A theory for equinus gait in cerebral palsy (CP) is that the strong plantarflexors prevent the weak dorsiflexors from achieving dorsiflexion, thereby causing the ankle to be in a plantarflexed position. Recent work has indicated that both the ankle dorsiflexors and plantarflexors are weak. The purpose of this research was to theoretically and experimentally demonstrate that equinus deformity gait could be a compensatory strategy for plantarflexor weakness. It was hypothesized that children with CP utilize an equinus position during gait as a consequence of their weakness. A two-dimensional, sagittal plane model estimating plantarflexor forces through the Achilles tendon was developed. Five able-bodied (AB) children were tested utilizing heel-toe and progressively increasing toe walking strategies. Four children with CP were tested as they walked using their equinus gait. Results demonstrated that AB children assuming the toe walking stance progressively reduced the plantarflexor force when compared to their heel-toe walking trials. However, their toe walking strategy could not reduce the plantarflexor force level to that of the children with CP during the gait cycle. It was concluded that the equinus deformity posture complemented the CP children's plantarflexor weakness. Therefore, by implementing a concomitant strategy to maintain a reduced force state, equinus deformity could be used as a compensatory mechanism for individuals with plantarflexor weakness.
David A. Hampton, Kevin W. Hollander and Jack R. Engsberg
Luciana Brondino, Esther Suter, Hae-Dong Lee and Walter Herzog
Muscle inhibition (MI) in human knee extensors increases with increasing maximal voluntary force as a function of knee angle. It was speculated that this angle-dependent MI was modulated by force-dependent feedback, likely Golgi tendon organ pathways. Such angle-dependent MI is of clinical and theoretical importance. The purpose of this study was to determine MI in human elbow flexors for maximal voluntary contractions. Muscle inhibition, elbow flexor force, and electromyographic (EMG) activity were measured in 31 volunteers at elbow angles between 30º and 120º. MI and elbow flexor EMG were the same at all elbow angles. Maximal isometric forces were greatest at the 70º angle, and never fell below 70% of the peak force at any of the tested angles. From these results it is concluded that force-dependent modulation of MI did not occur in the elbow flexors, possibly because maximal isometric force remained relatively close (within 30%) to the peak force. In contrast, force-dependent modulation of MI occurred in the knee extensors at the most extended angles, when the average knee extensor force had dropped to 50% or less of the maximal knee extensor force. It is likely that human maximal voluntary contractions are not associated with a given activation. Rather, activation appears to be modulated by force-dependent feedback at force levels below 70% of the absolute peak force, which manifests itself in a change of MI that parallels the level of maximal isometric force in voluntary contractions.
Tatiana G. Deliagina, Irina N. Beloozerova, Ludmila B. Popova, Mikhail G. Sirota, Harvey A. Swadlow, Gunnar Grant and Grigore N. Orlovsky
In this paper, we describe the postural activity in sitting rats and rabbits. An animal was positioned on the platform that could be tilted in the frontal plane for up to ±20-30°, and postural corrections were video recorded. We found that in both rat and rabbit, the postural reactions led to stabilization of the dorsal-side-up trunk orientation. The result of this was that the trunk tilt constituted only ~50% (rat) and 25% (rabbit) of the platform tilt. In addition, in the rabbit the head orientation was also stabilized. Trunk stabilization persisted in the animals subjected to the bilateral labyrinthectomy and blindfolding, suggesting that the somatosensory input is primarily responsible for trunk stabilization. Trunk stabilization was due to extension of the limbs on the side moving down, and flexion of the opposite limbs. EMG recordings showed that the limb extension was caused by the active contraction of extensor muscles. We argue that signals from the Golgi tendon organs of the extensor muscles may considerably contribute to elicitation of postural corrective responses to the lateral tilt.
Christopher J. Hasson, Richard E.A. van Emmerik and Graham E. Caldwell
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.
Harald Böhm, Gerald K. Cole, Gert-Peter Brüggemann and Hanns Ruder
The contribution of muscle in-series compliance on maximum performance of the muscle tendon complex was investigated using a forward dynamic computer simulation. The model of the human body contains 8 Hill-type muscles of the lower extremities. Muscle activation is optimized as a function of time, so that maximum drop jump height is achieved by the model. It is shown that the muscle series elastic energy stored in the downward phase provides a considerable contribution (32%) to the total muscle energy in the push-off phase. Furthermore, by the return of stored elastic energy all muscle contractile elements can reduce their shortening velocity up to 63% during push-off to develop a higher force due to their force velocity properties. The additional stretch taken up by the muscle series elastic element allows only m. rectus femoris to work closer to its optimal length, due to its force length properties. Therefore the contribution of the series elastic element to muscle performance in maximum height drop jumping is to store and return energy, and at the same time to increase the force producing ability of the contractile elements during push-off.
Kurt Manal, Dustyn P. Roberts and Thomas S. Buchanan
Ultrasonography was used to measure the pennation angle of the human tibialis anterior (TA), lateral gastrocnemius (LG), medial gastrocnemius (MG), and soleus (Sol). The right and left legs of 8 male and 8 female subjects were tested at rest and during maximum voluntary contraction (MVC). Joint angles were chosen to control muscle tendon lengths so that the muscles were near their optimal length within the length– tension relationship. No differences in pennation angle were detected between the right and left legs. Another consistent finding was that the pennation angle at MVC was significantly greater than at rest for all muscles tested. Optimal pennation angles for the TA, MG, and Sol were significantly greater for the men than for the women. Optimal pennation angles for the TA, LG, MG, and Sol for the male subjects were 14.3°, 23.7°, 34.6°, and 40.1° respectively, whereas values of 12.1°, 16.3°, 27.3°, and 26.3° were recorded for the female subjects. The results of this study suggest the following: (1) similar values for pennation angle can be used for the right and left TA, LG, MG, and Sol; (2) pennation angle is significantly greater at MVC than at rest for all muscles tested; and (3) sex-specific values for optimal pennation angle should be used when modeling the force-generating potential of the primary muscles responsible for ankle plantar and dorsiflexion.
Robert J. Gregor, Judith L. Smith, Dagan W. Smith, Alanna Oliver and Boris I. Prilutsky
Different forms of locomotion have been studied in the cat in an effort to understand the neural mechanisms involved in movement control. Recent studies have focused on the roles of one- and two-joint muscles, the integration of central commands with sensory input, and the notion that the control system may be organized around the mechanical actions of muscles and the number of joints they span. To investigate the load-sharing between the two-joint medial gastrocnemius and one-joint soleus muscles, a single cat was trained to walk in an instrumented Plexiglas enclosed walkway at slopes ranging ±75%. Surgically implanted tendon force transducers monitored force output from each muscle. Equations in Newtonian mechanics were used to calculate joint kinetics. Results suggest that as slope angle decreased, the one-joint soleus became the primary contributor to the plantar-flexor moment calculated during stance. Unexpectedly, as slope angle increased, force in the one-joint soleus decreased while force in the two-joint medial gastrocnemius increased in the presence of the increased plantar-flexor moment calculated during stance. One explanation is that activation and force in the two-joint medial gastrocnemius should increase in the presence of a knee flexor and plantar-flexor moment. This was the case during upslope walking, as two-joint muscles increase their activation when they act as an agonist at both joints they cross. Additionally, a force-dependent inhibition of the soleus by the medial gastrocnemius has been described as part of a neural control system organized around the mechanical actions of muscles and the number of joints they span. Hence, a decrease in one-joint soleus force might be expected under certain conditions in upslope walking.
Tetsuro Muraoka, Tadashi Muramatsu, Daisuke Takeshita, Hiroaki Kanehisa and Tetsuo Fukunaga
This study estimated the passive ankle joint moment during standing and walking initiation and its contribution to total ankle joint moment during that time. The decrement of passive joint moment due to muscle fascicle shortening upon contraction was taken into account. Muscle fascicle length in the medial gastrocnemius, which was assumed to represent muscle fascicle length in plantarflexors, was measured using ultrasonography during standing, walking initiation, and cyclical slow passive ankle joint motion. Total ankle joint moment during standing and walking initiation was calculated from ground reaction forces and joint kinematics. Passive ankle joint moment during the cyclical ankle joint motion was measured via a dynamometer. Passive ankle joint moment during standing and at the time (Tp) when the MG muscle-tendon complex length was longest in the stance phase during walking initiation were 2.3 and 5.4 Nm, respectively. The muscle fascicle shortened by 2.9 mm during standing compared with the length at rest, which decreased the contribution of passive joint moment from 19.9% to 17.4%. The muscle fascicle shortened by 4.3 mm at Tp compared with the length at rest, which decreased the contribution of passive joint moment from 8.0% to 5.8%. These findings suggest that (a) passive ankle joint moment plays an important role during standing and walking initiation even in view of the decrement of passive joint moment due to muscle fascicle shortening upon muscle contraction, and (b) muscle fascicle shortening upon muscle contraction must be taken into account when estimating passive joint moment during movements.
James R. Debenham, William I. Gibson, Mervyn J. Travers, Amity C. Campbell and Garry T. Allison
Eccentric exercises are increasingly being used to treat lower-limb musculoskeletal conditions such as Achilles tendinopathy. Despite widespread clinical application and documented efficacy, mechanisms underpinning clinical benefit remain unclear. Positive adaptations in motor performance are a potential mechanism.
To investigate how an eccentric loading intervention influences measures of stretch-shortening-cycle (SSC) behavior during a hopping task.
Within-subjects repeated-measures observational study.
University motion-analysis laboratory.
A single intervention of 5 sets of 10 eccentric plantar-flexion contractions at 6 repetitions maximum using a commercial seated calf-raise machine.
Main Outcome Measures:
Lower-limb stiffness, sagittal-plane ankle kinematics, and temporal muscle activity of the agonist (soleus) and antagonist (tibialis anterior) muscles, measured during submaximal hopping on a custom-built sledge-jump system.
Eccentric loading altered ankle kinematics during submaximal hopping; peak angle shifted to a less dorsiflexed position by 2.9° and ankle angle precontact shifted by 4.4° (P < .001). Lower-limb stiffness increased from 5.9 to 6.8 N/m (P < .001), while surface EMG measures of soleus occurred 14–44% earlier (P < .001) after the loading intervention.
These findings suggest that eccentric loading alters SSC behavior in a manner reflective of improved motor performance. Decreased ankle excursion, increased lower-limb stiffness, and alterations in motor control may represent a positive adaptive response to eccentric loading. These findings support the theory that mechanisms underpinning eccentric loading for tendinopathy may in part be due to improved “buffering” of the tendon by the neuromuscular system.
Michael F. Joseph, Kathryn Taft, Maria Moskwa and Craig R. Denegar
Systematic literature review.
To assess the efficacy of deep friction massage (DFM) in the treatment of tendinopathy.
Anecdotal evidence supports the efficacy of DFM for the treatment of tendinopathy. An advanced understanding of the etiopathogenesis of tendinopathy and the resultant paradigm shift away from an active inflammatory model has taken place since the popularization of the DFM technique by Cyriax for the treatment of “tendinitis.” However, increasing mechanical load to the tendinopathic tissue, as well as reducing molecular cross-linking during the healing process via transverse massage, offers a plausible explanation for observed responses in light of the contemporary understanding of tendinopathy.
The authors surveyed research articles in all languages by searching PubMed, Scopus, Pedro, CINAHL, PsycINFO, and the Cochrane Library using the terms deep friction massage, deep tissue massage, deep transverse massage, Cyriax, soft tissue mobilization, soft tissue mobilisation, cross friction massage, and transverse friction massage. They included 4 randomized comparison trials, 3 at the extensor carpi radialis brevis (ECRB) and 1 supraspinatus outlet tendinopathy; 2 nonrandomized comparison trials, both receiving DFM at the ECRB; and 3 prospective noncomparison trials—supraspinatus, ECRB, and Achilles tendons. Articles meeting inclusion criteria were assessed based on PEDro and Centre for Evidence-Based Medicine rating scales.
Nine studies met the inclusion criteria.
The heterogeneity of dependent measures did not allow for meta-analysis.
The varied locations, study designs, etiopathogenesis, and outcome tools used to examine the efficacy of DFM make a unified conclusion tenuous. There is some evidence of benefit at the elbow in combination with a Mills manipulation, as well as for supraspinatus tendinopathy in the presence of outlet impingement and along with joint mobilization. The examination of DFM as a single modality of treatment in comparison with other methods and control has not been undertaken, so its isolated efficacy has not been established. Excellent anecdotal evidence remains along with a rationale for its use that fits the current understanding of tendinopathy.