The effects of 12 weeks of walking with and without blood flow reduction on bone turnover markers in college-aged women

Walking while reducing blood flow to and from the working muscles has been shown to result in strength gains and increased muscle cross-sectional area (MCSA) in young men and older adults. However, little is known about the effects of this type of novel exercise on bone metabolism and bone health. PURPOSE: To determine the effects of 12 weeks of low-intensity treadmill walking with and without blood flow restriction (BFR) on serum markers of bone metabolism in college-aged women. Secondary objectives were to examine changes in thigh and calf MCSA, muscle strength, aerobic capacity, and bone characteristics of the tibia following the intervention. METHODS: Thirty-one young women, aged 18 to 30 years, were randomly assigned to one of three groups: low-intensity treadmill walking control (WALK) (n=10), low-intensity treadmill walking with blood flow restriction (BFR) (n-11), or a non-exercise control group (CON) (n=10). Subjects in the BFR and WALK groups walked on a treadmill at a speed associated with 45% VO2peak for up to 20 minutes four days per week for 12 weeks. The BFR group wore 5 cm wide electronically monitored elastic pressure cuffs around their upper thighs during walk training. BFR cuffs were inflated to an initial pressure of 140 mmHg for the first four weeks, and then increased by 20 mmHg at week five (160 mmHg) and again at the start of week nine (180 mmHg). The CON group was asked not to change their normal physical activity levels or dietary habits over the duration of the training period. Baseline and post-testing measurements included blood sampling for the assessment of bone-specific alkaline phosphatase (Bone ALP) and tartrate-resistant acid phosphatase isoform 5b (TRAP5b); one repetition maximum (1RM) and maximal voluntary contraction (MVC) strength testing for knee extension and flexion; graded treadmill exercise test (GXT) for the determination of VO2peak; dual energy x-ray absorptiometry (DXA) to measure areal bone mineral density (aBMD) and body compsition; and peripheral Quantitative Computed Tomography (pQCT) to measure volumetric bone mineral density (vBMD) and bone area of the tibia as well as MCSA of the thigh and calf. RESULTS: A significant group x time interaction occurred for Bone ALP (p=0.02), as serum concentrations of Bone ALP were reduced in both BFR (-5.8%) and CON (-9.7%) groups post-training. Serum levels of TRAP5b and the ratio of Bone ALP to TRAP5b did not significantly change post-training. A significant group x time interaction was found for body weight (p=0.034). However, follow up analyses failed to find post-training group differences or within group changes over time (p>0.05). After analyzing percent change in body weight from baseline, significant group differences were observed between BFR (-0.8%) and WALK (2.4%) groups (p=0.046). A significant time effect (p=0.02) and group x time interaction (p=0.002) was observed for MCSA at the tibia 66% site. Follow up analyses revealed that MCSA significantly increased from baseline in both BFR (1.8%) and WALK (3.6%) groups (p<0.05). Significant time effects were found for MVC knee extension strength at joint angles of 30 degrees (p=0.02) and 60 degrees (p=0.004), with no differences between groups. A significant group x time interaction occurred for 1RM knee extension strength (p=0.014), with follow up analysis revealing a significant (p=0.026) increase in strength in the BFR group (4.5%) post-training. Significant main effects for time were found for trabecular bone content (p=0.036) and trabecular vBMD (p=0.024) at the tibia 4% site, both of which decreased over the study duration. Significant time effects were also found for total bone content (p=0.036) and SSI (p=0.011) at the tibia 38% site as well as total bone content (p=0.043), total vBMD (p=0.029), total bone area (p=0.001), periosteal circumference (p=0.002), and endosteal circumference at the 66% site. Total vBMD at the 66% site decreased post-training, whereas the other variables with significant time effects increased over the study duration. CONCLUSION: Twelve weeks of walking with BFR resulted in reduced levels of bone formation with no change in bone resorption in young women. Additionally, BFR walking resulted in favorable neuromuscular changes

Electromyographic Analysis of Hip and Knee Exercises: a Continuum from Early Rehabilitation to Enhancing Performance

Introduction: Muscles around the hip and knee regions work in unison within the kinetic chain to produce functional movements. After a musculoskeletal injury, a progressive programme of rehabilitation exercises should be completed in order to return the athlete to full function. Aims: The primary aim was to identify a progressive continuum of lower limb exercises. A secondary aim was to analyse the muscle ratios between the vastus medialis oblique and vastus lateralis, along with the hamstrings to quadriceps ratio and the gluteus maximus to biceps femoris ratio. Objectives: Electromyography (EMG) was used to monitor the activity of the hip and knee muscles during twenty rehabilitation exercises. The normalised data was used to identify a continuum of exercises, based on the extent to which each muscle was activated. The muscle ratios were also calculated, allowing the identification of a scale of exercises to preferentially activate certain muscles. Subjects: Eighteen physically active volunteers participated in the study (males: n = 9, females: n = 9, mean ± standard deviation, age: 20 ± 1.3 years; height: 168.1 ± 9.7 cm; mass: 64.1 ± 9.8 kg). Method: Surface EMG was used to measure the muscle activity of the gluteus maximus, gluteus medius, biceps femoris, rectus femoris, vastus medialis oblique and vastus lateralis during exercises which ranged between a straight leg raise and a weighted squat. The exercises were performed in a randomised order and three trials were performed of each. The muscle activity was normalised to a maximal voluntary isometric contraction specific for each muscle. The muscle ratios were calculated using specific equations. Results: The counter movement jump and single-leg vertical jump frequently resulted in the production of the greatest EMG activity for each of the muscles, whilst the mini squat produced minimal muscle activity across all of the muscles. The bridging exercises activated the quadriceps to the least extent, resulting in these exercises producing the greatest hamstrings to quadriceps ratio. For the vasti ratio, the single-leg squat to 60° of knee flexion produced the greatest results. The step up exercise produced the highest gluteus maximus to biceps femoris ratio. Conclusions: The continuum of exercises was identified for the activity of each muscle in order to aid clinicians by providing a guide from non weight bearing exercises through to functional jumps. This will ensure exercises are performed at the correct stage of rehabilitation to continually bring about muscular adaptations

Translating Data from the Laboratory into Simulation: A Computational Framework for Subject-Specific Finite Element Musculoskeletal Simulation

Computational modeling is a powerful tool which has been used to inform decisions made by engineers, scientists, and clinicians for decades. Musculoskeletal modeling has emerged as a computational modeling technique used to understand the interaction between the body and its surroundings. There are several common approaches used for musculoskeletal modeling which take advantage of different model formulations to obtain information of interest. Unfortunately, models with different joint formulations inherit disparities in representations of ligament, muscle, and cartilage at joints of interest. These differences affect the way the joint functions and limit the insight it provides through computational analysis. Musculoskeletal models with high fidelity joint representations in a finite element framework have become increasingly viable in recent years, but three challenges limit progression: model personalization, modeling infrastructure, and computational efficiency. The goal of musculoskeletal modeling is almost entirely to understand the motion of the body, the mechanics of the joints, and the strain on the tissues in subjects performing various activities. These interests require models that act as the subject’s body would – a very complex task. Improving on methods in model personalization for calibrating joint strength, soft tissue response, and modeling geometry will continue to drive this work toward true subject specificity. Previously, software has been released which provides a modeling infrastructure for musculoskeletal modeling using rigid body dynamics. No such framework exists to build and perform musculoskeletal modeling with high fidelity joint representations in a finite element environment. A computational framework which provides methods to scale models and estimate joint kinematics and muscle forces directly from laboratory data would improve the accessibility and usability of these complex techniques. Developing tools which promote computational efficiency and manage effective parallelization of simulation and optimization will help improve the usability of musculoskeletal finite element modeling. The purpose of this work was to improve upon methods in musculoskeletal finite element modeling by developing novel techniques to evolve the current state-of-the-art in this area of research. Specifically, the first study calibrated the knee strength response of a musculoskeletal model of the lower limb to healthy data collected from subjects. The model was then used in the second study to perform concurrent estimation of muscle forces and tissue strain in subjects performing two activities. The third study considered markerbased motion and compared it to kinematics obtained from stereo radiography-based bone tracking. As part of this study a new set of polynomial splines describing the motion in 5 degrees of freedom at the knee were provided. Lastly, a computational framework was developed which served to scale a generic musculoskeletal finite element model and perform estimations of joint kinematics and muscle forces directly from laboratory data. The goal of this dissertation was to increase the accessibility of a powerful modeling approach to researchers around the globe by developing and advancing techniques which improve the usability of these methods