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

Phase angle as an independent predictor of sarcopenia and glycemic control in older adults with type 2 diabetes: a cross-sectional observational study

Objectives

The global rise in type 2 diabetes mellitus (T2DM) poses challenges, particularly with the increasing burden of sarcopenia and poor glycemic control. Phase angle (PhA) is a promising biomarker for early detection and management of these conditions. This study aimed to evaluate PhA as an independent predictor of sarcopenia and glycemic control.

Methods

This cross-sectional study included older adults with T2DM hospitalized for diabetes education between April 2021 and March 2023. Measurements included PhA, muscle mass, body fat mass, grip strength, knee extension strength, physical function (Short Physical Performance Battery and 6-min walk distance), and glycemic control (fasting blood glucose and hemoglobin A1c [HbA1c]). Sarcopenia was defined as low muscle mass and physical function. Analyses included Pearson correlations, receiver operating characteristic curve analysis, and multivariate logistic regression.

Results

PhA was moderately correlated with muscle mass (r = 0.42, p < 0.001), grip strength (r = 0.43, p < 0.001), and body mass index (r = 0.27, p = 0.001), and inversely correlated with HbA1c (r = - 0.34, p < 0.001) and age (r = - 0.26, p = 0.003). PhA showed a strong predictive ability for sarcopenia (AUC = 0.83, 95% CI: 0.76-0.90, p < 0.001). Logistic regression indicated PhA as an independent predictor of sarcopenia (OR = 0.105, 95% CI: 0.031-0.353, p < 0.001) and glycemic control (OR = 0.380, 95% CI: 0.201-0.719, p = 0.003).

Conclusions

PhA is a non-invasive, practical tool for predicting sarcopenia and monitoring glycemic control. Routine integration of PhA could identify high-risk patients and guide interventions. Future research should validate its application in diverse settings.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-025-01590-z.

Segmental phase angle and the extracellular to intracellular water ratio are associated with functional disability in community-dwelling older adults: A follow-up study of up to 12 years

BACKGROUND & AIMS

Muscle quality, including phase angle (PhA) and extracellular to intracellular water (ECW/ICW) ratio, assessed using multi-frequency bioelectrical impedance analysis (MF-BIA) to reflect the contractile components of the muscle, muscle cell mass, and membrane condition, is associated with health outcomes. However, its association with the incidence of disabilities remains unclear. The aim of this study was to examine the association between whole-body and segmental PhA, ECW/ICW ratio, and the incidence of functional disability compared to conventional muscle mass.

METHODS

A total of 858 older adults aged ≥65 years without functional disability at baseline were followed up for 12 years. Functional disabilities were identified using the database of the Japanese Long-Term Care Insurance System. Segmental muscle quality was assessed using the raw parameters of MF-BIA, including segmental PhA and the ECW/ICW resistance ratio. For comparison, the appendicular lean mass index (ALMI) and legMI were obtained using MF-BIA.

RESULTS

Functional disability was identified in 258 (30.1%) participants. Cox regression analysis showed that poorer leg PhA and ECW/ICW resistance ratios were significantly associated with a higher incidence of functional disability in both sexes, independent of covariates. A dose-response relationship indicated a higher risk for individuals with values below the median in the spline analysis. Conventional ALMI and legMI were not significantly associated with functional disability.

CONCLUSIONS

PhA and ECW/ICW ratio, especially in the leg, is a better predictor of functional disability than muscle mass. Muscle quality by BIA may be a useful biomarker for screening for future disabilities.

Muscle oxidative capacity but not specific force is greater in aerobic versus resistance trained young adults

PURPOSE

Near-infrared spectroscopy (NIRS) can be applied to assess skeletal muscle oxidative capacity ( m V ˙ O 2 ). Specific force (SF) and echo intensity (EI) represent muscle quality. However, it is unknown how exercise participation and biological sex impact m V ˙ O 2 , and if measures of muscle quality are related to m V ˙ O 2 . The aim was to assess training history- and biological sex-related differences in m V ˙ O 2 , SF, and EI in males and females.

METHODS

To determine training history, 50 adults (23 females, 66% resistance trained, age:22 ± 3 years) completed strength and cardiorespiratory fitness assessments. Ultrasonography assessed muscle cross-sectional area (mCSA) and EI of the dominant vastus lateralis. The ratio of maximal strength to mCSA was defined as SF. To assess m V ˙ O 2 , participants cycled for 5 min at 50% of their peak power observed at maximal oxygen consumption. Following this, a mono-exponential decay curve, deriving the rate constant (k), was created from post-exercise NIRS recovery slopes. Separate 2(Sex) × 2(Training History) ANOVAs examined differences in k, SF, and EI. Pearson's correlation coefficients evaluated relations among k, SF, and EI.

RESULTS

There was a significant interaction for k (p = 0.025,η p 2 = 0.105 ), such that k was greater in aerobically trained adults. Additionally, SF was significantly greater for resistance trained individuals (p < 0.001), whereas EI was not different between training history groups (p = 0.363). For the resistance trained group, SF and m V ˙ O 2 were related (r = - 0.455, p = 0.002). EI was associated with m V ˙ O 2 (r = 0.465, p = 0.006).

CONCLUSION

Chronic aerobic exercise promotes faster recovery following exercise bouts, whereas resistance training yields superior muscle quality, possibly demonstrating the consequences of a physiological trade-off and/or training-specificity.

Detrimental Effects of β2-Microglobulin on Muscle Metabolism: Evidence From In Vitro, Animal and Human Research

BACKGROUND

β2-Microglobulin (B2M) has garnered considerable interest as a potential pro-ageing factor, leading to speculation about its involvement in muscle metabolism and the development of sarcopenia, a key component of ageing phenotypes. To explore this hypothesis, we conducted a comprehensive investigation into the impact of B2M on cellular and animal muscle biology, as well as its clinical implications concerning sarcopenia parameters in older individuals.

METHODS

In vitro myogenesis was induced in mouse C2C12 myoblasts with 2% horse serum. For in vivo research, C57BL/6 mice aged 3 months were intraperitoneally given 250 μg of B2M daily, and muscular alterations were assessed one month later. Human blood samples were obtained from 158 participants who underwent assessments of muscle mass and function at an outpatient geriatric clinic affiliated with a teaching hospital. Sarcopenia and associated parameters were assessed using cut-off values specifically tailored for the Asian population. The concentration of serum B2M was quantified through an enzyme-linked immunosorbent assay.

RESULTS

Recombinant B2M inhibited in vitro myogenesis by increasing intracellular reactive oxygen species (ROS) production. Furthermore, B2M significantly induced differential myotube atrophy via ROS-mediated ITGB1 downregulation, leading to impaired activation of the FAK/AKT/ERK signalling cascade and enhanced nuclear translocation of FoxO transcription factors. Animal experiments showed that mice with systemic B2M treatment exhibited significantly smaller cross-sectional area of tibialis anterior and soleus muscle, weaker grip strength, shorter grid hanging time, and decreased latency time to fall off the rotating rod, compared to untreated controls. In a clinical study, serum B2M levels were inversely associated with grip strength, usual gait speed and short physical performance battery (SPPB) total score after adjustment for age, sex, and body mass index, whereas sarcopenia phenotype score showed a positive association. Consistently, higher serum B2M levels were associated with higher risk for weak grip strength, slow gait speed, low SPPB total score, and poor physical performance.

CONCLUSION

These results provide experimental evidence that B2M exerted detrimental effects on muscle metabolism mainly by increasing oxidative stress. Furthermore, we made an effort to translate the results of in vitro and animal research into clinical implication and found that circulating B2M could be one of blood-based biomarkers to assess poor muscle health in older adults.

Thirty-second chair stand test in older adults with chronic health conditions is associated with lower limb oxygen extraction capacity

BACKGROUND

The 30-s chair stand test (CS-30) is a well-known measure of muscle strength in older adults. However, factors other than muscle strength may also be involved in older adults with chronic health conditions who require support and care in daily living.

PURPOSE

To test the hypothesis that the CS-30 in older adults with chronic health conditions is associated with lower limb muscle oxygen extraction capacity.

METHODS

Twenty-seven older adults with chronic health conditions (those who needed support and care in daily living because of stroke, musculoskeletal disease, etc.) were recruited. Tissue and percutaneous oxygen saturations of the right vastus lateralis muscle were measured during CS-30 measurements, and muscle oxygen extraction rate (MOER) was calculated. Knee extension strength, skeletal muscle mass index (SMI), and phase angle (PhA) were measured. In a multiple regression analysis with CS-30 as the dependent variable, results were calculated for model 1 with SMI, PhA, and ΔMOER as independent variables and model 2 with knee extension muscle strength added to model 1.

RESULTS

Phase angle (model 1, β = 0.46, p = .014; model 2, β = 0.46, p = .016) and ΔMOER (model 1, β = 0.39, p = .032; model 2, β = 0.40, p = .039) were significantly associated in both models. Adjusted R2 was 0.26 (Model 1) and 0.23 (Model 2).

CONCLUSION

The CS-30 in older adults with chronic health conditions may be related to muscle oxygen extraction capacity. This indicates that CS-30 also considers lower limb endurance assessment in this population.

Differences in muscle morphology assessed by ultrasound at various muscle regions and their impact on voluntary and involuntary force production

The primary aim of this study was to investigate how measurements from different regions along the rectus femoris (RF) and vastus lateralis (VL) influence muscle morphology, including muscle thickness (MT), muscle stiffness, and muscle quality. An exploratory aim was to examine whether an association exists between voluntary and involuntary force and muscle morphology across the same regions. In one session, participants (n = 13) underwent ultrasound imaging (US), followed by knee extension maximal isometric voluntary contractions and evoked contractions. US recordings (at rest) and testing were conducted while participants were seated at 90º knee flexion (dominant leg) on an isokinetic dynamometer. Muscle morphology was recorded at proximal, medial, and distal regions of RF and VL. During maximum contractions, participants were instructed to exert maximal effort as fast and as forcefully as possible for 5 s, while evoked contractions were performed via femoral nerve stimulation. A one-way repeated measures ANOVA was used for the main aim, while Spearman bivariate correlations were used for the exploratory aim. The primary findings showed that the RF and VL muscles were significantly larger in the medial region (P ≤ 0.023), with no significant differences in muscle quality or stiffness within the same muscle. Additionally, a significant overall relationship was observed between muscle quality and the rate of force development in both muscles (P ≤ 0.037). In conclusion, muscle size varies across the length of the VL and RF muscles, with no changes in muscle quality or stiffness. Furthermore, muscle quality demonstrates a significant association with rate of force development.

Fork in the road: therapeutic and pathological actions for fibro-adipogenic progenitors following musculoskeletal injury

Musculoskeletal injuries are a substantial source of global disability through weakness and loss of function, which can be attributable, in part, to deficits in skeletal muscle quality. Poor muscle quality, resulting from fibrotic pathology or fatty infiltration, strongly predicts lower rates of patient recovery following injury and higher rates of re-injury. The cellular sources of fibrosis and fatty infiltration within skeletal muscle are mesenchymal fibro-adipogenic progenitors (FAPs), which are central effectors to support muscle homeostasis, regeneration and growth. However, following acute or chronic musculoskeletal injury, FAPs can promote fibro/fatty pathology within muscle that is likely to limit recovery and repair. Given their indispensable role within skeletal muscle, FAPs have emerged as a compelling cellular target to promote tissue recovery following acute and chronic injury. This review provides insight into the aetiology of FAP activity following various musculoskeletal injuries, in addition to signalling components that effect FAP differentiation. Contrasting pathology with therapeutic potential, insight into disease- and injury-specific FAP activation further cements their role as crucial effectors to improve muscle function and enhance patient outcomes.

Unraveling the role of muscle mass and strength in predicting type 2 diabetes risk: a systematic review

INTRODUCTION

Skeletal muscle is the largest insulin-sensitive tissue in the human body, alteration in muscle mass and strength substantially impact glucose metabolism. This systematic review aims to investigate further the relationship between muscle mass and strength towards type 2 diabetes mellitus (T2DM) incidence.

METHODS

This systematic review included cohort studies that examinedthe relationship between muscle mass and/or muscle strength on T2DM incidence. A comprehensive search was conducted across PubMed, EBSCO, ProQuest, and Google scholar employing specific Medical Subject Headings (MeSH) and relevant keywords related to or synonymous with "muscle mass", "muscle strength", and "Type 2 Diabetes Mellitus incidence".

RESULTS

Twenty-five cohort studies were included, 11 studies on muscle mass and 16 studies on muscle strength. Participants included were 278,475 for muscle mass and 400,181 for muscle strength. Skeletal muscle mass normalized to body weight (SMM/BW), appendicular skeletal musce mass normalized to body weight (ASM/BW), and handgrip strength normalized to body mass index (HGS/BMI) consistently demonstrate significant inverse association with T2DM even after sex and/or BMI stratification. Handgrip strength normalized to body weight (HGS/BW) demonstrates a strong inverse association with T2DM incidence, however, adiposity should be considered.

CONCLUSION

Muscle mass and strength demonstrate strong association with T2DM incidence. Adiposity, a key T2DM risk factor, should also be assessed through a simple BMI or a sophisticated technique with BIA or CT-scan. The combination of muscle variables and adiposity could further enhance T2DM risk assessment. However, T2DM risks are multifactorial, with various contributing factors, further large-scale studies are needed to validate these findings.

Gripping insights: prevalence of hypertension and its association with relative muscle strength-a cross-sectional study in an adult Indian population

BACKGROUND

Hypertension and muscle strength are known to be associated; however, identifying simple clinical indicators of this relationship is challenging. Relative muscle strength (RMS), defined as strength per unit muscle mass, has been proposed as a potential indicator, but its association with hypertension is unclear. This study aimed to estimate the prevalence of hypertension and determine its association with RMS in an adult Indian population attending a tertiary care center in Gujarat.

METHODS

This hospital-based cross-sectional study included 430 adults aged 18 years and older who were admitted to outpatient medicine clinics between January and October 2023. Grip strength and appendicular lean muscle mass (ALM), estimated using a validated formula, were measured. The RMS was calculated as grip strength/ALM. Hypertension was defined using standard criteria. Logistic regression was used to analyze the association between RMS (analyzed continuously and categorically in tertiles) and hypertension, adjusting for confounders. A p value of < 0.05 was considered significant.

RESULTS

The prevalence of prehypertension and hypertension was 187 (43%) and 96 (23%), respectively. Compared to participants in the low RMS tertile (0.00-2.45 kg/kg ALM), those in the high tertile (3.79-6.12 kg/kg ALM) had 26% lower odds of hypertension (OR 0.74, 95% CI 0.59-0.89) and 33% lower odds of prehypertension (OR 0.67, 95% CI 0.49-0.91) after adjusting for confounders. The RMS also showed strong negative correlations with systolic and diastolic blood pressure (r = - 0.559 and - 0.418, respectively; p < 0.001).

CONCLUSION

Increased RMS was significantly protective against prehypertension and hypertension. These findings highlight the potential importance of muscle quality, beyond muscle mass, in blood pressure regulation.

The water imbalance of skeletal muscle and muscle weakness in patients with heart failure

AIMS

A high extracellular water (ECW) to intracellular water (ICW) ratio of skeletal muscle as assessed by bioelectrical impedance analysis is reportedly associated with loss of muscle strength. However, the validity of this index for heart failure (HF), which is likely associated with changes in the water distribution, is unclear.

METHODS AND RESULTS

This study involved 190 patients with HF. The total ECW and ICW of both upper and lower extremities were measured, and a high ECW/ICW ratio was defined as an ECW/ICW ratio higher than the median (≥0.636 for men, ≥0.652 for women). Low muscle strength was defined as reduced handgrip strength according to the criteria established by the Asian Working Group for Sarcopenia. Patients with a high ECW/ICW ratio had a lower handgrip strength (21.1 ± 8.1 kg vs. 27.6 ± 9.3 kg, P ≤ 0.05) and 6 min walk distance (329 ± 116 m vs. 440 ± 114 m) than those with a low ECW/ICW ratio. An increasing ECW and/or decreasing ICW was associated with a higher ECW/ICW ratio and a lower handgrip strength (P < 0.05). In the multivariate logistic regression analysis, a high ECW/ICW ratio and low skeletal muscle mass were independently associated with low muscle strength (P < 0.05).

CONCLUSIONS

A high ECW/ICW ratio in limb muscles, that is, the water imbalance of increasing ECW and/or decreasing ICW, is useful in assessing muscle quality in patients with HF.

Dietary factors may be associated with measures of ultrasound-derived skeletal muscle echo intensity

Skeletal muscle echo intensity (EI) is affected by ageing and physical activity; however, the effects of nutrition are less understood. The aim of this study was to explore whether habitual nutrient intake may be associated with ultrasound-derived EI. Partial least squares regression (PLSR) models were trained on an initial sample (n = 100, M = 45; F = 55; 38 ± 15 years) to predict EI of two quadriceps muscles from 19 variables, using the "jack-knife" function within the "pls" package (RStudio), which was then tested in an additional dataset (n = 30, M = 13; F = 17; 38 ± 16 years). EI was determined using B-mode ultrasonography of the rectus femoris (RF) and vastus lateralis (VL) and nutritional intake determined via 3-day weighed food diaries. Mean daily intake of specific nutrients were included as predictor variables with age, sex, and self-reported physical activity. PLSR training model 1 explained ∼52% and model 2 ∼46% of the variance in RF and VL EI, respectively. Model 1 also explained ∼35% and model 2 ∼30% of the variance in RF and VL EI in the additional testing dataset. Age and biological sex were associated with EI in both models (P < 0.025). Dietary protein (RF: β = -7.617, VL: β = -7.480), and selenium (RF: β = -7.144, VL: β = -4.775) were associated with EI in both muscles (P < 0.05), whereas fibre intake (RF: β = -5.215) was associated with RF EI only and omega-3 fatty acids (n-3/ω-3 FAs, RF: β = 3.145) with VL EI only (P < 0.05). Therefore, absolute protein, selenium, fibre, and n-3 FAs may be associated with skeletal muscle EI, although further mechanistic work is required before claiming causal inference.

Improved trunk muscle quality in patients with stroke increases improvements in activities of daily living

BACKGROUND

This study aimed to determine whether an increased trunk muscle quality index (TMQI) is associated with activities of daily living (ADL) in patients ≥ 65 years of age with cerebral infarction in a convalescent rehabilitation ward.

METHODS

This retrospective observational study included patients aged ≥ 65 years who were admitted for post-stroke rehabilitation in Okinawa, Japan, between May 2018 and December 2022. The TMQI was calculated at admission and discharge using bioelectrical impedance analysis. Patients were divided into two groups based on the change in the TMQI during hospitalization: increase-in-TMQI and no-increase-in-TMQI groups. Multiple regression analysis was employed to explore the impact of increased TMQI on functional independence measure (FIM) -motor gain.

RESULTS

We included a total of 315 patients (79.1 ± 7.9 years of age, 51.7% men) in our analyses. Over half (165 [52.4%]) of the patients exhibited an increase in TMQI scores, and 150 (47.6%) patients did not exhibit an increase. No significant difference was observed in motor FIM score and motor FIM gain at admission and discharge between the groups with and without increased TMQI. Increased TMQI was independently associated with increased FIM-motor gain (adjusted R2 = 0.340 and R2 = 0.357, coefficient = 1.736, 95% confidence interval: 0.52-2.95, P = 0.005).

CONCLUSIONS

The results of this study suggest that increased TMQI has a positive effect on the recovery of physical function in patients with stroke. Further prospective studies are needed to elucidate the relationship between increased TMQI and ADL.

Can EWGSOP2 and SDOC Definitions of Sarcopenia Identify Functional Muscle Quality?

Objectives

To compare the European Working Group on Sarcopenia in Older People (EWGSOP2) and the Sarcopenia Definition and Outcomes Consortium (SDOC) in identifying muscle quality indexes (MQI) and lower limb muscle performance in older women aged ≥ 65.

Methods

Participants meeting EWGSOP2 and SDOC criteria were classified into the sarcopenia group (GS); others were placed in the non-sarcopenia group (GNS). Using an isokinetic dynamometer, we assessed peak torque (PT), maximal work (MW), and power (POW) of lower limbs. MQI was calculated as the ratio of muscle performance to appendicular lean mass, adjusted for body mass index (BMI) and lean tissue mass of the right lower limb (LTM).

Results

We included 96 older women. In both SDOC (n=37) and EWGSOP2 (n=48) sarcopenia groups, muscle performance and BMI-adjusted MQI were significantly lower. Sarcopenia (SDOC) was significantly associated with all lower limb muscle performance and MQI variables [adjusted model by age and race: MQIPOW/LTM OR = 0.67 (95% CI 0.52; 0.85); MQIPT/LTM OR = 0.76 (95% CI 0.64; 0.89)].

Conclusions

Older women diagnosed with sarcopenia by EWGSOP2 and SDOC criteria showed significant declines in muscle function and quality. The SDOC definition discriminated muscle contraction quality components in older individuals with and without sarcopenia.

Automatic Quantitative Assessment of Muscle Strength Based on Deep Learning and Ultrasound

Skeletal muscle is a vital organ that promotes human movement and maintains posture. Accurate assessment of muscle strength is helpful to provide valuable insights for athletes' rehabilitation and strength training. However, traditional techniques rely heavily on the operator's expertise, which may affect the accuracy of the results. In this study, we propose an automated method to evaluate muscle strength using ultrasound and deep learning techniques. B-mode ultrasound data of biceps brachii of multiple athletes at different strength levels were collected and then used to train our deep learning model. To evaluate the effectiveness of this method, this study tested the contraction of the biceps brachii under different force levels. The classification accuracy of this method for grade 4 and grade 6 muscle strength reached 98% and 96%, respectively, and the overall average accuracy was 93% and 87%, respectively. The experimental results confirm that the innovative methods in this paper can accurately and effectively evaluate and classify muscle strength.

Changes in Physical Fitness, Muscle Damage and Cognitive Function in Elite Rugby Players over a Season

This study proposes to monitor the physical, immune and cognitive responses and adaptations of elite rugby players throughout the season based on the loads performed. Anthropometric measurements, physical fitness tests (e.g., muscle strength and power, linear and change-of-direction speed, cardiorespiratory fitness) and analyses of serum concentrations of markers of muscle damage (creatine kinase [CK] and lactate dehydrogenase [LDH]) and brain-derived neurotrophic factor (BDNF) were carried out over a sporting season (24 weeks) for 17 elite rugby players (10 forwards and 7 backs) aged 18.91 ± 0.76 years. The physical fitness test results show improvements in the performance of both forwards and backs over the season (p < 0.05), with an advantage for backs compared with forwards in most tests (p < 0.05). Muscle damage markers decreased at the end of the season compared with the baseline levels for forwards (p < 0.05). CK levels were unchanged for the backs, but there were increased LDH concentrations at the end of the season compared with baseline (p < 0.05). Serum BDNF levels decreased for the total group between the second and third sampling (p < 0.05). The muscular and physical capacities of rugby players differ according to their playing position. Immune responses and adaptations, as well as BDNF levels, vary throughout the season and depend on the physical load performed.

Muscular fitness profiles in relation to the response in body fat during school-based high-intensity intervention

BACKGROUND

We aimed to assess the equivalence of the muscular fitness (MF) between body fat percentage (BFP) responders (RsBFP) and non-responders (NRsBFP) to school-based high-intensity interval training (HIIT). Adolescents aged 16 (N.=73, 42.5% of males) were identified as RsBFP (N.=45) or NRsBFP (N.=28). MF was assessed based on hand strength (HS), abdominal muscle strength (ABS), and leg power (VJ).

METHODS

Profile analysis showed distinct patterns of MF changes in both response categories. Despite the presence of parallelism (Wilks' Λ=0.979, Pillai's V=0.212, P=0.473), a gradient of increasing changes (HS-ABS-VJ) was found in the RsBFP, while a gradient of decreasing changes was shown in the NRsBFP, and a significant level of inequality (F(1,71)=7.823, P=0.047, partial eta-squared [η2p] 0.041).

RESULTS

One-way analysis showed a significant and moderate effect on VJ (F(1,71)=7.080, P=0.010, η2P=0.091), a close to significant effect on ABS (F(1,71)=3.300, P=0.074, η2P=0.044) and lack of an effect on HS (F(1,71)=0.699, P=0.406, η2P=0.010). The test of equal means across the condition categories (separately for RsBFP and NRsBFP) indicated that there was no multivariate statistically significant within-group effect (F(2, 70)=0.517, P=0.599).

CONCLUSIONS

The findings may help teachers assess the potential and indirect changes in muscle performance after employing a body weight intervention (based on the HIIT program). A more targeted approach to treating adolescents with excessive BF, in parallel with improving MF, can be individually tailored.

Could BIA-derived phase angle predict health-related musculoskeletal fitness? A cross-sectional study in young adults

OBJECTIVES

To our knowledge, little evidence exists on the relationships between body composition and health-related physical fitness; in particular, musculoskeletal fitness. Bioimpedance index phase angle (bioelectrical impedance analysis raw variables) is a candidate predictor of health-related fitness, a marker of fat-free and body cell mass, respectively. The aim of this study was to evaluate body composition, raw bioelectrical impedance analysis variables, and health-related fitness in young adults and investigate their mutual relationships to identify predictors of muscle strength.

METHODS

The study included 229 young adults (115 men and 114 women; 24.2 ± 3 y; body mass index 19-30 kg/m²). Anthropometry was measured with standardized procedures. Whole-body BIA (50 kHz) was performed for impedance and phase angle. Predictive equations estimated fat-free mass and percentage body fat. The bioimpedance index was calculated as stature²/impedance. Musculoskeletal fitness was assessed by handgrip strength, standing broad jump, squat jump, and countermovement jump.

RESULTS

In both sexes, health-related fitness had stronger associations with body composition than stature or weight. Handgrip strength was related to fat-free mass and bioimpedance index, while an inverse association with percent body fat emerged for standing broad jump, squat jump and countermovement jump. Phase angle is directly correlated with handgrip strength, standing broad jump, squat jump, and countermovement jump. In multiple regression analysis phase angle was an independent predictor of all health-related fitness tests, along with fat-free mass (or bioimpedance index) for handgrip strength, and with sex and percent body fat for the three jump tests.

CONCLUSIONS

The present study provided consistent information on the relationships between body composition and health-related fitness in young adults. Phase angle emerged as a significant predictor of all health-related fitness measures and might be useful for a more consistent assessment of musculoskeletal fitness.

Rectus Femoris Ultrasound Echo Intensity Is a Valid Estimate of Percent Intramuscular Fat in Patients Following Anterior Cruciate Ligament Reconstruction

OBJECTIVE

The aim of the work described here was to evaluate quadriceps muscle ultrasound metrics and common demographic variables to create a conversion equation that validly predicts magnetic resonance imaging (MRI) percent intramuscular fat after anterior cruciate ligament reconstruction (ACLR).

METHODS

We recruited 15 participants between the ages of 18 and 35 y who were 1-5 y post-ACLR. For the MRI assessment, we used an iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) sequence to assess the mid-thigh. A single reader manually segmented the rectus femoris on two consecutive MRI slices using ITK-Snap to estimate the percent intramuscular fat. For the ultrasound assessment, a single investigator captured transverse panoramic ultrasound images of the mid-thigh with the participant positioned supine and the knee flexed to 30°. A separate single reader used ImageJ to manually segment the rectus femoris ultrasound images. Ultrasound metrics included muscle cross-sectional area, echo intensity and subcutaneous fat thickness. A stepwise linear multiple regression was used to develop an equation to predict MRI percent intramuscular fat using the ultrasound metrics and common demographics (i.e., age, sex, height, mass). Additionally, intraclass correlation coefficients (ICC2,k) and Bland-Altman plots were used to assess the agreement between true and estimated percent intramuscular fat.

RESULTS

Echo intensity and age significantly predicted MRI intramuscular fat percent (p = 0.003, r2 = 0.62). When using the conversion equation, there was high agreement (ICC2,k = 0.87, 95% confidence interval: 0.62-0.96) between the estimated and true percent intramuscular fat.

CONCLUSION

Our patient population-specific conversion equation that uses quadriceps muscle ultrasound echo intensity and age is a valid estimate of MRI percent intramuscular fat.

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.

Genes and Athletic Performance: The 2023 Update

Phenotypes of athletic performance and exercise capacity are complex traits influenced by both genetic and environmental factors. This update on the panel of genetic markers (DNA polymorphisms) associated with athlete status summarises recent advances in sports genomics research, including findings from candidate gene and genome-wide association (GWAS) studies, meta-analyses, and findings involving larger-scale initiatives such as the UK Biobank. As of the end of May 2023, a total of 251 DNA polymorphisms have been associated with athlete status, of which 128 genetic markers were positively associated with athlete status in at least two studies (41 endurance-related, 45 power-related, and 42 strength-related). The most promising genetic markers include the AMPD1 rs17602729 C, CDKN1A rs236448 A, HFE rs1799945 G, MYBPC3 rs1052373 G, NFIA-AS2 rs1572312 C, PPARA rs4253778 G, and PPARGC1A rs8192678 G alleles for endurance; ACTN3 rs1815739 C, AMPD1 rs17602729 C, CDKN1A rs236448 C, CPNE5 rs3213537 G, GALNTL6 rs558129 T, IGF2 rs680 G, IGSF3 rs699785 A, NOS3 rs2070744 T, and TRHR rs7832552 T alleles for power; and ACTN3 rs1815739 C, AR ≥21 CAG repeats, LRPPRC rs10186876 A, MMS22L rs9320823 T, PHACTR1 rs6905419 C, and PPARG rs1801282 G alleles for strength. It should be appreciated, however, that elite performance still cannot be predicted well using only genetic testing.

Low Adherence to Mediterranean Diet Is Associated with Probable Sarcopenia in Community-Dwelling Older Adults: Results from the Longevity Check-Up (Lookup) 7+ Project

Muscle strength is a relevant metric of aging. Greater adherence to Mediterranean diet is associated with better health outcomes across all life stages; however, evidence on the relationship between Mediterranean diet and muscle strength in older adults is inconclusive. In this study, we evaluated the relationship between adherence to Mediterranean diet and handgrip strength in a large sample of community-dwelling older adults from the Longevity Check-up 7+ project. A total of 2963 participants (mean age 72.8 ± 5.7 years; 54.4% women) were analyzed. Mediterranean diet adherence was evaluated using a modified Medi-Lite score and categorized as low (≤8), good (9 to 11), or high (≥12). Handgrip strength was categorized as normal or low according to cut-points by the European Working Group on Sarcopenia in Older People 2. Older adults with lower Mediterranean diet adherence had a significantly higher prevalence of probable sarcopenia (25.9%) than those with good (19.1%) or high (15.5%) adherence. The proportion of participants with probable sarcopenia increased with age, but it remained lower in the good and high adherence groups. Logistic regression showed that greater Mediterranean diet adherence was associated with a lower risk of probable sarcopenia. Older age, female sex, and physical inactivity were associated with a greater risk of probable sarcopenia. Our findings emphasize the positive association between healthy lifestyles, including adherence to Mediterranean diet, and physical function in old age.