicating that the proposed mechanical system potentially represents a novel method for studying emulated pathological gait arising from artificially induced muscle contractures in neurologically intact individuals.     

In vivo behavior of muscle fascicles and tendinous tissues of human gastrocnemius and soleus muscles during twitch contraction.

The present study investigated the differences between the human medial gastrocnemius (MG) and soleus (SOL) muscles in length changes of muscle fascicles and tendinous tissues during twitch contraction induced by an electrical nerve stimulus. Also, the time-course characteristics of twitch torque were related with changes in the length of muscle fascicles and tendinous tissues. No significant difference was observed between MG and SOL in contraction and half relaxation times of the changes in lengths and velocities of both muscle fascicles and tendinous tissues. The time-course of changes in twitch torque was nearly identical to that of the length of muscle fascicles and tendinous tissues. It was suggested that the behavior of MG and SOL during twitch contraction is practically similar in spite of their known physiological and architectural differences, and that the time-course of twitch torque is greatly influenced by the changes in the length of muscle fascicles and tendinous tissues.     

Footwear affects the gearing at the ankle and knee joints during running

The objective of the study was to investigate the adjustment of running mechanics by wearing five different types of running shoes on tartan compared to barefoot running on grass focusing on the gearing at the ankle and knee joints. The gear ratio, defined as the ratio of the moment arm of the ground reaction force (GRF) to the moment arm of the counteracting muscle tendon unit, is considered to be an indicator of joint loading and mechanical efficiency. Lower extremity kinematics and kinetics of 14 healthy volunteers were quantified three dimensionally and compared between running in shoes on tartan and barefoot on grass. Results showed no differences for the gear ratios and resultant joint moments for the ankle and knee joints across the five different shoes, but showed that wearing running shoes affects the gearing at the ankle and knee joints due to changes in the moment arm of the GRF. During barefoot running the ankle joint showed a higher gear ratio in early stance and a lower ratio in the late stance, while the gear ratio at the knee joint was lower during midstance compared to shod running. Because the moment arms of the counteracting muscle tendon units did not change, the determinants of the gear ratios were the moment arms of the GRF's. The results imply higher mechanical stress in shod running for the knee joint structures during midstance but also indicate an improved mechanical advantage in force generation for the ankle extensors during the push-off phase.     

Multi-functionality of the cat medical gastrocnemius during locomotion

The functional role of biarticular muscles was investigated based on direct force measurement in the cat medial gastrocnemius (MG) and analysis of hindlimb kinematics and kinetics for the stance phase of level, uphill, and downhill walking. Four primary functional roles of biarticular muscles have been proposed in the past. These functional roles have typically been discussed independently of each other, and biarticular muscles have rarely been assigned more than one functional roles for different phases of the work cycle. The purpose of this study was to elucidate the functional role of the biarticular cat MG during locomotion. It was found that MG forces were primarily associated with the moment requirements at the ankle for most of the stance phase, but also helped to satisfy the moments at the knee in the initial phase of stance. In the second half of stance, MG transferred mechanical energy from the knee to the ankle from the knee to the ankle, while simultaneously producing a substantial amount of mechanical work. Based on these results, we hypothesize that MG's primary function is that of an ankle extensor. However, because of the coupling of the ankle extensor moment with a knee flexor moment in the initial, and a knee extensor moment in the final phase of stance, MG satisfies two joint moments in early stance, and transfers mechanical energy from the knee to the ankle in late stance. We conclude that cat MG has multiple functional roles during the stance phase of locomotion, and speculate that such multi-functionality also exists in other bi- and multi-articular muscles.     

Muscle spindle feedback differs between the soleus and gastrocnemius in humans

The Hoffmann (H) reflex and motor (M) response were studied in soleus and gastrocnemius during voluntary contraction in eight male volunteers. AIMS: To determine if the strength of spindle input to the muscles is the same. To assess if the M response size changes during contraction. RESULTS: The size of the maximum M response (M max) changed during contraction in each subject. Hence, all H reflex measurements were normalized to the M max at each level of contraction for each subject. The largest H/M max was bigger in soleus than gastrocnemius at every contraction level. The overall largest H/M max for soleus (97%) and gastrocnemius (55%) were achieved at 40 and 100% maximum voluntary contraction (MVC), respectively. CONCLUSION: Soleus receives greater spindle feedback than the gastrocnemius both at rest and during voluntary contraction.     

Muscle spindle feedback differs between the soleus and gastrocnemius in humans

The Hoffmann (H) reflex and motor (M) response were studied in soleus and gastrocnemius during voluntary contraction in eight male volunteers. Aims: To determine if the strength of spindle input to the muscles is the same. To assess if the M response size changes during contraction. Results: The size of the maximum M response (M max) changed during contraction in each subject. Hence, all H reflex measurements were normalized to the M max at each level of contraction for each subject. The largest H/M max was bigger in soleus than gastrocnemius at every contraction level. The overall largest H/M max for soleus (97%) and gastrocnemius (55%) were achieved at 40 and 100% maximum voluntary contraction (MVC), respectively. Conclusion: Soleus receives greater spindle feedback than the gastrocnemius both at rest and during voluntary contraction.