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Dario G. Liebermann, Murray E. Maitland, & Larry Katz. (2002). Lower-limb extension power: How well does it predict short distance speed skating performance? Isokinetics and Exercise Science, 10(2), 87–95.
Abstract: This study was aimed to explore the relationship between lower limb extension power measured by isokinetic knee extensions (IK) and vertical jumps performed on a force plate (VJ) and speed skating (SS) sprint power measured by a laser device.
Methods: Twenty elite short- and long-track speed skaters performed 100 m sprints followed by VJ and IK trials. Power-time curves were calculated off-line. Pearson correlation coefficients were used to determine the degree of association between the variables. Results: SS sprint power correlates strongly with VJ power (r=0.870; p<0.001) while IK power showed a weaker but significant correlation to both (r=0.707 and r=0.706, respectively; p<0.01). As expected, SS times at 15 m and 100 m were inversely associated with SS sprint power (r=-0.818 and r=-0.909; p<0.001) and VJ power (r=-0.730 and r=-0.763; p<0.001), and to a lesser degree with IK power (r=-0.602; r=-0.618; p<0.01). Conclusion: The analyses differentiate between methods of estimating power in speed skaters, and show a strong relationship between initial SS performance and muscular power. Given that 100 m split times strongly relate to final 500 m results (r=0.972; p<0.001, N=332), it is reasonable to believe that an initial power and a stable peak speed before the first curve may lead to achieving the winning edge in short SS events. A finding of particular interest is that isokinetic power results are correlated significantly with the practical outcomes of the performance in spite of the high specificity of the isokinetic testing method. |
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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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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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Frenkel-Toledoa, S., Bentin, S., Perry, A., Liebermann, D. G., & Soroker, N. (2014). Mirror-neuron system recruitment by action observation: Effects of focal brain damage on mu suppression. NeuroImage, 87, 127–137.
Abstract: Mu suppression is the attenuation of EEG power in the alpha frequency range (8-12 Hz), recorded over the sensorimotor cortex during execution and observation of motor actions. Based on this dual characteristic it is thought to signalize activation of a human analogue of the mirror neuron system (MNS) found in macaque monkeys, though much uncertainty remains concerning its specificity and full significance. To further explore the hypothesized relationship between mu suppression and MNS activation, we investigated how it is affected by damage to cortical regions, including areas where the MNS is thought to reside. EEG was recorded in 33 first-event stroke patients during observation of video-clips showing reaching and grasping hand movements. We examined the modulation of EEG oscillations at central and occipital sites, and analyzed separately the lower (8-10 Hz) and higher (10-12 Hz) segments of the alpha/mu range. Suppression was determined relative to observation of a non-biological movement. Normalized lesion data were used to investigate how damage to regions of the fronto-parietal cortex affects the pattern of suppression. The magnitude of mu suppression during action observation was significantly reduced in the affected hemisphere compared to the unaffected hemisphere. Differences between the hemispheres were significant at central (sensorimotor) sites but not at occipital (visual) sites. Total hemispheric volume loss did not correlate with mu suppression. Suppression in the lower mu range in the unaffected hemisphere (C3) correlated with lesion extent within the right inferior parietal cortex. Our lesion study supports the role of mu suppression as a marker of MNS activation, as suggested by findings gathered in previous studies in normal subjects.
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Uri, O., Pritsch, M., Oran, A., & Liebermann, D. G. (2014). Upper limb kinematics after arthroscopic and open shoulder stabilization. Journal of Shoulder and Elbow Surgery, .
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