Age-related reductions in muscle quality influence the relative differences in strength and power

Effects of High-Velocity Versus Low-Velocity Resistance Training on Muscle Echo Intensity in Healthy Young Women: A Randomized Controlled Trial

BACKGROUND

Improving muscle quality to prevent and treat muscle dysfunction is critical. However, effective measures to improve muscle quality remain poorly understood. We investigated the effects of high- and low-velocity resistance training (RT) on muscle quality, mass, and function before and after an 8-week intervention.

HYPOTHESIS

High-velocity RT would improve muscle quality more effectively than low-velocity RT.

STUDY DESIGN

Randomized controlled trial.

LEVEL OF EVIDENCE

Level 1.

METHODS

A total of 33 healthy young women (23.1 ± 2.2 years) were assigned randomly to high-velocity (n = 16) or low-velocity (n = 17) groups. Both groups underwent concentric knee extension RT with a 60% 1-repetition maximum (1RM) load, performing 10 repetitions of 4 sets, 3 times per week for 8 weeks. The high-velocity group was instructed to complete each repetition as quickly as possible (mean repetition duration of 0.5 seconds), while the low-velocity group was required to execute each repetition in 3 seconds. Before and after the 8-week intervention, quadriceps femoris echo intensity (EI), muscle thickness (MT), isokinetic peak torque (60 and 300 deg/s), rate of velocity development (RVD) at 300 deg/s, and 1RM were assessed. Split-plot factorial design analysis of variance was used to compare the group × time interaction.

RESULTS

A group×time interaction was observed for EI (P < 0.01). Only the high-velocity group showed a significant reduction in EI after the intervention. MT revealed a main effect of time (P < 0.01), with both groups significantly increasing MT. RVD showed a group × time interaction (P < 0.05), with significant increase only in the high-velocity group. Isokinetic peak torque and 1RM showed main effects of time (P < 0.01), with significant increases in both groups.

CONCLUSION

High-velocity RT may be superior to low-velocity RT in enhancing muscle quality and RVD.

CLINICAL RELEVANCE

These results emphasize the importance of RT velocity for muscle quality improvement.

Exploring the associations between skeletal muscle echogenicity and physical function in aging adults: A systematic review with meta-analyses

BACKGROUND

Assessment and quantification of skeletal muscle within the aging population is vital for diagnosis, treatment, and injury/disease prevention. The clinical availability of assessing muscle quality through diagnostic ultrasound presents an opportunity to be utilized as a screening tool for function-limiting diseases. However, relationships between muscle echogenicity and clinical functional assessments require authoritative analysis. Thus, we aimed to (a) synthesize the literature to assess the relationships between skeletal muscle echogenicity and physical function in older adults (≥60 years), (b) perform pooled analyses of relationships between skeletal muscle echogenicity and physical function, and (c) perform sub-analyses to determine between-muscle relationships.

METHODS

CINAHL, Embase, MEDLINE, PubMed, and Web of Science databases were systematically searched to identify articles relating skeletal muscle echogenicity to physical function in older adults. Risk-of-bias assessments were conducted along with funnel plot examination. Meta-analyses with and without sub-analyses for individual muscles were performed utilizing Fisher's Z transformation for the most common measures of physical function. Fisher's Z was back-transformed to Pearson's r for interpretation.

RESULTS

Fifty-one articles (n = 5095, female = ∼2759, male = ∼2301, 72.5 ± 5.8 years, mean ± SD (1 study did not provide sex descriptors)) were extracted for review, with previously unpublished data obtained from the authors of 13 studies. The rectus femoris (n = 34) and isometric knee extension strength (n = 22) were the most accessed muscle and physical qualities, respectively. The relationship between quadriceps echogenicity and knee extensor strength was moderate (n = 2924, r = -0.36 (95% confidence interval: -0.38 to -0.32), p < 0.001), with all other meta-analyses (grip strength, walking speed, sit-to-stand, timed up-and-go) resulting in slightly weaker correlations (r:  -0.34 to -0.23, all p < 0.001). Sub-analyses determined minimal differences in predictive ability between muscle groups, although combining muscles (e.g., rectus femoris + vastus lateralis) often resulted in stronger correlations with maximal strength.

CONCLUSION

While correlations were modest, the affordable, portable, and noninvasive ultrasonic assessment of muscle quality was a consistent predictor of physical function in older adults. Minimal between-muscle differences suggest that echogenicity estimates of muscle quality are systemic. Therefore, practitioners may be able to scan a single muscle to estimate full-body skeletal muscle quality/composition, while researchers should consider combining multiple muscles to strengthen the model.

Skeletal muscle fitness and physiology as determinants of firefighter performance and safety: a narrative review

Firefighters routinely perform tasks that are reliant on their muscular fitness, which includes muscular strength, power and endurance. Separately, firefighters can present with unique skeletal muscle physiology characteristics due to the strenuous nature of this occupation. This review aims to summarise muscular fitness and physiology as determinants of a firefighter's ability to perform occupation-specific tasks, identify the relevance of both muscular fitness and physiology to a firefighter's risk for sustaining a work-related injury, and address the contributions of muscular fitness and physiology on a firefighter's ability to recover from tasks and their readiness for performing subsequent or future tasks. The presented evidence reveals muscular fitness can determine a firefighter's capacity to perform their job effectively, while also influencing risk for occupational injury. Collectively, this review indicates exercise training emphasising improvements in muscular strength, power, and endurance (i.e. resistance training) should be encouraged in this occupation.

Older adults' lower-limb muscle power production throughout a full flight of stairs: Reliability and comparison between different stair models

Lower-limb muscle power should be closely monitored to prevent age-related functional ability declines. Stair-climbing (SC) power is a functionally relevant measurement of lower-limb muscle power. Body-fixed sensors can measure power production throughout the different steps of a flight of stairs to assess different aspects of performance. This study investigated: 1) power production throughout a full flight of stairs; 2) if staircases with less or more steps can provide similar information; and 3) test-retest reliability of SC power. 116 community-dwelling older adults (57 women) ascended three staircases as fast as possible: 12, 6 and 3 steps. Mean vertical power production per step was collected and analyzed using a commercial body-fixed sensor and software. Three phases were found in SC power production: 1) an acceleration phase, i.e., the power produced in step 1 (P1); 2) a phase where the highest performance (Pmax) is reached and; 3) a fatiguing phase with power loss (Ploss; only measurable on 12-step staircase). Mean power (Pmean) over the different steps was also evaluated. P1 did not differ between staircases (all p>0.05), whereas Pmax and Pmean were higher with increasing number of steps (p = 0.073 -p<0.001). P1, Pmax and Pmean were strongly correlated between staircases (r = 0.71-0.95, p<0.05). and showed good to excellent reliability (ICC = 0.66-0.95, p<0.05). Ploss showed poor reliability. To conclude, measurements of SC power production (P1, Pmax and Pmean) with a single sensor on the lower back are reliable across different staircases. A small, transportable, 3-step staircase can be used for measuring power production in clinical practices with no access to regular staircases. However, absolute values are dependent on the number of steps, indicating that measurements to track performance changes over time should always be done using an identical stair model.

Usefulness of muscle echo intensity for evaluating functional performance in the older population: A scoping review

Muscle echo intensity, as measured by ultrasonography, could be used as a new marker of functional performance in older populations. This scoping review aimed to present evidence on the utility of muscle echo intensity as determined by ultrasonography for assessing functional performance in older adults. The eligibility criterion included observational studies that investigated the associations between muscle echo intensity and functional performance in older adults. Terms, such as "echo intensity" and "older adults", were searched for in databases, such as PubMed, Web of Science, the Cochrane database of systematic reviews, and the Cumulative Index of Nursing and Allied Health Literature, in April 2021. Two independent reviewers screened and extracted the data; 46 papers, of which almost one-third were Japanese, were subsequently identified for inclusion. The representative functional performances included in this review were muscle strength, gait speed, sit-to-stand test results, and timed up-and-go test results. Poor to moderate associations were found between muscle echo intensity and functional performance; however, heterogeneities were observed in the characteristics of study participants. Moreover, the accurate effect size and causal inferences between muscle echo intensity and functional performance remained unclear. Further longitudinal studies are needed to determine these causal inferences.

Comparison of shear wave elastography with gray-scale USG and CT for quantitative evaluation of rectus femoris muscle

PURPOSE

The purpose of this study was to compare the measurement of shear wave elastography (SWE) and gray scale ultrasonography (GSU) and CT attenuation of mid-rectus femoris (RF) muscle in healthy adults.

METHODS

This prospective study included 70 participants with a healthy body mass index (<25 kg/m² ) between June 2019 and January 2020. Echo intensity (EI) grading of RF on GSU was performed. SWE was performed for the three levels of the RF. Measurements were repeated 10 min after the first measurement. The mid-RF attenuation on CT was also measured. Interobserver agreement of EI grade among three readers was assessed using weighted-kappa statistics. The reliability of SWE was assessed using intraclass correlation coefficient. The correlations between the SWE and CT/GSU measurements were analyzed.

RESULTS

Interobserver agreement of EI grade on GSU by the three radiologists was moderate to substantial (k = 0.562-0.767). The inter-session agreements for SWE were almost perfect for mid RF (k = 0.822-0.829) and substantial for proximal and distal RF (k = 0.767-0.795). There were significant correlations between SWE-EI and SWE-CT attenuation (p < 0.001, respectively) at the mid-RF.

CONCLUSIONS

SWE measurements on mid-RF demonstrated the highest reliability. SWE parameters showed a strong correlation with EI on GSU and attenuation on CT.

Ten-year longitudinal changes in muscle power, force, and velocity in young, middle-aged, and older adults

BACKGROUND

Maximum muscle power (P_max ) is a biomarker of physical performance in all ages. No longitudinal studies have assessed the effects of aging on P_max obtained from the torque-velocity (T-V) relationship, which should be considered the 'gold standard'. This study evaluated the longitudinal changes in the T-V relationship and P_max of the knee-extensor muscles in young, middle-aged, and older adults after 10 years of follow-up.

METHODS

Four hundred eighty-nine subjects (311 men and 178 women; aged 19-68 years) were tested at baseline and after a 10-year follow-up. Anthropometric data, daily protein intake, physical activity level (PAL), and knee-extension muscle function (isometric, isokinetic, and isotonic) were evaluated. A novel hybrid equation combining a linear and a hyperbolic (Hill-type) region was used to obtain the T-V relationship and P_max of the participants, who were grouped by sex and age (young: 20-40 years; middle-aged: 40-60 years; and old: ≥60 years). Linear mixed-effect models were used to assess effects of time, sex, and age on T-V parameters, P_max , and body mass index (BMI). Additional analyses were performed to adjust for changes in daily protein intake and PAL.

RESULTS

P_max decreased in young men (-0.6% per year; P < 0.001), middle-aged men and women (-1.1% to -1.4% per year; P < 0.001), and older men and women (-2.2% to -2.4% per year; P ≤ 0.053). These changes were mainly related to decrements in torque at P_max at early age and to decrements in both torque and velocity at P_max at older age. BMI increased among young and middle-aged adults (0.2% to 0.5% per year; P < 0.001), which led to greater declines in relative P_max in those groups. S/T₀ , that is, the linear slope of the T-V relationship relative to maximal torque, exhibited a significant decline over time (-0.10%T₀ ·rad·s^-1 per year; P < 0.001), which was significant among middle-aged men and old men and women (all P < 0.05). Annual changes in PAL index were significantly associated to annual changes in P_max (P = 0.017), so the overall decline in P_max was slightly attenuated in the adjusted model (-5.26 vs. -5.05 W per year; both P < 0.001).

CONCLUSIONS

P_max decreased in young, middle-aged, and older adults after a 10-year follow-up. The early declines in P_max seemed to coincide with declines in force, whereas the progressive decline at later age was associated with declines in both force and velocity. A progressively blunted ability to produce force, especially at moderate to high movement velocities, should be considered a specific hallmark of aging.

Factors of Muscle Quality and Determinants of Muscle Strength: A Systematic Literature Review

Muscle quality defined as the ratio of muscle strength to muscle mass disregards underlying factors which influence muscle strength. The aim of this review was to investigate the relationship of phase angle (PhA), echo intensity (EI), muscular adipose tissue (MAT), muscle fiber type, fascicle pennation angle (θf), fascicle length (lf), muscle oxidative capacity, insulin sensitivity (IS), neuromuscular activation, and motor unit to muscle strength. PubMed search was performed in 2021. The inclusion criteria were: (i) original research, (ii) human participants, (iii) adults (≥18 years). Exclusion criteria were: (i) no full-text, (ii) non-English or -German language, (iii) pathologies. Forty-one studies were identified. Nine studies found a weak−moderate negative (range r: [−0.26]−[−0.656], p < 0.05) correlation between muscle strength and EI. Four studies found a weak−moderate positive correlation (range r: 0.177−0.696, p < 0.05) between muscle strength and PhA. Two studies found a moderate-strong negative correlation (range r: [−0.446]−[−0.87], p < 0.05) between muscle strength and MAT. Two studies found a weak-strong positive correlation (range r: 0.28−0.907, p < 0.05) between θf and muscle strength. Muscle oxidative capacity was found to be a predictor of muscle strength. This review highlights that the current definition of muscle quality should be expanded upon as to encompass all possible factors of muscle quality.

The Influence of Ultrasound Image Depth and Gain on Skeletal Muscle Echo Intensity

Echo intensity may associate with indicators of skeletal muscle quality, but investigators often use different methodological approaches that may alter echo intensity when acquiring B-mode ultrasound images. We examined the influence of image depth and gain settings on the interpretation of echo intensity. Thirty-six college-aged males and females participated. Ultrasound images of the vastus lateralis were captured in the sagittal plane. Images were captured at depths of 3.0, 3.5, 4.0, 4.5, 5.0, 6.0, and 7.0cm and gain settings of 50 and 60 dB in random order. For both gain settings, echo intensity values were similar between 4.0 and 6.0cm. At a gain of 50dB, 7.0cm demonstrated greater values than all other depths. At a gain of 60dB, 7.0cm displayed greater values compared to all other depths, but 3.0cm displayed lower echo intensity values than other depths. Echo intensity was substantially higher when using a gain of 60dB compared to 50dB (mean difference ≥ 21.7 arbitrary units, d ≥ 3.47). When planning investigations in new research areas, researchers should carefully consider their study-specific image depth. Echo intensity values are stable between depths of 4.0 and 6.0cm, suggesting that changing image depth may not be problematic. Image gain must be kept constant. Novelty Bullets • Optimal approaches for B-mode ultrasound image acquisition of skeletal muscles remain unclear. • Echo intensity is similar between depths of 4.0 and 6.0cm, regardless of image gain. • Investigators should seek to utilize a constant depth setting, but small deviations may be acceptable.

The relationship between quantitative magnetic resonance imaging of the ankle plantar flexors, muscle function during walking and maximal strength in people with neuromuscular diseases

BACKGROUND

Progression of plantar flexor weakness in neuromuscular diseases is usually monitored by muscle strength measurements, although they poorly relate to muscle function during walking. Pathophysiological changes such as intramuscular adipose tissue affect dynamic muscle function independent from isometric strength. Diffusion tensor imaging and T2 imaging are quantitative MRI measures reflecting muscular pathophysiological changes, and are therefore potential biomarkers to monitor plantar flexor functioning during walking in people with neuromuscular diseases.

METHODS

In fourteen individuals with plantar flexor weakness diffusion tensor imaging and T2 scans of the plantar flexors were obtained, and the diffusion indices fractional anisotropy and mean diffusivity calculated. With a dynamometer, maximal isometric plantar flexor strength was measured. 3D gait analysis was used to assess maximal ankle moment and power during walking.

FINDINGS

Fractional anisotropy, mean diffusivity and T2 relaxation time all moderately correlated with maximal plantar flexor strength (r > 0.512). Fractional anisotropy and mean diffusivity were not related with ankle moment or power (r < 0.288). T2 relaxation time was strongly related to ankle moment (r = -0.789) and ankle power (r = -0.798), and moderately related to maximal plantar flexor strength (r < 0.600).

INTERPRETATION

In conclusion, T2 relaxation time, indicative of multiple pathophysiological changes, was strongly related to plantar flexor function during walking, while fractional anisotropy and mean diffusivity, indicative of fiber size, only related to maximal plantar flexor strength. This indicates that these measures may be suitable to monitor muscle function and gain insights into the pathophysiological changes underlying a poor plantar flexor functioning during gait in people with neuromuscular diseases.

The Influence of Motor Unit Number and Muscle Activation on Early Phase Rate of Torque Development in Younger and Older Men

This study examined the influence of muscle activation and motor unit number estimation (MUNE) on early phase voluntary rate of torque development (RTD) in younger (YM) and older (OM) men. Thirty-two YM (n = 17; Age = 22 yrs) and OM (n = 15; Age = 74 yrs) volunteered to participate in this study. Early phase RTD (first 50 ms of a rapid isometric contraction; RTD₅₀) and normalized surface electromyography (first 50 ms of muscle excitation; nEMG₅₀) were recorded from the right quadricep muscle group. MUNE was examined from the right vastus lateralis. Multiple linear regression analyses revealed that nEMG₅₀ had a significant effect on RTD₅₀ independent of age group (p ≤ 0.001). nEMG₅₀ had a significant effect on RTD₅₀ in the OM group (p = 0.037). MUNE had no effect on RTD₅₀ independent of age. Older adults may depend more on muscle activation at contraction onset of early phase RTD compared to younger adults.

The Influence of Sonographer Experience on Skeletal Muscle Image Acquisition and Analysis

The amount of experience with ultrasonography may influence measurement outcomes while images are acquired or analyzed. The purpose of this study was to identify the interrater reliability of ultrasound image acquisition and image analysis between experienced and novice sonographers and image analysts, respectively. Following a brief hands-on training session (2 h), the experienced and novice sonographers and analysts independently performed image acquisition and analyses on the biceps brachii, vastus lateralis, and medial gastrocnemius in a sample of healthy participants (n = 17). Test-retest reliability statistics were computed for muscle thickness (transverse and sagittal planes), muscle cross-sectional area, echo intensity and subcutaneous adipose tissue thickness. The results show that image analysis experience generally has a greater impact on measurement outcomes than image acquisition experience. Interrater reliability for measurements of muscle size during image acquisition was generally good-excellent (ICC2,1: 0.82-0.98), but poor-moderate for echo intensity (ICC2,1: 0.43-0.77). For image analyses, interrater reliability for measurements of muscle size for the vastus lateralis and biceps brachii was poor-moderate (ICC2,1: 0.48-0.70), but excellent for echo intensity (ICC2,1: 0.90-0.98). Our findings have important implications for laboratories and clinics where members possess varying levels of ultrasound experience.

The influence of age on the recovery from worksite resistance exercise in career firefighters

Resistance exercise is an important strategy to reduce injuries and improve performance in the fire service. However, given the large age range of firefighters, it is important to determine if age influences their recovery following an acute bout of resistance exercise.

PURPOSE

To examine the changes in indirect markers of muscle damage in young and older firefighters following a feasible worksite resistance exercise routine.

METHODS

Nineteen young (25.5 ± 3.4 years) and 19 older male career firefighters (50.3 ± 3.5 years) completed pre-testing, an acute bout of resistance exercise, and post-testing at 24, 48, and 72 h post-exercise at their fire station. Prior to all testing, firefighters completed a work-related fatigue (WRF) questionnaire to account for potential unanticipated differences in previous shift workloads. Testing included perceived muscle soreness, ultrasonography to quantify muscle size and echo intensity (EI) of the vastus lateralis (VL) and biceps brachii (BB), countermovement jump (CMJ) height and velocity, upper body (UB) peak force (PF), lower body (LB) PF and rapid force, and electromyographic (EMG) amplitude of the VL. The resistance training session included 3 sets of 8-10 repetitions of a deadlift, shoulder press, lunge, and upright row exercise at 80% 1-RM. All recovery variables were analyzed using a linear mixed model, controlling for WRF.

RESULTS

There was no interaction (age × time) for any of the variables and a similar training volume were completed between groups (P ≥ 0.171). Muscle soreness, CMJ height and velocity, UB PF, LB rapid force and EMG amplitude at later time intervals (100-200 ms), and VL and BB muscle size were altered from baseline (P ≤ 0.044) for 48, 24, 48, 72, and 72 h post-exercise, respectively. Young firefighters exhibited greater CMJ height and velocity, LB PF, LB rapid force (200 ms), and lower VL EI values than the older firefighters (P ≤ 0.047).

CONCLUSIONS

Age did not influence the recovery from an acute bout of worksite resistance exercise in firefighters. However, UB muscle strength, CMJ performance, and LB rapid force production were reduced 24-72 h post-exercise. Appropriately scheduled and chronic on-duty resistance training may mitigate these decrements.

Muscle Performance Changes with Age in Active Women

The purpose of this study was to examine age-related differences in muscle performance in women divided into young (YW, 20–39 years, n = 29) middle-aged (MAW, 40–59 years, n = 33), and older (OW, ≥60 years, n = 40) age groups. Methods: Hand grip strength, vertical jump performance, and knee extensor (KE) strength (0 deg/s, 60 deg/s, and 240 deg/s), speed of movement (SoM; at 1 Nm, 20%, 40%, and 60% isometric strength), and endurance (30-repetition test at 60 degs/s and 240 deg/s) were assessed. Computed tomography-acquired muscle cross-sectional area (mCSA) was measured and included to determine specific strength (KE strength/mCSA). Results: Hand grip strength was similar across groups, while jump performance declined with age (YW and MAW > OW, p < 0.001). KE strength declined significantly with age (all conditions p < 0.01), while specific strength was similar across groups. SoM was significantly higher for YW and MAW compared to OW (both p < 0.01). An age × velocity interaction revealed YW KE endurance was similar between conditions, whereas MAW and OW displayed significantly better endurance during the 60 deg/s condition. OW displayed impaired KE endurance at 240 deg/s (vs. YW and MAW, p < 0.01) but improved at 60 deg/s (vs. YW, p < 0.01). Dynamic torque decline increased with age (YW < OW, p = 0.03) and was associated with intramuscular adipose tissue (r = 0.21, p = 0.04). Conclusions: Performance declines were most evident among OW, but few performance deficits had emerged in MAW. Interestingly, strength declines disappeared after normalizing to mCSA and endurance appears to be velocity-dependent.

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.

Influence of joint angle on muscle fascicle dynamics and rate of torque development during isometric explosive contractions

Ankle angle influences the operating muscle fascicle lengths of gastrocnemius medialis and the rate of torque development during explosive isometric plantar flexions. The rate of torque development peaks in neutral angles where muscle fascicles shorten over the plateau of the force-length relationship. When fascicles operate over the plateau of the force-length relationship (neutral ankle positions), the force-velocity properties represent a limiting factor for the rapid force-generating capacity from 100 ms after the onset of explosive contractions.

The Influence of Age and Obesity-Altered Muscle Tissue Composition on Muscular Dimensional Changes: Impact on Strength and Function

The purpose of this study was to determine if muscular dimensional changes with increases in torque production are influenced by age- and obesity-related increases in intramuscular fat, and its relationship to percent body fat (%BF), echo intensity (EI), strength, and maximum walking speed. Sixty-six healthy men were categorized into 3 groups based on age and body mass index status (young normal weight [YNW], older normal weight [ONW], and older obese [OB]). Participants underwent %BF assessments, resting ultrasonography to determine muscle size (cross-sectional area [CSA]) and EI of the superficial quadriceps, and a 10-m maximum walking speed assessment. Maximal and submaximal (rest–100% MVC in 10% increments) isometric leg extension strength was assessed while changes in rectus femoris (RF) CSA, width, and depth were obtained with ultrasonography. Echo intensity and %BF were different among all groups (p ≤ .007), with the YNW and OB groups exhibiting the lowest and highest %BF and EI values, respectively. The RF increased in depth and decreased in width with increases in torque intensity for all groups. The ONW group demonstrated no change (−0.08%) in RF CSA across torque intensities, whereas the YNW group (−11.5%) showed the greatest decrease in CSA, and the OB group showed a more subtle decrease (−4.6%). Among older men, a greater change in RF CSA was related to poorer EI (r = −0.355) and higher %BF (r = −0.346), while a greater decrease in RF width was associated with faster walking speeds (r = −0.431). Examining muscular dimensional changes during contraction is a unique model to investigate the influence of muscle composition on functional performance.

Early and late rapid torque characteristics and select physiological correlates in middle-aged and older males

Purpose

The purpose of this study was to compare early and late rapid torque parameters of the plantar flexors (PFs) in middle-aged (MM) and older (OM) males, and determine the effect of normalization to peak torque (PT) and muscle cross-sectional area (CSA).

Methods

Twenty-nine healthy, MM (n = 14; 45 ± 2 yrs) and OM (n = 15; 65 ± 3 yrs) performed rapid, maximal isometric contractions of the PFs. PT, as well as rate of torque development and impulse during the early (0–50 ms; RTD_0-50, IMP_0-50) and late (100–200 ms; RTD_100-200, IMP_100-200) contraction phases were calculated. Torque at 50 (TQ₅₀), 100 (TQ₁₀₀), and 200 (TQ₂₀₀) ms was also obtained. CSA and echo-intensity (EI) of the gastrocnemii were acquired via ultrasonography. Torque variables were normalized to PT and CSA. Rate of EMG rise (RER) for the medial gastrocnemius was calculated at 30, 50 and 75 ms.

Results

TQ₁₀₀ (MM = 69.71 ± 16.85 vs. OM = 55.99 ± 18.54 Nm; p = 0.046), TQ₂₀₀ (MM = 114.76 ± 26.79 vs. OM = 91.56 ± 28.10 Nm; p = 0.031), and IMP_100-200 (MM = 4.79 ± 1.11 vs. OM = 3.83 ± 1.17 Nm·s; p = 0.032) were lower in OM. PT, TQ₅₀, RTD_0-50, IMP_0-50, RTD_100-200, RER, CSA, and EI were similar between groups (p > 0.05). No differences were found for normalized torque variables (p > 0.05). EI was moderately associated with normalized torque parameters only (r = -0.38 –-0.45). RER, at 75 ms, was moderately correlated with early, absolute torque measures and rapid torque variables made relative to PT and CSA (r = 0.41 –-0.64).

Conclusion

Late rapid torque parameters of the PFs were preferentially impaired in OM compared to MM, and PT as well as CSA appeared to mediate this result.

Neuromuscular function of the plantar flexors and predictors of peak power in middle-aged and older males

Little evidence exists regarding the contribution of torque and velocity to the age-related decrease in peak power (PP) for the plantar flexors (PFs). A comprehensive assessment of PF neuromuscular function is necessary to elucidate age-related changes, especially between middle-aged and older adults, in order to identify early, age-related decrements. Thus, the purpose of this study was to examine neuromuscular function of the PFs in middle-aged and older males, and identify predictors of PP. Twenty-eight healthy, middle-aged (n = 13; 45.1 ± 2.7 yrs) and older (n = 15; 65.3 ± 3.2 yrs) males performed concentric isotonic PF contractions ranging in intensity from 20% to 70% isometric strength using a dynamometer. PP in addition to velocity and torque at the moment in time PP occurred, as well as the rate of velocity, torque (RTD), and power (RPD) development were recorded. The rate of electromyography rise (RER) was derived from the linear slope of the normalized electromyography signal. Isometric and concentric dynamic strength were assessed, as well as cross-sectional area and muscle quality (i.e., echo intensity) of the PFs via panoramic ultrasonography. The relationship between serum c-terminal agrin levels and select variables was examined to explore the potential role of neuromuscular junction deterioration. Appendicular lean mass and physical activity level were similar between groups (p > 0.05), and only PP (p = 0.046; d = 0.79), RPD (p = 0.026; d = 0.90), RTD (p = 0.022; d = 0.91), and RER (p = 0.010; d = 1.04) were lower in older males. When groups were collapsed, RTD was the only significant predictor of PP, while c-terminal agrin levels were not associated with any variables. Our findings indicate that PP and time-dependent parameters of muscle activation and contractile function of the PFs are dramatically diminished in older adults compared to middle-aged adults. PP is produced at the same velocity and relative intensity in middle-aged and older males, and RTD is most influential for PP. The inability of the PFs to be rapidly activated appeared to be influential for the age-related impairment in PP and time-dependent contractile parameters.

Age-related changes in the passive properties of the plantarflexors: Influence of tissue size and quality

BACKGROUND

Limited research exists examining the influence of age on the passive mechanical properties of the muscle-tendon unit. The purpose of the present study was to 1) investigate the age-related differences in maximum range of motion (MRoM), stretch tolerance (maximal tolerable torque), and the dissipation coefficient (DC), and 2) examine the influence of plantarflexor muscle size and quality on the age-related differences in the DC.

METHODS

Twenty-one young and 14 older men completed a MRoM assessment to determine peak torque (PT_pass), energy stored (area under the loading curve), energy restituted (area under the unloading curve), and the DC (normalized hysteresis) from the angle-torque curve. Ultrasonography was used to determine muscle cross-sectional area (CSA) and subcutaneous fat corrected echo intensity (EI) of the gastrocnemii.

FINDINGS

The PT_pass, MRoM, and energy restituted were greater (P ≤ 0.046) in the young men, whereas the DC and EI were greater (P ≤ 0.024) in the older men. When accounting for CSA, differences between groups for the DC remained (P = 0.028), while there were no longer differences between groups when accounting for EI (P = 0.120). PT_pass was also strongly related to MRoM (r = 0.755, P < 0.001).

INTERPRETATION

Older men exhibited lower dorsiflexion MRoM and a greater DC, which may be explained by an altered stretch tolerance and qualitative changes (i.e., non-contractile tissue infiltration) in aged skeletal muscle leading to greater energy dissipated, respectively.

Influence of Muscle Quality on the Differences in Strength From Slow to Fast Velocities in Career Firefighters

Gerstner, GR, Giuliani, HK, Mota, JA, and Ryan, ED. Influence of muscle quality on the differences in strength from slow to fast velocities in career firefighters. J Strength Cond Res 32(10): 2982-2986, 2018-The purpose of this study was to examine the relationship between ultrasound-derived muscle quality and the %decrease in peak torque (PT) from slow to fast velocities in career firefighters. Thirty-nine male career firefighters (mean ± SD: age = 36.90 ± 6.87 years; stature = 180.93 ± 6.98 cm; mass = 109.30 ± 20.57 kg; and body mass index [BMI] = 33.24 ± 4.95 kg·m) performed 3 maximal concentric isokinetic contractions at a slow (1.05 rad·s) and fast (4.19 rad·s) velocity in random order. The velocity-related decrease in PT was calculated as the %decrease from 1.05 to 4.19 rad·s. Ultrasonography was used to determine subcutaneous fat corrected echo intensity (EI) to represent muscle quality before strength testing. The results indicated that there was a significant relationship between EI and %decrease in PT while adjusting for age (rpartial = 0.331, p = 0.042), and age and BMI (rpartial = 0.325, p = 0.050). These findings suggest that velocity-impaired isokinetic strength may be influenced by alterations in skeletal muscle tissue composition. Future studies are needed to determine whether the %decrease in PT is related to performance during critical firefighter tasks.

Echo Intensity Versus Muscle Function Correlations in Older Adults are Influenced by Subcutaneous Fat Thickness

Recently, an equation that allows investigators to correct echo intensity for subcutaneous fat was developed. We evaluated correlations between uncorrected and corrected echo intensity versus measures of lower-extremity function. Twenty-three older adults (11 men, 12 women; mean age = 72 y) participated. B-Mode ultrasonography was used to quantify rectus femoris echo intensity and subcutaneous fat thickness. Knee extensor isometric peak torque and rate of torque development at 200 ms (RTD200) were determined (joint angle = 90°). Fast gait speed was evaluated at 10- and 400-m distances. Partial correlations between normalized peak torque, RTD200 and 10- and 400-m gait speed versus uncorrected echo intensity were weak and insignificant. Correction for subcutaneous fat strengthened the correlations (peak torque r = -0.500, RTD200 r= -0.425, 10-m r = -0.409, 400-m r = -0.410). Correcting echo intensity values for subcutaneous fat strengthened the associations with lower-extremity muscle function in older adults.