All-Optical Photoacoustic Detection of Absorbers in Tissue Phantoms

Visualizing and characterizing vascular structures is important for many areas of health care, from accessing difficult veins and arteries for laboratory testing, to diagnosis and treatment of cardiovascular disease. Photoacoustic (PA) imaging, one of the fastest growing fields of biomedical imaging, is well suited for this task. PA imaging is based on the photoacoustic effect, which starts with a pulsed laser source incident on biological tissue. If the wavelength of the source matches an absorption wavelength of a chromophore within the tissue, a portion of the pulse energy is absorbed by the chromophore and converted into heat. A subsequent increase in temperature, followed by an increase in pressure occurs. Acoustic waves are emitted when this pressure relaxes, which can be detected at the surface of the tissue. PA imaging is considered absorption based, therefore spectroscopic information can be extracted. Yet, unlike purely optical imaging techniques, multiple centimeters of depth can be imaged. Vascular structures, in particular, can be viewed with high contrast using PA imaging, because the absorption coefficient of blood is up to six orders of magnitude higher than surrounding tissues [1]. Additional chromophores, such as lipids in atherosclerotic plaque, are beginning to be imaged using PA techniques in vitro [2]

Correlations Between Internal and External Power Outputs During Weightlifting Exercise

Identifying loads that maximize mechanical power is important because training at such loads may optimize gains in dynamic athletic performance. The purpose of this study was to examine correlations between measures of external mechanical power output and internal mechanical joint power output across different loads during a weightlifting exercise. Ten subjects performed 3 sets of the clean exercise at 65, 75, and 85% of 1 repetition maximum (1RM). Peak external mechanical power output was calculated with 4 commonly used methods, whereas an inverse dynamics approach was used to calculate peak internal mechanical power output for the hip, knee, and ankle joints along with the peak of the sum of all internal joint powers. All peak mechanical power outputs were expressed as relative peak power by either ratio (watts per kilogram) or allometrically scaling to body mass (W·kg-0.67). Correlation coefficients were used to compare power output measures. The greatest numbers of significant correlations between internal and external power outputs were observed at 85% of 1RM, at this load hip and knee joint power outputs were correlated to external mechanical power output when calculated with the traditional work-energy method. In addition, the peak sum of all mechanical joint powers was correlated to mechanical power output when calculated with the impulse-momentum method at loads of 75 and 85% of the 1RM. Allometric scaling of power outputs yielded one more significant correlation than did the ratio scaled power outputs. These findings support the use of the work-energy method when making inferences about internal joint powers from external power outputs when loads equal to 85% of 1RM are being lifted. In addition, the impulse-momentum method may be used to make inferences about the sum of all internal joint powers from external power outputs when loads between 75 and 85% of 1RM are being lifted

Lower Extremity Biomechanics During Weightlifting Exercise Vary Across Joint and Load

The purpose of this study was to determine the effect of load on lower extremity biomechanics during the pull-phase of the clean. Kinematic and kinetic data of the three joints of the lower extremity were collected while participants performed multiple sets of cleans at three percentages: 65, 75, and 85% of 1-Reptition maximum (RM). General linear models with repeated measures were used to assess the influence of load on angular velocities, net torques, powers, and rates of torque development at the ankle, knee, and hip joint. The results suggest that the biomechanical demands required from the lower extremities change with the lifted load and to an extent depend on the respective joint. Most notably, the hip and knee extended significantly faster than the ankle independent of load, while the hip and ankle generally produced significantly higher torques than the knee. Torque, rate of torque development, and power at the ankle and knee joint were maximal at 85% and 75% of 1-RM, respectively, whereas torque and rate of torque development at the hip were maximal at loads above 75% and 85% of 1-RM, respectively. This study provides important novel information about the mechanical demands of a weightlifting exercise and should be heeded in the design of resistance training programs

Kinematic and Kinetic Synergies of the Lower Extremities During the Pull in Olympic Weightlifting

The purpose of this study was to identify multijoint lower extremity kinematic and kinetic synergies in weightlifting and compare these synergies between joints and across different external loads. Subjects completed sets of the clean exercise at loads equal to 65, 75, and 85% of their estimated 1-RM. Functional data analysis was used to extract principal component functions (PCF\u27s) for hip, knee, and ankle joint angles and moments of force during the pull phase of the clean at all loads. The PCF scores were then compared between joints and across loads to determine how much of each PCF was present at each joint and how it differed across loads. The analyses extracted two kinematic and four kinetic PCF\u27s. The statistical comparisons indicated that all kinematic and two of the four kinetic PCF\u27s did not differ across load, but scaled according to joint function. The PCF\u27s captured a set of joint- and load-specific synergies that quantified biomechanical function of the lower extremity during Olympic weightlifting and revealed important technical characteristics that should be considered in sports training and future research

Energy Flow Analysis to Investigate Youth Pitching Velocity and Efficiency

Purpose The purposes of this study were 1) to investigate the transfer of energy through the kinetic chain by youth baseball pitchers during the pitching motion and 2) to provide insight into how the total magnitude of energy flow and its linear and rotational components relate to both velocity and joint torque per unit increment of pitch velocity (joint load efficiency). Methods Twenty-four youth baseball pitchers participated in this study. Data collection occurred in an indoor research laboratory equipped with a 14-camera infrared motion capture system and an instrumented pitcher’s mound with embedded force plates. Energy flow was calculated by integrating power transfer into and out of each segment. The magnitudes of key instances of energy flow were compared to pitch velocity and velocity-normalized joint torques using simple linear regressions. Results All of the energy flow variables calculated had a significant correlation to pitch velocity. Energy flow into the arm from the trunk had the strongest correlation to velocity of any variable investigated (r = 0.900, P = 0.000). The total magnitude of energy flow into the trunk had a significant correlation to increased horizontal shoulder adduction efficiency and shoulder internal rotation efficiency. The magnitude of energy flow into the trunk by only joint forces had a significant correlation to increased horizontal shoulder adduction efficiency, shoulder internal rotation efficiency, and elbow varus efficiency. Conclusions Energy flow analysis is an effective tool providing quantitative assessment of the kinetic chain to gain a deeper understanding of how energy moves through an athlete, and how specific pitching mechanics impact this movement. The results of this study support the importance of generating energy flow throughout the body to produce high velocities and energy flow through the trunk to increase pitch efficiency

Characterizing Phantom Arteries with Multi-Channel Laser Ultrasonics and Photo-Acoustics

Multi-channel photo-acoustic and laser ultrasonic waves are used to sense the characteristics of proxies for healthy and diseased vessels. The acquisition system is non-contacting and non-invasive with a pulsed laser source and a laser vibrometer detector. As the wave signatures of our targets are typically low in amplitude, we exploit multi-channel acquisition and processing techniques. These are commonly used in seismology to improve the signal-to-noise ratio of data. We identify vessel proxies with a diameter on the order of 1 mm, at a depth of 18 mm. Variations in scattered and photo-acoustic signatures are related to differences in vessel wall properties and content. The methods described have the potential to improve imaging and better inform interventions for atherosclerotic vessels, such as the carotid artery

Weightlifting Performance is Related to Kinematic and Kinetic Patterns of the Hip and Knee Joints

The purpose of this study was to investigate correlations between biomechanical outcome measures and weightlifting performance. Joint kinematics and kinetics of the hip, knee, and ankle were calculated while ten subjects performed a clean at 85% of 1-RM. Kinematic and kinetic time-series patterns were extracted with principal components analysis. Discrete scores for each time-series pattern were calculated and used to determine how each pattern was related to body-mass normalized 1-RM. Two hip kinematic and two knee kinetic patterns were significantly correlated with relative 1-RM. The kinematic patterns captured hip and trunk motions during the first pull and hip joint motion during the movement transition between the first and second pull. The first kinetic pattern captured a peak in the knee extension moment during the second pull. The second kinetic pattern captured a spatiotemporal shift in the timing and amplitude of the peak knee extension moment. The kinematic results suggest that greater lift mass was associated with steady trunk position during the first pull and less hip extension motion during the second-knee bend transition. Further, the kinetic results suggest that greater lift mass was associated with a smaller knee extensor moments during the first pull, but greater knee extension moments during the second pull, as well as an earlier temporal transition between knee flexion-extension moments at the beginning of the second pull. Collectively, these results highlight the importance of controlled trunk and hip motions during the first pull and rapid employment of the knee extensor muscles during the second pull in relation to weightlifting performance

Effect of Loading Condition on Traction Coefficient Between Shoes and Artificial Turf Surfaces

Background. The interaction between a shoe and a turf surface is highly complex and difficult to characterize. Over the three decades since artificial turf was introduced, researchers have attempted to understand the traction caused by the interaction. However, some of the methodologies used for traction measurements have not capitalized on advances in currently available technology for testing and most testing conditions have not simulated realistic physiological loads. Method of Approach. To assess the effect of test condition on traction results, the newly designed TurfBuster testing device was used to collect traction data on FieldTurf™ brand artificial turf under varying conditions. Four cleated athletic shoes were tested under eight different vertical loads ranging from 222-1780 N. The static, dynamic, and peak traction coefficient values were calculated and averaged over three trials for each shoe and condition. Results. In all but the lowest vertical load condition, the static traction coefficient was less than the dynamic traction coefficient. There was a distinct separation found between 666 N and 888 N loading conditions for all three variables measured. Below the load condition of 666 N only one significant difference was found in all comparisons across and within shoe styles. Above 888 N multiple differences were found across shoe styles, but differences were not found within a shoe style until a load of at least 1554 N. Conclusions. At loads below 666 N the cleats perform almost identically at all three variables measured, static, dynamic, and peak traction coefficients. At loads above 888 N, shoe traction was different among the cleat styles for all traction variables. However, at loads between 888 N and 1334 N there were no differences found within a shoe style. This implies that each shoe has no performance difference in loads representative of up to one bodyweight. Due to these results the measurement of traction characteristics between cleated shoes and FieldTurf should be conducted at a load of at least 888 N to determine differences across shoe styles and loads ranging from 888 N to at least 1554 N to determine individual shoe characteristics

Muscle Synergies During a Single-Leg Drop-Landing in Boys and Girls

The purpose of this study was to investigate muscle activation patterns during a landing task in boys and girls through the use of muscle synergies. Electromyographical (EMG) data from six lower extremity muscles were collected from 11 boys and 16 girls while they performed single-leg drop-landings. EMG data from six leg muscles were rectified, smoothed, and normalized to maximum dynamic muscle activity during landing. Data from 100 ms before to 100 ms after touchdown were submitted to factor analyses to extract muscle synergies along with the associated activation and weighing coefficients. Boys and girls both used three muscle synergies. The activation coefficients of these synergies captured muscle activity during the pre-landing, touchdown, and post-landing phases of the single-leg drop-landing. Analysis of the weighing coefficients indicated that within the extracted muscle synergies the girls emphasized activation of the medial hamstring muscle during the pre-landing and touchdown synergy whereas boys emphasized activation of the vastus medialis during the post-landing synergy. Although boys and girls use similar muscle synergies during single-leg drop-landings, they differed in which muscles were emphasized within these synergies. The observed differences in aspects related to the muscle synergies during landing may have implications with respect to knee injury risk

Influence of Towing Force Magnitude on the Kinematics of Supramaximal Sprinting

The purpose of this study was to determine the influence of towing force magnitude on the kinematics of supramaximal sprinting. Ten high school and collegiate aged track and field athletes ran 60m maximal sprints under 5 different conditions: non-towed (NT), Tow A (2.0% body weight), Tow B (2.8%BW), Tow C (3.8%BW), and Tow D (4.7%BW). Three-dimensional kinematics of a 4-segment model of the right side of the body were collected starting at the 35m point of the trial. Significant differences were observed in stride length (SL) and horizontal velocity of the center of mass (VH) during Tow C and Tow D. For Tow D, a significant increase in the distance from the center of mass to the foot at touchdown (DH) was also observed. Contact time (CT) decreased significantly in all towing conditions, while stride rate (SR) increased slightly (\u3c 2.0%) under towed conditions. There were no significant changes in joint or segment angles at touchdown, with the exception of a significant decrease in the flexion/extension angle at the hip during the Tow D condition. We concluded that towing force magnitude does influence the kinematics of supramaximal running. Furthermore, we suggest that coaches and practitioners adjust towing force magnitude for each individual and avoid using towing forces in excess of 3.8%BW