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Author Melzer, I.; Krasovsky, T.; Oddsson, L.I.E.; Liebermann, D.G. url  doi
openurl 
  Title Age-related differences in lower-limb force-time relation during the push-off in rapid voluntary stepping Type Journal Article
  Year 2010 Publication Clinical Biomechanics (Bristol, Avon) Abbreviated Journal Clin Biomech (Bristol, Avon)  
  Volume 25 Issue 10 Pages (down) 989-994  
  Keywords Accidental Falls/prevention & control; Age Factors; Aged; Aged, 80 and over; Aging/physiology; *Biomechanics; Female; Gait/*physiology; Humans; Male; *Postural Balance; Walking/*physiology  
  Abstract BACKGROUND: This study investigated the force-time relationship during the push-off stage of a rapid voluntary step in young and older healthy adults, to study the assumption that when balance is lost a quick step may preserve stability. The ability to achieve peak propulsive force within a short time is critical for the performance of such a quick powerful step. We hypothesized that older adults would achieve peak force and power in significantly longer times compared to young people, particularly during the push-off preparatory phase. METHODS: Fifteen young and 15 older volunteers performed rapid forward steps while standing on a force platform. Absolute anteroposterior and body weight normalized vertical forces during the push-off in the preparation and swing phases were used to determine time to peak and peak force, and step power. Two-way analyses of variance ('Group' [young-older] by 'Phase' [preparation-swing]) were used to assess our hypothesis (P </= 0.05). FINDINGS: Older people exerted lower peak forces (anteroposterior and vertical) than young adults, but not necessarily lower peak power. More significantly, they showed a longer time to peak force, particularly in the vertical direction during the preparation phase. INTERPRETATIONS: Older adults generate propulsive forces slowly and reach lower magnitudes, mainly during step preparation. The time to achieve a peak force and power, rather than its actual magnitude, may account for failures in quickly performing a preventive action. Such delay may be associated with the inability to react and recruit muscles quickly. Thus, training elderly to step fast in response to relevant cues may be beneficial in the prevention of falls.  
  Address Department of Physical Therapy, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0268-0033 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:20724044 Approved no  
  Call Number Serial 51  
Permanent link to this record
 

 
Author Hoffman, J.R.; Liebermann, D.; Gusis, A. url  openurl
  Title Relationship of leg strength and power to ground reaction forces in both experienced and novice jump trained personnel Type Journal Article
  Year 1997 Publication Aviation, Space, and Environmental Medicine Abbreviated Journal Aviat Space Environ Med  
  Volume 68 Issue 8 Pages (down) 710-714  
  Keywords *Aerospace Medicine; *Aviation; Biomechanics; Humans; Leg/*physiology; Male; Military Personnel/*education; *Physical Education and Training; Physical Fitness/*physiology; Range of Motion, Articular; Wounds and Injuries/etiology/*prevention & control  
  Abstract METHODS: There were 14 male soldiers who participated in this study examining the relationship of leg strength and power on landing performance. Subjects were separated into two groups. The first group (E, n = 7) were parachute training instructors and highly experienced in parachute jumping. The second group of subjects (N, n = 7) had no prior parachute training experience and were considered novice jumpers. All subjects were tested for one-repetition maximum (1 RM) squat strength and maximal jump power. Ground reaction forces (GRF) and the time to peak force (TPF) at landing were measured from jumps at four different heights (95 cm, 120 cm, 145 cm, and 170 cm). All jumps were performed from a customized jump platform onto a force plate. RESULTS: No differences were seen between E and N in either IRM squat strength or in MJP. In addition, no differences were seen between the groups for time to peak force at any jump height. However, significantly greater GRF were observed in E compared to N. Moderate to high correlations between maximal jump power and GRF (r values ranging from 0.62-0.93) were observed in E. Although maximal jump power and the TPF was significantly correlated (r = -0.89) at only 120 cm for E, it was interesting to note that the correlations between MJP and the time to peak force in E were all negative and that the correlations between these variables in N were all positive. CONCLUSIONS: These results suggest that experienced parachutists may use a different landing strategy than novice jumpers. This difference may be reflected by differences in GRF generated during impact and a more efficient utilization of muscle power during the impact phase of the landing.  
  Address Aeromedical Center, Physiological Training Unit, Israel Air Force, Israel  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0095-6562 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:9262813 Approved no  
  Call Number Serial 60  
Permanent link to this record
 

 
Author Krasovsky, T.; Berman, S.; Liebermann, D.G. url  doi
openurl 
  Title Kinematic features of continuous hand reaching movements under simple and complex rhythmical constraints Type Journal Article
  Year 2010 Publication Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology Abbreviated Journal J Electromyogr Kinesiol  
  Volume 20 Issue 4 Pages (down) 636-641  
  Keywords *Acoustic Stimulation; Adult; Biomechanics; *Cues; Female; Hand/*physiology; Humans; Male; Movement/*physiology  
  Abstract BACKGROUND: Auditory cues are known to alter movement kinematics in healthy people as well as in people with neurological conditions (e.g., Parkinson's disease or stroke). Pacing movement to rhythmical constraints is known to change both the spatial and temporal features of movement. However, the effect of complexity of pacing on the spatial and temporal kinematic properties is still poorly understood. The current study investigated spatial and temporal aspects of movement (path and speed, respectively) and their integration while subjects followed simple isochronous or complex non-isochronous rhythmical constraints. Spatiotemporal decoupling was expected under the latter constraint. METHODS: Ten subjects performed point-to-point hand movements towards visual targets on the surface of a hemisphere, while following continuous auditory cues of different pace and meter. The spatial and temporal properties of movement were compared to geodesic paths and unimodal bell-shaped speed profiles, respectively. Multiple two-way RM-ANOVAs (pace [1-2 Hz] x meter [duple-triple]) were performed on the different kinematic variables calculated to assess hand deviations from the model data (p< or = 0.05). RESULTS: As expected, increasing pace resulted in straighter hand paths and smoother speed profiles. Meter, however, affected only the path (shorter and straighter under triple) without significantly changing speed. Such an effect was observed at the slow pace only. CONCLUSIONS: Under simple rhythmic cues, an increase in pace causes spontaneous adjustments in spatial features (straighter hand paths) while preserving temporal ones (maximally-smoothed hand speeds). Complex rhythmical cues in contrast perturb spatiotemporal coupling and challenge movement control. These results may have important practical implications in motor rehabilitation.  
  Address Department of Physical and Occupational Therapy, Faculty of Medicine, McGill University, Canada  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1050-6411 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:20382031 Approved no  
  Call Number Serial 32  
Permanent link to this record
 

 
Author Issurin, V.B.; Liebermann, D.G.; Tenenbaum, G. url  doi
openurl 
  Title Effect of vibratory stimulation training on maximal force and flexibility Type
  Year 1994 Publication Journal of Sports Sciences Abbreviated Journal J Sports Sci  
  Volume 12 Issue 6 Pages (down) 561-566  
  Keywords Adult; Humans; Male; Muscle Contraction/physiology; Muscle, Skeletal/*physiology; *Physical Education and Training; Vibration/*therapeutic use  
  Abstract In this study, we investigated a new method of training for maximal strength and flexibility, which included exertion with superimposed vibration (vibratory stimulation, VS) on target muscles. Twenty-eight male athletes were divided into three groups, and trained three times a week for 3 weeks in one of the following conditions: (A) conventional exercises for strength of the arms and VS stretching exercises for the legs; (B) VS strength exercises for the arms and conventional stretching exercises for the legs; (C) irrelevant training (control group). The vibration was applied at 44 Hz while its amplitude was 3 mm. The effect of training was evaluated by means of isotonic maximal force, heel-to-heel length in the two-leg split across, and flex-and-reach test for body flexion. The VS strength training yielded an average increase in isotonic maximal strength of 49.8%, compared with an average gain of 16% with conventional training, while no gain was observed for the control group. The VS flexibility training resulted in an average gain in the legs split of 14.5 cm compared with 4.1 cm for the conventional training and 2 cm for the control groups, respectively. The ANOVA revealed significant pre-post training effects and an interaction between pre-post training and 'treatment' effects (P < 0.001) for the isotonic maximal force and both flexibility tests. It was concluded that superimposed vibrations applied for short periods allow for increased gains in maximal strength and flexibility.  
  Address Ribstein Centre for Research and Sport Medicine Sciences, Wingate Institute, Wingate Post, Israel  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0264-0414 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:7853452 Approved no  
  Call Number Serial 56  
Permanent link to this record
 

 
Author Liebermann, D.G.; Krasovsky, T.; Berman, S. url  doi
openurl 
  Title Planning maximally smooth hand movements constrained to nonplanar workspaces Type Journal Article
  Year 2008 Publication Journal of Motor Behavior Abbreviated Journal J Mot Behav  
  Volume 40 Issue 6 Pages (down) 516-531  
  Keywords Adaptation, Physiological; Adult; Algorithms; Female; Hand/*physiology; Humans; *Intention; Kinesthesis/*physiology; Male; Models, Statistical; Movement/*physiology; Psychomotor Performance/*physiology; Reference Values; Writing  
  Abstract The article characterizes hand paths and speed profiles for movements performed in a nonplanar, 2-dimensional workspace (a hemisphere of constant curvature). The authors assessed endpoint kinematics (i.e., paths and speeds) under the minimum-jerk model assumptions and calculated minimal amplitude paths (geodesics) and the corresponding speed profiles. The authors also calculated hand speeds using the 2/3 power law. They then compared modeled results with the empirical observations. In all, 10 participants moved their hands forward and backward from a common starting position toward 3 targets located within a hemispheric workspace of small or large curvature. Comparisons of modeled observed differences using 2-way RM-ANOVAs showed that movement direction had no clear influence on hand kinetics (p < .05). Workspace curvature affected the hand paths, which seldom followed geodesic lines. Constraining the paths to different curvatures did not affect the hand speed profiles. Minimum-jerk speed profiles closely matched the observations and were superior to those predicted by 2/3 power law (p < .001). The authors conclude that speed and path cannot be unambiguously linked under the minimum-jerk assumption when individuals move the hand in a nonplanar 2-dimensional workspace. In such a case, the hands do not follow geodesic paths, but they preserve the speed profile, regardless of the geometric features of the workspace.  
  Address Department of Physical Therapy, The Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel Aviv University, Israel. dlieberm@post.tau.ac.il  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0022-2895 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:18980905 Approved no  
  Call Number Serial 33  
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