John P. McCarthy

The missing risk: MRI and MRS phenotyping of abdominal adiposity and ectopic fat.

Individual compartments of abdominal adiposity and lipid content within the liver and muscle are differentially associated with metabolic risk factors, obesity and insulin resistance. Subjects with greater intra‐abdominal adipose tissue (IAAT) and hepatic fat than predicted by clinical indices of obesity may be at increased risk of metabolic diseases despite their “normal” size. There is a need for accurate quantification of these potentially hazardous depots and identification of novel subphenotypes that recognize individuals at potentially increased metabolic risk. We aimed to calculate a reference range for total and regional adipose tissue (AT) as well as ectopic fat in liver and muscle in healthy subjects. We studied the relationship between age, body‐mass, BMI, waist circumference (WC), and the distribution of AT, using whole‐body magnetic resonance imaging (MRI), in 477 white volunteers (243 male, 234 female). Furthermore, we used proton magnetic resonance spectroscopy (MRS) to determine intrahepatocellular (IHCL) and intramyocellular (IMCL) lipid content. The anthropometric variable which provided the strongest individual correlation for adiposity and ectopic fat stores was WC in men and BMI in women. In addition, we reveal a large variation in IAAT, abdominal subcutaneous AT (ASAT), and IHCL depots not fully predicted by clinically obtained measurements of obesity and the emergence of a previously unidentified subphenotype. Here, we demonstrate gender‐ and age‐specific patterns of regional adiposity in a large UK‐based cohort and identify anthropometric variables that best predict individual adiposity and ectopic fat stores. From these data we propose the thin‐on‐the‐outside fat‐on‐the‐inside (TOFI) as a subphenotype for individuals at increased metabolic risk.

Preferential loss of visceral fat following aerobic exercise, measured by magnetic resonance imaging.

The aim of this study was to use whole-body magnetic resonance imaging (MRI) together with biochemical and anthropometric measurements to study the influence of regular moderate exercise with no dietary intervention on adipose tissue distribution in nonobese healthy women. We found significant decreases in both total (28.86±2.24 vs. 27.00±2.27 liters, P<0.05) and regional fat depots (visceral fat: 1.68±0.21 vs. 1.26±0.18 liters, P<0.01) using whole-body MRI despite no significant change in body weight, body mass index, or the waist-to-hip ratio. Interestingly, no changes in body fat content were found using anthropometry or impedance. There was a significant increase in high density lipoprotein cholesterol (1.58 ±0.06 vs. 1.66±0.08 mmol/L P<0.02) following exercise although there were no changes in other blood lipids such as triglycerides. In summary, moderate aerobic exercise over a period of 6 mon resulted in a preferential loss in visceral fat in nonobese healthy women, and this may help to explain some of the health benefits associated with regular and moderate physical activity.

Estimation of abdominal fat compartments by bioelectrical impedance: the validity of the ViScan measurement system in comparison with MRI

Background/Objectives:Abdominal obesity, more specifically increased intra-abdominal adipose tissue, is strongly associated with increased risk of metabolic disease. Bioelectrical impedance analysis (BIA) has been proposed as a potential method of determining individual abdominal fat compartments in the form of the commercially available ViScan measurement system (Tanita Corporation), but it has yet to be independently validated. The objective of this study was to analyse the validity of the ViScan to assess adult abdominal adiposity across a range of body fatness.Subjects/Methods:This was a cross-sectional study with 74 participants (40 females and 34 males with body mass index (BMI) between 18.5 and 39.6 kg/m2). Total abdominal adipose tissue, subcutaneous abdominal adipose tissue (SAAT) and intra-abdominal adipose tissue (IAAT) were measured by magnetic resonance imaging (MRI). In addition, intra-hepatocellular lipid was obtained by magnetic resonance spectroscopy. Estimates of abdominal adiposity (total and compartmental) were obtained from BIA and anthropometry.Results:ViScan-derived percentage trunk fat strongly and significantly related with total abdominal adipose tissue and SAAT in both lean and overweight/obese individuals, and categorized individuals reliably in terms of total abdominal fat. ViScan-derived ‘visceral’ fat correlated significantly with IAAT but the strength of this relationship was much weaker in overweight/obese individuals, particularly those with higher SAAT, leading to less reliable classification of individuals for IAAT.Conclusions:The ViScan may serve as a useful tool for predicting total abdominal fat, but prediction of visceral fat (IAAT) may be limited, especially in abdominally obese individuals.

Reduction of total lung capacity in obese men: comparison of total intrathoracic and gas volumes

Restriction of total lung capacity (TLC) is found in some obese subjects, but the mechanism is unclear. Two hypotheses are as follows: 1) increased abdominal volume prevents full descent of the diaphragm; and 2) increased intrathoracic fat reduces space for full lung expansion. We have measured total intrathoracic volume at full inflation using magnetic resonance imaging (MRI) in 14 asymptomatic obese men [mean age 52 yr, body mass index (BMI) 35-45 kg/m2] and 7 control men (mean age 50 yr, BMI 22-27 kg/m2). MRI volumes were compared with gas volumes at TLC. All measurements were made with subjects supine. Obese men had smaller functional residual capacity (FRC) and FRC-to-TLC ratio than control men. There was a 12% predicted difference in mean TLC between obese (84% predicted) and control men (96% predicted). In contrast, differences in total intrathoracic volume (MRI) at full inflation were only 4% predicted TLC (obese 116% predicted TLC, control 120% predicted TLC), because mediastinal volume was larger in obese than in control [heart and major vessels (obese 1.10 liter, control 0.87 liter, P=0.016) and intrathoracic fat (obese 0.68 liter, control 0.23 liter, P<0.0001)]. As a consequence of increased mediastinal volume, intrathoracic volume at FRC in obese men was considerably larger than indicated by the gas volume at FRC. The difference in gas volume at TLC between the six obese men with restriction, TLC<80% predicted (OR), and the eight obese men with TLC>80% predicted (ON) was 26% predicted TLC. Mediastinal volume was similar in OR (1.84 liter) and ON (1.73 liter), but total intrathoracic volume was 19% predicted TLC smaller in OR than in ON. We conclude that the major factor restricting TLC in some obese men was reduced thoracic expansion at full inflation.

Proton magnetic resonance spectroscopy and ultrasound for hepatic fat quantification.

Aim:  The increasing prevalence of fatty liver disease requires routine assessment methods. Proton magnetic resonance spectroscopy (1H MRS) is increasingly used for steatosis measurement, but due to cost, is unlikely to become a widely‐used screening tool. Ultrasound is cheaper and more widely available, although subject to observer variability. Our aim was to determine the sensitivity and specificity of ultrasound against 1H MRS, using MRS as a gold standard, for the detection and quantification of hepatic fat content.

Fat distribution in men of different waist girth, fitness level and exercise habit

Background:The risk of chronic disease is lower in obese men who are fit and active than obese men who are unfit and inactive.Methods/Objectives:Magnetic resonance imaging and spectroscopy were used to assess total and regional adipose tissue in 13 men who were slim, fit and active (the slim-fit), in 12 men who were slim, unfit and inactive (the slim-unfit), in 13 men who were fat, fit and active (the fat-fit) and in 12 men who were fat, unfit and inactive (the fat-unfit), in order to investigate the hypothesis that visceral fat and liver fat are lower in the fat-fit than the fat-unfit. Waist girth was used to distinguish slim men (⩽90 cm) and fat men (⩾100 cm). Maximal oxygen consumption was used to identify fit men (above average for age) and unfit men (average or below for age). Fit men reported at least 60 min of vigorous aerobic activity per week and unfit men reported no regular moderate or vigorous activity in the last 2 years.Results:Total fat was not significantly different in the slim-fit and the slim unfit, but the proportion of internal fat was significantly lower (P<0.05) and the proportion of visceral fat was almost significantly lower (P=0.06) in the slim-fit than all other groups. Total fat was not significantly different in the fat-fit and the fat-unfit, but visceral fat and liver fat were significantly lower in the fat-fit than the fat-unfit (P<0.01). Waist girth and years of exercise explained 84% of the variance in total fat, waist girth and maximal oxygen consumption explained 70% of the variance in visceral fat, and waist girth alone explained 25% of the variance in liver fat.Conclusion:Chronic disease risk may be lower because visceral fat and liver fat are lower in men who are fat, fit and active.

Neonatal intrahepatocellular lipid

There is increasing evidence that preterm birth is a risk factor for the development of adiposity associated disease, although the pathophysiological basis is unclear. We have previously shown that preterm infants have increased internal abdominal (visceral) adiposity by term. In adults increased internal adiposity is associated with elevated intrahepatocellular lipid (IHCL). We measured IHCL using 1H NMR spectroscopy in 26 infants (eight healthy preterm-at-term and 18 term-born) and compared values with a reference group of 32 adults. There was no significant difference between adult and term-born IHCL content. In preterm-at-term infants IHCL was significantly elevated when compared with term-born infants and with adults (IHCL CH2/water median (interquartile range): preterm 1.69 (1.04–3.53), term 0.21 (0–0.54) and adult 0.55 (0.08–1.57).

Combined Aerobic and Strength Training and Energy Expenditure in Older Women.

PURPOSE To examine the effects of three different frequencies of combined resistance and aerobic training on total energy expenditure (TEE) and activity-related energy expenditure (AEE) in a group of older adults. METHODS Seventy-two women, 60-74 yr old, were randomly assigned to one of three groups: 1 d · wk(-1) of aerobic training and 1 d · wk(-1) of resistance training (1 + 1), 2 d · wk(-1) of aerobic training and 2 d · wk(-1) resistance training (2 + 2), or 3 d · wk(-1) of aerobic training and 3 d · wk(-1) of resistance training (3 + 3). Body composition (dual-energy x-ray absorptiometry), feeling of fatigue, depression, and vigor (questionnaire), strength (one-repetition maximum), serum cytokines (enzyme-linked immunosorbent assay), maximal oxygen uptake (progressive treadmill test), resting energy expenditure, and TEE were measured before and after 16 wk of training. Aerobic training consisted of 40 min of aerobic exercise at 80% maximum heart rate, and resistance training consisted of two sets of 10 repetitions for 10 different exercises at 80% of one repetition maximum. RESULTS All groups increased fat-free mass, strength, and aerobic fitness and decreased fat mass. No changes were observed in cytokines or perceptions of fatigue/depression. No time-group interaction was found for any fitness/body composition variable. TEE and AEE increased with the 2 + 2 group but not with the other two groups. Nonexercise training AEE (nonexercise training activity-related thermogenesis) increased significantly in the 2 + 2 group (+200 kcal · d(-1)), group 1 + 1 showed a trend for an increase (+68 kcal · d(-1)), and group 3 + 3 decreased significantly (-150 kcal · d(-1)). CONCLUSION Results indicate that 3 + 3 training may inhibit nonexercise training activity-related thermogenesis by being too time consuming and does not induce superior training adaptations to 1 + 1 and 2 + 2 training.

Potentiation of concentric force and acceleration only occurs early during the stretch-shortening cycle.

Abstract McCarthy, JP, Wood, DS, Bolding, MS, Roy, JLP, and Hunter, GR. Potentiation of concentric force and acceleration only occurs early during the stretch-shortening cycle. J Strength Cond Res 26(9): 2345–2355, 2012—The purpose of this study was to determine where stretch-shortening cycle (SSC) potentiation of force, power, velocity, and acceleration occurs across the concentric phase of ballistic leg presses. Second, we examined the influence of late eccentric phase force and length of the amortization phase on potentiated concentric phase performance variables. Twenty-one male runners (age: 31.9 ± 4.7 years) performed SSC and concentric-only (CO) ballistic leg press throws. Potentiations of concentric actions were calculated as the difference between SSC and CO contractions. An analysis splitting the concentric range of motion (ROM) into 6 equal time intervals determined force and acceleration were potentiated (p < 0.05) only during the first one-sixth time interval of concentric motion, whereas velocity and power were potentiated (p < 0.05) at all time intervals over the entire concentric motion with the exception of power over the last one-sixth time interval. A more precise analysis examining 20-millisecond time intervals across the first 200 milliseconds of concentric motion determined force was potentiated only over the first 140 milliseconds and acceleration only over the first 160 milliseconds. Eccentric force measured during the last 100 milliseconds of eccentric motion was related to potentiated force during the initial 200 milliseconds of concentric motion (r = 0.44, p < 0.05) and potentiated mean power across the full concentric ROM (r = 0.62, p < 0.01). Results indicate that in contrast to power and velocity, potentiation of force and acceleration occurs only early during the concentric phase of SSC ballistic leg presses. Correlational findings imply late eccentric phase force is important for generating force and power during the concentric phase of the SSC and thus training focusing on enhancing late phase eccentric force appears important for developing explosive force and power during SSC movements.