Vastus lateralis and rectus femoris echo intensity fail to reflect knee extensor specific tension in middle-school boys

Resistance training effects on pubertal children with a risk of developing pediatric dynapenia

PURPOSE

Many modern-day children are at risk of pediatric dynapenia (muscle weakness). We examined the effects of a 12-week resistance training (RT) program on neuromuscular function and body composition parameters in pubertal children with a risk of dynapenia.

METHODS

Twelve children (13.4 ± 0.9 y) with dynapenia performed a progressive RT program consisting of knee extension and flexion, bench press, abdominal crunch, back extension, lateral pull-down, elbow flexion, and upright row (1-2 sets of 10-15 repetitions/exercise) twice/week for 12 weeks. Outcome measures included one-repetition maximum (1-RM) strength, maximal voluntary isometric contraction (MVIC) torque, rate of torque development (RTD), electromyographic (EMG) activity, muscle thickness (MT), muscle quality (MQ) assessed by echo intensity (MQEI) of the knee extensors and specific tension of MVIC torque to thigh fat-free mass (MQST), and total and regional body and bone composition assessed by dual-energy X-ray absorptiometry. Changes in the measures before and after the 12-week RT and associations among the measures were analyzed by linear mixed models.

RESULTS

Significant (p < 0.05) increases in 1-RM (63.9 ± 4.5%), MVIC torque (16.3 ± 17.8%), MT (18.8 ± 5.5%) and MQ (MQEI: -25.9 ± 15.2%; MQST: 15.1 ± 18.8%;) were evident from pre- to post-training. Total fat-free mass (FFM) increased by 2.3 ± 3.2% from baseline (p = 0.01), but no changes (p > 0.05) in the other measures were observed. Significant (p < 0.05) associations between the changes in 1-RM and/or MVIC torque and the changes in quadriceps MT, MQEI, MQST and total body FFM were evident.

CONCLUSIONS

The 12-week RT was effective for improving neuromuscular and body composition parameters, and thereby reversed the risk of pediatric dynapenia.

The impact of inter-limb leg lean tissue mass asymmetry on stair climb performance in career firefighters

The purpose of this study was to examine the influence of inter-limb leg lean tissue mass (LTM) asymmetry on stair climb (SC) performance in firefighters. Forty-one career firefighters (age = 32.3 ± 8.2 years, body mass = 92.1 ± 18.6 kg, stature = 178.3 ± 7.9 cm) visited the laboratory on one occasion and completed a whole body and leg composition assessment followed by a timed and weighted SC task. Percent body fat (%BF) and leg LTM were determined during a DEXA scan and regional thigh analysis. Asymmetry was assessed by the percent difference between limbs (dominant limb LTM - non-dominant limb LTM)/dominant limb LTM × 100) and a ± 3% cut-off for asymmetry classification. Participants ascended and descended 26 stairs four times as quickly as possible while wearing a weighted (22 kg) vest. Point biserial correlations were used to assess the relationship of inter-limb leg LTM asymmetry and SC performance before and after controlling for age and %BF. Results indicated that inter-limb leg LTM asymmetry was associated with longer SC task time (poorer performance) both before (r = 0.432, P = 0.005) and after (r = 0.502, P = 0.001) controlling for age and %BF. Our findings indicated that inter-limb leg LTM asymmetry negatively impacts firefighter SC performance, which may be improved with appropriate exercise interventions.

Comparisons between skeletal muscle imaging techniques and histology in tracking midthigh hypertrophic adaptations following 10 weeks of resistance training

This study had two aims. AIM1 was to determine the agreement between mid-thigh vastus lateralis (VL) cross-sectional area measured by ultrasound (mCSA_US) versus magnetic resonance imaging (mCSA_MRI) at a single time point, and the ability of each to detect hypertrophic changes. AIM2 was to assess the relationships between pre-to-post training changes in thigh lean mass determined by DXA, VL mCSA_US, ultrasound-determined VL thickness (VL_Thick), and VL mean myofiber cross-sectional area (fCSA) with changes in VL mCSA_MRI. Twelve untrained males (Age: 20±1 y, BMI: 26.9±5.4 kg/m²; n=12) engaged in a 10-week resistance training program (2x/week) where right mid-thigh images and VL biopsies were obtained prior to and 72-hours following the last training bout. Participants' VL mCSA_MRI (p=0.005), DXA thigh lean mass (p=0.015), and VL_Thick (p=0.001) increased following training, whereas VL mCSA_US and fCSA did not. For AIM1, mCSA_US demonstrated excellent concordance (CCC = 0.830) with mCSA_MRI, albeit mCSA_US values were systematically lower compared to mCSA_MRI (mean bias: -2.29 cm²). Additionally, PRE-to-POST VL mCSA changes between techniques exhibited good agreement (CCC = 0.700; mean bias: -1.08 cm²). For AIM2, moderate, positive correlations existed for PRE-to-POST changes in VL mCSA_MRI and DXA thigh lean mass (r=0.580, p=0.048), mCSA_US (r=0.622, p=0.031), and VL_Thick (r=0.520, p=0.080). A moderate, negative correlation existed between mCSA_MRI and fCSA (r=-0.569, p=0.054). Our findings have multiple implications: i) resistance training-induced hypertrophy was dependent on the quantification method, ii) ultrasound-determined mCSA shows good agreement with MRI, and iii) tissue-level changes poorly agreed with mean fCSA changes and this requires further research.

Influence of muscle depth and thickness on ultrasound echo intensity of the vastus lateralis

BACKGROUND

Ultrasonography is used to evaluate muscle quality (i.e. echo intensity [EI]), but an attenuation of ultrasound waves occurs in deeper tissues, potentially affecting these measures.

PURPOSE

To determine whether muscle thickness (MT) affects EI and if EI varies between the superficial and deep portions of the muscle.

MATERIALS AND METHODS

MT, EI, subcutaneous adipose tissue thickness (SAT), tissue depth (DIS_DEEP), and EI of the overall (EI_FULL) as well as deep (EI_DEEP) and superficial (EI_SUPF) portions of the vastus lateralis (VL) were assessed in 33 resistance-trained males using ultrasonography. The difference (EI_DIFF) between EI_SUPF and EI_DEEP was calculated. Mean differences between EI_FULL, EI_SUPF, and EI_DEEP were analyzed using a repeated-measures analysis of variance (ANOVA). Relationships between measures of muscle depth/ thickness and EI were examined using Pearson's r.

RESULTS

EI_SUPF was greater than EI_DEEP (P < 0.001) and EI_FULL (P < 0.001). MT was negatively correlated with EI_FULL (P < 0.001) and positively correlated with EI_DIFF (P < 0.001). SAT was not correlated with any EI measure, but DIS_DEEP was positively correlated with EI_DIFF (P < 0.001).

CONCLUSION

EI of the VL is heterogeneous, as the deeper portion produces lower values than the superficial portion. Thicker muscles present lower EI but have greater discrepancies in EI between the superficial and deep portions. Although SAT was not correlated with EI, DIS_DEEP was related to EI_DIFF, demonstrating that the combination of MT and SAT should be considered when evaluating muscle quality. Future research is necessary to determine if changes in EI following resistance training are driven by increases in MT.

The Relationship Between Muscle Size and Strength Does not Depend on Echo Intensity in Healthy Young Adults

Muscle quality is typically defined as muscle strength relative to muscle size. Echo intensity has gained popularity as an index of skeletal muscle quality. There is common agreement that muscle size is related to strength at baseline and echo intensity is purported to impact this relationship. Thus, the purpose of this study was to examine whether echo intensity can be used as a physiological marker for muscle quality by investigating the moderating effect of echo intensity on the relationship between muscle size and strength. A sample of 96 participants was used for the upper body analysis and a separate sample of 96 participants was used for the lower body analysis. Echo intensity, muscle thickness, and strength measurements were measured on each limb. For strength, participants performed unilateral elbow flexion (upper body analysis) and knee extension (lower body analysis) to quantify 1-repetition maximum. Muscle thickness and echo intensity were determined from images captured using B-mode ultrasound. Muscle size correlated with muscle strength for all limbs. However, the relationship between muscle size and strength was not significantly moderated by echo intensity for Arm 1 (b = 0.042, p = 0.54) or Arm 2 (b = -0.002, p = 0.97). At the proximal site, no significant moderating effect of echo intensity was found in Leg 1 (b = 0.037, p = 0.67) or Leg 2 (b = -0.085, p = 0.29). Similarly, no significant moderating effect was observed at the distal site for Leg 1 (b = 0.03, p = 0.69) or Leg 2 (b = -0.026, p = 0.75). The results would indicate that the relationship between muscle size and strength does not depend on echo intensity. Therefore, the use of echo intensity as an index of muscle quality in healthy young adults may need to be reconsidered.

Does skeletal muscle morphology or functional performance better explain variance in fast gait speed in older adults?

BACKGROUND

Fast gait speed is being increasingly recognized as an important clinical tool in older adults. However, the underlying muscular and functional contributors to fast gait speed performance remain poorly understood.

AIM

We sought to determine predictors of fast gait speed in older adults. We hypothesized that lower-extremity skeletal muscle size and quality would be strong predictors.

METHODS

Ninety community-dwelling older adults (33 men, 57 women; mean ± SD age = 74 ± 6 years) participated. B-mode ultrasonography was used to capture images of the vastus lateralis, rectus femoris, and gastrocnemius in the transverse plane. Each participant performed 30-second chair stand, heel-rise, functional reach, and grip strength tests. Fast gait speed was measured using the NIH Toolbox 4-Meter Walk Test. ImageJ software was used to quantify cross-sectional area (CSA), subcutaneous tissue thickness, and echo intensity. Two separate stepwise regression analyses were performed, one using muscle morphology variables as independent variables, and another including the functional outcomes.

RESULTS

The ultrasound variables exhibited weak-to-moderate correlations with fast gait speed (|r| range = 0.168-0.416). The initial regression analysis indicated that the combination of medial gastrocnemius CSA and subcutaneous tissue thickness explained 22.8% of the variance in fast gait speed. The secondary analysis indicated that 30-second chair stand, heel-rise, and grip strength performance explained 45.5% of the variance.

CONCLUSION

While medial gastrocnemius morphology is important, measures of upper and lower-extremity muscle function are better predictors of fast gait speed. These results highlight a dissociation between skeletal muscle morphology and fast gait speed.

Measuring muscle quality: associations between echo intensity and normalized strength and power

OBJECTIVE

Muscle quality has received considerable attention within the literature due to its influence on health and performance. However, it has been assessed by various measures (e.g. ultrasound imaging, normalized strength), contributing to the lack of a consensus definition. The purpose of this study was to investigate the association between common muscle quality measures: vastus lateralis echo intensity (EI) and peak torque (PT) and power (PP) normalized to thigh lean mass (TLM) and thigh fat mass (TFM).

APPROACH

Participants' body composition was assessed via dual-energy Xray absorptiometry and custom thigh analysis. Subcutaneous fat-correction muscle EI was assessed via ultrasonography. Maximal strength and power assessments of the dominant leg extensors were completed. Maximal PT and PP was normalized to TLM and TFM, respectively. Pearson product-moment correlations were used to determine the relationships between EI and PT/TLM, PT/TFM, PP/TLM, and PP/TFM.

MAIN RESULTS

Greater muscle EI was significantly related with lower PT/TFM and PP/TFM (r=-0.74 - -0.70, P<0.001), but unrelated to PT/TLM or PP/TLM (P≥0.205).

SIGNIFICANCE

These findings suggest that muscle EI and normalized strength and power may not be used interchangeably to define muscle quality, and muscle EI may be more sensitive to the adiposity of the limb. Future studies should consider using unique definitions for these separate measures.

High-intensity interval training and essential amino acid supplementation: Effects on muscle characteristics and whole-body protein turnover

The purpose of this study was to compare the independent and combined effects of high-intensity interval training (HIIT) and essential amino acids (EAA) on lean mass, muscle characteristics of the quadriceps, and 24-hr whole-body protein turnover (WBPT) in overweight and obese adults. An exploratory aim was to evaluate potential modulatory effects of sex. Sixty-six adults (50% female; Age: 36.7 ± 6.0 yrs; %BF: 36.0 ± 7.8%) were assigned to 8 wks of: (a) HIIT, 2 days/wk; (b) EAA supplementation, 3.6 g twice daily; (c) HIIT + EAA; or (d) control. At baseline, 4 wks, and 8 wks, total body, thigh LM and muscle characteristics were measured via dual-energy x-ray absorptiometry and B-mode ultrasound, respectively. In a subsample, changes in WBPT was measured using [N15 ]alanine. Differences between groups were assessed using linear mixed models adjusted for baseline values, followed by 95% confidence intervals on adjusted mean change scores (Δ). HIIT and HIIT + EAA improved thigh LM (Δ: +0.17 ± 0.05 kg [0.08, 0.27]; +0.22 ± 0.05 kg [0.12,0.31]) and vastus lateralis cross-sectional area (Δ: +2.73 ± 0.52 cm2 [1.69,3.77]; +2.64 ± 0.53 cm2 [1.58,3.70]), volume (Δ: +54.50 ± 11.69 cm3 [31.07, 77.92]; +62.39 ± 12.05 cm3 [38.26, 86.52]), and quality (Δ: -5.46 ± 2.68a.u. [-10.84, -0.09]; -7.97 ± 2.76a.u.[-13.49, -2.45]). Protein synthesis, breakdown, and flux were greater with HIIT + EAA and EAA compared to HIIT (p < .05). Sex differences were minimal. Compared to women, men tended to respond more to HIIT, with or without EAA. For women, responses were greater with HIIT + EAA than HIIT. In overweight and obese adults, 8 weeks of HIIT, with or without EAA, improved thigh LM size and quality; EAA may enhance muscular adaptation via increases in protein turnover, supporting greater improvements in muscular size and quality.

Moving forward with the echo intensity mean analysis: Exploring echo intensity bands in different age groups

This study compared ultrasound characteristics in youth, younger adults, and older adults using two different methods of analysis: based on clusters of pixel concentration of the grayscale (i.e. EI bands) and the traditionally calculated echo intensity mean. Forty-four healthy youth (13.3 ± 1.4 y), 22 younger adults (31.8 ± 10.1 y) and 53 older adults (66.7 ± 4.6 y) volunteered for the assessment of rectus femoris EI via ultrasonography. Pixel concentration (i.e. EI bands) was calculated in intervals of 0-50, 51-100, 101-150, 151-200, and 201-255 of the gray scale, while EI mean was determined as the average pixels from 0 to 255. EI_0-50 significantly decreased with group age, while EI_{51-100, 101-150, 151-200, 201-255} and EI mean increased (P < 0.001). The differences between groups were greater using EI_0-50 compared to the EI mean (i.e. EI_0-50: youth = ~353% and younger adults = ~251% > older adults; whereas EI mean: youth = ~46% and younger adults = 29% < older adults). These results potentially indicate that EI bands method offer different information than the EI mean method. In addition, EI bands may be a promising approach to understand tissue-specific adaptations to physical training and neuromuscular diseases, yet future studies should validate this method.

Echo intensity as an indicator of skeletal muscle quality: applications, methodology, and future directions

PURPOSE

This narrative review provides an overview of the current knowledge of B-mode ultrasound-derived echo intensity (EI) as an indicator of skeletal muscle quality.

METHOD

PubMed and Google Scholar were used to search the literature. Advanced search functions were used to find original studies with the terms 'echo intensity' and/or 'muscle quality' in the title and/or abstract. Publications that conceptually described muscle quality but did not include measurement of EI were not a focus of the review.

RESULT

Importantly, the foundational premise of EI remains unclear. While it is likely that EI reflects intramuscular adiposity, data suggesting that these measurements are influenced by fibrous tissue is limited to diseased muscle and animal models. EI appears to show particular promise in studying muscular aging. Studies have consistently reported an association between EI and muscle function, though not all chronic interventions have demonstrated improvements. Based on the existing literature, it is unclear if EI can be used as a marker of muscle glycogen following exercise and nutritional interventions, or if EI is influenced by hydration status. Inconsistent methodological approaches used across laboratories have made comparing EI studies challenging. Image depth, rest duration, participant positioning, probe tilt, and the decision to correct for subcutaneous adipose tissue thickness are all critical considerations when interpreting the literature and planning studies.

CONCLUSION

While some areas show conflicting evidence, EI shows promise as a novel tool for studying muscle quality. Collaborative efforts focused on methodology are necessary to enhance the consistency and quality of the EI literature.

Effects of age on vertical jump performance and muscle morphology characteristics in females

BACKGROUND

Declines in muscle morphology and function are commonly reported as a consequence of aging. However, few studies have investigated the influence of age on a comprehensive set of muscle function-related measures (i.e., reactive strength, power, etc.) that focuses on a dynamic performance task such as the vertical jump across the adult life span. This study aimed to examine the effects of age on muscle morphology characteristics (muscle cross-sectional area [CSA] and echo intensity [EI]) and vertical jump height, power, and reactive strength index (RSI) in females.

METHODS

Twenty-six young (22±2 years), 30 middle-aged (36±5 years), and 23 older (71±5 years) females participated in this study. Muscle CSA and EI were determined from ultrasound scans of the vastus lateralis. Countermovement jumps were used to assess jump height, RSI, movement time, and peak power (Pmax).

RESULTS

Muscle CSA, jump height, and Pmax were higher for the young compared to the old and middle-aged (P≤0.027) and for the middle-aged compared to the old (P<0.001). Movement time and EI values were lower (P≤0.004) and RSI values were higher (P<0.001) for the young and middle-aged compared to the old; however, no differences were observed between the young and middle-aged (P=0.367-0.620).

CONCLUSIONS

Of all the variables assessed in this study, RSI exhibited the greatest decline (76%) between the young and old females. Such findings highlight the importance of reactive strength when assessing age-related changes in neuromuscular performance.

Declines in skeletal muscle quality vs. size following two weeks of knee joint immobilization

Background

Disuse of a muscle group, which occurs during bedrest, spaceflight, and limb immobilization, results in atrophy. It is unclear, however, if the magnitude of decline in skeletal muscle quality is similar to that for muscle size. The purpose of this study was to examine the effects of two weeks of knee joint immobilization on vastus lateralis and rectus femoris echo intensity and cross-sectional area.

Methods

Thirteen females (mean ± SD age = 21 ± 2 years) underwent two weeks of left knee joint immobilization via ambulating on crutches and use of a brace. B-mode ultrasonography was utilized to obtain transverse plane images of the immobilized and control vastus lateralis and rectus femoris at pretest and following immobilization. Effect size statistics and two-way repeated measures analyses of variance were used to interpret the data.

Results

No meaningful changes were demonstrated for the control limb and the rectus femoris of the immobilized limb. Analyses showed a large increase in vastus lateralis echo intensity (i.e., decreased muscle quality) for the immobilized limb (p = .006, Cohen’s d = .918). For vastus lateralis cross-sectional area, no time × limb interaction was observed (p = .103), but the effect size was moderate (d = .570). There was a significant association between the increase in vastus lateralis echo intensity and the decrease in cross-sectional area (r =  − .649, p = .016).

Conclusion

In female participants, two weeks of knee joint immobilization resulted in greater deterioration of muscle quality than muscle size. Echo intensity appears to be an attractive clinical tool for monitoring muscle quality during disuse.