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David A. Hampton, Kevin W. Hollander and Jack R. Engsberg

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.

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Courtney L. Pollock, Michael A. Hunt, Taian M. Vieira, Alessio Gallina, Tanya D. Ivanova and S. Jayne Garland

-correlation analysis between electromyography (EMG) signals of the ankle plantarflexor muscles and force platform recordings of postural sway, it has been shown that, in the sagittal plane, modulation of the ankle plantarflexor muscle activity is moderately correlated with, and precedes, postural sway position to

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Michael D. Ross, Shelly Hooten and Darren Moore

Objective:

To determine the relationship between asymmetries in lower leg girth and standing heel-rise after anterior cruciate ligament (ACL) reconstruction.

Design:

Single-group posttest.

Participants:

15 at a mean of 30 d after ACL reconstruction.

Measurements:

Lower leg girth and number of repetitions performed on the standing heel-rise test.

Results:

A significant decrease in lower leg girth and number of repetitions performed on the standing heel-rise test for the involved leg. There was also a low correlation between asymmetries in lower leg girth and standing heel-rise test (r = .25).

Conclusion:

Ankle plantar-flexor endurance should be considered when developing rehabilitation programs for the early stages after ACL reconstruction. In this study the ankle of the involved leg attained a significantly smaller angle of maximal standing plantar flexion, suggesting that ankle range of motion should also be assessed. Caution should be used in predicting standing heel-rise asymmetries from asymmetries in lower leg girth in ACL-reconstructed patients.

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Thomas Cattagni, Clément Billet, Christophe Cornu and Marc Jubeau

Context: Prolonged tendon vibration may induce muscle fatigue, as assessed by a decrease in maximal force production. It remains unknown, however, whether the decrease in muscle strength after prolonged Achilles tendon vibration is related to the vibration frequency. Objective: To assess the maximal capacity of plantar-flexor (PF) neuromuscular function before and after prolonged Achilles tendon vibration at low and high frequencies generated using a portable device. Design: Pre- and posttest intervention with control.Setting: University laboratory. Participants: 10 healthy men age 22.6 ± 4.0 y. Intervention: Each subject participated in 3 experimental sessions that were randomly distributed and separated by 1 wk. During each experimental session, 1 of the following vibration protocols was applied for 30 min: 40-Hz vibration, 100-Hz vibration, or no vibration (control protocol). Main Outcome Measures: Maximal-voluntary-contraction torque, voluntary activation level, twitch torque, maximal electromyographic activity, and maximal M-wave of PF muscles (measured before and after each vibration or control protocol).Results: Statistical analysis exhibited no significant effect of vibration protocol on the measured variables. Conclusions: The current study demonstrates that 30 min of Achilles tendon vibration at a low or high frequency using a portable stimulator did not affect the neuromuscular performance of the PF muscles. These results emphasize the limits of tendon vibration, whatever the frequency applied, for inducing neuromuscular fatigue.

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Mati Pääsuke, Jaan Ereline, Helena Gapeyeva and Heigo Maamägi

This study compared maximal voluntary-contraction (MVC) force and twitch-contractile properties of the plantar-flexor muscles in resting and postactivation potentiation slates of 2 groups of men matched for similar levels of physical activity: young (19- to 22-year-olds. n = 13) and 52–63 years old (n = 12). MVC force, twitch peak force (PT), maximal rates of force development and relaxation, and postactivation potentiation were higher (p < .05) in young than in 52- to 63-year-old men. In young men. potentiated-twitch PT was 23.3% higher (p < .01) than resting twitch. Resting- and potentialed-twitch-contraction times were 16.7% and 18.3% shorter, respectively (p < .001), in young than in 52- to 63-year-old men. These Findings suggest that late middle age is characterized by reduced capacity for evoked twitch-force generation and potentiation and slowed speed of contraction of the plantar-flexor muscles.

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Nick Caplan, Andrew Forbes, Sarkhell Radha, Su Stewart, Alistair Ewen, Alan St Clair Gibson and Deiary Kader

Context:

Ankle immobilization is often used after ankle injury.

Objective:

To determine the influence of 1 week’s unilateral ankle immobilization on plantar-flexor strength, balance, and walking gait in asymptomatic volunteers.

Design:

Repeated-measures laboratory study.

Setting:

University laboratory.

Participants:

6 physically active male participants with no recent history of lower-limb injury.

Interventions:

Participants completed a 1-wk period of ankle immobilization achieved through wearing a below-knee ankle cast. Before the cast was applied, as well as immediately, 24 h, and 48 h after cast removal, their plantar-flexor strength was assessed isokinetically, and they completed a single-leg balance task as a measure of proprioceptive function. An analysis of their walking gait was also completed

Main Outcome Measures:

Peak plantar-flexor torque and balance were used to determine any effect on muscle strength and proprioception after cast removal. Ranges of motion (3D) of the ankle, knee, and hip, as well as walking speed, were used to assess any influence on walking gait.

Results:

After cast removal, plantar-flexor strength was reduced for the majority of participants (P = .063, CI = −33.98 to 1.31) and balance performance was reduced in the immobilized limb (P < .05, CI = 0.84−5.16). Both strength and balance were not significantly different from baseline levels by 48 h. Walking speed was not significantly different immediately after cast removal but increased progressively above baseline walking speed over the following 48 h. Joint ranges of motion were not significantly different at any time point.

Conclusions:

The reduction in strength and balance after such a short period of immobilization suggested compromised central and peripheral neural mechanisms. This suggestion appeared consistent with the delayed increase in walking speed that could occur as a result of the excitability of the neural pathways increasing toward baseline levels.

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Patrice Rougier, Cyril Burdet and Nicolas Genthon

To assess whether prior stretching of a muscle can induce improved postural control, 15 healthy adults stood still upright with their eyes closed before and after a series of bilateral stretches of the triceps surae muscles. The analysis focused on the center of pressure (CP) and the vertical projection of the center of gravity (CGv) trajectories and their difference (CP – CGv). The prolonged stretching induced a forward shift of the mean position of the CGv. The frequency analysis showed a constancy of the amplitudes of both basic movements whereas an increased mean power frequency was seen for the CP – CGv movements. A fractional Brownian motion modeling of the trajectories indicates shortest time intervals and lower covered distances by the CGv before a change in its control occurs along the antero-posterior axis. This reorganization is thought to be a result of improved body movement detection, which allows postural control over the longest time intervals to be triggered more rapidly.

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Carly C. Sacco, Erin M. Gaffney and Jesse C. Dean

movement in clinical populations. In many functional tasks, individuals rely on processing proprioceptive feedback from more strongly contracting muscles. 27 , 28 For example, plantarflexor muscle activity is increased during the type of active postural positioning that accompanies a forward reach. 29

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Katie A. Conway, Randall G. Bissette and Jason R. Franz

(eg, stroke) are characterized by a reduced “push-off intensity” during a late stance, which we operationally define here at the joint level by peak ankle moment and power generation (ie, the mechanical output of the plantarflexor muscles) and at the limb level by peak propulsive forces (ie, the peak

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Samantha J. Wilson, Bryan Christensen, Kara Gange, Christopher Todden, Harlene Hatterman-Valenti and Jay M. Albrecht

research on humans that examines light stretching during immobilization. The objective of this study was to investigate changes in calf girth, plantarflexor (PF) peak torque, and dorsiflexion (DF) range of motion (ROM), when chronic static stretching was implemented during 2 weeks of ankle immobilization