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Theodoros Kannas, Eleftherios Kellis, Fotini Arampatzi, and Eduardo Saez Saez de Villarreal

The aim of this study was to examine the differences in muscle architecture during isometric tests between children and adults. Eight boys (age= 11.2 ± 0.26 years) and eight men (age= 22.3 ± 2.01 years) performed plantar flexion isometric efforts at angles of -15°, 0°, 15° at 0%, 40%, 60%, 80% of MVC. Analysis of variance tests indicated that adults showed greater fascicle length from rest to 80% of MVC (p < .05), greater pennation angle at 80% and 100% of MVC (p < .05) and greater aponeuroses displacement at levels of effort greater than 60% of MVC (p < .05). These differences observed in MG would appear to favor better utilization of the force-length and the force-velocity relationships, of the muscle in adults compared with children.

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Fotini Arabatzi, Dimitrios Patikas, Andreas Zafeiridis, Konstantinos Giavroudis, Theodoros Kannas, Vassilios Gourgoulis, and Christos M. Kotzamanidis

This study examined the post-activation potentiation (PAP) effects on squat jump (SJ) performance and on peak rate of force development (RFDpeak) in preadolescent (10–12 y), adolescents (14–15 y) and adults (20–25 y) males and females. All participants performed a SJ with and without prior conditioning stimulus (PAP and control protocol, respectively), consisting of 3 × 3-second maximal isometric squats. Jump height and RFDpeak of the vertical ground reaction force during SJ were assessed before, and at 20 seconds and at 4 minutes following the conditioning stimulus. The results revealed a different pattern of age-effect on SJ performance within males and females. The RFDpeak significantly increased as a factor of age in both males and females (P < .05). Increase in SJ performance after conditioning stimulus occurred only in men (P < .05), with no effects in teen-males, boys, and female groups. There was a significant PAP effect on RFDpeak in both adult groups (P < .05) and teen-males, with no effects in children. In conclusion, the PAP effects on SJ performance and RFDpeak are age- and sex-dependent; that is PAP appears as a viable method for acutely enhancing SJ performance in men but not in pediatric population.