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.

Background: Post activation potentiation (PAP) is an increased muscular performance thatoccurs after maximal voluntary contraction. Previous studies have shown a significantincrease in explosive movements, such as sprint and jump performance, as an effect ofthese maximal contractions. Aim: The aim of this study was to analyze if PAP, in terms of heavy squats, has aperformance enhancing effect on 30 meter sprint, with a hypothesis that the maximal effortin the squat has a performance enhancing effect on 30 meter sprint. Method: Twelve healthy male Crossfit athletes from Crossfit Halmstad, age between x-x,volunteered to participate in the study, eleven of these completed all of the test sessions in thiscross-sectional study. During the first test session, the subjects attempted to set a onerepetition max (1RM) in the back squat. During the second and third test session, the subjectswere randomly divided into two groups and the subjects got to perform both the non-PAP andthe PAP protocol during different sessions, depending on which group they were in. Thesprint time was measured with a handheld stopwatch. Wilcoxon Signed Rank Test was usedto determine significant differences between sprint time after the two different protocols, andthe level of significance was set at p < 0.05. Result: The result showed that there was no significant difference between PAP and non-PAPprotocols (p = 0,679). With a median value of 4,78 seconds, a minimum value of 4,59seconds and a maximum value of 5,54 seconds for the sprint trials after PAP and a medianvalue of 4,82 seconds, a minimum value of 4,59 seconds and a maximum value of 5,31seconds for the sprint trials without PAP, the results did not confirm the hypothesis. Conclusion: As an effect from the low number of participants, the result could be deceptive.The study could have show a different result if the number of participants would exceed atleast 25 subjects. There are no performance enhancing effects in the sprint after PAP, in thisstudy. Further research is required, to determine possible performance enhancing effectsfrom PAP.

Orientador: Antonio Carlos de Moraes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Educação Física / Made available in DSpace on 2018-08-18T10:39:27Z (GMT). No. of bitstreams: 1 Batista_AlexandreRosas_M.pdf: 1979642 bytes, checksum: 55273546a63064fe915ef9261d5c5750 (MD5) Previous issue date: 2011 / Resumo: O propósito do presente estudo foi comparar as respostas eletromiográficas dos músculos vasto lateral (VL), reto femoral (RF) e bíceps femoral (BF) durante exercício de agachamento em três protocolos distintos de treinamento com pesos: a) métodos de cargas crescentes (12-10-8-6 repetições), b) método de cargas decrescentes (6-8-10-12 repetições); c) método de cargas constantes (4x9 repetições). Participaram do estudo 7 indivíduos saudáveis do sexo masculino (idade = 18 a 35 anos). Para a coleta dos sinais eletromiográficos, foram utilizados eletrodos bipolares ativos colocados nos músculos VL, RF e BF do lado dominante do voluntário, como sugere a padronização do SENIAN. Para a análise estatística a ANOVA One-way foi utilizada para comparar o valor médio da root mean square (RMS) e frequência mediana (FM) nas quatro séries para cada músculo analisado. A ANOVA Two-way foi utilizada para comparar a RMS e a FM dos músculos VL, RF e BF nas quatro séries dos três protocolos. O post-hoc de Bonferroni foi utilizado para a localização das diferenças quando apontadas pela ANOVA. O nível de significância adotado para todas as análises foi de p<0,05. Diferenças significativas foram observadas entre as séries 1, 3 e 4 do protocolo 1 quando comparado com o protocolo 2 (p<0,05). Observou-se também diferença significativa entre a série 1 do protocolo 2 e sua série correspondente do protocolo 3 e entre a série 4 do protocolo 3 quando comparada com a série 4 do protocolo 1. Entretanto, não foram encontradas diferenças entre os valores médios das quatro séries de cada protocolo de treinamento. Conclui-se que o padrão de recrutamento e ativação dos músculos VL, RF e BF são iguais para os protocolos de cargas crescentes, decrescentes e contínuas / Abstract: The purpose of this study was to compare the electromyographic responses of the vastus lateralis (VL), rectus femoralis (RF) and biceps femoralis (BF) during squatting exercise at three different protocols of weight training: 1) protocol of increasing loads (12-10-8-6 repetitions); 2) protocol of decreasing loads (6-8-10-12 repetitions); 3) protocol of constant loads (4x9 repetitions). Seven healthy male subjects were included into the study (age range: 18-35 years). To evaluate the electromyographic signal, active bipolar electrodes were placed in the muscles VL, RF and LF on the dominant side of the volunteer, as suggested by the standardization of SENIAN. For statistical analyses, One-way ANOVA was used to compare the root mean square (RMS) and median frequency (MF) in four series for each muscle examined. Two-way ANOVA was used to compare the RMS and MF of VL, RF and LF muscles in the four series of three protocols. The post-hoc Bonferroni test was used to locate the differences when indicated by ANOVA. The level of significance for all tests was 5%. Significant differences were observed between first, third and fourth series of Protocol 1 when compared with protocol 2 (p <0.05). We also observed a significant difference between the first series of protocol 2 and its corresponding series of protocol 3. Finally, significant differences were found between the third and fourth series of protocol 3, compared with the fourth series of Protocol 1. However, there were no differences between mean values of the four series of each training protocol. We conclude that the pattern of recruitment and activation of muscles VL, RF and LF are the same when using training protocols of increasing, decreasing or constant loads / Mestrado / Ciencia do Desporto / Mestre em Educação Física

The purpose of this study was to understand the relationship between back squat one-repetition maximum relative to body mass (1RMrel), countermovement jump height (CMJH), and optimal drop height in drop jump (DHopt). Fifteen male participants with various sport backgrounds and training experience completed a one repetition maximum (1RM) back squat, maximum countermovement jump (CMJ), and drop jumps (DJ) from incrementally increasing drop heights to determine which drop height elicited the greatest jump height. The DHopt testing protocol was unique in that smaller increments were used to determine DHopt compared to what has been reported in literature previously. Pearson correlation coefficients revealed that DHopt had small (r=0.214) and moderate (r=0.464) relationships with 1RMrel and CMJH, respectively. A second analysis (n=13) was conducted after two participants (i.e. powerlifters) were identified as possibly being representative of a different population. The second analysis found that DHopt had strong relationships with 1RMrel (r=0.645) and CMJH (r=0.690). Results from this study seem to suggest that individuals with greater 1RMrel and CMJH tend to have a higher DHopt. However, this relationship may not be observed among all populations due to likely differences in sport background, genetics, and/or training experience.

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.

The ability to produce power during competition is essential. Football requires explosive power in order to get off the ball faster, increase speed of the first step, and increase the height of the vertical jump. Most strength training professionals use the back squat to increase power of the lower extremities; however, as large forces are placed on the back, athletes are at greater risk for injury. The trap bar dead lift is similar to the back squat in movement and form, but the trap bar dead lift reduces the force on the lower back. After testing for maximum vertical jump,athletes at Timpview High School participated in a strength program using either back squats or trap bar dead lift for seven weeks. A pre-test, mid-test and post-test were performed to calculate the increase in maximum vertical jump, if any. It was found that neither lift was significantly different than the other when testing for maximum vertical jump. These results will allow strength training professionals to use the trap bar dead lift instead of the back squats in subjects similar to those participating in the study.

In sports, peaking phases are often applied prior to important competitions. Peaking phases typically consist of a planned overreach followed by a taper ending with a few days of complete rest. However, during peaking phases, components of body composition such as body mass (BM), fat mass (FM), fat-free mass (FFM), and skeletal muscle mass (SMM) have been shown to be negatively impacted, which could compromise performance outcomes. Thus, the purpose of this study was to monitor body composition prior to and immediately after a peaking phase to determine if body composition changes occurred. Twelve powerlifters completed a seven-week training protocol designed to peak powerlifting performance. The first four weeks consisted of strength training designed to standardize participant training prior to the first testing session (T1). Following T1, the participants performed a one-week overreach followed by a one-week step-taper ending with 2 and 4 days of complete rest followed by a second testing session (T2). Each testing session consisted of a) measuring BM, FM, FFM, and SMM via bioelectrical impedance, and b) 1-repetition maximum (1RM) testing on back squat (BS), bench press (BP), and deadlift (DL). 1RM performances were summed together for a Powerlifting Total (PT), and Wilks Scores were applied to determine relative performance changes. There were no statistically significant changes in BM (p > 0.99), FM (p > 0.99), FFM (p > 0.99), or SMM (p > 0.99), suggesting a maintenance of body composition during the peaking phase. There were, however, statistically significant changes in 1RM-BS (p = 0.04), PT (p = 0.05), and Wilks Score (p = 0.02). These data suggest that two-week peaking phase can result in the maintenance of body composition alongside improvements in strength performance.

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.

Traditional core stability training was developed as a method of treating and preventing back pain. It was however, seamlessly applied to healthy and athletic populations without scientific evidence supporting its efficacy. Traditional core stability focussed on isolating and training the anatomical region between the pelvis and diaphragm, using isometric or low load exercises to enhance spinal stability. Scientific research challenged this approach for healthy function and athletic performance, resulting in a more functional anatomical definition, which included pelvic and shoulder girdles. Hence, a revised definition of dynamic trunk stability; the efficient coordination, transfer and resistance by the trunk, of force and power generated by upper and lower appendicular skeletal extremities during all human movement. This led to an integrated exercise training approach to dynamic trunk stability. Although early evidence suggested loaded compound exercises preformed upright, in particular back squat, were effective in activating and developing trunk muscles, evidence was inconclusive. Accordingly, the aims of this PhD were to investigate neuromuscular trunk function in loaded, free barbell back squat to understand training implications for trunk stability in dynamic athletic activity. Five research studies were conducted; 4 are published and 1 is being prepared for re-submission. The literature review revealed evidence that back squat was an effective method of activating trunk stabilzers and showed that these muscles were load sensitive (study 1). A survey of practitioners reported an understanding and appreciation of the challenge against core stability training for athletic populations. Furthermore, perceptions were aligned with growing evidence for dynamic and functional trunk stability training (study 2). A test-retest neuromuscular study established interday reliability and sensitivity of electromyographical measurement of trunk muscle activity in squats (study 3). Trunk muscle activation in back squat was higher than hack squat at the same relative, but lower absolute loads (study 4). Trunk muscle activation was lower in squats and bodyweight jumps in the strong compared to weak group (study 5). Furthermore, activation of the trunk muscles increased in each 30o segment of squat descent and was highest in first 30o segment of ascent for all loads (study 5). In conclusion, this series of studies confirmed acute effect of squats on trunk stabilizers and demonstrated that external load increases activation in these muscles. Parallel squat depth is important in optimizing trunk muscle activation. Finally, high levels of squat strength result in lower trunk muscle activation in loaded squats and explosive jumps.