Publication Date: 2006
Journal of Electromyography and Kinesiology (18735711)16(3)pp. 257-263
Surface electromyography has been useful in comparing muscular activity among different sports movements and it is a valuable technique for evaluating muscle activation, co-ordination and fatigue. Since these important variables have not been investigated during the full game in soccer, the present study aimed to investigate the activity of major muscles of the lower extremity during a soccer-simulation fatiguing protocol. Ten amateur soccer players (age 21.40 ± 3.13 years; height 1.77 ± 0.06 m; mass 74.55 ± 8.5 kg) were tested. The exercise protocol, performed on a programmable motorised treadmill, consisted of the different intensities observed during soccer match-play (walking, jogging, running, sprinting). Electromyographic activity was recorded from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius (GC) muscles before exercise, at half-time and immediately after the 90-min exercise protocol. The EMG data were analysed using custom-written software to compute the root mean square (RMS) value over ten gait cycles. With regard to RF, BF and TA, a significant main effect (P < 0.05) was found for condition (pre-game, half-time and post-game), speed (6, 12, 15 and 21 km h-1) (P < 0.05) and interaction between condition and speed (P < 0.05). For GC, a significant effect was not found for condition or interaction between condition and speed, but a significant main effect (P < 0.001) was found for speed, with the RMS value increasing continually with increasing speed from 6 to 21 km h-1. The results indicated that after a simulation of the exercise intensity of soccer-play the EMG activity in major lower-limb muscles was less than before. This decrease indicated that prolonged intermittent exercise had an effect on muscle activity even when work-rate was sustained. © 2005 Elsevier Ltd. All rights reserved.
Movahedi, A.,
Sheikh, M.,
Bagherzadeh, F.,
Hemayattalab, R.,
Ashayeri, H. Publication Date: 2007
Journal of Motor Behavior (00222895)39(6)pp. 457-462
The authors propose a practice-specificity-based model of arousal for achieving peak performance. The study included 37 healthy male physical education students whom they randomly assigned to a high-arousal (n = 19) or low-arousal group (n = 18). To manipulate participants' level of arousal, the authors used motivational techniques. They used heart rate and the Sport Competition Anxiety Test (R. Martens, 1977) to measure the level of arousal that participants achieved. At the determined and given arousal state, the 2 groups performed the task (basketball free throws) for 18 sessions. Both groups performed a retention test at the 2 arousal levels immediately after the last exercise session, in the posttest, and after 10 days. Results showed that both groups learned the task similarly and achieved their peak performance at their experienced arousal level. When tested at an arousal level that differed from the one that they experienced throughout practice sessions, participants' performance had deteriorated significantly. Performance of the task seemed to have integrated with the arousal level of the participants during the task learning. The findings of this study suggest a practice-specificity-based explanation for achieving peak performance. Copyright © 2007 Heldref Publications.
Publication Date: 2007
Journal of Science and Medicine in Sport (14402440)10(1)pp. 27-35
The aim of this study was to compare the effects of two high-intensity interval training (HIT) programmes on maximal oxygen uptake (over(V, ̇) O2 max), the lactate threshold (LT) and 3000 m running performance in moderately trained male runners. over(V, ̇) O2max, the running speed associated with over(V, ̇) O2max (vover(V, ̇) O2 max), the time for which vover(V, ̇) O2 max can be maintained (Tmax), the running speed at LT (vLT) and 3000 m running time (3000mTT) were determined before and following three different training programmes performed for 10 weeks. Following the pre-test, 17 moderately trained male runners (over(V, ̇) O2max = 51.6 ± 2.7 ml k g- 1 mi n- 1) were divided into training groups based on their 3000mTT (Group 1, G1, N = 6, 8× 60% of Tmax at vover(V,̇) O2 max, 1:1 work:recovery ratio; Group 2, G2, N = 6, 12× 30s at 130% vover(V, ̇) O2max, 4.5 min recovery; control group, GCON, N = 5, 60 min at 75% vover(V, ̇) O2 max). G1 and G2 performed two HIT sessions and two 60 min recovery run sessions (75% vover(V, ̇) O2max) each week. Control subjects performed four 60 min recovery run sessions (75% vover(V, ̇) O2 max) each week. In G1, significant improvements (p < 0.05) following HIT were found in over(V, ̇) O2 max (+9.1%), vover(V, ̇) O2 max (+6.4%), Tmax (5%), vLT (+11.7%) and 3000mTT (-7.3%). In G2, significant improvements (p < 0.05) following HIT were found in over(V, ̇) O2 max (+6.2%), vover(V, ̇) O2max (+7.8%), Tmax (+32%) and 3000mTT (-3.4%), but not in vLT (+4.7%; p = 0.07). No significant changes in these variables were found in GCON. The present study has shown that 3000 m running performance, over(V, ̇) O2 max, vover(V, ̇) O2 max, Tmax and vLT can be significantly enhanced using different HIT programmes in moderately trained runners, but that changes in performance and physiological variables may be more profound using prolonged HIT at intensities of vover(V, ̇) O2max with interval durations of 60% Tmax. © 2006 Sports Medicine Australia.
Mathematical modeling and optimization of snatch technique based on dynamic synthesis is the main purpose of this study. The barbell trajectory is proposed as the main index which was evaluated experimentally by several researchers who introduced optimum trajectory according to percentage of their owners' success. We believe that in optimizing the barbell trajectory we should consider the mechanical principles. Therefore we use a five-link biomechanical model to evaluate its behaviour and to predict the optimum barbell trajectory which minimizes the specific mechanical criterion by using genetic algorithm (GA) which is theoretically and empirically proven to provide a robust search in complex spaces, thereby offering a valid approach to problems requiring efficient and effective searches. Comparing the results of this model and experimental observations of other researchers, we show an improvement to introduce a good predictive model. Using this model can help the coaches to improve the performance of weightlifters.
