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pubmed: (kellis, elefthrerio... https://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Search&db=PubMed&term=%28Kellis%2C%20Elefthrerios%5BAuthor%5D%29%20OR%20Amiridis%2C%20Ioannis%20G%5BAuthor%5D NCBI: db=pubmed; Term=(Kellis, Elefthrerios[Author]) OR Amiridis, Ioannis G[Author] en-us http://blogs.law.harvard.edu/tech/rss 1440 NCBI pubmed https://www.ncbi.nlm.nih.gov/entrez/query/static/gifs/iconsml.gif https://www.ncbi.nlm.nih.gov/sites/entrez PubMed comprises more than millions of citations for biomedical literature from MEDLINE, life science journals, and online books. Citations may include links to full-text content from PubMed Central and publisher web sites. Neuromuscular electrical stimulation can improve mobility in older adults but the time course varies across tasks: Double-blind, randomized trial. https://www.ncbi.nlm.nih.gov/pubmed/29738790?dopt=Abstract

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Neuromuscular electrical stimulation can improve mobility in older adults but the time course varies across tasks: Double-blind, randomized trial.

Exp Gerontol. 2018 Jul 15;108:269-275

Authors: Mani D, Almuklass AM, Amiridis IG, Enoka RM

Abstract
Declines in mobility with advancing age are often associated with a reduction in the use of lower leg muscles. We examined the influence of two interventions that involved neuromuscular electrical stimulation (NMES) applied to the triceps surae muscles on the mobility and muscle function of older adults. Thirty healthy older adults (73.5 ± 4.8 yrs) participated in a 6-week intervention comprising 3 weekly sessions of either narrow- or wide-pulse NMES. Motor function was assessed at Weeks 0, 4, 7, and 10. There were no statistically significant differences in the changes in mobility for the two groups of participants, so the data for the two groups were combined to examine changes across time. Time to walk 400 m decreased and maximal walking speed increased after 3 wks of NMES (Week 4) but did not change further at Weeks 7 and 10. In contrast, time to complete the chair-rise and rapid-step tests decreased progressively up to Week 7 but did not change further at Week 10. Moreover, the increase in plantar flexor strength was only observed at Week 7. NMES can elicit improvements in the motor function of older adults, but the time course of the adaptations differs across the mobility tests.

PMID: 29738790 [PubMed - in process]

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Mani D, Almuklass AM, Amiridis IG, Enoka RM Exp Gerontol PubMed:29738790 Motor unit activity in biceps brachii of left-handed humans during sustained contractions with two load types. https://www.ncbi.nlm.nih.gov/pubmed/27334949?dopt=Abstract

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Motor unit activity in biceps brachii of left-handed humans during sustained contractions with two load types.

J Neurophysiol. 2016 Sep 01;116(3):1358-65

Authors: Gould JR, Cleland BT, Mani D, Amiridis IG, Enoka RM

Abstract
The purpose of the study was to compare the discharge characteristics of single motor units during sustained isometric contractions that required either force or position control in left-handed individuals. The target force for the two sustained contractions (24.9 ± 10.5% maximal force) was identical for each biceps brachii motor unit (n = 32) and set at 4.7 ± 2.0% of maximal voluntary contraction (MVC) force above its recruitment threshold (range: 0.5-41.2% MVC force). The contractions were not sustained to task failure, but the duration (range: 60-330 s) was identical for each motor unit and the decline in MVC force immediately after the sustained contractions was similar for the two tasks (force: 11.1% ± 13.7%; position: 11.6% ± 9.9%). Despite a greater increase in the rating of perceived exertion during the position task (task × time interaction, P < 0.006), the amplitude of the surface-recorded electromyogram for the agonist and antagonist muscles increased similarly during the two tasks. Nonetheless, mean discharge rate of the biceps brachii motor units declined more during the position task (task × time interaction, P < 0.01) and the variability in discharge times (coefficient of variation for interspike interval) increased only during the position task (task × time interaction, P < 0.008). When combined with the results of an identical study on right-handers (Mottram CJ, Jakobi JM, Semmler JG, Enoka RM. J Neurophysiol 93: 1381-1392, 2005), the findings indicate that handedness does not influence the adjustments in biceps brachii motor unit activity during sustained submaximal contractions requiring either force or position control.

PMID: 27334949 [PubMed - indexed for MEDLINE]

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Gould JR, Cleland BT, Mani D, Amiridis IG, Enoka RM J Neurophysiol PubMed:27334949 Fatigue-induced adjustment in antagonist coactivation by old adults during a steadiness task. https://www.ncbi.nlm.nih.gov/pubmed/26846553?dopt=Abstract

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Fatigue-induced adjustment in antagonist coactivation by old adults during a steadiness task.

J Appl Physiol (1985). 2016 05 01;120(9):1039-46

Authors: Arellano CJ, Caha D, Hennessey JE, Amiridis IG, Baudry S, Enoka RM

Abstract
The purpose of this study was to determine the adjustments in the level of coactivation during a steadiness task performed by young and old adults after the torque-generating capacity of the antagonist muscles was reduced by a fatiguing contraction. Torque steadiness (coefficient of variation) and electromyographic activity of the extensor and flexor carpi radialis muscles were measured as participants matched a wrist extensor target torque (10% maximum) before and after sustaining an isometric contraction (30% maximum) with wrist flexors to task failure. Time to failure was similar (P = 0.631) for young (417 ± 121 s) and old (452 ± 174 s) adults. The reduction in maximal voluntary contraction torque (%initial) for the wrist flexors after the fatiguing contraction was greater (P = 0.006) for young (32.5 ± 13.7%) than old (21.8 ± 6.6%) adults. Moreover, maximal voluntary contraction torque for the wrist extensors declined for old (-13.7 ± 12.7%; P = 0.030), but not young (-5.4 ± 13.8%; P = 0.167), adults. Torque steadiness during the matching task with the wrist extensors was similar before and after the fatiguing contraction for both groups, but the level of coactivation increased after the fatiguing contraction for old (P = 0.049) but not young (P = 0.137) adults and was twice the amplitude for old adults (P = 0.002). These data reveal that old adults are able to adjust the amount of antagonist muscle activity independent of the agonist muscle during steady submaximal contractions.

PMID: 26846553 [PubMed - indexed for MEDLINE]

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Arellano CJ, Caha D, Hennessey JE, Amiridis IG, Baudry S, Enoka RM J Appl Physiol (1985) PubMed:26846553 Modulation of motor unit activity in biceps brachii by neuromuscular electrical stimulation applied to the contralateral arm. https://www.ncbi.nlm.nih.gov/pubmed/25930023?dopt=Abstract

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Modulation of motor unit activity in biceps brachii by neuromuscular electrical stimulation applied to the contralateral arm.

J Appl Physiol (1985). 2015 Jun 15;118(12):1544-52

Authors: Amiridis IG, Mani D, Almuklass A, Matkowski B, Gould JR, Enoka RM

Abstract
The purpose of the study was to determine the influence of neuromuscular electrical stimulation (NMES) current intensity and pulse width applied to the right elbow flexors on the discharge characteristics of motor units in the left biceps brachii. Three NMES current intensities were applied for 5 s with either narrow (0.2 ms) or wide (1 ms) stimulus pulses: one at 80% of motor threshold and two that evoked contractions at either ∼10% or ∼20% of maximal voluntary contraction (MVC) force. The discharge times of 28 low-threshold (0.4-21.6% MVC force) and 16 high-threshold (31.7-56.3% MVC force) motor units in the short head of biceps brachii were determined before, during, and after NMES. NMES elicited two main effects: one involved transient deflections in the left-arm force at the onset and offset of NMES and the other consisted of nonuniform modulation of motor unit activity. The force deflections, which were influenced by NMES current intensity and pulse width, were observed only when low-threshold motor units were tracked. NMES did not significantly influence the discharge characteristics of tracked single-threshold motor units. However, a qualitative analysis indicated that there was an increase in the number of unique waveforms detected during and after NMES. The findings indicate that activity of motor units in the left elbow flexors can be modulated by NMES current and pulse width applied to right elbow flexors, but the effects are not distributed uniformly to the involved motor units.

PMID: 25930023 [PubMed - indexed for MEDLINE]

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Amiridis IG, Mani D, Almuklass A, Matkowski B, Gould JR, Enoka RM J Appl Physiol (1985) PubMed:25930023 Postural leaning direction challenges the manifestation of tendon vibration responses at the ankle joint. https://www.ncbi.nlm.nih.gov/pubmed/24289985?dopt=Abstract

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Postural leaning direction challenges the manifestation of tendon vibration responses at the ankle joint.

Hum Mov Sci. 2014 Feb;33:251-62

Authors: Kanakis I, Hatzitaki V, Patikas D, Amiridis IG

Abstract
In this study, we examined the interaction between central and peripheral proprioceptive afferent pathways by applying ankle tendon vibration during postural leaning in different directions. Twenty young participants stood for 60s over the midline of two adjacent force platforms in (a) neutral stance distributing Body Weight (BW) equally between the platforms, (b) forward leaning transferring 80% of BW to the front platform and (c) backward leaning transferring 80% of BW to the rear platform. Participants controlled the degree of leaning by receiving on-line visual feedback of BW distribution matched to a target line. Vibration (80Hz, 1.5-1.8mm) was applied over the Achilles or tibialis anterior tendon during the middle 20s of standing. This induced a postural shift towards the vibration side and an increase in the variability of the BW distribution that was greater in backward compared to forward leaning. EMG responses to tendon vibration were independent of the leaning direction. Antagonistic activity also increased in response to vibration, the amplitude of this increase however was direction dependent. These results favor the hypothesis about the central co-modulation of the vibration evoked proprioceptive inflow based on postural and visual feedback rather than muscle tension constraints.

PMID: 24289985 [PubMed - indexed for MEDLINE]

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Kanakis I, Hatzitaki V, Patikas D, Amiridis IG Hum Mov Sci PubMed:24289985 Side-alternating vibration training for balance and ankle muscle strength in untrained women. https://www.ncbi.nlm.nih.gov/pubmed/23914911?dopt=Abstract

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Side-alternating vibration training for balance and ankle muscle strength in untrained women.

J Athl Train. 2013 Sep-Oct;48(5):590-600

Authors: Spiliopoulou SI, Amiridis IG, Tsigganos G, Hatzitaki V

Abstract
CONTEXT: Side-alternating vibration (SAV) may help reduce the risk of falling by improving body balance control. Such training has been promoted as a strength-training intervention because it can increase muscle activation through an augmented excitatory input from the muscle spindles.
OBJECTIVE: To determine the effect of SAV training on static balance during 3 postural tasks of increasing difficulty and lower limb strength.
DESIGN: Randomized controlled clinical trial.
SETTING: Laboratory.
PATIENTS OR OTHER PARTICIPANTS: A total of 21 healthy women were divided into training (n = 11; age = 43.35 ± 4.12 years, height = 169 ± 6.60 cm, mass = 68.33 ± 11.90 kg) and control (n = 10; age = 42.31 ± 3.73 years, height = 167 ± 4.32 cm, mass = 66.29 ± 10.74 kg) groups.
INTERVENTION(S): The training group completed a 9-week program during which participants performed 3 sessions per week of ten 15-second isometric contractions with a 30-second active rest of 3 exercises (half-squat, wide-stance squat, 1-legged half-squat) on an SAV plate (acceleration = 0.91-16.3g). The control group did not participate in any form of exercise over the 9-week period.
MAIN OUTCOME MEASURE(S): We evaluated isokinetic and isometric strength of the knee extensors and flexors and ankle plantar flexors, dorsiflexors, and evertors. Static balance was assessed using 3 tasks of increasing difficulty (quiet bipedal stance, tandem stance, 1-legged stance). The electromyographic activity of the vastus lateralis, semitendinosus, medial gastrocnemius, tibialis anterior, and peroneus longus was recorded during postural task performance, baseline and pretraining, immediately posttraining, and 15 days posttraining.
RESULTS: After training in the training group, ankle muscle strength improved (P = .03), whereas knee muscle strength remained unaltered (P = .13). Improved ankle-evertor strength was observed at all angular velocities (P = .001). Postural sway decreased in both directions but was greater in the mediolateral (P < .001) than anteroposterior (P = .02) direction. The electromyographic activity of the peroneus longus increased during the sharpened tandem (P = .001) and 1-legged tasks (P = .007). No changes were seen in the control group for any measures.
CONCLUSIONS: The SAV training could enhance ankle muscle strength and reduce postural sway during static balance performance. The reduction in mediolateral sway could be associated with the greater use of ankle evertors due to their strength improvement.

PMID: 23914911 [PubMed - indexed for MEDLINE]

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Spiliopoulou SI, Amiridis IG, Tsigganos G, Hatzitaki V J Athl Train PubMed:23914911 Synergetic and antagonist muscle strength and activity in women with knee osteoarthritis. https://www.ncbi.nlm.nih.gov/pubmed/23635991?dopt=Abstract

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Synergetic and antagonist muscle strength and activity in women with knee osteoarthritis.

J Geriatr Phys Ther. 2014 Jan-Mar;37(1):17-23

Authors: Patsika G, Kellis E, Kofotolis N, Salonikidis K, Amiridis IG

Abstract
BACKGROUND AND PURPOSE: People with knee osteoarthritis (OA) display limitations in daily activities and a lower quality of life. The purpose of this study was to investigate the differences in strength balance and activation during maximum strength efforts between women with knee OA and asymptomatic women.
METHODS: Twelve women with knee OA (age 60.33 ± 6.66 years) and 11 controls (age 56.54 ± 5.46 years) performed maximum isokinetic eccentric and concentric knee extension and flexion tests at 60°/s, 120°/s, and 150°/s. Surface electromyography (EMG) was recorded from the biceps femoris (BF), vastus lateralis (VL), and vastus medialis (VM). Hamstrings-to-quadriceps moment ratios (H/Q), the synergetic (VL/VM), and co-contraction (BF/[VM + VL]) EMG ratios were calculated.
RESULTS: Analysis-of-variance designs showed that women experiencing knee OA had significantly higher H/Q moment ratios and VM/VL EMG ratios than controls (P < 0.05). The co-contraction index was significantly lower in the OA group only during knee flexion (P < 0.05).
CONCLUSIONS: Women with knee OA showed a higher H/Q moment ratios probably because of the need for better joint stability or a lower quadriceps capacity. This deficiency was accompanied by a higher VM activation, which probably serves to stabilize the patella upon maximum contraction as well as a higher activation of antagonist muscles.

PMID: 23635991 [PubMed - indexed for MEDLINE]

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Patsika G, Kellis E, Kofotolis N, Salonikidis K, Amiridis IG J Geriatr Phys Ther PubMed:23635991 Biomechanical differences between incline and plane hopping. https://www.ncbi.nlm.nih.gov/pubmed/22080320?dopt=Abstract

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Biomechanical differences between incline and plane hopping.

J Strength Cond Res. 2011 Dec;25(12):3334-41

Authors: Kannas TM, Kellis E, Amiridis IG

Abstract
Kannas, TM, Kellis, E, and Amiridis, IG. Biomechanical differences between incline and plane hopping. J Strength Cond Res 25(12): 3334-3341, 2011-The need for the generation of higher joint power output during performance of dynamic activities led us to investigate the force-length relationship of the plantar flexors during consecutive stretch-shortening cycles of hopping. The hypothesis of this study was that hopping (consecutive jumps with the knee as straight as possible) on an inclined (15°) surface might lead to a better jumping performance compared with hopping on a plane surface (0°). Twelve active men performed 3 sets of 10 consecutive hops on both an incline and plane surface. Ground reaction forces; ankle and knee joint kinematics; electromyographic (EMG) activity from the medial gastrocnemius (MG), soleus (Sol) and tibialis anterior (TA); and architectural data from the MG were recorded. The results showed that participants jumped significantly higher (p < 0.05) when hopping on an inclined surface (30.32 ± 8.18 cm) compared with hopping on a plane surface (27.52 ± 4.97 cm). No differences in temporal characteristics between the 2 types of jumps were observed. Incline hopping induced significantly greater ankle dorsiflexion and knee extension at takeoff compared with plane hopping (p < 0.05). The fascicle length of the MG was greater at initial contact with the ground during incline hopping (p < 0.05). Moreover, the EMG activities of Sol and TA during the propulsion phase were significantly higher during incline compared with that during plane hopping (p < 0.05). It does not seem unreasonable to suggest that, if the aim of hopping plyometrics is to improve plantar flexor explosivity, incline hopping might be a more effective exercise than hopping on a plane surface.

PMID: 22080320 [PubMed - indexed for MEDLINE]

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Kannas TM, Kellis E, Amiridis IG J Strength Cond Res PubMed:22080320 Incline plyometrics-induced improvement of jumping performance. https://www.ncbi.nlm.nih.gov/pubmed/22038146?dopt=Abstract

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Incline plyometrics-induced improvement of jumping performance.

Eur J Appl Physiol. 2012 Jun;112(6):2353-61

Authors: Kannas TM, Kellis E, Amiridis IG

Abstract
The aim of this study was to examine the effects of incline plyometrics training on muscle activation and architecture during vertical jumping and maximum strength. Twenty male participants were divided in two training groups which followed after a 4 week training program. The incline plyometrics group (n = 10) trained by performing consecutive jumps on an inclined surface (15°) while the plane plyometrics (PP) group (n = 10) performed the same jumps on a plane surface. Both groups trained four times per week and performed 8 sets of 10 jumps in each session. Subjects performed squat jumps, counter movement jumps and drop jumps (DJ) prior to and immediately after the training period, while the electromyographic activity of the medial gastrocnemius (MGAS) and tibialis anterior muscles and the architecture of MGAS were recorded. Maximal isokinetic and isometric strength of the plantar flexors were performed. Analysis of variance showed that only the IP group improved fast DJ height performance by 17.4 and 14.4% (20 and 40 cm, p < 0.05). This was accompanied by a significantly higher MGAS activity during the propulsion phase (24% from 20 cm and 50% from 40 cm, p < 0.05) of the DJ and a longer working fascicle length (5.08%, p < 0.05) compared with the PP group. There were no significant changes in isokinetic and isometric strength of the plantar flexors after training for both groups. The increase of jumping performance, after incline plyometrics should be taken into consideration by coaches, when they apply hopping exercise to improve explosiveness of the plantar flexors.

PMID: 22038146 [PubMed - indexed for MEDLINE]

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Kannas TM, Kellis E, Amiridis IG Eur J Appl Physiol PubMed:22038146 Responses to Achilles tendon vibration during self-paced, visually and auditory-guided periodic sway. https://www.ncbi.nlm.nih.gov/pubmed/21748332?dopt=Abstract

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Responses to Achilles tendon vibration during self-paced, visually and auditory-guided periodic sway.

Exp Brain Res. 2011 Sep;213(4):423-33

Authors: Radhakrishnan SM, Hatzitaki V, Patikas D, Amiridis IG

Abstract
Achilles tendon vibration (ATV) alters proprioceptive input of the triceps surae muscles resulting in a posterior postural shift during standing. When this is applied in combination with a more dynamic proprioceptive perturbation, postural responses to ATV are attenuated. In this study, we applied ATV during self-paced, visually and auditory guided voluntary periodic sway in order to examine how the vibration-induced afferent input is processed and reweighted at the presence of inter-sensory guidance stimuli. Seventeen healthy adults (aged 26.7 ± 4.23 years) performed 15 cycles of periodic sway under three sensory guidance conditions: (a) self-paced, (b) auditory paced (0.25 Hz), and (c) visually driven by matching the resultant force vector to a target sine-wave (0.25 Hz). Bilateral ATV (80 Hz, 3 mm) was applied between the 5th and 10th sway cycles. ATV evoked an earlier burst onset and increased activity of the plantarflexors consistent with a reduction in the amplitude and duration of forward sway. This in turn resulted in an increase in dorsiflexors' activity in order to compensate for the greater backward sway. Postural responses to ATV were augmented when sway was auditory and visually guided. Forward sway variability increased with ATV and remained high while backward sway variability decreased in the post-vibration phase. Our results suggest that sensory context-dependent constraints that determine the degree of active control of posture and associated postural challenge involved in a particular task determine how the vibration-induced Ia afferent input will be registered and further processed by the central nervous system.

PMID: 21748332 [PubMed - indexed for MEDLINE]

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Radhakrishnan SM, Hatzitaki V, Patikas D, Amiridis IG Exp Brain Res PubMed:21748332 Neuromuscular efficiency during sit to stand movement in women with knee osteoarthritis. https://www.ncbi.nlm.nih.gov/pubmed/21689947?dopt=Abstract

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Neuromuscular efficiency during sit to stand movement in women with knee osteoarthritis.

J Electromyogr Kinesiol. 2011 Oct;21(5):689-94

Authors: Patsika G, Kellis E, Amiridis IG

Abstract
The purpose of this study was to investigate the neuromuscular efficiency of women with knee osteoarthritis (OA) when performing a sit-to-stand movement and during maximum strength efforts. Twelve women with unilateral knee OA (age 60.33±6.66 years, height 1.61±0.05 m, mass 77.08±9.2 kg) and 11 controls (age 56.54±5.46 years, height 1.64±0.05 m, mass 77.36±13.34 kg) participated in this study. Subjects performed a sit-to-stand movement from a chair while position of center of pressure and knee angular speed were recorded. Furthermore, maximal isokinetic knee extension and flexion strength at 60°/s, 120°/s and 150°/s was measured. Surface, electromyography (EMG) from the biceps femoris (BF), vastus lateralis (VL) and vastus medialis (VM) was recorded during all tests. Analysis of variance (ANOVA) showed that during the sit-to-stand OA group demonstrated significantly lower knee angular speed (44.49±9.61°/s vs. 71.68±19.86°/s), a more posterior position of the center of pressure (39.20±7.02% vs. 41.95±2.49%) and a higher antagonist BF activation (57.13±20.55% vs. 32.01±19.5%) compared with controls (p<0.05). Further, women with knee OA demonstrated a lower Moment-to-EMG ratio than controls in extension and eccentric flexion at 60°/s and 150°/s, while the opposite was found for concentric flexion at 60°/s (p<0.05). Among other factors, the slower performance of the sit-to-stand movement in women with OA is due to a less efficient use of the knee extensor muscles (less force per unit of EMG) and, perhaps, a higher BF antagonist co-activation. This may lead subjects with OA to adopt a different movement strategy compared with controls.

PMID: 21689947 [PubMed - indexed for MEDLINE]

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Patsika G, Kellis E, Amiridis IG J Electromyogr Kinesiol PubMed:21689947 Changes in the limits of stability induced by weight-shifting training in elderly women. https://www.ncbi.nlm.nih.gov/pubmed/21240818?dopt=Abstract

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Changes in the limits of stability induced by weight-shifting training in elderly women.

Exp Aging Res. 2011 Jan;37(1):46-62

Authors: Gouglidis V, Nikodelis T, Hatzitaki V, Amiridis IG

Abstract
This study examined the impact of visually guided weight-shifting training on elderly women's limits of stability during static leaning and dynamic swaying in different directions. Sixty-three elderly women were assigned into a group that practiced weight shifting (30-min sessions, 3 sessions/week, 4 weeks) either in the anterior/posterior or medio/lateral direction and a control group. Training resulted in a reduction of upper body rotation and an increase of shank rotation and center of pressure displacement. It is concluded that weight-shifting practice increases the limits of stability and enhances the inverted pendulum pivoting of the human body during leaning and dynamic swaying balance tasks.

PMID: 21240818 [PubMed - indexed for MEDLINE]

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Gouglidis V, Nikodelis T, Hatzitaki V, Amiridis IG Exp Aging Res PubMed:21240818 Muscle coactivation before and after the impact phase of running following isokinetic fatigue. https://www.ncbi.nlm.nih.gov/pubmed/21214346?dopt=Abstract

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Muscle coactivation before and after the impact phase of running following isokinetic fatigue.

J Athl Train. 2011 Jan-Feb;46(1):11-9

Authors: Kellis E, Zafeiridis A, Amiridis IG

Abstract
CONTEXT: The effects of fatigue on impact loading during running are unclear, with some authors reporting increased impact forces and others reporting decreased forces.
OBJECTIVE: To examine the effects of isokinetic fatigue on muscle cocontraction ratios about the knee and ankle during running.
DESIGN: Cross-sectional study.
SETTING: Neuromechanics laboratory.
PATIENTS OR OTHER PARTICIPANTS: Female middle-distance runners (age  =  21.3 ± 1.93 years) with at least 5 years of training experience.
INTERVENTION(S): Participants ran on the treadmill at 3.61 m/s before and immediately after the fatigue protocol, which consisted of consecutive, concentric knee extension-flexion at 120°/s until they could no longer produce 30% of the maximum knee-extension moment achieved in the familiarization session for 3 consecutive repetitions.
MAIN OUTCOME MEASURE(S): Electromyographic (EMG) amplitude of the vastus medialis (VM), biceps femoris (BF), gastrocnemius (GAS), and tibialis anterior (TA) was recorded using surface electrodes. Agonist∶antagonist EMG ratios for the knee (VM∶BF) and ankle (GAS∶TA) were calculated for the preactivation (PR), initial loading response (LR(1)), and late loading response (LR(2)) phases of running. Hip-, knee-, and ankle-joint angular displacements at initial foot contact were obtained from 3-dimensional kinematic tracings.
RESULTS: Fatigue did not alter the VM∶BF EMG ratio during the PR phase (P > .05), but it increased the ratio during the LR(1) phase (P < .05). The GAS∶TA EMG ratio increased during the LR(1) phase after fatigue (P < .05) but remained unchanged during the PR and LR(2) phrases (P > .05).
CONCLUSIONS: The increased agonist EMG activation, coupled with reduced antagonist EMG activation after impact, indicates that the acute decrease in muscle strength capacity of the knee extensors and flexors results in altered muscle-activation patterns about the knee and ankle before and after foot impact.

PMID: 21214346 [PubMed - indexed for MEDLINE]

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Kellis E, Zafeiridis A, Amiridis IG J Athl Train PubMed:21214346 On the Evaluation of Postural Stability after ACL Recostruction. https://www.ncbi.nlm.nih.gov/pubmed/24137059?dopt=Abstract

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On the Evaluation of Postural Stability after ACL Recostruction.

J Sports Sci Med. 2011;10(2):422-3

Authors: Kellis E, Amiridis IG, Kofotolis N

PMID: 24137059 [PubMed]

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Kellis E, Amiridis IG, Kofotolis N J Sports Sci Med PubMed:24137059 Force variability during isometric wrist flexion in highly skilled and sedentary individuals. https://www.ncbi.nlm.nih.gov/pubmed/19756710?dopt=Abstract

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Force variability during isometric wrist flexion in highly skilled and sedentary individuals.

Eur J Appl Physiol. 2009 Dec;107(6):715-22

Authors: Salonikidis K, Amiridis IG, Oxyzoglou N, de Villareal ES, Zafeiridis A, Kellis E

Abstract
The association of expertness in specific motor activities with a higher ability to sustain a constant application of force, regardless of muscle length, has been hypothesized. Ten highly skilled (HS group) young tennis and handball athletes and 10 sedentary (S group) individuals performed maximal and submaximal (5, 10, 20, 50, and 75% of the MVC) isometric wrist flexions on an isokinetic dynamometer (Kin-Com, Chattanooga). The wrist joint was fixed at five different angles (230, 210, 180, 150, and 1300). For each position the percentages of the maximal isometric force were calculated and participants were asked to maintain the respective force level for 5 s. Electromyographic (EMG) activation of the Flexor Carpi Ulnaris and Extensor Digitorum muscles was recorded using bipolar surface electrodes. No significant differences were observed in maximal isometric strength between HS and S groups. Participants of HS group showed significantly (P < 0.05) smaller force coefficient of variability (CV) and SD values at all submaximal levels of MVC at all wrist angles. The CV and SD values remained unaltered regardless of wrist angle. No difference in normalized agonist and antagonist EMG activity was observed between the two groups. It is concluded that long-term practice could be associated with decreased isometric force variability independently from muscular length and coactivation of the antagonist muscles.

PMID: 19756710 [PubMed - indexed for MEDLINE]

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Salonikidis K, Amiridis IG, Oxyzoglou N, de Villareal ES, Zafeiridis A, Kellis E Eur J Appl Physiol PubMed:19756710 Static balance control and lower limb strength in blind and sighted women. https://www.ncbi.nlm.nih.gov/pubmed/19701648?dopt=Abstract

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Static balance control and lower limb strength in blind and sighted women.

Eur J Appl Physiol. 2009 Nov;107(5):571-9

Authors: Giagazoglou P, Amiridis IG, Zafeiridis A, Thimara M, Kouvelioti V, Kellis E

Abstract
The aim of the present study was to examine isokinetic and isometric strength of the knee and ankle muscles and to compare center of pressure (CoP) sway between blind and sighted women. A total of 20 women volunteered to participate in this study. Ten severe blind women (age 33.5 +/- 7.9 years; height 163 +/- 5 cm; mass 64.5 +/- 12.2 kg) and 10 women with normal vision (age 33.5 +/- 8.3 years; height 164 +/- 6 cm; mass 61.9 +/- 14.5 kg) performed 3 different tasks of increasing difficulty: Normal Quiet Stance (1 min), Tandem Stance (20 s), and One-Leg Stance (10 s). Participants stood barefoot on two adjacent force platforms and the CoP variations [peak-to-peak amplitude (CoPmax) and SD of the CoP displacement (CoPsd)] were analyzed. Sighted participants performed the tests in eyes open and eyes closed conditions. Torque/angular velocity and torque/angular position relationships were also established using a Cybex dynamometer for knee extensors and flexors as well as for ankle plantar and dorsiflexors. The main finding of this study was that the ability to control balance in both anterior/posterior and medio/lateral directions was inferior in blind than in sighted women. However, when sighted participants performed the tests blindfolded, their CoP sway increased significantly in both directions. There were no differences in most isometric and concentric strength measurements of the lower limb muscles between the blind and sighted individuals. Our results demonstrate that vision is a more prominent indicator of performance during the postural tasks compared to strength of the lower limbs. Despite similar level of strength, blind individuals performed significantly worse in all balance tests compared to sighted individuals.

PMID: 19701648 [PubMed - indexed for MEDLINE]

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Giagazoglou P, Amiridis IG, Zafeiridis A, Thimara M, Kouvelioti V, Kellis E Eur J Appl Physiol PubMed:19701648 Direction-induced effects of visually guided weight-shifting training on standing balance in the elderly. https://www.ncbi.nlm.nih.gov/pubmed/18594127?dopt=Abstract

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Direction-induced effects of visually guided weight-shifting training on standing balance in the elderly.

Gerontology. 2009;55(2):145-52

Authors: Hatzitaki V, Amiridis IG, Nikodelis T, Spiliopoulou S

Abstract
BACKGROUND: Controversial findings exist in the literature with respect to the efficacy of visually guided weight-shifting (WS) training as a means of improving balance in healthy older adults.
OBJECTIVE: The purpose of this study was to investigate the impact of two direction-specific, visually guided WS training protocols on standing balance of healthy elderly women.
METHODS: Forty-eight community-dwelling elderly women, all free of any neurological or musculoskeletal impairment, were randomly assigned into: a group that practiced WS in the anterior/posterior direction (A/P group, n=19), a group that practiced WS in the medio/lateral direction (M/L group, n=15) and a control group (n=14). Participants performed 12 training sessions of visually guided WS (3 sessions a week for 25 minutes per session). Static balance was measured before and after training in normal (bipedal) quiet stance (NQS) and sharpened-Romberg stance (SRS) by recording center of pressure (CoP) variations and angular segment kinematics.
RESULTS: In NQS, neither of the two training protocols had a significant impact on postural sway measures, although a significant decrease in interlimb asymmetry of CoP displacement was noted for the A/P group. In SRS, A/P training induced a significant reduction of CoP displacement, lower limb pitch and upper trunk roll rotation.
CONCLUSION: The results of the study stress the importance of using direction-specific WS tasks in balance training, particularly in the A/P direction, in order to improve control of static balance in elderly women.

PMID: 18594127 [PubMed - indexed for MEDLINE]

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Hatzitaki V, Amiridis IG, Nikodelis T, Spiliopoulou S Gerontology PubMed:18594127 Aging effects on postural responses to self-imposed balance perturbations. https://www.ncbi.nlm.nih.gov/pubmed/16214664?dopt=Abstract

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Aging effects on postural responses to self-imposed balance perturbations.

Gait Posture. 2005 Nov;22(3):250-7

Authors: Hatzitaki V, Amiridis IG, Arabatzi F

Abstract
The present study investigated how young and older individuals organize their posture in response to self-induced balance perturbations evoked by oscillatory single limb movements. Eleven old (70.1+/-4.3 years) and nine young (20.1+/-2.4 years) participants performed repeatedly for 5s hip flexion/extension movements using full range of motion and maximum velocity. Two-dimensional joint kinematics (sampling rate: 60Hz), center of pressure (CoP) and EMG activity of tibialis anterior (TA), medial gastrocnemius (MGAS) rectus femoris (RF) and, semitendinosus (ST) in the stance limb were recorded and analysed. Cross-correlation function (CCF) analysis was used to identify the degree of coupling between the swinging limb (SL), center of gravity (CoG) and CoP motions. Old adults significantly limited SL, CoG and CoP range of anterior/posterior (A/P) motion in response to the forceful leg swinging. In the stance limb, significantly lower levels of ankle muscle activity resulted in reduced hip and knee joint excursions and increased ankle instability. By contrast, young performers produced sufficient ankle muscle activity to stabilize the foot to the ground while progressively increasing joint range of motion from the ankle to the hip. Center of pressure and SL movements were strongly correlated in an anti-phase relationship in both age groups. In older adults, however, the relationship between CoG-SL and CoG-CoP movements was neither strong nor synchronous, reflecting a weaker coupling and lack of coordination between component movements. It is concluded that insufficient ankle muscle activity, central integration deficits and increased anxiety to postural threat are important factors implicated for the weaker postural synergies and freezing of degrees of freedom seen in the elderly during performance of single limb oscillations.

PMID: 16214664 [PubMed - indexed for MEDLINE]

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Hatzitaki V, Amiridis IG, Arabatzi F Gait Posture PubMed:16214664 Age-induced modifications of static postural control in humans. https://www.ncbi.nlm.nih.gov/pubmed/14550913?dopt=Abstract

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Age-induced modifications of static postural control in humans.

Neurosci Lett. 2003 Oct 30;350(3):137-40

Authors: Amiridis IG, Hatzitaki V, Arabatzi F

Abstract
We examined how young and older adults adapt their posture to static balance tasks of increasing difficulty. Participants stood barefoot on a force platform in normal quiet, Romberg-sharpened and one-legged stance. Center of pressure (CoP) variations, electromyographic (EMG) activity of ankle and hip muscles and kinematic data were recorded. Both groups increased postural sway as a result of narrowing the base of support. Greater CoP excursions, EMG activity and joint displacements were noted in old compared to younger adults. Older adults displayed increased hip movement accompanied by higher hip EMG activity, whereas no similar increase was noted in the younger group. It is concluded that older adults rely more on their hip muscles when responding to self induced perturbations introduced by increased task constraints during quiet standing.

PMID: 14550913 [PubMed - indexed for MEDLINE]

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Amiridis IG, Hatzitaki V, Arabatzi F Neurosci Lett PubMed:14550913

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