Squatting is a common strength training exercise used for rehabilitation, fitness training, and in preparation for competition. Knowledge about the loading and the motion of the back during the squat exercise is crucial to avoid overuse or injury. The aim of this study was the measurement and comparison of the kinematics of the lower leg, trunk, and spine during unrestricted and restricted (knees are not allowed beyond toes) squats. A total of 30 subjects performed unrestricted and restricted barbell squats with an extra load of 0, 25, and 50% bodyweight. Motion was tracked using a 12-camera Vicon system. A newly developed marker set with 24 trunk and 7 pelvic markers allowed us to measure 3D segmental kinematics between the pelvic and the lumbar regions, between the lumbar and the thoracic segments, and the sagittal curvatures of the lumbar and the thoracic spine. In an unrestricted squat, the angle of the knee is larger and the range of motion (ROM) between the lumbar and the thoracic segments is significantly smaller compared with a restricted squat (p < 0.05). The studied subjects showed significantly increased ROM for thoracic curvature during restricted squats. The unrestricted execution of a squat leads to a larger ROM in the knee and smaller changes in the curvature of the thoracic spine and the range of smaller segmental motions within the trunk. This execution in turn leads to lower stresses in the back. To strengthen the muscles of the leg, the unrestricted squat may be the best option for most people. Thus, practitioners should not be overly strict in coaching against anterior knee displacement during performance of the squat.

Kinematics of the trunk and the lower extremities during restricted and unrestricted squats.

Flexible and highly sensitive pressure sensors have versatile biomedical engineering applications for disease diagnosis and healthcare. The fabrication of such sensors based on porous structure composites usually requires complex, costly, and nonenvironmentally friendly procedures. As such, it is highly desired to develop facile, economical, and environment-friendly fabrication strategies for highly sensitive lightweight pressure sensors. Herein, a novel design strategy is reported to fabricate porous composite pressure sensors via a simple heat molding of conductive fillers and thermoplastic polyurethane (TPU) powders together with commercially available popcorn salts followed by water-assisted salt removal. The obtained TPU/carbon nanostructure (CNS) foam sensors have a linear resistance response up to 60% compressive strain with a gauge factor (GF ) of 1.5 and show reversible and reproducible piezoresistive properties due to the robust electrically conductive pathways formed on the foam struts. Such foam sensors can be potentially utilized for guiding squatting exercises and respiration rate monitoring in daily physical training.

Design Strategy for Porous Composites Aimed at Pressure Sensor Application

A comprehensive assessment of the musculoskeletal system: The CAMS-Knee data set.

Soft tissue artefact affects the determination of skeletal kinematics. Thus, it is important to know the accuracy and limitations of kinematic parameters determined and modelled based on skin marker data. Here, the curvature angles, as well as the rotations of the lumbar and thoracic segments, of seven healthy subjects were determined in the sagittal plane using a skin marker set and compared to measurements taken in an open upright MRI scanner in order to understand the influence of soft tissue artefact at the back. The mean STA in the flexed compared to the extended positions were 10.2±6.1 mm (lumbar)/9.3±4.2 mm (thoracic) and 10.7±4.8 mm (lumbar)/9.2±4.9 mm (thoracic) respectively. A linear regression of the lumbar and thoracic curvatures between the marker-based measurements and MRI-based measurements resulted in coefficients of determination, R2, of 0.552 and 0.385 respectively. Skin marker measurements therefore allow for the assessment of changes in the lumbar and thoracic curvature angles, but the absolute values suffer from uncertainty. Nevertheless, this marker set appears to be suitable for quantifying lumbar and thoracic spinal changes between quasi-static whole body postural changes.

/pdf/soft-tissue-artefacts-of-the-human-back-comparison-of-the-sguxp4olzq.pdf

Soft Tissue Artefacts of the Human Back: Comparison of the Sagittal Curvature of the Spine Measured Using Skin Markers and an Open Upright MRI

The aim of this study was to systematically review the current literature on the electromyographic (EMG) activity of six core muscles (the rectus abdominis, the internal and external oblique, the transversus abdominis, the lumbar multifidus, and the erector spinae) during core physical fitness exercises in healthy adults. A systematic review of the literature was conducted on the Cochrane, EBSCO, PubMed, Scopus, and Web of Science electronic databases for studies from January 2012 to March 2020. The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were used. The inclusion criteria were as follows: (a) the full text available in English; (b) a cross-sectional or longitudinal (experimental or cohorts) study design; (c) the reporting of electromyographic activity as a percentage of maximum voluntary contraction (% MVIC), millivolts or microvolts; (d) an analysis of the rectus abdominis (RA), transversus abdominis (TA), lumbar multifidus (MUL), erector spinae (ES), and the internal (IO) or external oblique (EO); (e) an analysis of physical fitness exercises for core training; and (f) healthy adult participants. The main findings indicate that the greatest activity of the RA, EO, and ES muscles was found in free-weight exercises. The greatest IO activity was observed in core stability exercises, while traditional exercises showed the greatest MUL activation. However, a lack of research regarding TA activation during core physical fitness exercises was revealed, in addition to a lack of consistency between the studies when applying methods to measure EMG activity.

https://www.mdpi.com/1660-4601/17/12/4306/pdf

Core Muscle Activity during Physical Fitness Exercises: A Systematic Review

Strength training exercises, require a specific joint range of motion and muscle-specific loading to avoid injury and allow adaptation of tissue. The purpose of this study was to design suitable strength training exercises for the hip abductor muscles based on predicted joint loading and motion. Using Opensim modeling, hip abduction/adduction movement was combined with internal/external rotation of the hip and an external force that was applied to the foot. The direction of the force was systematically rotated to mimic a change of the position towards the cable pulley system. M. gluteus medius was divided into an anterior and a posterior part. It was not possible to find a single exercise that allowed the training of the anterior and the posterior part simultaneously with a muscle activation >50%. Herein, it has been shown that modeling can be used to design strength-training exercises.

/pdf/design-of-strength-exercises-for-the-abductor-muscles-using-4oibkigm61.pdf

Design of strength exercises for the abductor muscles using musculoskeletal modeling

Simulated muscle forces provide crucial knowledge for rehabilitation and training exercise design. To accurately simulate the internal loading conditions, input kinematics of the skeletal structures without soft tissue artefact (STA) are required. The aim of this study was to evaluate the ability of two numerical approaches to reduce STA for squat kinematics. Squat repetitions of 6 elderly subjects were examined using skin markers and video-fluoroscopy. Kinematic analysis was performed with a segmental and musculoskeletal simulation approach and compared to fluoroscopic data. The averaged RMS errors relative to the maximum knee range of motion were 8.8%, 32% and 49% for flexion/extension, ab-/adduction, and internal/external rotation, respectively. Skin marker based underestimation of the flexion angle could be corrected with a linear factor of 1.15.

/pdf/soft-tissue-artefacts-cause-an-underestimation-in-knee-yr0an3fhhb.pdf

Soft tissue artefacts cause an underestimation in knee flexion angle in skinmarker based squat simulations

Back extension (BE) is a strength exercise for training the dorsal trunk and hip muscles. To optimise training recommendations that avoid overloading and possible injury, the aim of this study was to determine the loading conditions and the influence of different execution forms of BE on spine, hip and knee ranges of motion (RoMs), joint moments and muscle activity. The kinematics, kinetics and muscle activity (EMG) of two execution types (BEh: dynamic hip, BEs: dynamic spine) and two versions (one-legged and two-legged) of BE were measured in 16 subjects. RoMs and external joint moments were calculated using an inverse dynamics approach and analysed with a linear mixed model. Although lumbar spine flexion was observed in both execution types, thoracic spine flexion predominantly occurred during BEs, whereas thoracic spine extension was observed during BEh. Larger maximal back and hip moments were observed for BEh than for BEs. The activity of the dorsal back and hip muscles, as observed using EMG, was increased for one-legged executions. To strengthen the hips and lower back, BEh seem to be more efficient due to the higher moments, with higher or similar RoMs in the hip and lower back. One-legged BEs seem to provide an effective training for the hamstrings and hip regions without subjecting the spine to excessive loading, possibly promoting this as an effective exercise during training and rehabilitation.

/pdf/loading-conditions-in-the-spine-hip-and-knee-during-48vljpaa7f.pdf

Loading conditions in the spine, hip and knee during different executions of back extension exercises.

To ensure an efficient and targeted adaptation with low injury risk during strength exercises, knowledge of the participant specific internal loading conditions is essential. The goal of this study was to calculate the lower limb muscles forces during the strength exercises deadlifts, goodmornings and splits squats by means of musculoskeletal simulation. 11 participants were assessed performing 10 different variations of split squats by varying the step length as well as the maximal frontal tibia angle, and 13 participants were measured performing deadlift and goodmorning exercises. Using individualised musculoskeletal models, forces of the Quadriceps (four parts), Hamstrings (four parts) and m. gluteus maximus (three parts) were computed. Deadlifts resulted highest loading for the Quadriceps, especially for the vasti (18–34 N/kg), but not for the rectus femoris (8–10 N/kg), which exhibited its greatest loading during split squats (13–27 N/kg) in the rear limb. Hamstrings were loaded isometrically during goodmornings but dynamically during deadlifts. For the m. gluteus maximus, the highest loading was observed during split squats in the front limb (up to 25 N/kg), while deadlifts produced increasingly, large loading over large ranges of motion in hip and knee. Acting muscle forces vary between exercises, execution form and joint angle. For all examined muscles, deadlifts produced considerable loading over large ranges of motion, while split squats seem to be highly dependent upon exercise variation. This study provides key information to design strength-training programs with respect to loading conditions and ranges of motion of lower extremity muscles.

/pdf/towards-evidence-based-strength-training-a-comparison-of-4e34hqs27u.pdf

Towards evidence based strength training: a comparison of muscle forces during deadlifts, goodmornings and split squats

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Design of strength exercises for the abductor muscles using musculoskeletal modeling

Soft tissue artefacts cause an underestimation in knee flexion angle in skinmarker based squat simulations

Loading conditions in the spine, hip and knee during different executions of back extension exercises.

Towards evidence based strength training: a comparison of muscle forces during deadlifts, goodmornings and split squats