A Full-Field Calibration Approach on Material Parameter Identification

In the recent years, the usage of HS-steels has risen significantly in the automotive field. Their characteristics, such as hardness and favorable weight to strength ratio, can increase safety, fuel efficiency and overall product profitability. In this context, for the design with this material it has become crucial to be able to characterize precisely HS-steels and accurately predict their failure in many complex conditions, to fully exploit their capabilities. One of the most accredited ways to approach the prediction of failure for a wide range of materials is the generalized incremental stress-state dependent damage model GISSMO. The model is highly flexible and provides a framework inside LS-DYNA in which failure parameters can be tuned to reproduce experimental data. The definition of the optimal parameters is an inverse problem, therefore it was implemented using LS-OPT. In this work, the experimental evaluation of the MS1500 was carried out using the digital image correlation (DIC). With such technology, the displacements’ field of the test specimen is recorded.The evalueted field was processed as a family of stress-strain curves (hyper-curves) and became the objective of the optimization. This approach is named full field calibration and in this work was split in two phases. First, the stress-strain curve of the material was defined, then the tuning of the GISSMO parameters was performed. To evaluate the effectiveness of the full field approach a parallel study was implemented. The same routine of optimization run with a single stress-strain curve, which was measured with an extensometer. The comparison between the results obtained with the traditional approach and the results obtained with the full field approach highlighted the strenghts and the limitations of the two methods

Somatotyping of Division I Athletes

Somatotyping has previously examined athletes\u27 genetic morphology. Categorization of somatotyping can be utilized in athletes for specialized, adaptive sports performance. PURPOSE: The purpose of this study was to report somatotyping differences (ectomorph, mesomorph, and endomorph) in selected Division I athletes. METHOD: 39 male football athletes and seven female softball Division I athletes were recruited for this investigation. Height (m), weight (kg), waist-to-hip ratio (cm), and a 4-site skinfold measurement was collected. Skinfold locations were recorded from the triceps (mm), subscapular (mm), supraspinal (mm), and the medial calf (mm). Biepicondylar breadth measures of the humerus (cm), and the femur (cm) were recorded at a respective 90°. Additionally, the girth of the subject’s dominant upper arm (cm) and dominant calf (cm) were recorded. All measurement locations were taken from the Heath-Carter Anthropometric protocol, respectfully. The Heath Carter Somatotype Worksheet consists of a rating scale that is based on a 3-component categorization. All measures are considered when calculating a participant\u27s score. Scores between .5 and 2.5 are low, 3 to 5 are moderate, 5.5 to 7 are high and anything over a 7.5 is considered very high. The first component calculated scores of endomorphy, the second calculated mesomorphy scores, and the last component calculated ectomorph scores. Using these measurements, equations are used to determine a participant’s score to a specific somatotype. The athletes\u27 numbers were then processed and plotted on a 2-D graph plotting the somatotype (X= ectomorph-endomorph, Y=2 x mesomorphy- (endomorphy+ectomorph)). RESULTS: There was a clear indication that somatotyping had variety based on sports and position specialization in football athletes. Football athletes consisted of 6 endomorphs, 30 mesomorphs, and 3 ectomorphs, while softball athletes consisted of 7 meso-endomorphs. CONCLUSION: Due to the anthropometric position differences in male football athletes there was a considerable amount of variety and lack of specificity, while the female softball athletes consisted of a lesser variety in anthropometric measures

Time Course Change of Muscle Thickness of the Tibialis Anterior Following Blood Flow Restricted Training

Traditional resistance training programs recommend training loads of at least 60% 1-repetition maximum (1RM) to stimulate muscle hypertrophy within 3 weeks. Low-load blood flow restricted (BFR) resistance training (RT) has implications in rehabilitation since this modality has shown comparable muscle hypertrophy to high-load RT at intensities as low as 30% 1RM. However, the recommended effects of BFR on muscle size in various musculature throughout an intervention has not been thoroughly examined. PURPOSE: Therefore, the purpose of this investigation is to measure temporal changes in muscle thickness (MT) on the tibialis anterior (TA) throughout 4 weeks of BFR training. METHODS: Thirteen untrained participants were randomized into two groups: (BFR; n=8) (177.6 ± 4.1 cm, 84.8 ± 15.1 kg, 21.3 ± 1 years) or control non-BFR (n=5) (172.6 ± 8.2 cm, 76.7 ± 11.1 kg, 23.4 ± 2.7 years) who were matched for training sessions, sets, and reps. During the 4-week period (8 sessions), participants underwent twice-weekly sessions of unilateral isokinetic dorsiflexion training at 30% of their daily peak torque at a velocity of 60°/s with or without BFR. Ultrasound-derived measures of muscle thickness were captured at one-third the distance from the fibular head to the medial malleolus prior to the pre- and post-intervention testing sessions. Two separate linear regression analyses were used to examine group slope differences in MT across all training sessions. RESULTS: Linear regression analyses indicated that the control (i.e., non-BFR) exhibited a significant, positive (b = 0.023, SE = 0.01, r2=0.626, p=0.006) increase in MT from pre- to post testing. However, there was no significant change (b=0.021, SE = 0.01, r2=0.324, p=0.086) in MT across Time for the BFR group. CONCLUSION: Low-load RT without BFR induces temporal changes in muscle size following a short 4-week intervention. This exemplifies the efficacy of low-load training in inducing detectible changes in muscle thickness of the TA, and does not indicate BFR has an additive effect on temporal changes in muscle size of novice males following a 4-week intervention

Regional Motor Unit Firing Behaviors of Mono- and Bi-Articular Leg Extensor Muscles

Motor unit (MU) activation patterns provide vast insight into skeletal muscle contractions and may differ depending on architectural differences. Previous findings have suggested that MU activation patterns, specifically within the quadriceps group, are region-specific; this, along with the architectural differences between the quadriceps muscles, may further influence force production as reflected within the relationships between the firings. PURPOSE: To examine regional activation in proximal and distal regions of biarticular [rectus femoris (RF)] and monoarticular [vastus lateralis (VL)] knee extensors during submaximal isometric knee extensions. METHODS: On two separate randomized visits, eight lower-body resistance trained individuals, 6 males (n=6, age= 25.2 ±3.77) and 2 females (n=2, age= 21 ±1.4), performed submaximal isometric contractions at 30% and 70% of their maximal voluntary contractions (MVC) in a custom-built seat using an S-beam load-cell. Two separate 5-pin surface electromyography (EMG) sensors were used to record activation in the proximal and distal locations of either the VL or RF. Signals were recorded and decomposed into their constituent motor unit action potential (MUAP) trains, validated, and assessed for relative behavioral properties. For subsequent analysis of firing behaviors, the relationships (Slopes and intercepts) between motor unit action potential size (MUAPsize,) recruitment threshold (RT%), and mean firing rate (MFR) were calculated. Twelve separate two-way repeated measures analyses of variance (ANOVA) (location [proximal v distal] x muscle [VL v RF]) were used to compare slopes and intercepts of MFR vs. RT%, MUAPsize vs. RT%, and MFR vs. MUAPsize at both 30% and 70% MVC. RESULTS: There was a significant location x muscle interaction in the MFR v MUAPsize slopes during 30% MVC contraction (pCONCLUSION: The location by muscle interaction in the MFR v MUAPsize slopes during 30% MVC may indicate muscle fiber type distribution differences between sensor locations specifically, more type II fibers in the distal location of the VL

Effects of a Ten Week Barbell Deadlift Training Program on Vertical Jump Height in College-Aged Women

The barbell deadlift is a large muscle mass exercise that primarily involves extension at the hip and knee joints. Although it is often incorporated into strength training programs with a variety of other exercises (e.g., back squat), no previous studies have examined the effects of deadlift training on strength or power adaptations. The purpose of this investigation was to examine the effects of a ten week barbell deadlift training program on vertical jump height in previously untrained women. Twenty-eight women (mean ± SD age = 22 ± 2 years) were randomly assigned to either the training group (n = 17) or the control group (n = 11). The training group visited the laboratory for supervised exercise twice per week for ten weeks. Each training session involved five sets of the barbell deadlift, and each set utilized the heaviest external load that allowed for five repetitions with proper exercise technique. If all repetitions were performed with correct technique, additional weight (≤ 2.27 kg) was added to the barbell during the next training session. The control group was asked to refrain from lower-body exercise throughout the course of the study. Vertical jump height was assessed with a Vertec before and after the ten week intervention. An analysis of covariance (ANCOVA) was used to examine the data, and the pretest and posttest values were used as the covariate and dependent variable, respectively. The ANCOVA indicated that the posttest mean for the training group (42.5 cm) was significantly greater than that for the control group (39.0 cm) after adjusting for the pretest vertical jump height scores (p = .012, η² = .229). The effect size for the unadjusted mean increase for the training group (3.6 cm) was considered small-to-moderate (Cohen’s d = .37). These findings demonstrated that a ten week exercise training program using only the barbell deadlift significantly improved vertical jump height in college-aged women

Linear Progression for Increased External Loads during Strength Training

Improvements in muscular strength require an individual to train with progressively increased external loads over time. While it is well documented that the initial adaptations to strength training occur rapidly, previous researchers have not thoroughly examined the most effective means of inducing these changes. The purpose of this study was to examine the ability to add 2.27 kg to the barbell for 20 consecutive training sessions, and to compare these responses between the sexes. Thirty-four subjects ([mean ± SD age = 23 ± 3 years] men, n = 17; women, n = 17) participated in this study. The subjects were taught how to perform the barbell deadlift exercise, and received individual instruction and verbal feedback regarding their technique throughout the entire investigation. The subjects visited the laboratory twice per week for ten weeks. The external loads corresponded to the maximum weight that each subject could use to perform five sets of five repetitions with correct technique. If five sets of five repetitions were performed, 2.27 kg were added to the barbell for the following training session. The mean external load for each training session was recorded. The data were analyzed with bivariate regression and repeated measures analyses of variance (ANOVAs). The mean ± SD external loads used in this study increased from 66.2 ± 22.3 to 123.1 ± 21.8 kg for the men and 37.8 ± 7.0 to 70.7 ± 12.2 for the women. The results from the repeated measures ANOVAs indicated that men were able to add 2.27 kg to the barbell for 17 consecutive training sessions. For the women, however, the progress stalled at roughly week six. As a result, the coefficient of determination for the external load versus training session number relationship was r2 = .960 for the men and r2 = .881 for the women. These findings demonstrated that adding 2.27 kg to the barbell for each training session was an effective method for progressively increasing the external load over a ten week period. Many of the women had a difficult time with this gradual increase after week six, however, suggesting that smaller absolute changes with fractional plates (e.g., 0.91 kg) may be necessary

Differences in Quadriceps Activation During Return-to-play in Lower Body Resistance-Trained Females

Muscular activation in the quadriceps is indicative of proper muscular function, which is the sole determinant of a return-to-play assessment. Specifically, the activation within the knee extensors is essential to the evaluation of ACL tears. PURPOSE: The purpose of the study was to bilaterally compare muscular activation of the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) during isokinetic knee extensions across velocities. METHODS: 8 lower-body resistance-trained females (n=8; age= 19 ±1, height= 169.06 ±3.85 cm, weight= 64.46 ±4.76 kg) completed this study. Using an isokinetic dynamometer, subjects performed continuous isokinetic knee extensions at velocities of 60°/sec, 180°/sec, and 240°/sec. Three separate 4-pin surface electromyography (EMG) sensors were used to record activation within the VL, VM, and RF during the protocol. Average root mean squared (RMS) values were calculated via manual editing techniques across the contractions at all three velocities. A three-way mixed factorial analysis of variance (ANOVA) (velocity [60°/sec v 180°/sec v 240°/sec] x muscle [VL v VM v RF] x leg [dominant v non-dominant]) was used to compare average RMS values during the differing velocities. RESULTS: There were no significant velocity x muscle x leg interactions (p\u3e0.05) in the RMS values. However, when collapsed by muscle and leg, there was a significant main effect (p\u3c0.05) for muscle activation at each separate velocity. CONCLUSION: These could be due to evaluation and EPOC windows during manual editing techniques, which account for potential electromechanical delays and onset of torque production

A Bilateral Comparison of Overuse Shoulder Rotation in Overhead Throwing Athletes

Repetition of an unnatural movement may lead to skeletal muscle and/or connective tissue injury resulting in bilateral deficits. These discrepancies can be identified via the assessment of electromyographic activation and peak torque (PT) values during concentric internal and external rotation. PURPOSE: The purpose of this study was to examine the bilateral differences in PT output and root mean squared (RMS) values during isokinetic internal and external shoulder rotation with association to overuse injuries. METHODS: Six overhead throwing athletes (n=6, age=19 ± 1 year; height=181.8 ± 7.5 cm; weight= 85.1 ± 7.9 kg) completed bilateral isokinetic internal and external rotation of the shoulder using an isokinetic dynamometer (Biodex System 4) while seated in an upright position. Subjects completed three contractions on command through 90 degrees of external rotation and 30 degrees of internal rotation at 60°/sec, 120°/sec, and 180°/sec. Two separate four-pin surface electromyography (EMG) sensors were used to record activation in the anterior and posterior deltoids. The PT and RMS values were averaged across contractions of the three separate velocities and used for statistical comparisons. Three separate two-way mixed factorial analysis of variance (ANOVAs) (rotation [internal v external] x arm [dominant v non-dominant]) were used to compare PT at the chosen velocities. Two separate two-way mixed factorial ANOVAs (velocity [60°/sec v 120°/sec v 180°/sec] x arm [dominant v non-dominant]) were used to compare RMS values at the chosen velocities for each muscle. RESULTS: For PT, there were no significant rotation x arm interaction (p\u3e0.01). However, when collapsed by arm there was a significant main effect for rotation (p0.05). CONCLUSION: Greater internal PT production during low velocity contractions is expected as torque and angular velocity are inversely proportional. Comparisons between internal and external PT is significant as overhead throwing mechanics require more proficiency in internal rotation than external rotation. Additionally, non-significant bilateral comparison may suggest that the subjects have been well trained to overcome expected deficiencies with overuse in sports specific tasks

Neuromuscular Adaptations to Low-intensity Blood Flow Restricted Training

Low-intensity blood flow restricted (BFR) training has been shown to induce adaptations in muscular strength and size similar to traditional high-intensity resistance training. However, the reporting of peripheral neuromuscular adaptations is lacking within the current literature. PURPOSE: The purpose of this investigation was to examine the effects of BFR training on motor unit (MU) firing behaviors. METHODS: 13 untrained males (age: 22 ± 2yrs; height: 175.7 ± 6.0cm; weight: 81.9 ± 13.3kg) were randomly assigned to the BFR (n = 7) or non-BFR (n = 6) group. All subjects completed preliminary testing consisting of 3 isometric maximal voluntary contractions (MVC) of dorsiflexion muscle action, along with subsequent randomized ramp contractions at 25%, 50%, 75%, and 100% MVC. Surface electromyography (EMG) was used to record muscle activation of the tibialis anterior and later decomposed into their constituent motor unit action potential (MUAP) trains. Both groups completed 4 weeks (8 sessions) of isokinetic dorsiflexion training at 30%MVC of their daily peak torque values at 60°/s. At least 48 hours after the last training session, subjects repeated the pretesting protocol where MUAPS were then validated and assessed for relative behavioral properties of slopes and y-intercepts between MUAP size and mean firing rate (MFR). Separate two-way repeated measures ANOVAs (group [BFR v non-BFR] x time [pre v post]) were used to compare the slopes and y-intercepts of MFR vs. MUAP at all intensities. RESULTS: In regard to slopes, there were no significant group x time interactions at any of the intensities (p\u3e0.05); however, at the 25% slopes, there was a significant main effect for time (p = 0.038). Specifically, the 25% MFR v MUAP slope coefficient increased from pre- to post- (-0.105 ± 0.010 to -0.081 ± 0.005; mean ± SE). In regard to the intercepts, there were no significant group x time interactions or main effects for any of the intensities (p\u3e0.05). CONCLUSION: The main effect for time in the 25% slopes, in addition to a lack of differences in the 25% intercepts, indicates MUAP size increased independently from MFR following BFR training. This shift within the MU pool may be due to the recruitment of MUs at slightly higher thresholds during low intensity contractions, which is common within concurrent literature

A Contralateral Comparison of Beta-Band Oscillations in the Motor Cortex Following Blood Flow Restriction Training

Contralateral adaptations following unilateral training is commonly associated with the cross-education phenomena. Identifying the contributions to peripheral activation of voluntary muscle contractions can be represented in Beta-band (13-30Hz) oscillations within the human motor cortex. These individualistic electrophysiological changes may display potential hemispheric differences that contribute to skeletal muscle activation patterns following single limb training common in rehabilitation settings. PURPOSE: The purpose of this investigation was to compare the responses of beta-band mean power frequency (MPF) in the motor cortex during varying isometric contraction intensities after blood flow restriction training. METHODS: 13 untrained males (age: 21.7 ± 1.7yrs; height: 176.6 ± 5.2cm; weight: 83.4 ± 12.4kg) were randomly assigned to a BFR (n=8) and non-BFR (n=5) group. Both groups completed 8 isokinetic dorsiflexion training sessions separated by 48 hours at 30% of their session peak torque at a velocity of 60°/s. Pre and post isometric dorsiflexion trapezoidal ramp tracings were recorded at 25%, 50%, 75%, and 100% of their maximal voluntary contraction (MVC). A 64-channel electroencephalography (EEG) cap recorded neural activity during the isometric tracings. Signals were filtered to reject artifact and compute Fast Fourier Transforms. Separate 3-way mixed factorial ANOVAs (group [BFR v non-BFR] x time [pre v post] x location [C5 v C3 v C1 v C2 v C4 v C6]) were used to compare MPF values of the beta-band at all intensities. Additional ANOVAs (group [BFR v non-BFR] x time [pre v post] x leg [right v left] were used to compare the CZ location MPF values of the beta-band at all intensities. RESULTS: There were no significant group x time x location interactions or main effects for MPF at 25%, 50%, or 100% intensities, however there was a main effect for location at 75% (p = .045) (C5 [944.383 ± 150.647], C3 [834.815 ± 150.647], C1 [745.956 ± 150.647], C2 [1057.821 ± 150.647], C4 [1082.626 ± 150.647], C6 [1246.386 ± 150.647]; mean ± SE). When comparing group x time x leg, there was a significant interaction at 25% (p = .049) and main effect on time at 75% (p = .030) (pre [755.646 ± 126.276], post [1052.475 ± 126.276]; mean ± SE). CONCLUSION: Beta-band oscillations are often linked with various cognitive and motor functions. These results support a presence of contra-lateralization of the motor cortex with voluntary muscle activation patterns of the tibialis anterior during isometric contractions