An examination of the hamstring and the quadriceps muscle kinematics during the front and back squat in males

Background The aim of the current investigation was to examine the influence of the front and back squat variants on the hamstring and the quadriceps muscles kinematics. Material/Methods Eighteen male participants were recruited with 1 repetition maximum values of 122.7±16.4 and 88.7 ±13.9kg for the back and front squat lifts. Participants completed both back and front squats at 70% of their front squat 1 repetition maximum. The hamstring and the quadriceps muscle kinematics were determined during kinetic situations using motion capture data, in addition to segmental and joint kinematics. Results Differences between squat conditions were examined using paired samples t-tests. The results showed that there were no differences in either segmental/joint or muscle kinematics between the front and back squat lifts. Conclusions These findings lead to the conclusion that neither the front nor the back squat conditions differ in terms of their eccentric and concentric recruitment of the quadriceps and hamstring muscles

Effects of different heel heights on lower extremity joint loading in experienced and in-experienced users: A musculoskeletal simulation analysis

Purpose This study examined the effects of different high-heeled footwear heights on lower extremity compressive joint loading and triceps-surae muscle–tendon kinematics during walking, using a musculoskeletal simulation-based approach, in both experienced and in-experienced high heel users. Methods The current investigation examined 12 experienced and 12 in-experienced high-heel wearers, walking in four different footwear (high heel, medium heel, low heel, and trainer). Walking kinematics were collected using an eight-camera motion capture system and kinetics via an embedded force plate. Lower extremity joint loading and triceps-surae muscle kinematics were explored using a musculoskeletal simulation approach. Results Irrespective of experience, when wearing high heels of increasing height, compressive loading parameters at the medial tibiofemoral compartment and patellofemoral joint were significantly greater and exceeded the minimum clinically important difference (MCID). Furthermore, irrespective of wearers’ experience, the triceps-surae muscle–tendon units were placed in a shortened position when wearing high heels of increasing height, with the differences exceeding the MCID. Conclusions It can be concluded that heeled footwear increases the mechanical factors linked to the aetiology of degenerative joint osteoarthritis and chronic shortening of the triceps-surae muscle–tendon units. Therefore, the current investigation provides evidence that irrespective of experience, heeled footwear of increasing height may negatively influence female’s lower extremity musculoskeletal health

Sex differences in ACL loading and strain during typical athletic movements: a musculoskeletal simulation analysis

Purpose Female athletes experience anterior cruciate ligament (ACL) injuries at a much greater rate than males, yet the mechanisms responsible for this are not well-understood. The current investigation aimed using a musculoskeletal simulation-based approach, to examine sex differences in ACL loading parameters during cut and hop movements. Methods Fifteen male and fifteen female participants completed 45° cut and maximal one legged hop movements. Three-dimensional motion capture and ground reaction force data during the stance phase of the cut movement and landing phase of the one legged hop were obtained. Lower extremity muscle forces, ACL forces and ACL strains were extracted via a simulation-based approach using a musculoskeletal model, with an ACL insertion into the femur and tibia. Results During the hop movement, females were associated with significantly greater peak ACL forces (male = 15.01 N/kg and female = 15.70 N/kg) and strains (male = 6.87% and female = 10.74%). In addition, for both the cut (male = 4.45 and female = 1.45) and hop (male = 2.04 and female = 1.46) movements, the soleus/gastrocnemius ratio was significantly larger in males. Conclusions The current investigation provides new information regarding sex differences during athletic movements that provide further insight regarding the increased incidence of ACL injuries in females

Acute biomechanical effects of a lightweight, sock-style minimalist footwear design during running; a musculoskeletal simulation and statistical parametric mapping approach

The aim of this study was to examine the effects of existing minimalist footwear, new sock-style minimalist footwear and conventional running footwear on lower extremity biomechanics, using a musculoskeletal simulation and statistical parametric mapping (SPM) approach. Thirteen male participants ran over an embedded force plate at 4.0 m/s, in (1) existing minimalist footwear, (2) new sock-style minimalist footwear and (3) conventional running shoes. Kinematics of the lower extremities was collected using an eight-camera motion analysis system and lower extremity joint loading was also explored using a musculoskeletal simulation approach. Differences between footwear conditions were examined using SPM and one-way repeated measures ANOVA. The strike index indicated that the foot contact position was significantly more anterior in existing minimalist footwear (44.19%) and new sock-style minimalist footwear (42.33%) compared to conventional running shoes (29.00%). The instantaneous loading rate was also significantly larger in existing minimalist footwear (271.68 BW/s) and new sock-style minimalist footwear (299.26 BW/s) in relation to conventional running shoes (122.48 BW/s). In addition, during the late stance phase compressive hip joint loading was significantly larger in both minimalist footwear. Similarly, Achilles tendon loading was statistically greater in both minimalist footwear compared to the conventional running shoe during the early and middle aspects of the stance phase. The observations from this analysis show that minimalist footwear may place non-habituated runners at greater risk from the mechanical factors linked to the aetiology of chronic lower limb running-related injuries

Supported transition metal catalysts for para- to ortho-hydrogen conversion

The main goal of this study was to develop and improve on existing catalysts for the conversion of ortho- to para-hydrogen. Starting with a commercially available Air Products nickel silicate, which had a beta value of 20, we were trying to synthesize catalysts that would be an improvement to AP. This was accomplished by preparing silicates with various metals as well as different preparation methods. We also prepared supported ruthenium catalysts by various techniques using several metal precursors to improve present technology. What was also found was that the activation conditions prior to catalytic testing was highly important for both the silicates and the supported ruthenium catalysts. While not the initial focus of the research, we made some interesting observations into the adsorption of H2 on ruthenium. This helped us to get a better understanding of how ortho- to para-H2 conversion takes place, and what features in a catalyst are important to optimize activity. Reactor design was the final area in which some interesting conclusions were drawn. As discussed earlier, the reactor catalyst bed must be constructed using straight 1/8 feet OD stainless steel tubing. It was determined that the use of 1/4 feet OD tubing caused two problems. First, the radius from the center of the bed to the wall was too great for thermal equilibrium. Since the reaction of ortho- to para-H2 is exothermic, the catalyst bed center was warmer than the edges. Second, the catalyst bed was too shallow using a 1/4 feet tube. This caused reactant blow-by which was thought to decrease the measured activity when the flow rate was increased. The 1/8 feet tube corrected both of these concerns

Urinary Steroid Profile in Ironman Triathletes

The aim of this study was to determine variations in the urinary steroid profile of triathletes following an Ironman event. A total of 10 male participants (age = 36.0 ± 1.27 years; body height = 179.29 ± 10.77 cm; body mass = 74.50 ± 1.04 kg) completed an Ironman Championship. Urine samples were collected before, immediately after, and 24 hours following the race. Gas chromatography-mass spectrometry (GC/MS) was used to detect and quantify catabolic and anabolic hormones: Androsterone, Dehydroepiandrosteone (DHEA), Androstenedione and Testosterone (T), Betaestradiol, Estrone, Progesterone, Cortisol (C), Cortisone, Tetrahydrocortisol (THE) and Tetrahydrocortisone (THF). These were measured in their glucuroconjugated and free forms. Androsterone (3297.80 ± 756.83 vs. 2154.26 ± 1375.38), DHEA (47.80 ± 19.21 vs. 32.62 ± 15.96) and Beta-estradiol (59.36 ± 11.7 vs. 41.67 ± 10.59) levels decreased after the event. The significant decrease of DHEA (47.80 ± 19.21 vs. 32.11 ± 14.03) remained at 24 hours. Cortisol (200.38 ± 56.60 vs. 257.10 ± 74.00) and THE (238.65 ± 81.55 vs. 289.62 ± 77.13) increased after exercise and remained elevated 24 hours later (200.38 ± 56.60 vs. 252.48 ± 62.09; 238.65 ± 81.55 vs. 284.20 ± 66.66). The following anabolic/catabolic ratios fell after exercise: T/C (0.85 ± 0.54 vs. 0.54 ± 0.29), T/THE (0.66 ± 0.29 vs. 0.40 ± 0.08), T/THE+THF (0.38 ± 0.17 vs. 0.24 ± 0.06), DHEA/THE (0.22 ± 0.05 vs. 0.12 ± 0.05), DHEA/THF (0.34 ± 0.02 vs. 0.21 ± 0.01) and DHEA/THE+THF (0.12 ± 0.02 vs. 0.08 ± 0.03). The steroid profile showed that athletes were fatigued after finishing the competition and a catabolic state remained 24 hours later

The Reliability of Electromyographic Normalization Methods for Cycling Analyses

Electromyography (EMG) is normalized in relation to a reference maximum voluntary contraction (MVC) value. Different normalization techniques are available but the most reliable method for cycling movements is unknown. This study investigated the reliability of different normalization techniques for cycling analyses. Twenty‐five male cyclists (age 24.13 ± 2.79 years, body height 176.22 ± 4.87 cm and body mass 67.23 ± 4.19 kg, BMI = 21.70 ± 2.60 kg∙m‐1) performed different normalization procedures on two occasions, within the same testing session. The rectus femoris, biceps femoris, gastrocnemius and tibialis anterior muscles were examined. Participants performed isometric normalizations (IMVC) using an isokinetic dynamometer. Five minutes of submaximal cycling (180 W) were also undertaken, allowing the mean (DMA) and peak (PDA) activation from each muscle to serve as reference values. Finally, a 10 s cycling sprint (MxDA) trial was undertaken and the highest activation from each muscle was used as the reference value. Differences between reference EMG amplitude, as a function of normalization technique and time, were examined using repeated measures ANOVAs. The test‐retest reliability of each technique was also examined using linear regression, intraclass correlations and Cronbach’s alpha. The results showed that EMG amplitude differed significantly between normalization techniques for all muscles, with the IMVC and MxDA methods demonstrating the highest amplitudes. The highest levels of reliability were observed for the PDA technique for all muscles; therefore, our results support the utilization of this method for cycling analyses

ECOREGIONAL DIFFERENCES IN LATE-20TH-CENTURY LAND-USE AND LAND-COVER CHANGE IN THE U.S. NORTHERN GREAT PLAINS

Land-cover and land-use change usually results from a combination of anthropogenic drivers and biophysical conditions found across multiple scales, ranging from parcel to regional levels. A group of four Level III ecoregions located in the u.s. northern Great Plains is used to demonstrate the similarities and differences in land change during nearly a 30-year period (1973-2000) using results from the U.S. Geological Survey\u27s Land Cover Trends project. There were changes to major suites of land-cover; the transitions between agriculture and grassland/shrubland and the transitions among wetland, water, agriculture, and grassland/shrubland were affected by different factors. Anthropogenic drivers affected the land-use tension (or land-use competition) between agriculture and grassland/shrubland land-covers, whereas changes between wetland and water land-covers, and their relationship to agriculture and grassland/shrubland land-covers, were mostly affected by regional weather cycles. More land-use tension between agriculture and grassland/shrubland landcovers occurred in ecoregions with greater amounts of economically marginal cropland. Land-cover change associated with weather variability occurred in ecoregions that had large concentrations of wetlands and water impoundments, such as the Missouri River reservoirs. The Northwestern Glaciated Plains ecoregion had the highest overall estimated percentage of change because it had both land-use tension between agriculture and grassland/shrubland land-covers and wetland-water changes

3-D kinematic comparison of treadmill and overground running.

Studies investigating the mechanics of human movement are often conducted using the treadmill. The treadmill is an attractive device for the analysis of human locomotion. Studies comparing overground and treadmill running have analyzed discrete variables, however differences in excursion from footstrike to peak angle and range of motion during stance have yet to be examined. This study aimed to examine the 3-D kinematics of the lower extremities during overground and treadmill locomotion to determine the extent to which the two modalities differ. Twelve participants ran at 4.0m/s in both treadmill and overground conditions. 3-D angular kinematic parameters during the stance phase were collected using an eight camera motion analysis system. Hip, knee and ankle joint kinematics were quantified in the sagittal, coronal and transverse planes, then compared using paired t-tests. Of the parameters analyzed hip flexion at footstrike 12° hip range of motion 17°, peak hip flexion 12.7°, hip transverse plane range of motion 8° peak knee flexion 5° and peak ankle excursion range 6.6°, coronal plane ankle angle at toe-off 6.5° and peak ankle eversion 6.3° were found to be significantly different. These results lead to the conclusion that the mechanics of treadmill locomotion cannot be generalized to overground

Effects of a prophylactic knee bracing on patellofemoral loading during cycling

Purpose The aim of the current investigation was to utilize a musculoskeletal simulation approach to examine the effects of prophylactic knee bracing on patellofemoral joint loading during the pedal cycle. Methods Twenty-four (12 male and 12 female) healthy recreational cyclists rode a stationary cycle ergometer at fixed cadences of 70, 80 and 90 RPM in two different conditions (brace and no-brace). Patellofemoral loading was explored using a musculoskeletal simulation approach and participants were also asked to subjectively rate their perceived stability and comfort whilst wearing the brace. Results The results showed that the integral of the patellofemoral joint stress was significantly lower in the brace condition (male: 70 RPM = 8.89, 80 RPM = 9.76, and 90 RPM = 12.30 KPa/kg s and female: 70 RPM = 11.59, 80 RPM = 13.07 and 90 RPM = 14.14 KPa/kg s) compared to no-brace (male: 70 RPM = 10.23, 80 RPM = 10.96 and 90 RPM = 13.20 and female: 70 RPM = 12.43, 80 RPM = 14.04 and 90 RPM = 15.45 KPa/kg s). In addition, it was also revealed that participants rated that the knee brace significantly improved perceived knee joint stability. Conclusions The findings from the current investigation, therefore, indicate that prophylactic knee bracing may have the potential to attenuate the risk from the biomechanical parameters linked to the aetiology of patellofemoral pain in cyclists. Future, longitudinal analyses are required to confirm the efficacy of prophylactic knee braces for the attenuation of patellofemoral pain symptoms in cyclists