Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 1 1 2015 9 1 The Effect of Pedaling and Fatigue on Changes of Knee Muscles Co-contraction During Running in Triathletes 5 13 FA Mehrdad Anbarian Bu Ali Sina University, Hamedan, Iran. Mostafa Sepehrian Bu Ali Sina University Farzad Nazem Bu Ali Sina University Behrooz Hajiloo Bu Ali Sina University Objective: The purpose of this study was to determine the effect of cycling fatigue on co-activation of knee muscles during running in novice triathletes. Methods: Twelve novice male triathletes aged 23.7±2.1 years participated in this quasi experimental study. Surface electromyographic activity from gastrocnemius, rectus femoris, vastus medialis, vastus lateralis, biceps femoris and semitendinosus were recorded during support and non-support phases of running before and after cycling fatigue protocol. General and directed co-activation of the knee muscles were calculated. Paired t-test was used to analyze the data(p<0.05). Results: General co-activation was significantly reduced in propulsion sub-phase, total support and non-support phases after fatigue (p=0.001), but there were not any differences in heel contact and midstance sub-phases. Fatigue only altered directed co-activation of medial and lateral knee muscles during heel contact sub-phase (p=0.034). Extensor and flexor directed co-activation during non-support phase of running significantly decreased after fatigue (p=0.011). Conclusion: Changes in the co-activation during running after cycling fatigue can alter running pattern and reduce the knee function consequently, causing injuries to the lower limbs in novice triathletes.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 1 1 2015 9 1 Comparison of Static Stability Parameters in Healthy, Osteopenic and Osteoporotic Women Using the Center of Pressure Sway 15 24 FA Giti Torkaman Malihe Darbani Tarbiat Modares University, Tehran, Iran. Shafieh Movasseghe Noushin Bayat Objective: Change of control strategy in osteoporotic people and their focus on the hip strategy, also the occurred postural changes, result in the displacement of center of pressure (COP). This study was carried out to compare the static stability parameters in healthy, osteopenic and osteoporotic women. Methods: Seventy-one volunteer postmenopausal women aged 48-65 years were divided into three Normal (n=15), Osteopenic (n=26) and Osteoporotic (n=30) groups according to their bone mineral density of lumbar spine. Static balance was evaluated using force plate, in two positions: double leg standing (DLS) and Romberg standing (Rom), with eyes open, for 20 s. Standard deviation of velocity and amplitude of COP displacement in A-P and M-L direction and path length were evaluated. Results: In DLS, SD of velocity and amplitude for A-P displacement, showed a significant increase in osteoporotic and osteopenic groups in comparison with normal women (P <0.05). In Rom, SD of amplitude for AP displacement, in osteoporotic group showed a significant increase compared with the normal group (P=0.03). Path length of COP displacement in DLS position in osteoporotic and osteopenic groups was significantly more than the normal group (P =0.05). There was a significant negative correlation between bone mineral density and SD velocity and amplitude in AP direction, and also path length in two static positions. Conclusion: Increase in SD velocity and SD amplitude of COP displacement in A-P direction, that increase with the decrease in bone mineral density, may be due to the change of control strategy mechanisms in osteopenic and osteoporotic women. Investigation of these changes will be necessary to design the therapeutic methods for prevention of falling and bone fracture in osteoporotic patients.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 1 1 2015 9 1 The Effect of Sprint Start Speed on Lower-limb Stiffness in Sprint Runners 25 33 FA Mansour Eslami Mazandaran University, Sari, Iran. Effat Hoseinzadeh Alireza Safaei Kenari Objective: Lower extremity stiffness is associated with variables such as the frequency and length of running steps, the amount of muscle force and power production. Previous studies showed contradictory findings regarding the relationship between lower extremities joints stiffness and start velocity. Sprint start can be highly affected by two key components of lower limb stiffness, namely, force and time. However, no research has yet investigated the effect of start velocity changes on lower–limb stiffness during sprint start. To test the effect of velocity changes on lower-limb stiffness during sprint start. Method: 15 male members of track and field were selected for this study. Leg stiffness was calculated dividing peak ground reaction force by the leg length. Joint stiffness was also estimated dividing the muscle moment of force by joint angular displacement. Subjects performed a start with three different speeds. Results: From low to high start velocity, means of leg stiffness, knee stiffness and ankle stiffness increased by 67.53%, 41.9% and 39.03% respectively. Conclusion: The findings show that lower-limb stiffness could be a key factor in changing runners' acceleration during sprint start.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 1 1 2015 9 1 The Effect of Eight Weeks of High Intensive Special Preparation on Selected Biomechanical and Anthropometrical Parameters in Young Elite Wrestlers 35 44 FA Hamidreza Naserpour Department of Sport Biomechanics, Faculty of Physical Education and Sport Sciences, Kharazmi University, Tehran, Iran. Hadi Habibi Heydar Sadeghi Objective: The aim of this study was to investigate the effect of eight weeks of high intensive exercise on selected biomechanical and anthropometrical variables in elite wrestlers. Methods: Sixteen young wrestlers (age 19.1±1 years and weight 74.9±17.3 kg) attending the national Greco-Roman camps participated in this study. Biomechanical and anthropometrical variables included weight, body fat percentage, body mass index, balance, general body speed and acceleration, active range of motion of the joints, upper and lower extremities power and hand grip strength. These variables were measured before and after 8 weeks (67 sessions) of special exercise training. The normality of data was checked by Kolmogorov- Smirnov normality measure and data were analyzed with Paired- samples t-test to compare variables before and after training program, with a significance level of (P≤0.05). Results: Results showed that there were significant differences between weight, body fat percentage, body mass index, semi-dynamic balance in the medial and anterior-medial directions, upper extremities power, the range of lateral flexion to the right of the neck and hip flexion of pre and post-test. Conclusion: Based on the results, it seems that applied training program had main effect on biomechanical and anthropometrical variables such as weight, body fat percentage, body mass index, power, balance and active range of motion of elite wrestlers that will increase the qualitative athletic performance.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 1 1 2015 9 1 The Effect of Ratio of Contraction to Relaxation Durations in PNF Exercises on the Muscle Strength and Range of Motion of Hip Joint 45 51 FA Hossein Rashedi Department of Physical Education and Sport Sciences, Faculty of Humanities, Islamic Azad University, Hamedan branch, Hamedan, Iran. Amir Ali Jafarnezhadgero Naser Farokhroo Objective: The aim of the present study was to compare the effect of ratios of contraction- Relaxation on the muscle strength and range of motion of hip joint in PNF exercises. Methods: Thirty nine nonathletic male students (Mean±SD; age, 13±1.2 years; body mass, 55±9.8 kg) were assigned .Three groups designated as I, II and III groups. The ratios of contraction to relaxation periods for groups were 1, 2 and 3 respectively. Training program included three sessions per week (CR-PNF) for 6 weeks. Measurements of hip extensors muscles stretch and strength were performed at the beginning and at the end of training using an inclinometer (during leg raise test) and dynamometer. Data were analyzed using dependent samples t-test and one-way ANOVA. Results: The results of the present study showed significant increases in hip extensor muscles flexibility and strength for three groups. This increase the in the strength in group I equaled 6 kg, in group II 4 kg and in group III 7 kg. The amount of increase in the hip extensor muscles flexibility in group I, II and II were 15, 8 and 12 degrees, respectively.  The increase in these two variables was significant and similar in all three groups. Conclusion: Different contraction to relaxation ratio normally, 0.5, 1 and 2, did not show any meaningful differences on hip extensor muscular strength and hip range of motion.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 1 1 2015 9 1 The Effect of Various Standing Positions in Muscles Activity between Healthy Young Men and those with Genu Varum 53 61 FA Amir Hossein Barati Rajaee University of Tehran, Tehran, Iran. Objective: Genu varum is considered a risk factor for knee osteoarthritis. Being aware of the changes in muscles activity in various standing positions among genu varum patients, can provide insight for preventing osteoarthritis in this population. This study is undertaken to compare muscles activity in various standing positions between young healthy and genu varum male individuals. Methods: 80 healthy male university students, 40 normal and 40 subjects with genu varum deformity, participated in this study. Deformity of genu varum was assessed with caliper and Goniometer. Each subject stood in five different positions and muscles activity was recorded with EMG device. For data analysis, Matlab and SPSS software were employed and Mixed variance analysis test (Mixed ANOVA) was run to compare the dependent variables at a significance level of P ≤ 0.05. Results: Significant differences were observed between the two groups for muscles activity of the tensor fasia latae (at single leg with closed eye position), tertius fibulae and gluteus medius muscles (at single leg with closed eye and upward head postions)( p≤0.05) while no significant differences were observed in other muscles. Conclusion: According to the obtained results, it can be suggested that frontal knee angle may affect muscles activity. Perhaps one of the reasons for higher injury risk and knee osteoarthritis in genu varum population is the increase in muscles activity. Therefor, It is proposed that focusing on corrective exercises can reduce these risks.