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Liebermann, D. G., & Hoffman, J. R. (2005). Timing of preparatory landing responses as a function of availability of optic flow information. J Electromyogr Kinesiol, 15(1), 120–130.
Abstract: This study investigated temporal patterns of EMG activity during self-initiated falls with different optic flow information ('gaze directions'). Onsets of EMG during the flight phase were monitored from five experienced volunteers that completed 72 landings in three gaze directions (downward, mid-range and horizontal) and six heights of fall (10-130 cm). EMG recordings were obtained from the right gastrocnemius, tibialis anterior, biceps femoris and rectus femoris muscles, and used to determine the latency of onset (L(o)) and the perceived time to contact (T(c)). Impacts at touchdown were also monitored using as estimates the major peak of the vertical ground reaction forces (F(max)) normalized to body mass, time to peak (T(max)), peak impulse (I(norm)) normalized to momentum, and rate of change of force (dF(max)/dt). Results showed that L(o) was longer as heights of fall increased, but remained within a narrow time-window at >50 cm landings. No significant differences in L(o) were observed when gaze direction was changed. The relationship between T(c) and flight time followed a linear trend regardless of gaze direction. Gaze direction did not significantly affect the landing impacts. In conclusion, availability of optic flow during landing does not play a major role in triggering the preparatory muscle actions in self-initiated falls. Once a structured landing plan has been acquired, the relevant muscles respond relative to the start of the fall.
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Dario G. Liebermann, Larry Katz, & and Ruth Morey Sorrentino. (2005). Experienced Coaches’ Attitudes Towards Science and Technology. International Journal of Computer Science in Sport, 4(1), 21–28.
Abstract: In this study, the attitude of experienced coaches towards technologies and sport
sciences was assessed. A questionnaire was used to evaluate three areas: (1)
Attitudes towards technology and sport science in coaching, (2) Technology and
scientific knowledge in practice, and (3) Perceived importance of technology and
science in enhancing sport results. A group of 27 highly experienced coaches
completed the questionnaire. The questionnaire consisted of three parts, starting
with demographic information, followed by a series of 27 questions with answers
on a Likert scale ranging from strongly agree to strongly disagree, and finally,
coaches were requested to rank 14 well-defined ‘coaching goals’ from 1 (most
important) to 14 (least important). Results showed that top-level coaches rated
having a good relationship with the athletes’ as a major goal. Overall, members of
this group of experienced coaches seem to recognize the general importance of
sport sciences, and appear to be positive about the use of sport technologies, but
do not necessarily translate these positive attitudes into actual practice within
their competitive sport environments, even when they all use information
technology for other activities. According to these results, sport science
researchers and technology developers need to adapt their strategies. Coaching
education should encourage coaches to incorporate technologies as part of their
coaching routines. Developing innovative resources and incorporating them in
coaching education, as is done in some countries, may be a starting point.
However, placing the emphasis on educating successful coaches on the practical
use of technology and scientific knowledge is suggested as a short-term goal.
This may allow for a more immediate effect on the attitude and practice of less
senior coaches that tend to adopt methods and training routines through following
the personal example provided by top-level coaches.
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Liebermann, D. G., & Franks, I. M. (2004). The use of feedback-based technologies in skill acquisition. In M. Hughes, & I.M. Franks (Eds.), Notational analysis of Sport and Coaching Science. E & FN Spon Pub.
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Flash, T., Richardson, M. E., Handzel, A. A., & Liebermann, D. G. (2003). Computational Models and Geometric Approaches in Arm Trajectory Control Studies. In M. L. Latash, & M. F. Levin (Eds.), Progress in Motor Control III: From Basic Science to Applications. Champaign, Il: Human Kinetics.
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Dario G. Liebermann, & Larry Katz. (2003). On the assessment of lower-limb power capability. Isokinetics and Exercise Science, 11(2), 87–94.
Abstract: Purpose: This study assessed the reliability and validity of different methods used to estimate lower-limb muscular power capability based on mechanical variables. For this purpose, vertical jumping was compared with isokinetic knee extensions and with power tests used by practitioners.
Methods: Four groups of subjects (N = 106) were tested in different conditions. Group-I performed countermovement vertical jumps (CMJ) on a force plate followed by left and right knee extensions on an isokinetic device at 120, 180 and 240 deg�s-1. Group-II performed CMJ trials followed by 20-m sprints, hand-reach jumps and 1RM leg-press testing. Group-III carried out squat jumps (SJ) in addition to CMJ trials. Finally, Group-IV performed the CMJ test and was retested twice after a short inter-session interval (1–4 days) and after a long one (4.5–5 months). The Pearson correlation was used to assess the validity and reliability of CMJ (p ≤ 0.01, **).
Results: Mean peak power during CMJ was correlated with sprint time (r = -0.882) and leg-press 1 RM (r = 0.797), but less with peak hand-reach height (r = 0.695; p ≤ 0.05). Isokinetic knee extension power showed also a significant correlation with CMJ power, but its strength depended on the angular velocity (Isok-120 r = 0.702; Isok-180 r = 0.737; Isok-240 r = 0.599). Test-retests showed a strong correlation after a short interval (r = 0.915) and after a long one (r = 0.890). Using the SJ technique did not have any effect on reliability (r = 0.914).
Conclusions: CMJ matches other methods used for testing lower-limb power capability. It is highly reliable and it allows a valid assessment of muscular power. Since CMJ is also simple and accurate to perform, it is the recommended method.
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