Search Results (32)

The aim of this study was to analyze the activation of selected upper limb muscles. For the purposes of this article, we present results concerning the following muscles: triceps brachii, anterior and posterior deltoid, and trapezius in women aged 50 and above during simulated riding of the Torqway device, using surface electromyography (sEMG). The primary objective was to compare muscle activity across two movement phases: active and passive. Accordingly, the following research hypotheses were formulated: muscle activity (measured by RMS values) will be significantly higher during the active phase compared to the passive phase, and MPF (mean power frequency) values will decrease over time, indicating the onset of muscle fatigue. Additionally, the potential of surface electromyography was assessed as a diagnostic tool for evaluating ergonomics and muscle effort in the context of designing personalized mobility devices for older adults. As the study of the Torqway device represents a pioneering research effort, this publication makes a significant contribution to the biomechanical analysis of new forms of active mobility supported by wearable sensor technologies. Full article

Background: Pain manifestations as well as increased muscle tone and stiffness noted in the course of delayed-onset muscle soreness (DOMS) are reflected in altered values of the biomechanical and visco-elastic parameters of muscles. This study aimed to compare the effects of soft tissue mobilization with foam rolling and percussive massage on symptoms of DOMS induced by a standardized muscle fatigue protocol. Methods: Healthy volunteers (n = 60) were divided into three groups: FR group—foam rolling (n = 20), PM group—percussive massage (n = 20) and CON group—control/passive rest (n = 20). The fatigue protocol for the gastrocnemius muscle was carried out for development of DOMS in subsequent days. Therapeutic procedures were applied to participants for 3 consecutive days. The results of therapy were assessed by means of myotonometry, performed five times (before, three times during the treatment procedure, and after the end of the procedure). Results: Foam rolling significantly reduced the onset and duration of increased muscle tone (p = 0.006) and stiffness (p < 0.001), unlike percussive massage. The control group exhibited higher tone and stiffness after 48 h, at the peak of DOMS-related pain symptoms. Only foam rolling improved elasticity (decrement, p < 0.001), while visco-elastic properties (relaxation, creep) varied inversely with tone and stiffness. Foam rolling led to significantly lower stiffness (day 2) and reduced decrement and relaxation (day 4) compared to the control. Neither therapy was more effective than passive rest for pain relief during the observation period. Conclusions: Foam rolling and percussive massage accelerate recovery of muscle tone, stiffness, and elasticity after DOMS as compared to passive rest but offer no added benefit for pain relief. Full article

The aim of this study is to examine the biomechanical interaction between an assistive wearable exoskeleton and the human body. For this purpose, a passive exoskeleton is designed to provide support during the transition from a squatting position to standing, while also enabling the resilient components to become active during the initial and mid-swing phases of level walking. The active period can be adjusted by a slot, which triggers the activation of the resilient components when the exoskeleton’s flexion angle exceeds a critical value. This study also compares the effect of using different passive powered components in the exoskeleton. Electromyography (EMG) signals and angular velocity during human motion are collected and analyzed. Experimental results indicate that the designed assistive exoskeleton effectively reduces muscle effort during squatting/standing motion, as intended. The exoskeleton reduces the flexion/extension (x-axis) angular velocity during both squatting/standing and the swing phase of gait. The oscillation of the angular velocity curve about the y-axis during gait is larger without the exoskeleton, suggesting that the exoskeleton may introduce interference but also a stabilizing effect in certain dimensions during gait. This study provides a stronger foundation for advancing the design of both passive and active powered exoskeletons. Full article

Hip fractures represent a significant public health challenge, particularly among the elderly, due to their high incidence, morbidity, and mortality rates. This review provides a comprehensive understanding of hip fractures through clinical, biomaterial, and biomechanical perspectives. Clinically, we examined key risk factors, including age, bone mineral density, and the high prevalence of falls, which account for over 95% of hip fractures. However, current clinical tools, such as FRAX, have notable limitations in accurately assessing fracture risk in individuals due to their reliance on statistical models, the treatment of interdependent risk factors as independent, and the omission of key variables like diabetes. From a biomaterial perspective, we analyzed bone composition—specifically the balance of inorganic minerals, organic proteins, and water—and its role in determining bone strength and fracture susceptibility. Various risk factors ultimately influence this composition balance, thereby affecting bone strength. Therefore, accurately measuring bone composition may provide a more reliable assessment of hip fracture risk. Although emerging imaging technologies such as dual-energy CT and MRI show promise for in vivo assessments of bone composition, these techniques still face significant challenges and remain an active area of research. Biomechanically, we explored the forces generated during falls, noting that impact forces can vastly exceed normal physiological loads and may exploit the anisotropic properties of bone, leading to fractures even in healthy individuals with strong bones. This understanding emphasizes the critical role of fall prevention in reducing fracture risk and highlights the limitations of using fall-induced fracture incidence as a validation metric for clinical assessment tools. Lastly, we discuss preventive strategies, including passive measures like environmental modifications for individuals diagnosed with low bone strength and proactive measures such as muscle strengthening and cognitive training. While passive measures are necessary for immediate protection, proactive strategies are more effective in the long term by addressing underlying risk factors for falls and promoting sustained bone health. This interdisciplinary review underscores the need to integrate clinical, biomaterial, and biomechanical factors to improve diagnostic accuracy, prevention, and treatment strategies for hip fractures, ultimately advancing public health outcomes in aging populations. Full article

Objectives: The purpose of this study is to quantitatively evaluate the combined effects of sports massage, blood flow restriction (BFR), and cold therapy on quadriceps recovery in mixed martial arts (MMA) athletes following eccentric exercise, focusing on muscle biomechanical properties, pain, and strength. Methods: This randomized, single-blind clinical trial involved 36 men and women MMA-trained participants, divided into three groups: massage (n = 12) received massage, BFR/cool (n = 12) received combined BFR and cooling, and control (n = 12) received passive rest as a control. The fatigue protocol involved MMA fighters performing five sets of plyometric jumps on a 50 cm box until exhaustion, with 1-min breaks between sets. After that, the massage group received a 20-min massage overall using standardized techniques; BFR/cool underwent a 20-min alternating blood flow restriction (200 mmHg) and cooling treatment with ice bags on the quadriceps; and the final group served as the control group with passive rest and no intervention. Participants were assessed four times—before exercise, immediately after exercise, 24 h post-exercise (after two recovery sessions), and 48 h post-exercise (after four recovery sessions)—for perfusion unit (PU), muscle elasticity, pressure pain threshold (PPT), reactive strength index (RSI), and total quality recovery (TQR). Results: The statistical analysis revealed significant effects of both massage and BFR/cooling interventions across key recovery outcomes, with large effect sizes for time-related changes in RSI (p < 0.0001; η² = 0.87), elasticity (p < 0.0001; η² = 0.84), and PPT (p < 0.0001; η² = 0.66). Notably, post-exercise 48 h values for RSI, elasticity, PU, and TQR were significantly improved in both the massage and BFR/cool groups compared to control (p < 0.05)), while no significant group differences were observed for PPT. Conclusions: The study concludes that both massage and combined blood flow restriction with cooling interventions significantly enhance post-exercise recovery—improving muscle perfusion, elasticity, reactive strength, and perceived recovery—compared to passive rest. Full article

(1) Background: Peripheral artery disease (PAD) and related conditions significantly impair walking ability. Previous studies demonstrated that passive lightweight exosuits can improve walking biomechanics. However, most of these devices focus on assisting hip flexion. The aim of this study was to investigate the effects of flexion and extension assistance on joint kinetics and muscle activation. We hypothesized that there would be an optimal combination of flexion and extension assistance for measured parameters. (2) Methods: Four patients with PAD and six healthy individuals walked on a treadmill while wearing a passive exosuit with adjustable hip flexion and extension assistance. Lower limbs’ power, moment, and muscle activation were recorded. (3) Results: We found that passive hip assistance effectively reduced hip kinetics in both healthy and PAD participants. We also found different effects between the groups, with the PAD group utilizing the exosuit to reduce plantarflexion kinetics and gastrocnemius activity. (4) Conclusions: These findings suggest that patients with PAD can leverage the exosuit to ameliorate impairment-specific deficits. Future research should explore more real-world applicability of passive exosuits. Full article

Military operators performing vehicle maintenance work are at times subject to onerous tasks such as lifting and transporting heavy loads, potentially in confined spaces. As this presents a risk for developing musculoskeletal injury, it is of interest to evaluate if a passive back-support exosuit could help reduce back muscle load. This study used wireless electromyographic (EMG) sensors to evaluate the biomechanical effects of exosuits during lifting tasks. Ten male participants performed military-relevant lifting tasks with and without wearing the exosuit in randomised orders. The lifting tasks included (1) vertical lifts of different weights (15 and 25 kg) onto different platform heights (0.5 m and 1.2 m) and (2) a lateral walk task across 4 m in a confined space while carrying a 39 kg weight. EMG activities of three back muscle groups (longissimus, iliocostalis, and multifidus) were measured and normalised to maximal isometric back extension tasks. The results showed no significant differences in muscle activation between conditions in most lifting tasks, except for a reduction in longissimus muscle activity when using the exosuit during lateral walking. Individual responses varied substantially, with some participants showing reduced muscle activity, while others did not. These findings highlight the challenges in implementing exosuits in reducing back muscle load during military lifting tasks. While passive back-support exosuits may provide benefits to some users, their effectiveness varies among individuals and may be task-dependent. Full article

Knowledge of realistic loads is crucial in the engineering design process of medical devices and for assessing their interaction with the spinal system. Depending on the type of modeling, current numerical spine models generally either neglect the active musculature or oversimplify the passive structural function of the spine. However, the internal loading conditions of the spine are complex and greatly influenced by muscle forces. It is often unclear whether the assumptions made provide realistic results. To improve the prediction of realistic loading conditions in both conservative and surgical treatments, we modified a previously validated forward dynamic musculoskeletal model of the intact lumbosacral spine with a muscle-driven approach in three scenarios. These exploratory treatment scenarios included an extensible lumbar orthosis and spinal instrumentations. The latter comprised bisegmental internal spinal fixation, as well as monosegmental lumbar fusion using an expandable interbody cage with supplementary posterior fixation. The biomechanical model responses, including internal loads on spinal instrumentation, influences on adjacent segments, and effects on abdominal soft tissue, correlated closely with available in vivo data. The muscle forces contributing to spinal movement and stabilization were also reliably predicted. This new type of modeling enables the biomechanical study of the interactions between active and passive spinal structures and technical systems. It is, therefore, preferable in the design of medical devices and for more realistically assessing treatment outcomes. Full article

Knee joint stability comprises passive (ligaments), active (muscles), and static (articular congruency) contributors. The stability of total knee replacement (TKR) implants can be assessed pre-clinically using joint motion simulators. However, contemporary testing methods with these platforms do not accurately reproduce the biomechanical contributions of passive stabilizers, active stabilizers, or both. A key component of joint stability is therefore missing from laxity tests. A recently developed muscle actuator system (MAS) pairs the quadriceps-driven motion capabilities of an Oxford knee simulator with the prescribed displacements and laxity testing methods of a VIVO robotic knee testing system, which also includes virtual ligament capabilities. Using a TKR-embedded non-cadaveric joint analogue, TKR with two different virtual ligament models were compared to TKR with no active ligaments. Laxity limits were then obtained for both developed models using the conventional style of laxity testing (the VIVO’s force/displacement control) and compared with results obtained under similar conditions with the MAS (gravity-dependent muscle control). Differences in joint control methods identified the need for muscle forces providing active joint stability, while differences in the effects of the virtual ligament models identified the importance of physiological representations of collateral ligaments during testing. Full article

Background/Objectives: This study explores an optimization-based strategy for muscle force estimation by employing simplified cost functions integrated with physiologically relevant muscle models. Methods: Considering elbow flexion as a case study, we employ an inverse-dynamics approach to estimate muscle forces for the biceps brachii, brachialis, and brachioradialis, utilizing different combinations of cost functions and muscle constitutive models. Muscle force generation is modeled by accounting for active and passive contractile behavior to varying degrees using Hill-type models. In total, three separate cost functions (minimization of total muscle force, mechanical work, and muscle stress) are evaluated with each muscle force model to represent potential neuromuscular control strategies without relying on electromyography (EMG) data, thereby characterizing the interplay between muscle models and cost functions. Results: Among the evaluated models, the Hill-type muscle model that incorporates both active and passive properties, combined with the stress minimization cost function, provided the most accurate predictions of muscle activation and force production for all three arm flexor muscles. Our results, validated against existing biomechanical data, demonstrate that even simplified cost functions, when paired with detailed muscle models, can achieve high accuracy in predicting muscle forces. Conclusions: This approach offers a versatile, EMG-free alternative for estimating muscle recruitment and force production, providing a more accessible and adaptable tool for muscle force analysis. It has profound implications for enhancing rehabilitation protocols and athletic training, not only broadening the applicability of muscle force estimation in clinical and sports settings but also paving the way for future innovations in biomechanical research. Full article

Supersonic shear image (SSI) ultrasound elastography provides a quantitative assessment of tissue stiffness using the velocity of shear waves. SSI’s great potential has allowed researchers in fields like biomechanics and muscle physiology to study the function of complex muscle groups in different conditions. The aim of this study is to use SSI to investigate changes in the stiffness of the vastus lateralis (VL) muscle as a consequence of passive elongation, isometric contraction, and repeated muscle activity. In a single session, 15 volunteers performed a series of isometric, concentric, and eccentric contractions. SSI images were collected from the VL to assess its stiffness before and after the contractions and at various knee angles. Two-way within-subjects ANOVA was used to test the effects of muscle contraction type and knee angle on VL stiffness. Linear regression analysis was employed to assess the relationship between muscle stiffness and the intensity of isometric contractions. After maximal contractions, VL stiffness increased by approximately 10% compared to baseline values, and following maximal isometric (p < 0.01) and eccentric contractions (p < 0.05). Yet, there was no change in VL shear modulus at the end of concentric contractions. The relaxed VL shear modulus increased with knee flexion both before and after the knee extensor contractions (p < 0.001). A linear relationship between the shear modulus and the degree of isometric contraction was observed, although with notable individual variation (R² = 0.125). Maximal contractile activity produces modest increases in relaxed muscle stiffness. The SSI-measured shear modulus increases linearly with the degree of isometric contraction. Full article

Background and Objectives: Management of acetabular fractures is aimed at anatomically reducing and fixing all displaced or unstable fractures, as the accuracy of fracture reduction has been demonstrated to strongly correlate with clinical outcomes. However, there is a noticeable gap in the literature concerning the perioperative and postoperative care of patients with acetabular fractures, which ultimately can be potential risk factors for adverse outcomes and permanent disabilities. This study aimed to systematically review the available literature regarding rehabilitation practices, including weight-bearing protocols, across time points in surgically treated acetabular fracture patients and correlate these practices with functional outcomes. Methods: We systematically reviewed the Medline and PubMed databases and the Cochrane Central Register of Controlled Trials in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The inclusion criteria were studies with adult patients (19+ years), publications from the last 10 years, articles focusing on rehabilitation or mentioning any aspect related to rehabilitation (such as weight-bearing or muscle training), and describing the surgical management of acute, isolated acetabulum fractures. Specific information was collected, including the fracture classification, time to surgery, surgical approach, surgical time, blood loss, fixation strategy, quality of reduction, postoperative rehabilitation protocol, complication rate, type(s) of complication, and outcome measurement(s). The choice(s) of surgical approach, surgical time, blood loss, and fixation strategy were stratified based on the fracture classification. The complication rate and type(s) of complication were calculated for all studies. Fractures were classified based on the Letournel classification. Results: A total of 494 articles were identified from the initial search, of which 22 (1025 patients) were included in the final review. The most common rehabilitation protocol favored isometric quadriceps and abductor strengthening exercises starting on the first postoperative day, with passive hip movement at 1–3 days postoperatively and active hip movement ranging from the first postoperative day to 4 weeks postoperatively. Partial weight-bearing with a walker or a pair of crutches was permitted from 1 to 12 weeks after surgery, and full weight-bearing was allowed depending on the patient’s general condition and fracture healing state (generally at the end of 3 months). In only three studies did the patients start bearing weight in the early postoperative period (≤1 week). Meta-regression analysis was not performed due to the discrepancy between studies that reported a weight-bearing protocol ≤1 week and >1 week postoperatively. Conclusions: Our study suggests that an accelerated postoperative rehabilitation protocol, including early permissive weight-bearing, does not appear to increase the risk of loss of reduction or the rate of complications after surgical treatment of acetabular fractures. However, a proper meta-analysis was not possible, and the heterogeneity of the included studies did not allow us to conclude anything about the potential biomechanical and clinical benefits nor the negative effects related to this rehabilitation regimen in terms of functional results. There is an inconsistent use of PROMs for objectively calculating the effect size of the accelerated protocol compared with restricted weight-bearing regimes. We pose the need for higher-level evidence to proof our hypothesis. Full article

Levosimendan’s calcium sensitizing effects in heart muscle cells are well established; yet, its potential impact on skeletal muscle cells has not been evidently determined. Despite controversial results, levosimendan is still expected to interact with skeletal muscle through off-target sites (further than troponin C). Adding to this debate, we investigated levosimendan’s acute impact on fast-twitch skeletal muscle biomechanics in a length-dependent activation study by submersing single muscle fibres in a levosimendan-supplemented solution. We employed our MyoRobot technology to investigate the calcium sensitivity of skinned single muscle fibres alongside their stress–strain response in the presence or absence of levosimendan (100 µM). While control data are in agreement with the theory of length-dependent activation, levosimendan appears to shift the onset of the ‘descending limb’ of active force generation to longer sarcomere lengths without notably improving myofibrillar calcium sensitivity. Passive stretches in the presence of levosimendan yielded over twice the amount of enlarged restoration stress and Young’s modulus in comparison to control single fibres. Both effects have not been described before and may point towards potential off-target sites of levosimendan. Full article

Metabolic cost plays a critical role in gait biomechanics, particularly in rehabilitation. Several factors influence metabolic cost during walking. Therefore, this study aimed to examine the relationship between metabolic cost and muscle activity, focusing on the frequency of EMG signals during walking. We recruited nine participants (five male and four female, age range 20–48 years) who walked for four minutes at six different speeds (ranging from 1.8 to 5.9 mph). EMG data were collected from the dominant lower leg muscles, specifically the lateral gastrocnemius (GAS-L) and the anterior tibialis (AT). Oxygen respiration was measured using open-circuit spirometry. Energy expenditure was estimated as the cost of transport (COT). The EMG data were analyzed using frequency domain features, such as the area under the curve of power spectral density (PSD-AUC) and the maximal distance between two points before and after the peak of the power spectral density curve (MDPSD). The results indicated that PSD-AUC is a better measure than MDPSD for understanding the relationship between activation frequency and COT. PSD-AUC demonstrated an increasing curvilinear trend (R² = 0.93 and 0.77, second order polynomial fit), but the AT displayed higher variability. MDPSD exhibited more nonlinearity (R² = 0.17–28, second order polynomial fit), but MDPSD demonstrated statistically significant differences (p < 0.05, t-test independent) in frequency between the GAS-L (64–237 Hz) and AT (114–287 Hz) during slow walking. Additionally, the relationship between COT and PSD-AUC revealed a U-shaped curve, suggesting that high COT is a function of both active and passive dynamics during walking. These findings will be valuable in rehabilitating individuals who suffer from gait-related disorders, especially those related to muscle inefficiency. Full article

Patients with aggressive cancer, e.g., gastrointestinal cancer, are prone (≥50% chance) to developing cancer cachexia (CC). Little is known about the effects of CC on the biomechanical function of muscle. A promising prevention strategy was found in the form of a multi-modal therapy combining mild resistance exercise (e.g., whole-body electro-myostimulation, WB-EMS) and a protein-rich diet. In a previous study of ours, this was effective in counteracting the loss of muscle mass, yet a systematic and comprehensive assessment of active and passive single muscle fibre functions was so far absent. This pilot study investigated the biomechanical function of single muscle fibres (rectus abdominis) from the biopsies of conventionally treated (pre-)cachectic cancer ((pre-)CC) patients (m = 9), those receiving the multi-modal therapy comprising WB-EMS training and protein-rich nutrition (m = 3), and a control group (m = 5). Our findings not only align with previous findings showing the absolute force loss in CC that is accelerated by atrophy but also speak in favour of a different, potentially energy- and Ca²⁺-homeostasis-related effect that compromises muscle contraction (F ~0.9 mN vs. F ~0.6 mN in control patients). However, myofibrillar Ca²⁺ sensitivity and the quality of contraction were unaltered (pCa50: 5.6–5.8). Single fibres from the (pre-)CC patients receiving WB-EMS training and protein supplementation were significantly more compliant (p < 0.001 at ≥130% of resting length L₀). Those fibres displayed a similar softness to the ones from the control patients (axial compliance ~15 m/N at ≥130% L₀), while single fibres from the patients with (developing) cachexia were significantly stiffer (axial compliance ~7 m/N, p < 0.001 at ≥130% L₀). Adjuvant multi-modal therapy (WB-EMS training and nutritional support) contributes to maintaining the axial compliance of single fibres and potentially improves the quality of life for patients at risk of developing CC. Full article