Intramyocellular and Extramyocellular Lipids Are Associated With Arterial Stiffness

Fibro-adipogenic progenitors in physiological adipogenesis and intermuscular adipose tissue remodeling

Excessive accumulation of intermuscular adipose tissue (IMAT) is a common pathological feature in various metabolic and health conditions and can cause muscle atrophy, reduced function, inflammation, insulin resistance, cardiovascular issues, and unhealthy aging. Although IMAT results from fat accumulation in muscle, the mechanisms underlying its onset, development, cellular components, and functions remain unclear. IMAT levels are influenced by several factors, such as changes in the tissue environment, muscle type and origin, extent and duration of trauma, and persistent activation of fibro-adipogenic progenitors (FAPs). FAPs are a diverse and transcriptionally heterogeneous population of stromal cells essential for tissue maintenance, neuromuscular stability, and tissue regeneration. However, in cases of chronic inflammation and pathological conditions, FAPs expand and differentiate into adipocytes, resulting in the development of abnormal and ectopic IMAT. This review discusses the role of FAPs in adipogenesis and how they remodel IMAT. It highlights evidence supporting FAPs and FAP-derived adipocytes as constituents of IMAT, emphasizing their significance in adipose tissue maintenance and development, as well as their involvement in metabolic disorders, chronic pathologies and diseases. We also investigated the intricate molecular pathways and cell interactions governing FAP behavior, adipogenesis, and IMAT accumulation in chronic diseases and muscle deconditioning. Finally, we hypothesize that impaired cellular metabolic flexibility in dysfunctional muscles impacts FAPs, leading to IMAT. A deeper understanding of the biology of IMAT accumulation and the mechanisms regulating FAP behavior and fate are essential for the development of new therapeutic strategies for several debilitating conditions.

Dioscorea esculenta Intake with Resistance Training Improves Muscle Quantity and Quality in Healthy Middle-Aged and Older Adults: A Randomized Controlled Trial

Resistance training and Dioscorea esculenta intake have a positive effect on muscle. Therefore, we aimed to determine whether 12-week Dioscorea esculenta intake combined with resistance exercise more effectively improves muscle quantity, quality, and cardiometabolic parameters in healthy middle-aged and older adults. This study is a double-blind trial with 66 volunteers (21 males/45 females; age 53 ± 5 years; body weight 61 ± 11 kg; BMI 24 ± 4 kg) who were randomly divided into four groups: sedentary-control with placebo (Sed and PL) or Dioscorea (Sed and Dio) and resistance training with placebo (RT and PL) or Dioscorea (RT and Dio). Resistance training sessions using elastic bands were performed 3 days/week for a 12-week period. Dioscorea esculenta tablets were ingested at 2000 mg/day once per day. The RT and Dio group showed greater improvements in the femoris muscle's thickness, echo intensity for the rectus femoris (index of muscle quality), and the five times sit-to-stand test compared to that of the Sed and PL group; the echo intensity in the RT and Dio group further improved compared to those in the Sed and Dio, and RT and PL groups (p < 0.05). The circulating levels of C1q (a potential biomarker of muscle fibrosis) in the RT and Dio group were significantly lower than those in the Sed and PL, and Sed and Dio groups (p < 0.05). Chronic Dioscorea esculenta intake combined with low-intensity resistance exercise may more effectively improve muscle quantity and quality indices in healthy middle-aged and older adults.

Mutation c.-379 C>T in DGAT1 affects intramyocellular lipid content by altering MYOD1 binding affinity

Intramuscular fat (IMF) is one of the most important indexes of pork taste quality. Diacylglycerol acyltransferase 1 (DGAT1), belonging to the acyl-coenzyme A: DGAT enzymes family, is a rate-limiting enzyme responsible for the final step of triglyceride (TG) synthesis. It is involved in TG storage in skeletal muscle; however, the underlying mechanism is not well understood. This study aimed to uncover functional mutations that can influence DGAT1 expression and consequently affect IMF deposition in pork. Two experimental groups containing individuals with high and low IMF content (6.23 ± 0.20 vs. 1.25 ± 0.05, p < 0.01) were formed from 260 Duroc × Large White × Yorkshire (D × L × Y) cross-bred pigs. A novel SNP c.-379 C>T was uncovered in the DGAT1 gene using comparative sequencing with pool DNA of high- and low-IMF groups. The IMF content of CT genotype individuals (3.19 ± 0.11%) was higher than that of CC genotype individuals (2.86 ± 0.11%) when analyzing 260 D × L × Y pigs (p < 0.05). The DGAT1 expression levels revealed a significant positive correlation with IMF content (r = 0.33, p < 0.01). Luciferase assay revealed that the DGAT1 promoter with the c.-379 T allele has a higher transcription activity than that bearing the C allele in C2C12 myoblast cells, but not in 3T3-L1 pre-adipocytes. Online prediction followed by chromatin immunoprecipitation-polymerase chain reaction assay confirmed that myogenic determination factor 1 (MYOD1) binds to the DGAT1 promoter with the c.-379 C allele but not the T allele. In vitro experiments demonstrated that MYOD1 represses DGAT1 transcription and lipogenesis. As a muscle-specific transcription factor, MYOD1 can inhibit the transcription of DGAT1 with the c.-379 C allele in muscle cells. However, in the absence of MYOD1 binding to the mutated DGAT1 promoter with the c.-379 T allele, DGAT1 expresses at a higher level in the muscle cells of the c.-379 T genotype, leading to more intramyocellular lipid accumulation than in the muscle cells of the c.-379 C genotype. The SNP c.-379 C>T in the promoter region of the DGAT1 gene provides a promising molecular marker for improving pork IMF content without affecting other fat depots.

Importance of skeletal muscle lipid levels for muscle function and physical function in older individuals

The skeletal muscle contains lipids inside (intramyocellular lipids, IMCL) or outside (extramyocellular lipids, EMCL) its cells. The muscle lipid content increases with age; however, the characteristics of IMCL and EMCL in older individuals are not well known. We aimed to examine the characteristics of skeletal muscle lipids by investigating their relationship with muscle function and physical functions. Seven elderly men and 16 elderly women participated. The skeletal muscle lipid content, including IMCL and EMCL, was measured in the vastus lateralis by proton magnetic resonance spectroscopy. Isometric knee extension with maximal voluntary contraction (MVC) and time-to-task failure for knee extension with 50% MVC were measured as muscle functions. The participants performed six physical function tests: preferred gait speed, maximal gait speed, Timed Up and Go, chair sit-to-stand, handgrip strength, and stand from the floor. The time to knee extension task failure had a significant relationship with the IMCL (r_s = -0.43, P < 0.05), but not with the EMCL content. Significant relationships were confirmed in the EMCL content with the sit-to-stand (r_s = -0.48, P < 0.05) and stand-from-the-floor (r_s = 0.53, P < 0.05) tests. These findings indicated that muscle lipids are associated with muscle and physical functional performances in older individuals. Novelty: No relationship was confirmed between IMCL and EMCL in older individuals. Muscle endurance performance had a relationship with IMCL, but not with EMCL. Relationships between EMCL and physical functional tests (e.g., sit-to-stand and stand from the floor) were confirmed.

Noninvasive NMR/MRS Metabolic Parameters to Evaluate Metabolic Syndrome in Rats

(1) Background: Ectopic fat deposition and its effects, metabolic syndrome, have been significantly correlated to lifestyle and caloric consumption. There is no specific noninvasive evaluation tool being used in order to establish clinical markers for tracing the metabolic pathway implicated in obesity-related abnormalities that occur in the body as a result of a high-fat diet (HFD). The purpose of this work is to investigate in vivo ectopic fat distribution and in vitro metabolite profiles given by HFDs, as well as how they are inter-related, in order to find surrogate metabolic biomarkers in the development of metabolic syndrome utilizing noninvasive approaches. (2) Methods: Male Wistar rats were divided into a standard normal chow diet, ND group, and HFD group. After 16 weeks of different diet administration, blood samples were collected for proton nuclear magnetic resonance (¹H NMR) and biochemical analysis. Magnetic resonance imaging/proton magnetic resonance spectroscopy (MRI/¹H MRS) was performed on the abdomen, liver, and psoas muscle of the rats. (3) Results: Visceral fat showed the strongest relationship with blood cholesterol. Although liver fat content (LFC) was not associated with any biophysical profiles, it had the highest correlation with metabolites such as (-CH₂)_n very-low-density lipoprotein/low-density lipoprotein (VLDL/LDL), lactate, and N-acetyl glycoprotein of serum ¹H NMR. HFD showed no obvious influence on muscle fat accumulation. Acetoacetate, N-acetyl glycoprotein, lactate, (-CH₂)_n VLDL/LDL, and valine were the five possible metabolic biomarkers used to differentiate HFD from ND in the present study. (4) Conclusions: Our study has validated the influence of long-term HFD-induced ectopic fat on body metabolism as well as the metabolic profile deterioration both in vivo and in vitro.

In Vivo Renal Lipid Quantification by Accelerated Magnetic Resonance Spectroscopic Imaging at 3T: Feasibility and Reliability Study

A reliable and practical renal-lipid quantification and imaging method is needed. Here, the feasibility of an accelerated MRSI method to map renal fat fractions (FF) at 3T and its repeatability were investigated. A 2D density-weighted concentric-ring-trajectory MRSI was used for accelerating the acquisition of 48 × 48 voxels (each of 0.25 mL spatial resolution) without respiratory navigation implementations. The data were collected over 512 complex-FID timepoints with a 1250 Hz spectral bandwidth. The MRSI sequence was designed with a metabolite-cycling technique for lipid–water separation. The in vivo repeatability performance of the sequence was assessed by conducting a test–reposition–retest study within healthy subjects. The coefficient of variation (CV) in the estimated FF from the test–retest measurements showed a high degree of repeatability of MRSI-FF (CV = 4.3 ± 2.5%). Additionally, the matching level of the spectral signature within the same anatomical region was also investigated, and their intrasubject repeatability was also high, with a small standard deviation (8.1 ± 6.4%). The MRSI acquisition duration was ~3 min only. The proposed MRSI technique can be a reliable technique to quantify and map renal metabolites within a clinically acceptable scan time at 3T that supports the future application of this technique for the non-invasive characterization of heterogeneous renal diseases and tumors.

Both lean and fat body mass associate with blood pressure

High body mass index (BMI) is known to be associated with elevated blood pressure (BP). The present study aims to determine the relative importance of the two components of BMI, fat mass and lean body mass index, on BP levels. We assessed body composition with bioimpedance and performed 24 hour ambulatory BP measurements in 534 individuals (mean age 61 ± 3 years) who had no cardiovascular medication. Fat mass index and lean mass index were calculated analogously to BMI as fat mass or lean body mass (kg) divided by the square of height (m²). Both fat mass index and lean mass index showed a positive, small to moderate relationship with all 24 hour BP components independently of age, sex, smoking, and leisure-time physical activity. There were no interaction effects between fat mass index and lean mass index on the mean BP levels. Adult lean body mass is a significant determinant of BP levels with an equal, albeit small to moderate magnitude as fat mass. Relatively high amount of muscle mass may not be beneficial to cardiovascular health.

Cardiac 1H MR spectroscopy: development of the past five decades and future perspectives

Continued advances in laboratory medicine are required to realize the potential of individualized medicine to impact common cardiovascular diseases. Magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques have advanced over recent years and offer unique, powerful insights into cardiac anatomic and metabolic changes, respectively, occurring in both nascent and advanced heart disease. Although numerous MRI-based in vivo diagnostics are already used in routine clinical practice and more are anticipated, MRS has been less incorporated into routine clinical practice. Given the ability of ¹H MRS to identify and quantify specific molecules with high sensitivity and specificity, its potential utility should be successfully transition from "bench-to-bedside" is tantalizing. The present review will highlight the development of ¹H MRS techniques for cardiac applications, observations in seminal studies with ¹H MRS, and the prospects and challenges for widespread application in patients with cardiovascular disease.

Aerobic exercise training-induced irisin secretion is associated with the reduction of arterial stiffness via nitric oxide production in adults with obesity

This study aimed to clarify whether muscle-derived irisin secretion induced by aerobic exercise training is involved in reduction of arterial stiffness via arterial nitric oxide (NO) productivity in obesity. In animal study, 16 Otsuka Long-Evans Tokushima Fatty (OLETF) rats with obesity were randomly divided into 2 groups: sedentary control (OLETF-CON) and 8-week aerobic treadmill training (OLETF-EX) groups. In human study, 15 subjects with obesity completed 8-week aerobic exercise training for 45 min at 60%-70% peak oxygen uptake intensity for 3 days/week. As a result of animal study, carotid-femoral pulse wave velocity (cfPWV) was decreased, and arterial phosphorylation levels of AMP-activated protein kinase (AMPK), protein kinase B (Akt), and endothelial NO synthase (eNOS), circulating levels of nitrite/nitrate (NOx) and irisin, and muscle messenger RNA expression of fibronectin type III domain containing 5 (Fndc5) were increased in the OLETF-EX group compared with OLETF-CON group. In a human study, regular aerobic exercise reduced cfPWV and elevated circulating levels of NOx and irisin. Furthermore, change in circulating irisin levels by regular exercise was positively correlated with circulating NOx levels and was negatively correlated with cfPWV. Thus, aerobic exercise training-induced increase in irisin secretion may be related to reduction of arterial stiffness achieved by NO production via activated arterial AMPK-Akt-eNOS signaling pathway in obesity. Novelty Aerobic exercise training promoted irisin secretion with upregulation of muscle Fndc5 gene expression in rats with obesity. Irisin affected the activation of arterial AMPK-Akt-eNOS signaling by aerobic exercise training. Increased serum irisin level by aerobic exercise training was associated with reduction of arterial stiffness in obese adults.

Fat-water separation by fast metabolite cycling magnetic resonance spectroscopic imaging at 3 T: A method to generate separate quantitative distribution maps of musculoskeletal lipid components

PURPOSE

To provide a rapid, noninvasive fat-water separation technique that allows producing quantitative maps of particular lipid components.

METHODS

The calf muscles in 5 healthy adolescents (age 12-16 years; body mass index = 20 ± 3 kg/m² ) were scanned by two different fat fraction measurement methods. A density-weighted concentric-ring trajectory metabolite-cycling MRSI technique was implemented to collect data with a nominal resolution of 0.25 mL within 3 minutes and 16 seconds. For comparative purposes, the standard Dixon technique was performed. The two techniques were compared using structural similarity analysis. Additionally, the difference in the distribution of each lipid over the adolescent calf muscles was assessed based on the MRSI data.

RESULTS

The proposed MRSI technique provided individual fat fraction maps for eight musculoskeletal lipid components identified by LCModel analysis (IMC/L [CH₃ ], EMCL [CH₃ ], IMC/L [CH₂ ]_n , EMC/L [CH₂ ]_n , IMC/L [CH₂ -CH], EMC/L [CH₂ -CH], IMC/L [-CH=CH-], and EMC/L [-CH=CH-]) with mean structural similarity indices of 0.19, 0.04, 0.03, 0.50, 0.45, 0.04, 0.07, and 0.12, respectively, compared with the maps generated by the used Dixon method. Further analysis of voxels with zero structural similarity demonstrated an increased sensitivity of fat fraction lipid maps from the data acquired using this MRSI technique over the standard Dixon technique. The lipid spatial distribution over calf muscles was consistent with previously published findings in adults.

CONCLUSION

This MRSI technique can be a useful tool when individual lipid fat fraction maps are desired within a clinically acceptable time and with a nominal spatial resolution of 0.25 mL.

Effects of aerobic exercise training on the arterial stiffness and intramyocellular or extramyocellular lipid in overweight and obese men

Intramyocellular lipid (IMCL) and extramyocellular lipid (EMCL) of ectopic fat in muscles are associated with arterial stiffness in normal-weight individuals. Furthermore, aerobic exercise training-induced changes in IMCL or EMCL content are related to a decrease in arterial stiffness in elderly people. Though arterial stiffness is strongly related with obesity, but the effects of aerobic exercise training on IMCL or EMCL content, with a particular focus on arterial stiffness, in obese individuals remains unclear. Here, we investigated the effects of aerobic exercise training on IMCL or EMCL content and arterial stiffness in obese individuals. First, in a cross-sectional study, we examined the relationship between arterial stiffness and IMCL or EMCL content in 24 overweight and obese men. Secondly, we investigated the effects of aerobic exercise intervention on arterial stiffness and IMCL or EMCL content in 21 overweight and obese men. In the cross-sectional study, EMCL content was positively correlated with baPWV and β-stiffness index, whereas IMCL content was negatively correlated with baPWV. In the intervention study, there were no significant changes in baPWV, β-stiffness index, and IMCL and EMCL contents after aerobic exercise training. However, exercise-induced change in baPWV and β-stiffness index were positively correlated with changes in EMCL content. Moreover, the group of improvements in baPWV was only correlated significantly with reduced EMCL content. These results suggest that IMCL and EMCL contents may affect arterial stiffness in overweight and obese men.

Aerobic exercise training-induced changes in serum C1q/TNF-related protein levels are associated with reduced arterial stiffness in middle-aged and older adults

Adiponectin regulates endothelial nitric oxide synthase in endothelial cells, and body fat loss by aerobic exercise training promotes adiponectin secretion. Recently, C1q/tumor necrosis factor-related proteins (CTRPs) have been identified as novel adipokines and are paralogs of adiponectin, but the association between exercise training-induced reduction of arterial stiffness and circulating CTRPs levels remains unclear. This study aimed to clarify whether the reduction of arterial stiffness in middle-aged and older adults is associated with the change in serum levels of CTRPs induced by exercise training. A total of 52 middle-aged and older participants were randomly divided into two groups: a training group ( n = 26) and a sedentary control group ( n = 26). Participants in the training group completed 8 wk of aerobic exercise training (60–70% peak oxygen uptake for 45 min, 3 days/wk). The reduction of percent whole body fat, abdominal visceral fat area, and carotid-femoral pulse-wave velocity (cfPWV) was significantly greater in the training group than in the control group ( P < 0.05). Moreover, the increase in serum adiponectin, CTRP3, and CTRP5 from baseline to 8 wk was significantly higher in the training group compared with the control group ( P < 0.05). Additionally, the training-induced change in cfPWV was negatively correlated with the training-induced change in serum adiponectin, CTRP3, and CTRP5 levels ( r = −0.51, r = −0.48, r = −0.42, respectively, P < 0.05), and increased plasma nitrite/nitrate level by exercise training was correlated only with adiponectin levels ( r = 0.41, P < 0.05). These results suggest that the exercise training-induced increase in serum CTRPs levels may be associated with the reduction of arterial stiffness in middle-aged and older adults.

Current body composition measurement techniques

PURPOSE OF REVIEW

The current article reviews the most innovative and precise, available methods for quantification of in-vivo human body composition.

RECENT FINDINGS

Body composition measurement methods are continuously being perfected. Ongoing efforts involve multisegmental and multifrequency bioelectrical impedance analysis, quantitative magnetic resonance for total body water, fat, and lean tissue measurements, imaging to further define ectopic fat depots. Available techniques allow for the measurement of fat, fat-free mass, bone mineral content, total body water, extracellular water, total adipose tissue and its subdepots (visceral, subcutaneous, and intermuscular), skeletal muscle, select organs, and ectopic fat depots.

SUMMARY

There is an ongoing need for methods that yield information on metabolic and biological functions. Based on the wide range of measurable properties, analytical methods and known body composition models, clinicians, and scientists can quantify a number of body components and with longitudinal assessment, can track changes in health and disease with implications for understanding efficacy of nutritional and clinical interventions, diagnosis, prevention, and treatment in clinical settings. With the greater need to understand precursors of health risk beginning prior to conception, a gap exists in appropriate in-vivo measurement methods with application beginning during gestation, that is, fetal development.

Association between aerobic exercise training effects of serum adropin level, arterial stiffness, and adiposity in obese elderly adults

Serum levels of adropin, which enhances endothelial cell release of nitric oxide (NO), are lower in obese patients. Although habitual aerobic exercise reduces arterial stiffness and adiposity, the relationship between these effects and circulating levels of adropin remains unclear. The purpose of this study was to determine if serum adropin level is associated with the effects of aerobic exercise training on arterial stiffness and adiposity in obese adults. In Experiment 1, we examined whether serum adropin levels are associated with cardiorespiratory fitness, carotid β-stiffness, plasma nitrite/nitrate (NOx) level, and abdominal visceral fat in 27 normal, 20 overweight, and 25 obese adults (age, 41-79 years). In Experiment 2, we examined the effects of an 8-week aerobic exercise training program on the relationship between serum adropin level and arterial stiffness or adiposity in 13 obese adults (age, 54-76 years). Serum adropin levels in normal, overweight, and obese adults negatively correlated with carotid β-stiffness and abdominal visceral fat, and positively correlated with plasma NOx level and cardiorespiratory fitness. After the 8-week exercise program, serum adropin levels in obese adults were elevated, and correlated with training-induced changes in carotid β-stiffness (r = -0.573, P < 0.05), plasma NOx level (r = 0.671, P < 0.05), and abdominal visceral fat (r = -0.585, P < 0.05). These findings suggest that the exercise training-induced increase in serum adropin may be related to the training effects of arterial stiffness and adiposity in obese adults.

Daily ingestion of catechin-rich beverage increases brown adipose tissue density and decreases extramyocellular lipids in healthy young women

Purpose

Brown adipose tissue (BAT) contributes to the regulation of non-shivering thermogenesis and adiposity. Increasing BAT has recently attracted much attention as a countermeasure to obesity. Animal studies have shown that prolonged catechin treatment increases uncoupling protein 1, a thermogenic protein in BAT. On the other hand, supportable evidence in human is lacking. Thus, the purpose of this study was to examine whether BAT increases after catechin ingestion in humans.

Methods

Twenty-two healthy young women were given either a catechin-rich (540 mg/day; catechin) or placebo beverage every day for 12 weeks in a double-blind design. BAT density was measured using near-infrared time-resolved spectroscopy (NIR_TRS), visceral fat area were measured using magnetic resonance imaging, extramyocellular lipids (EMCL) using proton magnetic resonance spectroscopy, and body fat mass using dual-energy X-ray absorptiometry scans.

Results

BAT density was significantly increased (18.8 %), and EMCL was decreased (17.4 %) after the 12-week ingestion. There was a significant negative correlation between the changes in BAT density and those in EMCL (r = −0.66, P < 0.05). There were no notable changes in other parameters.

Conclusions

In conclusion, prolonged ingestion of a catechin-rich beverage increases the BAT density in parallel with a decrease in EMCL.

Effects of habitual aerobic exercise on the relationship between intramyocellular or extramyocellular lipid content and arterial stiffness

The accumulation of intramyocellular lipid (IMCL) and extramyocellular lipid (EMCL) is associated with arterial stiffness in middle-aged and older adults. Habitual aerobic exercise induces the improvement of arterial stiffness with reduction in fat accumulation. However, the relationship between aerobic exercise-induced changes in muscular lipids and arterial stiffness remains unclear. The purpose of this study was to investigate whether habitual aerobic exercise-induced changes in IMCL and EMCL content would lead to an improvement of arterial stiffness. First, in a cross-sectional study, we investigated whether cardiorespiratory fitness level affects the association between IMCL or EMCL content and arterial stiffness in 60 middle-aged and older subjects (61.0±1.3 years). Second, in an intervention study, we examined whether aerobic exercise training-induced changes in IMCL and EMCL content are associated with a reduction in arterial stiffness in 18 middle-aged and older subjects (67.0±1.7 years). In the cross-sectional study, IMCL content was negatively correlated with brachial-ankle pulse wave velocity (baPWV) (r=-0.47, P<0.05), whereas EMCL content was positively correlated with baPWV (r=0.48, P<0.05) in the low-fitness group, but was not correlated in the high-fitness group. Furthermore, 8-week aerobic exercise training in older adults increased IMCL content and reduced EMCL content. The training-induced change in baPWV was negatively correlated with training-induced changes in IMCL but was positively correlated with training-induced changes in EMCL. These findings suggest that aerobic exercise training-induced changes in IMCL and EMCL content may be related to a reduction in arterial stiffness in middle-aged and older adults.

A 3-day high-fat/low-carbohydrate diet does not alter exercise-induced growth hormone response in healthy males

OBJECTIVE

The purpose of the present study was to examine the effects of 3 days isoenergetic high-fat/low-carbohydrate diet (HF-LC) relative to low-fat/high-carbohydrate diet (LF-HC) on the exercise-induced growth hormone (GH) response in healthy male subjects.

DESIGN

Ten healthy young males participated in this study. Each subject consumed the HF-LC (18±1% protein, 61±2% fat, 21±1% carbohydrate, 2720 kcal per day) for 3 consecutive days after consuming the LF-HC (18±1% protein, 20±1% fat, 62±1% carbohydrate, 2755 kcal per day) for 3 consecutive days. After each dietary intervention period, the hormonal and metabolic responses to an acute exercise (30 min of continuous pedaling at 60% of V˙O2max) were compared. The intramyocellular lipid (IMCL) contents in the vastus lateralis, soleus, and tibialis anterior were evaluated by proton magnetic resonance spectroscopy.

RESULTS

Serum GH concentrations increased significantly during the exercise after both the HF-LC and LF-HC periods (P<0.05). However, the exercise-induced GH response was not significantly different between the two periods. Fat utilization and lipolytic responses during the exercise were enhanced significantly after the HF-LC period compared with the LF-HC period. IMCL content did not differ significantly in any portion of muscle after the dietary interventions.

CONCLUSIONS

We could not show that short-term HF-LC consumption changed significantly exercise-induced GH response or IMCL content in healthy young males.