The purpose of this work was to provide a simple method to determine reactive strength during the 6-meter timed hop test (6mTH) and evaluate its association with isokinetic peak torque in patients following anterior cruciate ligament reconstruction (ACLR). Twenty-nine ACLR patients who were at least four months from surgery were included in this analysis. Participants were brought into the laboratory on one occasion to complete functional testing. Quadriceps and hamstring isokinetic testing was completed bilaterally at 60, 180, and 300 deg∙s-1, using extension peak torque from each speed as the outcome measure. The 6mTH was completed bilaterally using a marker-based motion capture system, and reactive strength ratio (RSR) was calculated from the vertical velocity of the pelvis during the test. An adjustment in RSR was made using the velocity of the 6mTH test to account for different strategies employed across participants. Repeated measures correlations were used to determine associations among isokinetic and hop testing variables. A two-way mixed analysis of variance was used to determine differences in isokinetic and hop testing variables between operated and non-operated legs and across male and female participants. Moderate positive associations were found between RSR (and adjusted RSR) and isokinetic peak torque at all speeds (r = .527 to .577). Mean comparisons showed significant main effects for leg and sex. Patients showed significant deficits in their operated versus non-operated legs in all isokinetic and hop testing variables, yet only isokinetic peak torque and timed hop time showed significant differences across male and female groups. Preliminary results are promising but further development is needed to validate other accessible technologies available to calculate reactive strength during functional testing after ACLR. Pending these developments, the effects of movement strategies, demographics, and levels of participation on RSR can then be explored to translate this simple method to clinical environments.

Frailty is a significant predictor of a range of adverse outcomes in surgical patients, including increased mechanical ventilation time, longer hospital stays, unplanned readmissions, stroke, delirium, and death. However, accessible tools for screening in clinical settings are limited. Computed tomography of the psoas muscle is the current standard imaging device for measuring frailty, but it is expensive, time-consuming, and exposes the patient to ionizing radiation. Recently, the use of point-of-care ultrasound (POCUS) has emerged as a potential tool to determine the presence of frailty and has been shown to accurately predict frailty and postoperative outcomes. In this article, we will describe the image acquisition of the quadriceps muscles and explain how they can be used to determine frailty and predict postoperative adverse events. We will present information on probe selection, patient positioning, and troubleshooting. Images from a demonstration will be used to present the POCUS technique and example results. The article will culminate in a discussion of the use of these images in medical decision-making and potential limitations.

We explored the impact of running in the severe intensity domain on running mechanics and muscle oxygenation in competitive runners by investigating the relationship between mechanical deviations from typical stride characteristics and muscle oxygen saturation (SmO2) in the quadriceps muscle. Sixteen youth competitive runners performed an 8-min exhaustive running test on an outdoor track. Running mechanics were continuously monitored using inertial measurement units. Rectus femoris SmO2 and total hemoglobin (a measure of blood volume) were continuously monitored by near-infrared spectroscopy. One-class support vector machine (OCSVM) modeling was employed for subject-specific analysis of the kinematic data. Statistical analysis included principal component analysis, ANOVA, and correlation analysis. Mechanical deviations from typical stride characteristics increased as the running test progressed. Specifically, the percentage of outliers in the OCSVM model rose gradually from 2.2 ± 0.8% at the start to 43.6 ± 28.2% at the end (p < 0.001, mean ± SD throughout). SmO2 dropped from 74.3 ± 8.4% at baseline to 10.1 ± 6.8% at the end (p < 0.001). A moderate negative correlation (r = -0.61, p = 0.013) was found between the average SmO2 and the percentage of outlier strides during the last 15% of the run. During high-intensity running, alterations in running biomechanics may occur, linked to decreased quadriceps muscle oxygenation. These parameters highlight the potential of using running kinematics and muscle oxygenation in training to optimize performance and reduce injury risks. Our research contributes to understanding biomechanical and physiological responses to endurance running and emphasizes the importance of individualized monitoring.

BACKGROUND: For the study of quantitative and qualitative muscle parameters, ultrasound and bioelectric impedance analysis are reliable, non-invasive, and reproducible. The aim of this study was to test the combined role of those techniques for the diagnosis of sarcopenia in a population of hospitalized older males and females.
METHODS: A total of 70 subjects were recruited, including 10 healthy adults and 60 hospitalized elderly patients with a good level of independence and cooperation, with and without sarcopenia. The rectus femoris cross-sectional area (CSA), thickness, echogenicity, and compressibility were measured with ultrasound echography. The phase angles (PhAs) and skeletal muscle mass were calculated by bioimpedence analysis. The muscle quality index (MQI) was calculated as the product of CSA and PhA.
RESULTS: Muscle compressibility was greater and PhA was lower in sarcopenic when compared with non-sarcopenic subjects. The threshold values for sarcopenia diagnosis in both sexes of CSA, of PhA, and of the MQI were identified. The obtained CSA values showed an AUC of 0.852 for women and 0.867 for men, PhA of 0.792 in women and 0.898 in men, while MQI was 0.900 for women and 0.969 for men.
CONCLUSIONS: The newly calculated cut-off values of CSA, PhA, and MQI predicted the presence of sarcopenia with good sensitivity and specificity values. The use of the MQI proved to be more promising than the separate use of CSA and PhA in both male and female subjects.

Rehabilitation from musculoskeletal injuries focuses on reestablishing and monitoring muscle activation patterns to accurately produce force. The aim of this study is to explore the use of a novel low-powered wearable distributed Simultaneous Musculoskeletal Assessment with Real-Time Ultrasound (SMART-US) device to predict force during an isometric squat task. Participants (N = 5) performed maximum isometric squats under two medical imaging techniques; clinical musculoskeletal motion mode (m-mode) ultrasound on the dominant vastus lateralis and SMART-US sensors placed on the rectus femoris, vastus lateralis, medial hamstring, and vastus medialis. Ultrasound features were extracted, and a linear ridge regression model was used to predict ground reaction force. The performance of ultrasound features to predict measured force was tested using either the Clinical M-mode, SMART-US sensors on the vastus lateralis (SMART-US: VL), rectus femoris (SMART-US: RF), medial hamstring (SMART-US: MH), and vastus medialis (SMART-US: VMO) or utilized all four SMART-US sensors (Distributed SMART-US). Model training showed that the Clinical M-mode and the Distributed SMART-US model were both significantly different from the SMART-US: VL, SMART-US: MH, SMART-US: RF, and SMART-US: VMO models (p < 0.05). Model validation showed that the Distributed SMART-US model had an R2 of 0.80 ± 0.04 and was significantly different from SMART-US: VL but not from the Clinical M-mode model. In conclusion, a novel wearable distributed SMART-US system can predict ground reaction force using machine learning, demonstrating the feasibility of wearable ultrasound imaging for ground reaction force estimation.

In critical care settings, ultrasound (US) of the quadriceps muscle and Bioelectrical Impedance Analysis (BIA) are noninvasive and widely available tools to evaluate muscle mass. We studied whether baseline muscle mass affects physical function in intensive care unit (ICU) survivors after discharge. This retrospective review of a prospective cohort enrolled 30 patients admitted to the medical ICU between April 2016 and June 2018. On ICU admission, quadriceps muscle thickness and skeletal muscle mass were measured using US and BIA, respectively. Muscle strength and physical function were measured using handgrip dynamometry, the 6-min walk test, and the Barthel index questionnaire survey during every clinic visit at 1, 3, 6, and 12 months after hospital discharge. Skeletal muscle mass at ICU admission was statistically correlated with the 6-min walk distance (6MWD) and Barthel index score. The segmental lean mass of the right arm was also positively correlated with handgrip muscle strength at 6 months after discharge. Likewise, the correlation between quadriceps muscle thickness at ICU admission and 6MWD at 6 months after discharge was positive and statistically significant. Multivariate regression analysis showed that skeletal muscle mass was associated with a reduced 6MWD, but the length of ICU stay was not. The segmental lean mass of the right arm also showed a significant association with handgrip strength after discharge. Low muscle mass on ICU admission is associated with reduced muscle strength, causing impaired physical function after hospital discharge in ICU survivors.

Patellar tendinopathy is more prevalent in males versus female athletes and commonly presents in the medial region of the tendon. Separate measures of patellar tendon strain in the medial, central, and lateral regions of the tendon, however, have not been quantified. The purpose was to investigate the differences in tendon strain between the medial, lateral, and central regions of the patellar tendon in healthy men and women. Strain in the medial and lateral regions of the patellar tendon in healthy participants (10 males, 10 females) was evaluated using ultrasound during isometric quadriceps contractions at 20%, 40%, 60%, 80%, and 100% of maximum voluntary contraction (MVIC) in 60° and 90° of knee flexion. Central strain was also measured at 60% MVIC in 90° of knee flexion. Mixed models were used to determine strain between tendon regions and sex at 60% MVIC in 90° of knee flexion. Sequential modeling was used to fit region, sex, %MVIC, and angle to predict strain. The central region had less strain compared with both medial and lateral regions. The lateral region had higher strain compared with the medial region regardless of sex. Females had higher strain compared with males, regardless of region. Knee position did not influence tendon strain. Patellar tendon strain differs by region and sex. The varying prevalence between sex and in location of patellar tendinopathy may in part be explained by the unbalanced strains. Differential assessment of regional patellar tendon strain may be of importance for understanding injury risk and recovery with exercise.

OBJECTIVE: To compare the effect of rectus femoris diagnostic motor nerve blocks (DNB) with anaesthetics and rectus femoris muscle botulinum toxin (BoNT-A) injection in multiple sclerosis patients with unilateral stiff-knee gait.
METHODS: Prospective observational study Subjects/Patients: Multiple sclerosis patients in stable condition.
METHODS: Patients underwent evaluation before and 1 hour after the anaesthetic block, and 1 month after the botulinum injection. Assessment included a 10-m walking test, a 6-minute walking test, a timed-up-and-go (TUG) test, and a Baseline Expanded Disability Status Scale (EDSS). Post-DNB and post-BoNT-A satisfaction was measured with the global assessment of efficacy scale.
RESULTS: Fourteen patients with unilateral stiff-knee gait due to multiple sclerosis underwent a DNB, among whom 13 received botulinum injections in the rectus femoris muscle after a satisfying test result. Positive post-DNB results correlated with significant functional improvements after BoNT-A. Higher EDSS and longer time from diagnosis correlated with poorer post-DNB and post-BoNT-A absolute outcomes.
CONCLUSIONS: DNB showed predictive value for BoNT-A outcomes, especially in the case of worse functional status. It effectively predicted endurance and walking speed improvement, while TUG showed greater improvement after botulinum. In cases of uncertain therapeutic benefit, nerve blocks may provide a valuable diagnostic support, particularly in patients with lower functional status.

BACKGROUND: Preventing severe arthrogenic muscle inhibition (AMI) after knee injury is critical for better prognosis. The novel Sonnery-Cottet classification of AMI enables the evaluation of AMI severity but requires validation. This study aimed to investigate the electromyography (EMG) patterns of leg muscles in the examination position from the classification during isometric contraction to confirm its validity. We hypothesised that the AMI pattern, which is characterised by quadriceps inhibition and hamstring hypercontraction, would be detectable in the supine position during isometric contraction.
METHODS: Patients with meniscal or knee ligament injuries were enrolled between August 2023 and May 2024. Surface EMG was assessed during submaximal voluntary isometric contractions (sMVIC) at 0° extension in the supine position for the vastus medialis (VM) and vastus lateralis (VL) muscles and at 20° flexion in the prone position for the semitendinosus (ST) and biceps femoris (BF) muscles. Reference values for normalisation were obtained from the EMG activity during the gait of the uninjured leg. The Kruskal-Wallis test was used to compare the activation patterns of the muscle groups within the same leg, and the post-hoc tests were conducted using the Mann-Whitney U test and Bonferroni correction.
RESULTS: Electromyographic data of 40 patients with knee injuries were analyzed. During sMVIC, the extensor and flexor muscles of the injured leg showed distinct behaviours (P < 0.001), whereas the uninjured side did not (P = 0.144). In the injured leg, the VM differed significantly from the ST (P = 0.018), and the VL differed significantly from the ST and BF (P = 0.001 and P = 0.026, respectively). However, there were no statistically significant differences within the extensor muscle groups (VM and VL, P = 0.487) or flexor muscle groups (ST and BF, P = 0.377).
CONCLUSIONS: AMI was detectable in the examination position suggested by the Sonnery-Cottet classification. The flexor and extensor muscles of the injured leg exhibited distinct activation behaviours, with inhibition predominantly occurring in the quadriceps muscles, whereas the hamstrings showed excitation.

BACKGROUND: Muscle ultrasound is a valid tool to monitor muscle mass loss in critically ill patients. The level of experience is essential to the accuracy of the measurements.
OBJECTIVE: To evaluate the interobserver reliability of experienced and novice raters measuring muscle thickness and echo intensity of the quadriceps and tibialis anterior.
METHODS: Cross-sectional observational study. Twenty-four critical care physiotherapists participated (5 experienced and 19 novice). Following a standardized ultrasound protocol, each rater measured the thickness (centimeters) of the quadriceps and tibialis anterior of 10 healthy and young models using linear and convex probes of portable devices. The Intraclass Correlation Coefficient and the Minimal Detectable Change (95% confidence interval) were calculated. Additionally, the novices scored the echo intensity of 19 muscle ultrasound images of critically ill patients using the Heckmatt score (qualitative assessment). The agreement with experienced raters was evaluated (Spearman Rho).
RESULTS: 960 muscle thickness measurements were performed (experienced = 200 and novice = 760). The mean thickness of the quadriceps and tibialis anterior was 4.4 ± 0.77 and 2.4 ± 0.35 centimeters for the experienced and 4.2 ± 0.80 and 2.2 ± 0.39 centimeters for the novices, respectively. Quadriceps\' and tibialis\' anterior reliability were 0.82 and 0.86 for experienced and 0.76 and 0.41 for novices, respectively. The Minimal Detectable Change ranged from 0.14-0.33 centimeters. The mean Heckmatt score was 2.6 ± 0.83 points, with a reliability of 0.68 and an agreement with the experimenters of 0.78 [p < 0.001].
CONCLUSIONS: Interobserver reliability was excellent for experienced raters and moderate to good for novice raters. The level of experience could determine the reliability of the results.