In this study, we investigated the pennation angles of ankle muscles as they relate to muscle contraction intensity (MCI). Eight male subjects with no history of musculoskeletal injuries ...participated. In each patient, the ankle joint was fixed at 15° dorsiflexion and 0°, 15° and 30° plantarflexion. Ultrasound images (SonoAce Pico, Samsung Medison, Korea) were taken to measure the pennation angle of tibialis anterior (TA), gastrocnemius medial (GCM), gastrocnemius lateral (GCL), and soleus (SOL). The torque dynamometer (Biodex system 3, Biodex Medical System, USA) was used to measure the ankle contraction intensity corresponding to 0, 30, 70 and 100% of maximum voluntary contraction (MVC) respectively. Pennation angles in ankle muscles on sub-maximal muscle contraction were determined. In the present study, the significant differences was found at between 0% of MVC and sub-maximal MVCs, between 0° and 15° of dorsiflexion, and between 15° of plantarflexion and 15° of dorsiflexion. This study may be beneficial in implementing a more realistic muscle model of muscle force.
Aim
Reaction times of the hip abductor were reported to be longer in elderly women than in elderly men, and this was suggested to be related to mediolateral balance performance. The aim of the ...present study was to investigate the effects of age and gender on the reaction performance of ankle muscles, which have predominant roles in anterioposterior balance control.
Methods
A total of 40 elderly subjects and 40 young subjects (even number of men and women) carried out a series of isometric plantarflexions and dorsiflexions, as forcefully and quickly as possible, in response to auditory stimulus. Surface electromyogram at the dorsiflexor and plantarflexor were recorded, together with foot plantar force. Premotor time, motor time and total reaction time derived from the experimental data were compared between age groups and genders by two‐way anova.
Results
Both dorsiflexor and plantarflexor showed similar reaction performance. Premotor time increased with age with no gender difference. Motor time increased with age in women and not in men, resulting in longer motor time in elderly women than in elderly men. Total reaction time was dominated by premotor time, so that it was longer in the elderly with no gender difference.
Conclusion
Although age‐related elongation of motor time was greater in women, total reaction time was not different between the genders. This may be related to no gender difference in anterioposterior balance performance. Geriatr Gerontol Int 2014; 14: 94–99.
The purpose of this study was to investigate how the recruitment properties of the corticospinal pathway are modulated in the soleus (SOL) and tibialis anterior (TA) muscles depending on postures. A ...wide range of stimulus intensities were applied via transcranial magnetic stimulation over the primary motor cortex during standing (STD) and sitting (SIT) with a comparable background activity level in each muscle. The relationship between the stimulation intensities and the size of motor-evoked potentials was assessed by the Boltzmann sigmoid function, which is characterized by a plateau value, maximum slope, and threshold. The plateau value and maximum slope were significantly higher during STD than during SIT in the SOL muscle (STD vs. SIT, plateau value: 50.0 ± 21.8 vs. 33.9 ± 12.3 mV ms, maximal slope: 1.6 ± 0.7 vs. 1.2 ± 0.5 mV ms/% maximal stimulator output). Similar changes of the parameters were also observed in the TA muscle (STD vs. SIT, plateau value: 71.0 ± 22.9 vs. 41.4 ± 16.1 mV ms, maximal slope: 5.0 ± 2.0 vs. 2.5 ± 0.7 mV ms/% maximal stimulator output). The threshold did not differ significantly between the two conditions and both muscles. These results indicate that the central nervous system requires a different control for each postural condition; that is, the relative balance of the excitatory and inhibitory inputs to the corticospinal pathways as well as the number of neurons of subliminal fringe in the corticospinal pathway was increased during STD compared with those during SIT.
Anticipatory postural adjustments (APA) were studied in a dynamic multi-joint movement, in which the legs serve both a focal and a postural role. Eight male subjects bimanually lifted a barbell (20% ...of body mass) after several unloaded movement cycles using two distinct lifting techniques. Picking up a load induces a perturbation to balance, because the centre of mass (CoM) of the combined body and load shifts forward at the moment of load pick-up. Furthermore, the inertia of the load decelerates the backward rotation of the body towards the erect posture. Both perturbations were found to be counteracted by APA in kinematics, kinetics and leg muscle activity patterns. The APA were characterized by an increase in the backward directed horizontal CoM momentum, an increase in the backward directed whole body angular momentum and a forward shift of the centre of foot pressure (CoP) for both techniques. Anticipatory adjustments in activity of muscles crossing the ankle joint were shown to control the CoP position, which was important to accomplish the required combination of anticipatory changes in horizontal and angular momenta. The APA in kinematics and kinetics were modulated according to the dynamic requirements of each lifting technique, although it could have been expected that picking up and lifting the same load at equal speed would have yielded a similar perturbation in each condition.
The purpose of this study was to determine whether a motor learning effect exists during concentric isokinetic testing of the ankle invertor and evertor muscles of the dominant and non-dominant leg. ...Thirty-three subjects aged 22 to 57 years without any experience in isokinetic testing, were randomly assigned to one out of three test velocity groups (30, 60 or 120 degree /s). Each velocity group consisted of 11 subjects. Invertors and evertors of the dominant and non-dominant leg were tested. All subjects performed five sets of two maximal concentric inversion-eversion movements on a calibrated CYBEX 6000 dynamometer. For the invertors of the dominant leg at 30 and 120 degree /s. the mean PKTQ%BW generated in the second set was significantly higher than in the first set. For the evertors of the dominant leg and the invertors and evertors of the non-dominant leg no statistically significant difference was found. To exclude possible bias of learning effects in concentric isokinetic testing of inversion-eversion muscles, we advise a practice session of two sets of two maximal inversion-eversion movements.
Reciprocal Ia inhibition from ankle flexors to extensors was studied during voluntary tonic isometric dorsiflexion and plantar flexion in five normal subjects. The Ia inhibition was examined as the ...short-latency suppression of the soleus H-reflexes by stimulation of the low-threshold afferents in the common peroneal nerve (Mizuno et al. 1971). At rest, weak Ia inhibition was demonstrated in four subjects out of five, the maximal amount being 14.1 +/- 5.0% suppression of the control H-reflex. The absolute amount of inhibition, which was calculated by subtracting the mean size of the conditioned H-reflex from that of the control H-reflex and expressed as a percentage of the maximal M-response, increased during ankle dorsiflexion, and decreased or disappeared during plantar flexion in parallel with the amount of contraction. The neural mechanisms for facilitation of the Ia inhibitory pathway during dorsiflexion were considered to support the hypothesis of "alpha-gamma-linkage in reciprocal inhibition", i.e. combined facilitatory effects on the Ia inhibitory interneuron from the supraspinal centers directly and indirectly via the gamma motoneuron--Ia afferent route. The mechanism for inhibition of the pathway during plantar flexion was considered to be inhibition of the Ia interneuron of the flexor side by Ia interneuron of antagonist extensors. A quantitative aspect of activity in the reciprocal Ia inhibitory pathway on the performance of voluntary movement is revealed in this study.
Reflex activity in human ankle muscles in response to 36 deg./s dorsi-flexion rotations of the feet was investigated in subjects standing upright and when leaning back so as to preactivate ankle ...flexor muscles. Short latency stretch reflex activity in soleus and inhibition in tibialis anterior muscles occurred at 50 ms from ankle rotation onset. Two prominent bursts of tibialis activity followed at 83 and 131 ms. and preceded large stabilizing ankle torques. Head movements commenced 20 ms after foot rotations and acquired accelerations exceeding 100 deg./s2 within 60 ms. It is suggested that the tibialis anterior activity is either a vestibulospinal reflex resulting from the head movement, or a stretch reflex only present during standing, since this activity was not observed when seated subjects received identical foot rotations.
PDF
