Gena R. Gerstner

Neural and muscular contributions to the age-related reductions in rapid strength

Introduction The purposes of this study were to investigate the age-related differences in absolute and normalized plantarflexion rate of torque development (RTD) at early (0–50 ms) and late (100–200 ms) time intervals and to examine specific neural and muscular mechanisms contributing to these differences. Methods Thirty-two young (20.0 ± 2.1 yr) and 20 older (69.5 ± 3.3 yr) recreationally active men performed rapid plantarflexion isometric muscle actions to examine absolute and normalized RTD and muscle activation using EMG at early and late time intervals. Ultrasonography was used to examine medial gastrocnemius muscle size, echo intensity (EI), and muscle architecture (fascicle length [FL] and pennation angle [PA]). Results The older men were weaker (23.9%, P < 0.001) and had lower later absolute and normalized RTD (P = 0.001–0.034) variables when compared with the young men. The older men also had higher EI (P < 0.001), smaller PA (P = 0.004), and lower later EMG amplitude values (P = 0.009–0.046). However, there were no differences in early RTD and EMG amplitude values, muscle size, or FL between groups (P = 0.097–0.914). Lower late RTD values were related to higher EI, smaller PA, and lower EMG amplitude values (r = −0.28–0.59, P = 0.001–0.044); however, late RTD values were no longer related to PA after normalizing to peak torque. Conclusions Age-related alterations in muscle quality (EI), architecture, and muscle activation may influence rapid torque production at late time intervals (≥100 ms) from contraction onset. These findings highlight specific neuromuscular factors that influence the age-related reductions in RTD, which has been shown to significantly influence function and performance in older adults.

The influence of subcutaneous fat on the relationship between body composition and ultrasound-derived muscle quality

Ultrasound echo intensity (EI) values are a popular assessment of muscle quality. The relationship between EI and total (%fat) and regional (%fatlimb) body composition was examined in 40 men, prior to and after accounting for subcutaneous fat thickness. Uncorrected EI values suggest that muscle quality improves (r = -0.329 to -0.224; P = 0.038-0.165) with greater %fat and %fatlimb. However, corrected EI values indicated that muscle quality decreases (r = 0.711 to 0.798; P < 0.001) with greater %fat and %fatlimb.

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

ABSTRACT Age‐related changes in the relative differences in isokinetic strength and power may reflect fast twitch fiber function. We aimed to examine the influence of muscle quality on the relative differences in strength and power in younger and older men. Twenty younger (20.1 ± 1.5 yrs) and 20 older (69.5 ± 3.1 yrs) healthy, recreationally active men performed two plantarflexion maximal voluntary isometric contractions (MVCs) and three maximal concentric isokinetic contractions at a slow (0.52 rad·s− 1) and fast (2.09 rad·s− 1) velocity. Absolute and normalized (%MVC) isokinetic peak torque (PT), mean power (MP), peak power (PP), the relative differences in PT (%decrease), MP and PP (%increase) from 0.52 to 2.09 rad·s− 1, and electromyographic (EMG) amplitude were examined. Ultrasonography was used to determine subcutaneous fat corrected echo intensity (EI) to represent muscle quality. The younger men exhibited greater absolute isometric PT, isokinetic PT, MP, and PP at 0.52 and 2.09 rad·s− 1 (P = 0.001–0.003); but these differences were no longer present following normalization (P = 0.079–0.954). The older men exhibited similar EMG amplitude values but higher EI values (P < 0.001), a greater %decrease in PT (43.6% vs. 38.9%; P = 0.006), and a lower %increase in MP (167.5% vs. 186.3%; P = 0.049) and PP (125.5% vs. 144.5%; P = 0.006). Echo intensity was related to the %decrease in PT (r = 0.605; P < 0.001), %increase in MP (r = − 0.419; P = 0.009), and %increase in PP (r = − 0.605; P < 0.001) from 0.52 to 2.09 rad·s− 1. The absolute age‐related reductions in isokinetic strength and power were no longer present following normalization to isometric strength. However, age‐related differences in strength and power remained intact when examining the relative differences from slow to fast velocities, which appear to be influenced by the qualitative changes in skeletal muscle. HighlightsAge‐related differences in strength and power are no longer present when normalized to isometric strength.Age‐related differences remained intact when examining the relative differences from slow to fast velocities.Relative differences from slow to fast velocities are related to the qualitative changes in skeletal muscle.

Validity of a Multi-compartment Body Composition Model Using Body Volume Derived from Dual-Energy X-ray Absorptiometry: 3715 Board #154 June 4, 8: 00 AM - 9: 30 AM.

Measuring body composition may serve as an important clinical tool in assessing health risks. A four-compartment (4C) model utilizing body mass, body volume (BV), total body water (TBW), and bone mineral content (BMC) is a widely accepted criterion method for predicting body composition. BV is commonly assessed using air displacement plethysmography (BodPod). However, dual-energy x-ray absorptiometry (DXA) has been proposed as an alternative method for BV, reducing time and equipment required for a multi-compartment model. PURPOSE: To assess the validity of a DXA-derived body volume 4C model for calculation of percent body fat (%BF), fat mass (FM), and lean mass (LM). METHODS: A total sample of 126 men and women (Mean ± SD; Age: 35.8 ± 9.4 years; Body Mass: 97.31 ± 20.4 kg; Height: 176.04 ± 9.2 cm) completed a 4C body composition reference assessment, including BV from Bodpod, TBW from bioelectrical impedance spectroscopy, and BMC from DXA. Using a sample of 99 subjects, a DXA-derived body volume 4C model (4C DXA) was created by linearly regressing BodPod BV with DXA FM, LM, and BMC as independent factors. The 4C DXA model was validated in a sub-sample of 27 subjects. RESULTS: The density coefficients of FM, LM, and BMC determined to predict BV were 0.84 (p CONCLUSIONS: The 4C DXA model using the determined coefficients was demonstrated to be a valid method of estimating FM, LM, and %BF when compared to a traditional 4C model. The alternative method of predicting BV using DXA may eliminate the need for a BodPod when using a 4C model to assess body composition.

Examination of muscle morphology and neuromuscular function in normal weight and overfat children aged 7-10 years

Neuromuscular function in young overweight/obese (OF) children is not well described.

The Influence of Habitual Protein Intake on Body Composition and Muscular Strength in Career Firefighters

ABSTRACT Objective: The aim of this research was to determine the relationship among protein (PRO) intake, body composition, and muscle strength in overweight and obese firefighters. A secondary objective was to evaluate differences in body composition and muscle strength among overweight and obese firefighters with low (L; < 0.8 g·kg−1), moderate (M; 0.8–1.0 g·kg−1), and high (H; > 1.0 g·kg−1) PRO intake. Methods: Relative PRO intake [r_PRO] was evaluated from 3-day dietary logs, self-reported by 43 overweight and obese male career firefighters (mean ± standard deviation; age = 37.3 ± 7.2 years; body mass index = 33.2 ± 5.0 kg·m−2; percent body fat [%BF] = 28.9 ± 4.0%). Body composition (fat mass [FM], %BF, lean mass [LM], percent LM [%LM]) and muscle strength (peak torque [PT], relative peak torque [r_PT] of the leg extensors) were measured using dual-energy x-ray absorptiometry and isokinetic dynamometry, respectively. Results: Greater r_PRO was associated with less FM, %BF, LM (r = −0.498 to −0.363) and greater %LM (r = 0.363), but not muscle strength (p > 0.05). Fat mass (r = −0.373) and %BF (r = −0.369) were associated with lower r_PT; %LM was associated with greater r_PT (r = 0.373). Individuals with L r_PRO had greater FM (mean difference ± standard error: L–H = 10.08 ± 3.18 kg), %BF (L–H = 3.8% ± 1.4%) and lower %LM (L–H = −3.7% ± 1.3%) than those with H r_PRO (p < 0.05) but no significant differences in muscle strength (p > 0.05). Conclusions: Protein intake > 0.8 g·kg−1 was associated with more favorable body composition in male career firefighters.

Consistency of a mobile body composition trailer: a novel portable laboratory assessment?

The purpose of this investigation was to (i) assess the test–retest reliability and minimum difference (MD) values of air‐displacement plethysmography (ADP) and the Siri 3‐compartment (3‐C) model in a mobile trailer, and (ii) identify any environmental fluctuations in the trailer.