Abstract Background: The squat is one of the most used exercises in the field of strength and conditioning. It is included as a core exercise in many sports training programmes to enhance athletic performance due to its biomechanical and neuromuscular similarities of a wide range of athletic movements. The barbell squat commonly used by athletes participating in resistance training and it is generally performed using regular athletic shoes or specially designed weightlifting shoes. However it is now getting more common to perform the barbell back squat in barefoot or in barefoot-inspired foot wear. Weightlifting shoes may be well known to weightlifters but to the noncompetitive lifters and professional athletes they are in general unfamiliar. It is believed that the structure of the weightlifting shoe supports proper squat mechanism. There is however limited scientific data reporting on the use of weightlifting shoes and therefore, it may be needed to investigate how weightlifting shoes affects the lower body lifting kinematics in the back squat compared to other conditions. Aim: The aim of the study was to compare the kinematic differences that appears in the sagittal plane when performing a barbell back squat wearing weightlifting shoes and barefoot. Method: Fifteen healthy participants (n=15) completed the study. The study included the barbell back squat in three sets of three repetitions on 50, 60 and 70% of the participant’s 1RM. The participants performed the movement in both weightlifting shoes and barefoot in an order randomly chosen and all movements was recorded with a digital camera from the sagittal plane. Results: The results showed that the angles were greater in the weightlifting shoe condition on all percentage. The results showed that there was no statistical significance in the hip angle at 50% of 1RM (p= 0,370) or at 70% (p = 0,053) but a statistical significance in the hip angle at 60 % (p = 0,028). The results showed no statistical significance in the ankle angle at 50% of 1RM (p = 0,997), 60% (p = 0,182) or 70 % (p = 0,332). Conclusion: Findings from this study did not demonstrate that there was a significant difference between performing a barbell back squat in weightlifting shoes and barefoot. More research is needed to investigate and compare more variables in the difference between performing a barbell back squat wearing weightlifting shoes and barefoot.

The purpose of this paper to discuss the monopoly and duopoly firm¡¦s pricing model and the optimal location choice in the Barbell Model. In this study, the first part of this article is that the assumption of market for a barbell market, the monopolist in the face of symmetric and asymmetric barbell market, firm in considering the case of the transportation costs to adopt a different pricing strategy to its optimal location choice. The latter part of this article is to consider if the same circumstances, to a duopoly market, the Cournot and Bertrand competition, the two plants how to choose the most suitable location choice. Also, we discuss the social welfare analysis under different circumstances and when it will reach the principle of minimum differential, or the principle of maximum differential.

Background: Strength training for children and adolescents was for a long time a controversial subject but is nowadays proven safe and beneficial and recommendations for children’s strength training have been put forward by scientific sports boards in several western countries. Despite that, in Sweden strength training is not very commonly applied in children and adolescent’s sport. Strength training has proven to increase the sports performance and decrease the risk of injuries both in adults and children and would therefore be a good additional training method to the sport-specific training at any age. Different types of strength training have in several studies shown to improve the jumping ability, sprint performance and several other aspects. Purpose: The aim of the present study was to investigate the differences between pre- and post-test for the physical performance test after the 8-week strength training intervention both for the whole training group together and divided by type of intervention. Method: Eighteen adolescent boys were divided in two strength training groups, a friction Flowin® training group (FTR) and a barbell training group (BTR). They were tested pre and post an eight weeks intervention for 5-10-30 m sprint, Agility zig-zag test and two different counter movement jump (CMJ) tests. Result: The 30 m sprint improved after 8 weeks intervention for both groups together (n=18) (p= 0.036). Splitting into groups based on intervention, only the BTR group improved their performance in 30 m sprint after 8 weeks intervention (p=0.036). Both the BTR and FTR decreased their performance in 5 m sprint after the 8-week intervention (BTR p=0.007, FTR p=0.014). There was no statistical significant difference between or within the groups regarding any other tests. Conclusion: Eight weeks of strength training can improve the 30m sprint performance for adolescent male soccer players after 8 weeks intervention. More research is needed to conclude whereas the increase and explosive performance for adolescents are more affected by the duration of strength training or the strength training methods. Keywords: Children, adolescent, strength training, Flowin, barbell, physical soccer performance

The purpose of the study was to compare the kinematics of the barbell back squat between two footwear conditions and to evaluate the results with respect to recommendations put forth in the National Strength and Conditioning Association position statement for proper squat technique. Twenty-five subjects with 5 - 7 years of resistance training experience participated. Selected kinematics were measured during a 60% of 1RM barbell back squat in both barefoot and athletic shoe conditions. Paired-samples T tests were performed to compare the two footwear conditions. Significant differences were found in trunk (50.72±8.27 vs. 46.97±9.87), thigh (20.94±10.19 vs. 24.42±11.11), and shank segment angles (59.47±5.54 vs. 62.75±6.17), and knee joint angles (81.33±13.70 vs. 88.32±15.45) at the peak descent position. Based on the kinematic analysis of the barefoot squat, two kinematic advantages are countered by two disadvantages. Coaches and instructors should acknowledge these results with respect to a performer's capability, and be aware the advantages and disadvantages of barefoot squat from a kinematic perspective.

The purpose of the study was to compare the kinematics of the barbell back squat between two footwear conditions and to evaluate the results with respect to recommendations put forth in the National Strength and Conditioning Association position statement for proper squat technique. Twenty-five subjects with 5 - 7 years of resistance training experience participated. Selected kinematics were measured during a 60% of 1RM barbell back squat in both barefoot and athletic shoe conditions. Paired-samples T tests were performed to compare the two footwear conditions. Significant differences were found in trunk (50.72±8.27 vs. 46.97±9.87), thigh (20.94±10.19 vs. 24.42±11.11), and shank segment angles (59.47±5.54 vs. 62.75±6.17), and knee joint angles (81.33±13.70 vs. 88.32±15.45) at the peak descent position. Based on the kinematic analysis of the barefoot squat, two kinematic advantages are countered by two disadvantages. Coaches and instructors should acknowledge these results with respect to a performer's capability, and be aware the advantages and disadvantages of barefoot squat from a kinematic perspective.

Peak barbell velocity is an important determinant of weightlifting performance 2 . However, direct comparisons of this measure between elite men and women weightlifters is limited 7,8 . Therefore, the present study sought to establish a reference of the current status and trajectory of sexbased peak barbell velocity differences among elite weightlifters. This study examined performances of men and women in the 69 kg weight class in order to obviate the influence of body mass on performance. The purpose of this investigation was to help practitioners identify training needs of elite men and women weightlifters to improve weightlifting performance based upon between-group differences in peak barbell velocity.

The aim of the study was to examine repetition to repetition changes of bar velocity and its variations from barbell back squat. Participants (N=19) performed back squat with a relative intensity of 78-80% of 1 RM. Bar velocity was captured using wireless device (PUSHtm) placed on their forearm. Data were collected from 3 sets of 10 repetitions. One-way repeated measures ANOVA was used to identify the velocity changes over 10 repetitions. Statistical significance was found (F(1,17)=45.06.~ 0 . 0 0 0 1 )T.h is indicates that the bar velocity decreased significantly over the 10 repetitions. At the same time, coefficient of variance also increased as the repetitions went higher, indicating that there were differences in individual responses of bar velocity changes. Further examination will be aimed to investigate the bar velocity changes from various strength level of individuals.

The purposes of the study were to track weightlifters' barbell acceleration with a portable accelerometer over three training sessions to examine test–retest reliability and to compare peak barbell acceleration at different training intensities. Twelve nationally ranked weightlifters volunteered for this study. The portable accelerometer was attached to the right side of the barbell to measure barbell resultant acceleration during the snatch lift at a sampling frequency of 100 Hz. The data were collected over three training sessions at intensity levels of 80%, 85%, and 90% of one repetition maximum. The data were analyzed using intra-class correlation coefficients (ICCs) for the three training sessions and one-way repeated measure ANOVA to compare the difference in peak barbell acceleration at three intensities. Results showed that the device was highly reliable with an ICC of 0.88 and 95% confidence interval of 0.81–0.93. There were significant differences in peak barbell acceleration at various lifting intensities, indicating a decline of the acceleration as the mass of the barbell became heavier. The portable accelerometer seems useful in measuring barbell acceleration data, which can be analyzed in future studies to monitor a weightlifter's performance in a practical setting instead of testing at a laboratory.

The purpose of this study was to determine if concentric velocities of lighter loads of could be augmented if they are performed heavier working sets. Twelve trained males with experience in the barbell back squat performed a 5RM and completed two separate squat training session conditions that consisted of three sets of five repetitions with 85% of their 5RM. Both conditions differed in the placement of a reduced-load set that was either performed after the working sets or during the warm-up period. No significant differences were observed in the working set MCVs in both conditions. Additionally, no significant differences were observed amongst MCVs in the Down Set and equivalent warm-up set loads. The results of this study suggest that postactivation potentiation may not occur using a similar set-load scheme.

The fitness device market is young and rapidly growing. More people than ever before take count of how many steps they walk, how many calories they burn, their heart rate over time, and even their quality of sleep. New, and as of yet, unreleased fitness devices have promised the next evolution of functionality with exercise technique analysis. These next generation of fitness devices have wrist and armband style form factors, which may not be optimal for barbell exercises such as back squat, bench press, and overhead press where a sensor on one arm may not provide the most relevant data about a lift. Barbell path analysis is a well-known visual tool to help diagnose weightlifting technique deficiencies, but requires a camera pointed at the athlete that is integrated with motion-tracking software. This camera set up is not available at most gyms, so this motivates the use of a small, unobtrusive sensor to obtain data about an athlete's weightlifting technique. Researchers have shown that an accelerometer attached to a barbell while the athlete is lifting yields just as accurate acceleration information as a camera. The LIFT (Leveraging Information For Training) automated weight lifting coach attempts to implement a simple, unobtrusive system for analyzing and providing feedback on barbell weight lifting technique.