Search Results (98)

Aging induces sarcopenia and reduces bone mineral density, altering body composition. These modifications contribute to physical decline, increase non-communicable disease risk and increase the likelihood of hospitalization, thereby representing a substantial public health burden. In this study, we assessed the effects of isometric training with neuromuscular electrical stimulation conditioning contractions (ISO-NMES) and dynamic resistance training (DRT) on physical and functional capacities. Moreover, we investigated the impact of ISO-NMES training on the force and power of the trained and untrained leg. Eighteen sessions of ISO-NMES training for knee extensors were performed by 10 older adults (age: 70.1 ± 4.9 years; ISO-NMES group). The DRT group (n = 12; age: 70.5 ± 2.8 years) performed 18 sessions of dynamic resistance training at a local fitness center. Maximum voluntary contraction (MVC) and peak power (P) of lower limbs as well as functional capacities assessed with the 5 Sit to Stand, Timed Up and Go and 6 Minutes Walking Tests were examined in both groups before and after the related training protocols. At the end of the training period, only the ISO-NMES group had improved MVC (+30.4%, p < 0.001) and bilateral force (ISO-NMES: +6.3%, p = 0.032). Moreover, both groups had significantly improved functional capacities. Finally, in the ISO-NMES group, MVC, force and power significantly increased in both legs with a greater effect for MVC in the trained than untrained leg (+30.4 vs. +13.5%, p < 0.001). These findings suggest that ISO-NMES training was an effective strategy to improve physical and functional capacities in older adults. Thus, it could be considered as a potential intervention, particularly when the mobility to perform physical training is limited. Full article

Aim: This study examined how load size and symmetry affect trunk muscle activation patterns, vertical ground reaction forces, and estimated lumbar spine compression during overground walking in individuals with chronic low back pain (CLBP) and those without symptoms. Methods: Thirty male participants (15 with CLBP, 15 controls; ages 23–28 years) performed walking tests under four load conditions: symmetric and asymmetric carriage at 10% and 20% of body weight. Bilateral surface electromyography measured activation from seven trunk muscles (rectus abdominis, external oblique, internal oblique, latissimus dorsi, lumbar erector spinae, multifidus) and the thoracolumbar fascia region, normalized to maximum voluntary isometric contractions (%MVIC). Force plates recorded vertical ground reaction forces synchronized with heel-strike events. A repeated-measures ANOVA with Bonferroni corrections was used to analyze the effects of load configuration and magnitude. Results: Asymmetric loading at 20% body weight caused significantly higher peak vertical ground reaction forces compared to symmetric loading (mean difference = 47.3 N, p < 0.001), with a significant interaction between load magnitude and configuration (p = 0.004, ηp² = 0.26). Participants with CLBP showed consistently higher trunk muscle activation throughout the gait cycle (peak: 37% MVIC vs. 30% MVIC in controls; p < 0.001, d = 1.68), with maximum recruitment at shorter muscle lengths and 24% less activation at optimal length (95% CI: 18.2–29.8%). The lumbar erector spinae and multifidus muscles exhibited the highest activation during asymmetric 20% loading in CLBP participants (0.282 and 0.263%MVIC, respectively), indicating compensatory neuromuscular strategies. Conclusion: Asymmetric load carriage creates disproportionately high mechanical and neuromuscular demands, effects that are greatly amplified in individuals with CLBP. These findings support rehabilitation strategies that improve load distribution and restore motor control, thereby reducing compensatory strain and enhancing trunk stability. Full article

Objectives: Shoulder joint strength and muscle activation during overhead reaching are critical for ergonomic task design, rehabilitation, and exoskeleton support. The objective of this study was to characterize maximum shoulder torque and flexor muscle activation profiles across functional elevation angles in healthy adult males. Methods: A total of 14 healthy male participants performed maximum voluntary isometric contractions at eight arm elevation angles (90–160°, sagittal plane, and standing). Shoulder torque was measured using a calibrated force sensor and normalized to each participant’s overall maximum. Electromyography (EMG) was recorded from the anterior deltoid, medial deltoid, biceps brachii, and clavicular pectoralis major; EMG for the medial deltoid, biceps brachii, and pectoralis major was normalized to muscle-specific isometric MVCs, whereas the anterior deltoid was normalized to the peak value at 90° during the main task. All EMG signals were smoothed using a 0.5 s RMS-based moving average window. Linear regression was used to analyze the torque–angle relationship, and linear mixed-effects models were used to test EMG differences across angles. Summary statistics included mean ± SD, coefficient of variation, R², p-values (significance threshold: p < 0.05), Cohen’s d, and 95% confidence intervals where appropriate. Results: Maximum torque declined with elevation angle (y = −0.6317x + 157.21; R² = 0.99), from 77.2 Nm at 90° to 43.2 Nm at 160°, with normalized values from 99.6% to 55.3%. Medial deltoid activation increased significantly with elevation (p < 0.001, from 87.5 ± 19.9% at 90° to 109.4 ± 25.6% at 150°), while pectoralis major declined sharply (p < 0.001, from 68.9 ± 24.2% at 90° to 19.8 ± 5.6% at 160°). Anterior deltoid and biceps brachii activations were high and showed no systematic change with angle (p = 0.37 and 0.81, respectively), remaining within approximately 95–102% and 70–85% of their reference levels across 90–160°. Normalization reduced inter-participant variability, clarifying muscle-specific trends. Conclusions: This study provides preliminary biomechanical reference values for shoulder torque and muscle activation across elevation angles in healthy males under isometric standing conditions, confirming an inverse torque–angle relationship and distinct muscle activation strategies at higher positions. These findings may inform ergonomic assessment and exoskeleton design, while recognizing that generalization to dynamic tasks and other populations requires caution. Full article

Background/Objectives: Low-cost portable load cell dynamometers allow for real-time assessment of muscular strength. This study evaluated the reliability and repeatability of the G-Force load cell system during isometric hip abduction and adduction in young physically active Chilean adults. Methods: In total, 24 participants (19 men, 5 women) performed two maximal voluntary contractions per movement, repeated after a 24 h interval. Measured variables included Peak Force, peak rate of force development (Peak RFD), RFD at 50, 100, and 200 ms (RFD50, RFD100, RFD200), and maximum jerk. Reliability was assessed using intraclass correlation coefficients (ICCs), standard error of measurement (SEM), coefficient of variation (CV%) and Bland–Altman plots. Results: Peak Force showed excellent within-day (ICC = 0.94–0.96) and high between-day reliability (ICC = 0.87–0.89; CV = 20–30%). Bland–Altman analysis indicated negligible bias for Peak Force in abduction (−6.54 N; 95% CI −19.55 to 6.47) and adduction (−17.57 N; 95% CI −37.24 to 2.09), confirming the absence of systematic error. Peak RFD, RFD50–200, and maximum Jerk showed moderate repeatability and lower between-day reliability (ICCs = 0.39–0.70; CVs = 34–57%), indicating higher variability in explosive force indices compared with maximal strength. Conclusions: The G-Force load cell reliably measures maximal isometric hip strength, while Peak RFD, RFD50–200, and maximum jerk should be interpreted cautiously. These findings support the device as a practical, low-cost tool for sports and rehabilitation, though future studies should validate dynamic indices in larger and more diverse populations. Full article

Although previous studies have examined various factors that influence biceps brachii activation, such as grip position, load, and exercise variation, to our knowledge, no prior studies have compared muscle activation during a traditional biceps curl and a Bayesian cable curl. Therefore, this study aimed to examine the differences in biceps brachii muscle activation between these two training modalities. Data from eleven volunteers (age: 25 ± 6 y; weight: 86 ± 13 kg; height: 177 ± 8 cm) were included in the analysis. Muscle activity was assessed using the normalized root mean square (RMS) values obtained from surface electromyography (sEMG). A within-subjects, counterbalanced design was utilized where all participants completed both testing conditions in a randomized order to control for potential order effects. Participants visited the laboratory and fitness center on two occasions. On the first day, anthropometric measurements were obtained, along with one repetition maximum (1-RM) for both the dumbbell biceps curl and the Bayesian curl. On the second day, participants performed an isometric maximal voluntary contraction (MVC), followed by electromyographic assessment of muscle activity during the dumbbell biceps curl and the Bayesian curl, each performed at 80% of their respective 1-RM. When the normal distribution was confirmed via the Shapiro–Wilk test (p > 0.05), a paired t-test was used for statistical analysis. On the other hand, when normality was not confirmed, the Wilcoxon test was utilized. Statistically significant differences (p = 0.003) were observed in the EMG amplitude (%) between the biceps curl (111.46 ± 26.80) and the Bayesian curl (93.39 ± 15.65) with a large effect size (d = 0.82). Based on the EMG analysis, the dumbbell biceps curl elicited significantly greater muscle activation compared to the Bayesian curl, suggesting that the conventional movement places a higher mechanical and neuromuscular demand on the biceps brachii. Full article

This study aimed to investigate if there are differences in neck strength between dental students in their fourth and fifth years, with and without neck pain. Neck muscle strength was assessed in flexion, extension, and lateral flexion to both sides using a handheld dynamometer while participants performed maximum voluntary isometric contractions with a make test procedure. Differences between groups were evaluated through a one-way analysis of variance followed by Tukey’s post hoc comparison. Forty-three students (twenty-one fourth-year and twenty-two fifth-year students) participated in the study. Fifth-year students with neck pain (P5) (n = 14) showed less strength (p = 0.018) compared to the no-pain group (NP) (n = 15) in neck flexion and lateral flexion for both sides (p < 0.001). The fourth-year symptomatic students (P4) (n = 14) showed reduced right lateral flexion strength compared to the NP group (p = 0.035). No significant differences were observed in neck extension across all groups (p = 0.085). Our research indicates a progressive decline in neck muscle strength in flexion and lateral flexion among students with neck pain over their training years. Our findings suggest that this may be linked to the increasing mechanical demands of clinical practice during training, potentially affecting muscle balance and cervical function. This pain could be associated with changes in motor behavior and reduced cervical muscle strength. Full article

Objective: This study aimed to evaluate the effects of Cistanche deserticola Y.C. Ma (CD) supplementation on muscle strength and recovery in individuals with and without resistance training experience. Methods: A randomized, double-blind, placebo-controlled trial was conducted with 48 male participants, including 24 resistance-trained and 24 untrained individuals. Participants were stratified by training status and randomly assigned to either the CD or placebo (PLAC) group. All subjects completed a standardized resistance training program three times per week for eight weeks. The CD group received 5 g of CD extract twice daily, while the PLAC group consumed a matched placebo. Assessments included one-repetition maximum (1RM) for bench press and squat, maximal voluntary isometric contraction (MVIC), and repetitions to failure (RTF). Blood biomarkers including serum testosterone, cortisol, C-reactive protein (CRP), and creatine kinase (CK) were also measured. Results: No significant differences in dietary energy intake or macro-nutrient composition were observed based on two 5-day dietary records collected before baseline testing and at the end of the intervention. Among untrained individuals, the CD group showed significantly greater improvements in 1RM bench press and squat compared with the PLAC group (p < 0.05), with MVIC and RTF also significantly increased (p < 0.01). Serum cortisol levels were reduced (p < 0.05), and significant improvements were observed in testosterone, CRP, and CK (p < 0.01). In trained individuals, CD supplementation led to significant increases in 1RM squat and MVIC (p < 0.05), along with improvements in testosterone and cortisol levels (p < 0.05) and marked reductions in CRP and CK (p < 0.01). Conclusions: Daily supplementation with 5 g of CD extract for eight consecutive weeks significantly enhanced muscle strength and endurance in males with different training backgrounds and facilitated post-exercise recovery by modulating hormonal responses and reducing stress levels and inflammation. These findings provide experimental evidence supporting the application of CD in sports nutrition. Full article

This study aimed to describe and compare the serratus anterior (SA) and latissimus dorsi (LD) muscle activity during six hypopressive exercise (HE) positions performed in open and closed kinetic chains. While previous studies analyzed abdominal and pelvic muscle activity during HE, research on scapular stabilizers like SA and LD remains underreported. Twenty-five healthy adults (mean age, 42.9 ± 8.4 years; BMI, 22.1 ± 2.4 kg/m²) with prior HE experience performed three open and three closed-chain HE positions. Surface electromyography recorded bilateral SA and LD activity, normalized to maximum voluntary isometric contraction (MVIC). SA showed greater activation than LD across all positions, with moderate activation levels (20–40% MVIC), while LD activation remained mild (<20% MVIC). Significant differences were found across positions and kinetic chain conditions. SA activation was higher during closed-chain standing (W = 41; p < 0.001; r = −0.74) and kneeling (W = 9; p < 0.001; r = −0.94), while LD activity increased significantly in the seated closed-chain position (left LD: W = 26; p < 0.001; r = −0.84; right LD: W = 20; p < 0.001; r = −0.87). These findings suggest body and kinetic chain positioning influence scapular muscle recruitment during HE. Further research is warranted to determine clinical applications. Full article

Background: Lower limb motor output contributes to determining functional performance in many motor tasks. This study investigated the effects of non-invasive spinal cord transcutaneous stimulation (scTS) applied during an exercise-based priming protocol on lower limb muscle force and power generation. Methods: Twelve young, physically active male volunteers (age: 22.7 ± 2.1 years) participated in this randomized crossover, sham-controlled study. The maximal voluntary contraction and low-level torque steadiness of knee extensors, as well as the maximal explosive extension of lower limbs, were assessed before and after the priming protocol with scTS or sham stimulation over a total of four experimental sessions. Further, characteristics of evoked potentials to scTS related to spinal circuitry excitability were assessed in the supine position before and after the scTS priming protocol. The exercise component of the ~25 min priming protocol consisted of low-volume, low- and high-intensity lower limb motor tasks. Results: scTS priming protocol tended to increase or maintain maximum isometric torque during knee extension (4.7%) as well as peak force (0.2%) and rate of force development (6.0%) during explosive lower limb extensions, whereas sham priming protocol tended to decrease them (−4.3%, −3.3%, and −15.1%, respectively). This resulted in significant interactions (p = 0.001 to 0.018) and medium–large differences between scTS and sham protocols. These findings were associated with meaningful trends of some neurophysiological variables. Conversely, priming protocols did not affect low-level torque steadiness. Conclusions: scTS counteracted the unexpected fatigue induced by the exercise-based priming protocol, supporting lower limb performance during maximal efforts. Future studies are warranted to assess the implementation of scTS with optimized exercise-based priming protocols during training and rehabilitation programmes that include high-intensity neuromuscular efforts. Full article

Background: Short sessions of isometric exercise have been shown to reduce blood pressure (BP) in normotensive and hypertensive subjects. However, there are few data in hypertensive patients with underlying ischemic heart disease (IHD). In the present study, we compared post-exercise hypotension (PEH) induced by isometric versus combined, aerobic plus dynamic resistance exercise in IHD patients. Methods: Twenty-five stable patients with established IHD and with treated hypertension were enrolled. The study had a cross-over design. All patients performed in a random order and on different days: (1) isometric exercise session (IES) consisting of bilateral knee extension, performed at 20% of maximal voluntary contraction and lasting 20 min; (2) combined exercise session (CES) including moderate-intensity continuous exercise at and dynamic resistance exercise performed at 60% of one repetition maximum, and lasting 60 min and (3) control session (no exercise). BP was measured at rest, immediately after the training and then every 15 min up to 90 min. Results: The repeated measures ANOVA analysis showed that systolic BP significantly decreased after the CES session compared to the control (F = 6.2; p 0.001) and IES (F = 4.4; p 0.004). Systolic BP significantly decreased after IES compared to the control (F = 3.6; p 0.036). Diastolic BP did not show significant changes after CES and IES compared to the control (CES vs. control: F = 2.2; p 0.142; IES vs. control (F = 2.5; p 0.062). There were no significant differences in diastolic BP changes between CES and IES (CES vs. IES: F = 1.8; p 0.156). Conclusions: We observed that CES was more effective than IES in reducing systolic BP; IES was as effective as CES in inducing diastolic PEH in hypertensive patients with underlying IHD. Full article

Background/Objectives: The aim of this study was to assess the effects of cold-water immersion (CWI) post-eccentric muscle contraction exercise on skin temperature, pain score, maximum voluntary isometric contraction (MVIC), muscle damage, and muscle mechanical properties. Methods: Twenty-seven male participants (age 20.6 ± 0.6; body mass 69.4 ± 8.1; body fat % 13.7 ± 4.3) were divided into three treatments: whole-body CWI treatment group (n = 9), lower-body CWI treatment group (n = 9), and control treatment group (n = 9). Results: MVIC did not show a significant interaction effect between group and time but demonstrated a significant main effect for time (p = 0.001). The pain scale demonstrated a significant interaction effect between group and treatment (p = 0.049), in addition to significant main effects for both time and treatment (both p = 0.001). While blood creatine kinase (CK) concentration revealed no significant interaction effect between group and time, a significant main effect was observed for time (p = 0.001). Blood lactate dehydrogenase (LDH) concentration showed both a significant interaction effect between group and time (p = 0.02) and a significant main effect for time (p = 0.001). The tensiomyography (TMG) results for Dm showed a significant interaction effect between group and treatment (p = 0.047), as well as a significant main effect for time (p = 0.001). Conclusions: Lower-body CWI is effective in reducing pain indices and blood LDH levels, a marker of muscle damage. It may serve as an effective method for preventing and minimizing pain and muscle damage, comparable to whole-body CWI. Full article

Background: Ageing is associated with a progressive decline in muscle strength, particularly in the lower limbs, which compromises functional independence. While both maximum voluntary isometric contraction (MVIC) and one-repetition maximum (1RM) are widely employed to assess muscle strength, the intra-session reliability and predictive capacity of MVIC for estimating 1RM in older women remain insufficiently explored. Objectives: This study aims to evaluate the intra-session reliability of MVIC in knee extensors, analyse its correlation with 1RM, and develop a predictive model for estimating 1RM from MVIC in older women. Methods: Using a randomised split-sample design, 82 women aged 60–69 years performed two MVIC trials and one 1RM test using a leg extension machine. Intra-session reliability was assessed by calculating the intraclass correlation coefficient (ICC), the standard error of measurement (SEM), and the minimal detectable change (MDC). Furthermore, a linear regression model was developed to predict 1RM based on MVIC. Results: MVIC demonstrated excellent intra-session reliability (ICC = 0.96, SEM = 4.3%, MDC = 11.9%), and a strong correlation between MVIC and 1RM was observed (R² = 0.618). Although the predictive equation 1RM = [(0.932 × MVIC) − 3.852] did not yield statistically significant differences between the estimated and actual 1RM values (p = 0.791), it exhibited a prediction error of 13.4%. Conclusions: MVIC is a highly reliable measure in older women and represents a practical tool for estimating 1RM. Nonetheless, its predictive accuracy is limited, highlighting the need for further studies to refine predictive models by incorporating additional variables. Full article

Surface electromyography (sEMG) is a critical tool for quantifying muscle activity and inferring biomechanical function, enabling the detection of neuromuscular deficits through the analysis of electrical potential propagation. However, the inherent variability in sEMG signal amplitude, influenced by factors such as electrode placement, equipment characteristics, and individual physiology, necessitates robust normalization techniques for accurate comparative analysis. This study investigates the reliability and effectiveness of several normalization methods in the context of bicep and tricep muscle activation during dynamic and isometric exercises: maximum voluntary contraction (MVC), submaximal voluntary contraction (SMVC), remote voluntary contraction (RVC), mean, and peak normalization. We conducted a comprehensive experimental protocol involving healthy volunteers, capturing sEMG signals during controlled bicep curls, tricep extensions, and isometric contractions. The efficacy of each normalization method was evaluated based on its ability to minimize inter-subject variability and enhance signal consistency. Specifically, while SMVC, MVC, and RVC methods exhibited generally superior performance in normalizing bicep and tricep signals, the optimal method varied depending on the task and muscle, providing consistent and reliable data for biomechanical analysis. These results underscore the importance of selecting appropriate normalization techniques to improve the accuracy of sEMG-based assessments in clinical and sports biomechanics, contributing to the development of more effective rehabilitation protocols and performance enhancement strategies. Full article

Background/Objectives: Optimal activation of the quadriceps femoris, particularly the vastus medialis, while minimizing excessive activation of the vastus lateralis, is crucial for treating knee injuries like ACL ruptures and patellofemoral pain syndrome. Restoring proper muscle balance may enhance rehabilitation outcomes, but effective strategies for modulating muscle activity remain unclear. High-velocity low-amplitude hip manipulation has shown potential to influence neuromuscular function, yet its impact on quadriceps activation during knee extension has not been well studied. Therefore, the main aim of this study is to examine the effects of a single session of high-velocity low-amplitude hip manipulation on quadriceps femoris muscle activation and maximum voluntary contraction during knee extension. Methods: This study utilizes a randomized controlled design. Thirty physically active men and women (mean age: 21.9 ± 1.7 years) were randomly assigned to either an experimental group (n = 15; receiving hip joint manipulation) or a control group (n = 15; undergoing a sham intervention). Participants in the intervention group received a treatment involving hip manipulation and short-duration traction. Muscle activity of the rectus femoris, vastus lateralis, and vastus medialis was assessed using surface electromyography before and after the intervention, while muscle performance was measured by evaluating isometric knee extension strength in the lower limb. The isometric strength test was conducted in a seated position with the knee flexed at 60 degrees in Biodex System 4. Results: This study finds that the experimental group had significantly higher vastus lateralis mean amplitude (p = 0.020; effect size = 0.186) and vastus medialis mean amplitude (p < 0.001; effect size = 0.577) of electromyography root mean square electromyography compared to the control group. The experimental group also showed greater vastus medialis max amplitude (p < 0.001; effect size = 0.435). No significant differences were noted for rectus femoris mean amplitude (p = 0.078; effect size = 0.110), vastus lateralis max amplitude (p = 0.363; effect size = 0.031), rectus femoris max amplitude (p = 0.069; effect size = 0.117), or median frequency of the raw electromyography signal across muscle groups. Conclusions: In conclusion, high-velocity low-amplitude hip manipulation significantly enhances vastus medialis activation, highlighting its potential to improve quadriceps balance. These findings support the incorporation of hip manipulation into rehabilitation protocols. Full article

This study aimed to develop new parameters for electromyography (EMG)-based muscle fatigue assessments. First, various combinations of frequency band parameters, including the high-frequency band (HFB: >95 Hz), medium-frequency band (MFB: 46–95 Hz), and low-frequency band (LFB: 15–45 Hz), were assessed to evaluate the fatigue detection performance of individual parameters during isometric muscle contractions. The experimental design involved applying three force levels (30%, 40%, and 50% of the maximum voluntary contraction) and targeting three muscles (upper trapezius, mid-deltoid, and pectoralis major) due to their relevance in shoulder load postures associated with musculoskeletal disorders. A total of 15 participants were involved in this study. The effectiveness of each parameter was assessed through response sensitivity evaluations. Through these evaluations, we confirmed that the previously mentioned individual frequency bands, along with the proposed H/(M + L) frequency band, exhibited high statistical significance and sensitivity under various experimental conditions. Specifically, our findings demonstrated that the H/(M + L) frequency band effectively assessed fatigue levels with high sensitivity and accuracy at low force levels during static isometric contractions. Overall, these results are expected to improve the accuracy of evaluations of individual shoulder muscle fatigue, thereby reducing the risk of shoulder injuries. Full article