Search Results (68)

Hamstring-to-quadriceps (H/Q) strength ratios describe knee flexor-to-extensor torque balance, but their interpretation may depend on joint angle, contraction mode, and denominator stability. This exploratory repeated-measures study examined whether angle-matched H/Q ratios obtained from isometric and isokinetic dynamometry are directly interchangeable. Fourteen healthy young adults performed maximal knee extension and flexion using a Biodex System 4 Pro. Isometric testing was conducted at 10°, 30°, 60°, 90°, and 110° of knee flexion; isokinetic testing was performed at 60°/s, 150°/s, and 300°/s, with torque extracted at matched angles. H/Q ratios were calculated as flexor torque divided by extensor torque for each angle, limb, and mode and analyzed after log transformation. In the all-angle model, log-transformed H/Q ratio showed a significant angle effect (F(4,52) = 14.60, p < 0.001, partial η² = 0.529), limb effect (F(1,13) = 5.54, p = 0.035, partial η² = 0.299), angle × mode interaction (F(12,156) = 2.78, p = 0.002, partial η² = 0.176), and angle × mode × limb interaction (F(12,156) = 2.60, p = 0.004, partial η² = 0.167). After excluding endpoint angles, the angle × mode interaction remained significant (F(6,78) = 8.60, p < 0.001, partial η² = 0.398). These findings suggest that angle-specific H/Q ratios are influenced by joint position and testing mode. Because of the small sample and absence of protocol-specific test-retest reliability, the results should be interpreted as exploratory and hypothesis-generating. Isometric and isokinetic H/Q ratios should not be treated as directly interchangeable, and endpoint ratios should be interpreted together with the underlying flexor and extensor torque values. Full article

Background/Objectives: Rigidity has been defined as an increase in muscle tone that is independent of the velocity of the stretch in Parkinson’s disease (PD). However, there is an ongoing debate about this non-velocity-dependent nature of rigidity in PD. To investigate the behaviour of axial muscle tone at different examination velocities using isokinetic dynamometry, and to determine whether trunk muscle resistance is velocity-dependent in people with PD compared with healthy controls (HCs). Methods: A cross-sectional study was conducted with HC and people with PD (I–III stages of Hoehn and Yahr and assessed by the UPDRS, Section III: motor aspects) by a senior neurologist. The trunk extension–flexion component of an isokinetic dynamometer measured axial muscle tone over a range of 50° (S: 30-50-80). The continuous passive mode with three angular speeds (30°/s, 45°/s and 60°/s) was used to assess muscle tone. Peak torque (N), work (J) and work recorded in the first and in the last third of the explored trunk range of motion were calculated (J) were registered. All these outcomes were performed within 1–3 h of the administration of anti-Parkinsonian medication (ON phase) in the PD sample. Results: People with PD (N = 36) and healthy controls (N = 20) completed the study. Our results showed largely similar behaviour in work and peak torque registered in both groups, by which, resistance measures, like peak torque, weakly increased with mobilisation speed from 30°/s to 45°/s, without reaching statistical significance, but increased from 45°/s to 60°/s, only in the flexors. No clear increase was observed in the work. Furthermore, greater torque measures in PD than controls were only observed for peak torque at 30°/s. Conclusions: Peak torque of trunk flexors–extensors tends to increase as the angular speed increases in both PD and controls. This may suggest that the (relatively slow) tested speeds were likely evaluating the non-neural component of muscle tone. This has implications for the clinical assessment of axial rigidity in PD. Full article

Ankle dorsiflexion plays a vital role in ensuring safe and effective walking post-stroke, yet the best methods for assessing it and their clinical significance are still uncertain. This research compiles the existing sensor-based technologies used to measure ankle dorsiflexion in adults who have experienced a stroke and examines how these measurements correlate with walking performance. It also compares these findings with traditional clinical evaluation methods like manual muscle testing (MMT). We conducted a systematic search of PubMed, IEEE Xplore, and the Cochrane Library (2000–2025) for both observational and experimental studies that utilized sensor-based techniques (such as handheld or isokinetic dynamometry, load cells, and proprioceptive devices) to quantify ankle dorsiflexion and reported their relationship with gait outcomes. Additionally, studies employing conventional, non-instrumented clinical grading (e.g., ankle-dorsiflexor MMT) were included if they explored the connection between ankle function and gait, although these were not included in the quantitative analysis. Eighteen studies involving 783 stroke survivors met the inclusion criteria and were evaluated using the Newcastle–Ottawa Scale. Generally, individual studies found a positive association between ankle-dorsiflexor strength and both gait speed and endurance, although some negative correlations were noted. The strength and sometimes direction of these associations varied depending on the sensing technology, dorsiflexion index, gait outcome, and stroke chronicity. Overall, the current evidence indicates a generally positive but highly variable relationship between ankle dorsiflexion measurements and gait post-stroke, emphasizing the need to identify sources of variability and to create standardized, clinically applicable sensor-based assessment protocols. Full article

Objectives: This study investigated bilateral strength asymmetry, the bilateral asymmetry index, and the bilateral deficit ratio during one-repetition maximum leg press testing performed under bilateral, unilateral, and split-load conditions and examined their associations with isokinetic knee and hip strength asymmetries. Methods: 31 resistance-trained males completed 1RM leg press tests in all loading modes, followed by isokinetic knee flexion/extension and hip extension assessments at 60°·s⁻¹. Results: The repeated measure ANOVA showed that split-load leg press had a significantly greater bilateral deficit ratio (14.29 ± 7.71%) compared to the bilateral condition (5.16 ± 9.60%, p < 0.001). Isokinetic testing showed significant inter-limb differences for knee flexion and extension but not hip extension. The bilateral strength asymmetry varied across tasks (5.17 ± 4.44% in leg press to 17.84 ± 12.40% in eccentric hip extension), while bilateral asymmetry index remained consistently lower. Bilateral strength asymmetry differed significantly across leg press conditions, whereas the bilateral asymmetry index did not. Knee flexion bilateral asymmetry index correlated with dominant and non-dominant hamstring to quadriceps ratios (respectively, r = 0.61; r = 0.37) and cross-limb flexor–extensor ratios (r = 0.42). No significant relationships were found for hip extension asymmetry. Conclusions: Split-load leg press might be used to test lower limb bilateral deficit, because it provides easily detectable deficit values. Unilateral leg press might be used to detect lateral strength differences, since it provides relation to isokinetic strength of knee flexors and extensors. Full article

Monitoring eccentric hamstring strength is critical for reducing injury risk in soccer players, yet laboratory-based technologies such as isokinetic dynamometry remain costly and impractical for field use. The purpose of this study was to examine the association and exploratory predictive relationship between variables derived from a smartphone application (My Jump Lab) and eccentric hamstring strength outputs obtained with an instrumented field device (NordBord, Vald Performance, Australia), while also quantifying their absolute agreement during the Nordic hamstring exercise (NHE). Thirty-one professional soccer players from a second-division United Arab Emirates team performed the NHE on the NordBord, while a simultaneous two-dimensional (2D) kinematic analysis was conducted using the My Jump Lab app (version 5.0 for iOS; My Jump Lab, Madrid, Spain). Pearson correlations, linear regression models, and Bland–Altman analyses were used to distinguish linear association/prediction from agreement/interchangeability. Results revealed a very large association between My Jump Lab-derived torque estimates and NordBord peak torque (r = 0.77, p < 0.001), with moderate associations for breakpoint angle (r = 0.42–0.43). A combined regression model using My Jump Lab torque and breakpoint angle explained 69.2% of the variance in NordBord torque (SEE = 15.30 N·m), although this predictive result should be interpreted as exploratory because the variables are task-specific and partly share anthropometric and mechanical determinants. Bland–Altman analysis revealed poor agreement, with a large systematic difference and proportional bias, indicating that My Jump Lab overestimated torque values at higher strength levels (mean bias = +511.9 N·m). Therefore, torque values derived from the app should be interpreted as relative indicators rather than absolute equivalents to instrumented measurements. From a practical perspective, My Jump Lab may offer a low-cost option for broad screening or relative group profiling when instrumented devices are unavailable, but it should not be used as a substitute for instrumented devices or for individual longitudinal monitoring based on absolute torque values. Full article

Objective: The primary aim of this study was to compare eccentric knee flexion isokinetic performance at two commonly used angular velocities (60°·s⁻¹ and 180°·s⁻¹) between dominant and non-dominant limbs in healthy professional soccer players through the analysis of peak torque, mean peak torque, angle of peak torque, total work, and rate-of-torque-development-related variables. The secondary aim was to describe concentric knee extension and knee flexion strength variables assessed at 60°·s⁻¹. Methods: Forty male professional soccer players performed concentric knee flexion–extension testing at 60°·s⁻¹ and eccentric knee flexion testing at 60°·s⁻¹ and 180°·s⁻¹ using an isokinetic dynamometer. Peak torque (PT), mean peak torque (MPT), angle of peak torque (APT), total work (TW), and hamstrings: quadriceps ratios (H:Q ratios) were analyzed for dominant and non-dominant limbs. Inter-limb differences, repetition effects, and reliability indices were calculated. Results: No significant inter-limb differences were observed for most variables (trivial–small effect sizes), except for higher eccentric TW at 180°·s⁻¹ in the dominant limb (p = 0.009). Eccentric PT and MPT decreased at higher velocities in both dominant (p = 0.002 and p < 0.001, respectively) and non-dominant (p = 0.008 and p < 0.001, respectively) limbs, while APT shifted toward more flexed knee angles (p < 0.001). Reliability was good to excellent (ICC = 0.81–0.87), with low measurement error. Conclusion: Eccentric knee flexion assessment at 60°·s⁻¹ and 180°·s⁻¹ angular velocities provided different results in PT, MPT, and APT for the same group of players, supporting the use of more than one eccentric test for obtaining information about these variables in elite soccer. Full article

Background: We assessed the effects of a 6-week, low-volume Nordic hamstring exercise (NHE) intervention on hamstring flexibility, muscle mechanical properties and eccentric and isometric isokinetic knee flexion strength in recreationally active adults. Methods: Eighteen recreationally active adults were randomized into an NHE intervention group (IG; n = 9; females/males: 3/6; mean ± SD, age: 24.1 ± 1.3 years) and control group (CG; n = 9; females/males: 5/4; mean ± SD, age: 23.5 ± 1.8 years). The NHE intervention involved a progressive, supplementary training program performed initially one (weeks 1 and 2) and then two times per week over a 6-week period. The number of repetitions per session increased from 15 to 36 repetitions/week. The CG maintained their usual exercise routine over the same period. Standard goniometry, myotonometry, and isokinetic dynamometry (60°/s) were used to measure hamstring flexibility, muscle properties and isometric and eccentric isokinetic strength prior to and five days following the intervention. Results: The Linear Mixed Methods analysis identified a significant group × time interactions for isometric torque (IG: +5% vs. CG: −12%, p = 0.022) and flexibility (IG: +1% vs. CG: +7%, p = 0.023). Peak eccentric torque (IG: +7% vs. CG: −7%, p = 0.053) and muscle mechanical properties remained unchanged over the intervention period. Conclusions: Six weeks of low-volume NHE training marginally improved isometric and eccentric hamstring strength in recreationally active adults without changing hamstring flexibility or mechanical properties. The findings may have important implications for performance enhancement and hamstring injury risk reduction during high-intensity recreational sports. Full article

Background and Objectives: Present assessment methods have not effectively mitigated the risk of recurrent anterior cruciate ligament (ACL) injury following reconstruction (ACLR), suggesting that critical neuromuscular deficits may be underdiagnosed. This study aimed to compare limb asymmetries across strength, concentric and eccentric power, and deceleration metrics during return-to-sport (RTS) testing in professional athletes post-ACLR. Materials and Methods: Forty-four participants (33 males, 11 females; age 22.5 ± 5.8 years, body mass 75.9 ± 13.0 kg, height 180.5 ± 8.38 cm) (mean ± SD) with a unilateral reconstructed ACL (BTB = 33, HT = 11 graft) were included. They underwent isokinetic testing of knee flexor and extensor strength and bilateral countermovement jump (CMJ) assessments to measure concentric and eccentric peak power and deceleration metrics. Limb symmetry indices (LSI) were calculated for each parameter. Welch’s ANOVA and Games–Howell post hoc tests were used to compare LSIs among parameters. Results: Welch’s ANOVA showed that limb symmetry differed significantly across the measured neuromuscular parameters (F = 12,59, p < 0.001). Knee flexor strength LSI was significantly higher than knee extensor strength LSI (p = 0.003; d = 1.18), concentric peak power LSI (p < 0.001, d = 1.44), eccentric peak power LSI (p = 0.001, d = 1.71), and deceleration LSI (p = 0.001, d = 2.09). In addition, deceleration LSI was significantly lower than knee extensor strength LSI (p = 0.001, d = 1.34) and concentric peak power LSI (p = 0.007, d = 1.10). No significant difference was found between concentric and eccentric peak power, nor between knee extensor strength and either concentric or eccentric peak power LSIs. Conclusions: The findings of this study revealed significantly greater asymmetries in load absorption capacity compared to strength and concentric power measures at return-to-sport time frame in professional athletes post-ACLR. Full article

Background: Type 2 diabetes mellitus (T2DM) is linked to accelerated losses in muscle function. The aim of the present investigation was to evaluate the effect of chronic higher-protein intake on isokinetic knee performance in the older adults with type 2 diabetes mellitus (T2DM). Methods: Thirty adults (15 men and 15 women) aged 60–80 years with non-insulin-treated T2DM and sarcopenia-related deficits were randomized for 12 weeks to a higher-protein diet (1.2–1.5 g·kg⁻¹·day⁻¹) or a recommended protein diet (0.8–1.0 g·kg⁻¹·day⁻¹), with meal plans designed to maintain body mass. Protein was increased mainly through Mediterranean-style protein sources while diet was monitored using repeated 3-day recalls. Isokinetic knee extensors and flexors peak torque (angular velocity 60°/s) was assessed at baseline and at week 6 and at the end of the 12th week of intervention. Fatigability (20 maximal contractions at an angular velocity at 180°/s) and DXA body composition were assessed at baseline and at the end of the 12th week of intervention. Data were analyzed using two-way repeated-measures ANOVA with repeated measures on time (2 groups × 3 time points), followed by post hoc analysis when significant difference was occurred. Results: Thirty participants completed the trial. Energy intake and body mass remained stable in both groups. At the end of week 12, peak torque declined in the control group (p < 0.05) but remained stable in the higher-protein group. The fatigue index worsened over time in controls but was preserved in the higher protein group, resulting in a significant group d7 time interaction at week 12 (p < 0.05) (post hoc between-group difference at week 12, p < 0.05). Fat-free mass and blood pressure did not change. In fat mass, a decrease was observed with higher protein intake, whereas it remained stable in the control group. Conclusions: Higher protein intake for 12 weeks preserved knee muscle performance in older adults with T2DM without weight gain, supporting dietary protein optimization to counter functional decline. Full article

Chronic obstructive pulmonary disease, interstitial lung disease, and post-lung trans-plantation are often accompanied by skeletal muscle dysfunction that worsens the quality of life. Such physiological changes are driven by physical inactivity, systemic inflammation, oxidative stress, anabolic and hormonal resistance, and medication effects. Structural changes include impaired capillarization, fiber-type shifts (slow-to-fast in limb muscle and fast-to-slow in respiratory muscles), mitochondrial dysfunction, reduced oxidative capacity, and early lactate accumulation. Electromyography and dynamometry, both isokinetic and isometric, quantify neuromuscular drive through measuring strength, power, and endurance and are associated with functional outcomes (6-min walk, sit-to-stand, stair climbing tests). Pulmonary rehabilitation (PR) improves neuromuscular efficiency, dyspnea, exercise tolerance, and quality of life by combining resistance, endurance, and eccentric training. The effects of PR generally plateau at three months, emphasizing the need for maintenance and the personalization of rehabilitation plans. While nutritional optimization is important, supplements have shown little benefit. Future priorities include defining EMG/dynamometry thresholds to allow standardized routine testing for comparable benchmarks and more precise PR protocols. Future research targeting mitochondrial remodeling, inflammatory signaling, and anabolic resistance offer potential pathways for preventing and reversing muscle wasting. Full article

Objectives: To determine whether caffeine supplementation and its expectancy influence muscle strength (ST) and muscle endurance (ME) using a balanced-placebo design. Methods: Using a randomized, double-blind, balanced-placebo design, resistance-trained men (18–30 years; n = 16) participated in two assessment/familiarization visits (demographics; one repetition maximum (1RM) followed by four counterbalanced sessions: C/C (informed caffeine/used caffeine), P/C (informed placebo/used caffeine), C/P (informed caffeine/used placebo), P/P (informed placebo/used placebo). Caffeine dose was 5 mg/kg. Peak torque (PT) and maximum work (MW) were measured in the knee extensors at 0, 60, 180, and 300°/s, which was followed by ME testing (three sets of maximal repetitions using 60%1RM). Capillary blood lactate was measured after ME testing. Results: Caffeine increased PT only during static and 60°/s contractions (4%; p ≤ 0.003; d = 0.3 for both speeds), while MW increased across all speeds (4%; p < 0.001; d = 0.2). Caffeine did not increase ME (3%; p = 0.184; d = 0.1), but it did increase blood lactate levels (1.2 mmol/L; p < 0.001; d = 0.7). Caffeine expectation did not improve ST or ME, but increased blood lactate levels (0.7 mmol/L; p = 0.003; d = 0.4). Across ST and ME, responses to caffeine were markedly heterogeneous, with 50–88% of individuals considered responders (∆ > 0), and improvements in responders ranged from 1–16%. Conclusions: Caffeine significantly increased ST, despite ME increasing in 50% of participants, this was not significant. No placebo effect was observed in ST or ME, but it significantly increased lactate. Further research is necessary to elucidate the mechanisms behind this variability in the ME response, especially the role of fiber-type predominance. Full article

Background/Objectives: Persistent strength deficits and psychological impairments may compromise return to sport (RTS) after anterior cruciate ligament reconstruction (ACLR). We investigate the relationship between thigh muscle isokinetic strength recovery at six months after ACLR and long-term psychological outcomes related to RTS in competitive male soccer players. Methods: Sixty male soccer players who underwent primary ACLR with bone–patellar tendon–bone autograft were retrospectively analyzed. Isokinetic testing of quadriceps and hamstrings was performed one week before surgery and six months post-surgery at 90°/s and 180°/s. Limb symmetry index (LSI) was calculated both pre- and post-operatively. At long-term follow-up (mean ≈ 4 years after RTS), athletes completed questionnaires assessing RTS status, ACL re-injuries, sport-related perceptions, and kinesiophobia using the Tampa Scale for Kinesiophobia (TSK). Statistical analyses were conducted to explore associations between post-operative LSI and TSK scores and to compare psychological and neuromuscular outcomes between athletes with and without ACL re-injury. Results: Absolute quadriceps and hamstring peak torque values significantly increased from pre- to post-surgery, with quadriceps strength deficits persisting only in the operated limb. However, quadriceps LSI significantly decreased post-operatively, while hamstring LSI remained stable. Pearson correlation analysis revealed a weak positive association between post-operative quadriceps LSI at 90°/s and TSK scores (r = 0.34). Overall, RTS rate was 91.7%, but a second ACL injury occurred in 18.2% of athletes. No significant differences were observed between re-injured and non-re-injured athletes in TSK scores or post-operative LSI values at either angular velocity (all p > 0.29). High kinesiophobia (TSK ≥ 37) was present in 56.7% of the cohort at long-term follow-up. Conclusions: Despite significant strength gains, quadriceps limb symmetry worsened six months after ACLR, with deficits confined to the operated limb, suggesting persistent neuromuscular inhibition. These physical deficits coexist with long-term kinesiophobia despite high RTS rates. The weak associations between strength symmetry and psychological outcomes highlight the multifactorial nature of RTS and support the need for an integrated physical, psychological, and neuro-cognitive approach to rehabilitation and RTS decision-making. Full article

Background/Objectives: Hamstring injuries are highly prevalent in sports and often occur, particularly among recreational and professional athletes. Assessing eccentric hamstring strength is critical for injury prevention and rehabilitation, with isokinetic dynamometry being considered the gold standard. However, its accessibility is limited by cost and logistics. This study aimed to evaluate the validity and reliability of the My Jump Lab (version 4.0) mobile application in estimating eccentric peak torque in the break-point angle, compared with isokinetic dynamometry. Methods: Twenty-seven recreational athletes (twenty-six male, one female) were assessed bilaterally using the mobile application and isokinetic dynamometer, which is considered the gold standard for this type of strength assessment. Statistical analysis included Pearson’s correlation, intraclass correlation coefficient (ICC), standard error of measurement (SEM), coefficient of variation (CV), and Bland–Altman plots. Results: Results showed excellent inter-rater reliability (ICC = 0.999; CV = 0.66%) for both smartphone application evaluators and good comparative validity and reliability (ICC ≈ 0.76 with confidence interval: 0.5367–0.876; p < 0.001 and r ≈ 0.705;) when comparing with isokinetic dynamometry. Conclusions: My Jump Lab is a mobile application which can provide a practical and accessible mean for monitoring eccentric hamstring strength in field settings. The app may serve as a feasible field-based alternative to laboratory dynamometry for eccentric strength monitoring. Full article

Background/Objectives: Muscle strength is a vital indicator of the development and health-related fitness in children and adolescents, and it also plays a crucial role in clinical assessments across pediatric rehabilitation. The aim of this review was to evaluate the available literature on handheld dynamometry (HHD) assessments of the overall muscle strength in the pediatric population, focusing on measurement protocols, validity and reliability, and the availability of reference and normative data. Methods: Following PRISMA 2020 guidelines, a systematic review was conducted across PubMed, Scopus, Cochrane CENTRAL, CINAHL, and Web of Science. The protocol was registered in PROSPERO (CRD42024537557). Eligible studies (2005–2023) included healthy participants under the age of 18 reporting on isometric muscle strength using HHDs. Studies reporting handgrip strength or alternative methods (e.g., isokinetic and 1RM) of assessment were excluded. Due to the heterogeneity of the studies, the JBI and COSMIN risk of bias checklists were used to assess risk of bias. A narrative synthesis approach was used to summarize the findings. Results: Twelve studies were included, with a total of 1683 participants aged 4–17 years (764 girls and 919 boys). Test re-test reliability and low measurement error were established in measuring the toe strength, while the concurrent validity of lower limb torque was determined as poor. Conclusions: When standardized protocols and fixed stabilization are implemented, studies confirm good intra- and inter-rater reliability. Substantial heterogeneity in measurement protocols highlights the need for standardized procedures. It is essential to establish normative or reference values by age and sex to enhance clinical decision making and the utility of HHDs in pediatric overall strength assessments. Full article

Background: The high demands of professional soccer predispose players to musculoskeletal injuries. The primary challenge for identifying potential risk factors lies in determining the appropriate assessment methods and indicators to consider. Kinetic variables have been identified as potential indicators of injury risk. Objectives: To conduct a systematic review of the literature analyzing the relationship between kinetic variables and the risk of indirect musculoskeletal injuries of the lower limb in professional soccer players. Methods: A search was conducted on Web of Science, PubMed, and Scopus following the PRISMA guidelines. The search included articles that link kinetic variables assessed through dynamometry to indirect lower limb injuries. Sample characteristics, assessments, injury follow-ups, and statistical results were extracted for qualitative synthesis. Results: A total of 1096 studies were initially identified, of which 380 duplicates were removed. After screening 716 articles by title and abstract, 631 were excluded. Subsequently, 85 full-text articles were examined, resulting in 11 studies being included. Of the included articles, 10 used isokinetic dynamometry and the Nordic hamstring curl test to assess lower limb strength. Conclusions: The results of this review indicate that kinetic variables, particularly isokinetic strength measures at different angular velocities, are consistently associated with indirect musculoskeletal injury risk in professional soccer players. The most relevant indicators include eccentric hamstring force and concentric quadriceps torque, which help identify strength deficits and muscular disequilibrium. Monitoring these variables through validated assessments enables the development of targeted prevention strategies. Additionally, injury risk assessment should integrate kinetic data with contextual indicators such as well-being, fatigue, and training load. Full article