Statistical Methods for Health Care Research

We examined the neuromuscular adaptations following 3 and 6 weeks of 80% versus 30% one repetition maximum (1RM) resistance training to failure in the leg extensors Twenty-six men (age = 231 ± 47 yrs) were randomly assigned to a high- (80% 1RM; n = 13) or low-load (30% 1RM; n = 13) resistance training group and completed leg extension resistance training to failure 3 times per week for 6 weeks Testing was completed at baseline, 3, and 6 weeks of training During each testing session, ultrasound muscle thickness and echo intensity, 1RM strength, maximal voluntary isometric contraction (MVIC) strength, and contractile properties of the quadriceps femoris were measured Percent voluntary activation (VA) and electromyographic (EMG) amplitude were measured during MVIC, and during randomly ordered isometric step muscle actions at 10 – 100% of baseline MVIC There were similar increases in muscle thickness from Baseline to Week 3 and 6 in the 80% and 30% 1RM groups However, both 1RM and MVIC strength increased from Baseline to Week 3 and 6 to a greater degree in the 80% than 30% 1RM group VA during MVIC was also greater in the 80% versus 30% 1RM group at Week 6, and only training at 80% 1RM elicited a significant increase in EMG amplitude during MVIC The peak twitch torque to MVIC ratio was also significantly reduced in the 80%, but not 30% 1RM group, at Week 3 and 6 Finally, VA and EMG amplitude were reduced during submaximal torque production as a result of training at 80% 1RM, but not 30% 1RM Despite eliciting similar hypertrophy, 80% 1RM improved muscle strength more than 30% 1RM, and was accompanied by increases in VA and EMG amplitude during maximal force production Furthermore, training at 80% 1RM resulted in a decreased neural cost to produce the same relative submaximal torques after training, whereas training at 30% 1RM did not Therefore, our data suggest that high-load training results in greater neural adaptations that may explain the disparate increases in muscle strength despite similar hypertrophy following high- and low-load training programs

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Greater Neural Adaptations following High- vs. Low-Load Resistance Training.

Intramuscular adipose tissue determined by T1-weighted MRI at 3T primarily reflects extramyocellular lipids.

Objective To establish muscle-specific cut-off values for ultrasound-based detection of low muscle mass, and to assess its prevalence in a population of frail older subjects when applying the cut-points of different muscles and those of different sarcopenic indices. Design Cross-sectional study. Setting Geriatric outpatient clinic and clinical research laboratory. Methods A total of 44 older adults (30 women and 14 men, mean age 82 years, range 67-93 years) and 60 younger individuals (30 women and 30 men, mean age 26 years, range 20-36 years) participated. Body composition and thickness of 4 lower limb muscles (rectus femoris, vastus lateralis, tibialis anterior, medial gastrocnemius) were respectively assessed by bioelectrical impedance analysis (BIA) and ultrasonography. Main Outcome Measurements Site-specific cut-points for ultrasound-based assessment of low muscle mass (muscle thickness values 2 standard deviations below the gender-specific means of our sample of younger subjects) and comparative prevalence rates of low muscle mass. Results The following site-specific cut-points for muscle thickness were identified: rectus femoris: 20 mm in men and 16 mm in women; vastus lateralis: 17 mm in men and 15 mm in women; tibialis anterior: 23 mm in men and 22 mm in women; and medial gastrocnemius: 13 mm in both men and women. The prevalence of low muscle mass in older adults was highly dependent on the muscle being investigated; it varied from 86% for thigh muscles to 30% for leg muscles. Moreover, the prevalence of low muscle mass was highly dependent on the applied diagnostic criterion and on the adopted cut-off value; it ranged from 2% to 75% for different BIA-derived criteria. Conclusions We suggest that muscle ultrasonography provides physiatrists with a practical and accurate tool for identifying individuals with low muscle mass. However, the usability of cut-off values established in our group of healthy younger subjects of white ethnicity to identify low muscle mass in older individuals of different ethnic groups remains to be demonstrated in future studies.

https://www.pmrjournal.org/article/S1934-1482(15)01022-9/pdf

Ultrasound-Based Detection of Low Muscle Mass for Diagnosis of Sarcopenia in Older Adults

Musculoskeletal ultrasound imaging can be used to investigate the skeletal muscle structure in terms of architecture (thickness, cross-sectional area, fascicle length and fascicle pennation angle) and texture. Gray-scale analysis is commonly used to characterize transverse scans of the muscle. Gray mean value is used to distinguish between normal and pathologic muscles, but it depends on the image acquisition system and its settings. In this study, quantitative ultrasonography was performed on five muscles (biceps brachii, vastus lateralis, rectus femoris, medial gastrocnemius and tibialis anterior) of 20 healthy patients (10 women, 10 men) to assess the characterization performance of higher-order texture descriptors to differentiate genders and muscle types. A total of 53 features (7 first-order descriptors, 24 Haralick features, 20 Galloway features and 2 local binary pattern features) were extracted from each muscle region of interest (ROI) and were used to perform the multivariate linear regression analysis (MANOVA). Our results show that first-order descriptors, Haralick features (energy, entropy and correlation measured along different angles) and local binary pattern (LBP) energy and entropy were highly linked to the gender, whereas Haralick entropy and symmetry, Galloway texture descriptors and LBP entropy helped to distinguish muscle types. Hence, the combination of first-order and higher-order texture descriptors (Haralick, Galloway and LBP) can be used to discriminate gender and muscle types. Therefore, multi-texture analysis may be useful to investigate muscle damage and myopathic disorders.

Advances in Quantitative Muscle Ultrasonography Using Texture Analysis of Ultrasound Images

Objective: To assess the issue of muscle echo intensity reliability and to investigate the relationship between muscle echo intensity and size, shape and location of the region of interest (ROI) used for echo intensity quantification. Methods: Ultrasonographic scans of the following five muscles were acquired in twenty healthy subjects: biceps brachii, rectus femoris, vastus lateralis, tibialis anterior and medial gastrocnemius. Muscle echo intensity was quantified in each scan. Results: We found that the agreement between the different sized ROIs considered in each scan ranged from moderate (ICC: 054) to high (ICC: 086) and that the echo intensity consistency between equal sized ROIs of the three scans ranged from low (ICC: 042) to very high (091). The echo intensity of tibialis anterior and rectus femoris was different between different sized, shaped and located ROIs. The echo intensity of biceps brachii and tibialis anterior was higher than that of all other muscles, and females had higher echo intensity than males. Moreover, the muscle echo intensity was positively correlated with the subcutaneous layer thickness in three of five muscles. Conclusion: The echo intensity reliability was function of the ROI size. Muscle and gender variability in echo intensity was likely due to differences in fibrous and adipose tissue content and distribution. Possible explanations for the observed correlations between muscle echo intensity and subcutaneous layer thickness include the dependence of both variables on total body adiposity or the direct dependence of the extent of intramuscular fat on the amount of subcutaneous fat.

Giorgio Emanuel

Papers

Muscle echo intensity: reliability and conditioning factors.