Effects of 6 weeks of aerobic exercise combined with conjugated linoleic acid on the physical working capacity at fatigue threshold

Conjugated linoleic acid (CLA) as a functional food: Is it beneficial or not?

Conjugated linoleic acid (CLA) has attracted great attention in recent years as a popular class of functional food that is broadly used. It refers to a group of geometric and positional isomers of linoleic acid (LA) with a conjugated double bond. The main natural sources of CLA are dairy products, beef and lamb, whereas only trace amounts occur naturally in plant lipids. CLA has been shown to improve various health issues, having effects on obesity, inflammatory, anti-carcinogenicity, atherogenicity, immunomodulation, and osteosynthesis. Also, compared to studies on humans, many animal researches reveal more positive benefits on health. CLA represents a nutritional avenue to improve lifestyle diseases and metabolic syndrome. Most of these effects are attributed to the two major CLA isomers [conjugated linoleic acid cis-9,trans-11 isomer (c9,t11), and conjugated linoleic acid trans-10,cis-12 isomer (t10,c12)], and their mixture (CLA mix). In contrast, adverse effects of CLA have been also reported, such as glucose homeostasis, insulin resistance, hepatic steatosis and induction of colon carcinogenesis in humans, as well as milk fat inhibition in ruminants, lowering chicken productivity, influencing egg quality and altering growth performance in fish. This review article aims to discuss the health benefits of CLA as a nutraceutical supplement and highlight the possible mechanisms of action that may contribute to its outcome. It also outlines the feasible adverse effects of CLA besides summarizing the recent peer-reviewed publications on CLA to ensure its efficacy and safety for proper application in humans.

Effects of conjugated linoleic acid and exercise on body composition and obesity: a systematic review and meta-analysis

CONTEXT

Conjugated linoleic acid (CLA) has been reported to have anti-obesity and antidiabetic effects. However, the benefits of CLA combined with exercise remain unclear, and studies report conflicting results.

OBJECTIVE

A systematic review and meta-analysis were performed to investigate the synergistic effect of CLA and exercise on body composition, exercise-related indices, insulin resistance, and lipid profiles; and of the safety of CLA supplements.

DATA SOURCES

In October 2021, the PubMed, Embase, and Cochrane Library databases were searched for reports on clinical trials of the combined intervention of CLA and exercise.

DATA EXTRACTION

A total of 18 randomized controlled trials and 2 crossover trials were included. The methodological quality assessment was performed using the revised Cochrane risk-of-bias tool. Pooled effect sizes were reported as standardized mean difference (SMD) for continuous data and risk ratio for dichotomous data with their corresponding 95% confidence intervals (CIs). Heterogeneity was tested using the I2 statistic.

DATA ANALYSIS

The combination of CLA and exercise resulted in significantly decreased body fat (SMD, -0.42 [95%CI, -0.70, -0.14]; P = 0.003; I2 = 65) and insulin resistance (SMD, -0.25 [95%CI, -0.44, -0.06]; P = 0.01; I2 = 0) than did exercise alone. In subgroup analysis, the following factors were associated with significant outcomes: (1) body mass index ≥25 kg/m2; (2) female sex; (3) follow-up time >4 weeks; and (4) intervention duration >4 weeks. Nevertheless, supplementation with CLA during exercise programs was not effective for body-weight control, exercise performance enhancement, or lipid-profile improvement. CLA in combination with exercise did not result in a higher risk of adverse events (risk ratio, 1.32 [95%CI, 0.94-1.84]; P > 0.05; I2 = 0).

CONCLUSION

CLA combined with exercise is generally safe and can lower body fat and insulin resistance but does not reduce body weight, enhance exercise performance, or improve lipid profiles.

Application of the neuromuscular fatigue threshold treadmill test to muscles of the quadriceps and hamstrings

PURPOSE

The purposes of the present study were: (1) to determine whether the physical working capacity at the fatigue threshold (PWC_FT) model that has been used for estimating the onset of neuromuscular fatigue in the vastus lateralis (VL) during incremental treadmill running could also be applied to the vastus medialis (VM), biceps femoris (BF), and semitendinosus (ST) muscles; and (2) if applicable, to compare the running velocities associated with the PWC_FT among these muscles.

METHODS

Eleven subjects (age 21.7 ± 1.8 years) performed an incremental treadmill test to exhaustion with electromyographic signals recorded from the VL, VM, BF, and ST.

RESULTS

The results indicated there were no significant (p > 0.05) mean differences in the running velocities associated with the PWC_FT for the VL (14.4 ± 2.0 km/h), VM (14.3 ± 1.9 km/h), BF (13.8 ± 1.8 km/h), and ST (14.7 ± 2.3 km/h). In addition, there were significant inter-correlations (r = 0.68-0.88) among running velocities associated with the PWC_FT of each muscle. Individual results also indicated that 9 of the 11 subjects exhibited identical PWC_FT values for at least 3 of the 4 muscles, but there were no uniform patterns for any intra-individual differences.

CONCLUSION

The findings of the present study suggested that the PWC_FT test is a viable method to identify neuromuscular fatigue in the quadriceps and hamstrings during incremental treadmill exercise and results in consistent PWC_FT values among these muscles.

Metabolomics of Aerobic Exercise in Chronic Stroke Survivors: A Pilot Study

BACKGROUND

Understanding the metabolic response to exercise may aid in optimizing stroke management. Therefore, the purpose of this pilot study was to evaluate plasma metabolomic profiles in chronic stroke survivors following aerobic exercise training.

METHODS

Participants (age: 62 ± 1 years, body mass index: 31 ± 1 kg/m², mean ± standard error of the mean) were randomized to 6 months of treadmill exercise (N = 17) or whole-body stretching (N = 8) with preintervention and postintervention measurement of aerobic capacity (VO₂peak). Linear models for microarray data expression analysis was performed to determine metabolic changes over time, and Mummichog was used for pathway enrichment analysis following analysis of plasma samples by high-performance liquid chromatography coupled to ultrahigh resolution mass spectrometry.

RESULTS

VO₂peak change was greater following exercise than stretching (18.9% versus -.2%; P < .01). Pathway enrichment analysis of differentially expressed metabolites results showed significant enrichment in 4 pathways following treadmill exercise, 3 of which (heparan-, chondroitin-, keratan-sulfate degradation) involved connective tissue metabolism and the fourth involve lipid signaling (linoleate metabolism). More pathways were altered in pre and post comparisons of stretching, including branched-chain amino acid, tryptophan, tyrosine, and urea cycle, which could indicate loss of lean body mass.

CONCLUSIONS

These preliminary data show different metabolic changes due to treadmill training and stretching in chronic stroke survivors and suggest that in addition to improved aerobic capacity, weight-bearing activity, like walking, could protect against loss of lean body mass. Future studies are needed to examine the relationship between changes in metabolomic profiles to reductions in cardiometabolic risk after treadmill rehabilitation.

An Evolutionary Perspective on Linoleic Acid Synthesis in Animals

The diet of organisms generally provides a sufficient supply of energy and building materials for healthy growth and development, but should also contain essential nutrients. Species differ in their exogenous requirements, but it is not clear why some species are able to synthesize essential nutrients, while others are not. The unsaturated fatty acid, linoleic acid (LA; 18:2n-6) plays an important role in functions such as cell physiology, immunity, and reproduction, and is an essential nutrient in diverse organisms. LA is readily synthesized in bacteria, protozoa and plants, but it was long thought that all animals lacked the ability to synthesize LA de novo and thus required a dietary source of this fatty acid. Over the years, however, an increasing number of studies have shown active LA synthesis in animals, including insects, nematodes and pulmonates. Despite continued interest in LA metabolism, it has remained unclear why some organisms can synthesize LA while others cannot. Here, we review the mechanisms by which LA is synthesized and which biological functions LA supports in different organisms to answer the question why LA synthesis was lost and repeatedly gained during the evolution of distinct invertebrate groups. We propose several hypotheses and compile data from the available literature to identify which factors promote LA synthesis within a phylogenetic framework. We have not found a clear link between our proposed hypotheses and LA synthesis; therefore we suggest that LA synthesis may be facilitated through bifunctionality of desaturase enzymes or evolved through a combination of different selective pressures.

Effects of rumenic acid rich conjugated linoleic acid supplementation on cognitive function and handgrip performance in older men and women

The purpose of this study was to investigate the effects of 8weeks at 6g per day of RAR CLA versus placebo on cognitive function and handgrip performance in older men and women. Sixty-five (43 women, 22 men) participants (mean±SD; age=72.4±5.9yrs; BMI=26.6±4.2kg·m^-2) were randomly assigned to a RAR CLA (n=30: 10 men, 20 women) or placebo (PLA; high oleic sunflower oil; n=35: 12 men, 23 women) group in double-blind fashion and consumed 6g·d^-1 of their allocated supplement for 8weeks. Before (Visit 1) and after supplementation (Visit 2), subjects completed the Serial Sevens Subtraction Test (S₇), Trail Making Test Part A (TM_A) and Part B (TM_B), and Rey's Auditory Verbal Learning Test (RAVLT) to measure cognitive function. The RAVLT included 5, 15-item auditory word recalls (R_1-5), an interference word recall (R_B), a 6th word recall (R₆), and a 15-item visual word recognition trial (R_R). For handgrip performance, subjects completed maximal voluntary isometric handgrip strength (MVIC) testing before (MVIC_PRE) and after (MVIC_POST) a handgrip fatigue test at 50% MVIC_PRE. Hand joint discomfort was measured during MVIC_PRE, MVIC_POST, and the handgrip fatigue test. There were no treatment differences (p>0.05) for handgrip strength, handgrip fatigue, or cognitive function as measured by the Trail Making Test and Serial Seven's Subtraction Test in men or women. However, RAR CLA supplementation improved cognitive function as indicated by the RAVLT R₅ in men. A qualitative examination of the mean change scores suggested that, compared to PLA, RAR CLA supplementation was associated with a small improvement in joint discomfort in both men and women. Longer-term studies are needed to more fully understand the potential impact of RAR CLA on cognitive function and hand joint discomfort in older adults, particularly in those with lower cognitive function.

The Dmax method is a valid procedure to estimate physical working capacity at fatigue threshold

INTRODUCTION

The purpose of this study was to determine the validity of the maximal distance-electromyography (Dmax-EMG) method for estimating physical working capacity at fatigue threshold (PWC_FT ).

METHODS

Twenty-one men and women (age 22.9 ± 3.0 years) volunteered to perform 12 sessions of high-intensity interval training (HIIT) over 4 weeks. Before and after HIIT training, a graded exercise test (GXT) was used to estimate PWC_FT using the Dmax method and the original (ORG) method.

RESULTS

There was a significant increase in PWC_FT for both ORG (+10.6%) and Dmax (+12.1%) methods, but no significant difference in the change values between methods. Further, Bland-Altman analyses resulted in non-significant biases (ORG-Dmax) between methods at pre-HIIT (-6.4 ± 32.5 W; P > 0.05) and post-HIIT (-4.2 ± 33.1 W; P > 0.05).

CONCLUSION

The Dmax method is sensitive to training and is a valid method for estimating PWC_FT in young men and women. Muscle Nerve 55: 344-349, 2017.

Wet, volatile, and dry biomarkers of exercise-induced muscle fatigue

Background

The physiological background of exercise-induced muscle fatigue(EIMUF) is only poorly understood. Thus, monitoring of EIMUF by a single or multiple biomarkers(BMs) is under debate.

After a systematic literature review 91 papers were included.

Results

EIMUF is mainly due to depletion of substrates, increased oxidative stress, muscle membrane depolarisation following potassium depletion, muscle hyperthermia, muscle damage, impaired oxygen supply to the muscle, activation of an inflammatory response, or impaired calcium-handling. Dehydration, hyperammonemia, mitochondrial biogenesis, and genetic responses are also discussed. Since EIMUF is dependent on age, sex, degree of fatigue, type, intensity, and duration of exercise, energy supply during exercise, climate, training status (physical fitness), and health status, BMs currently available for monitoring EIMUF have limited reliability. Generally, wet, volatile, and dry BMs are differentiated. Among dry BMs of EIMUF the most promising include power output measures, electrophysiological measures, cardiologic measures, and questionnaires. Among wet BMs of EIMUF those most applicable include markers of ATP-metabolism, of oxidative stress, muscle damage, and inflammation. VO₂-kinetics are used as a volatile BM.

Conclusions

Though the physiology of EIMUF remains to be fully elucidated, some promising BMs have been recently introduced, which together with other BMs, could be useful in monitoring EIMUF. The combination of biomarkers seems to be more efficient than a single biomarker to monitor EIMUF. However, it is essential that efficacy, reliability, and applicability of each BM candidate is validated in appropriate studies.

Impact of Conjugated Linoleic Acid (CLA) on Skeletal Muscle Metabolism

Conjugated linoleic acid (CLA) has garnered special attention as a food bioactive compound that prevents and attenuates obesity. Although most studies on the effects of CLA on obesity have focused on the reduction of body fat, a number of studies have demonstrated that CLA also increases lean body mass and enhances physical performances. It has been suggested that these effects may be due in part to physiological changes in the skeletal muscle, such as changes in the muscle fiber type transformation, alteration of the intracellular signaling pathways in muscle metabolism, or energy metabolism. However, the mode of action for CLA in muscle metabolism is not completely understood. The purpose of this review is to summarize the current knowledge of the effects of CLA on skeletal muscle metabolism. Given that CLA not only reduces body fat, but also improves lean mass, there is great potential for the use of CLA to improve muscle metabolism, which would have a significant health impact.

A review on effects of conjugated linoleic fatty acid (CLA) upon body composition and energetic metabolism

Conjugated linoleic acid (CLA) is highly found in fats from ruminants and it appears to favorably modify the body composition and cardiometabolic risk factors. The capacity of CLA to reduce the body fat levels as well as its benefic actions on glycemic profile, atherosclerosis and cancer has already been proved in experimental models. Furthermore, CLA supplementation may modulate the immune function, help re-synthetize of glycogen and potentiate the bone mineralization. CLA supplementation also could increase the lipolysis and reduce the accumulation of fatty acids on the adipose tissue; the putative mechanisms involved may be its action in reducing the lipase lipoprotein activity and to increase the carnitine-palmitoil-transferase-1 (CAT-1) activity, its interaction with PPARγ, and to raise the expression of UCP-1. Although studies made in human have shown some benefits of CLA supplementation as the weight loss, the results are still discordant. Moreover, some have shown adverse effects, such as negative effects on glucose metabolism and lipid profile. The purpose of this article is to review the available data regarding the benefits of CLA on the energetic metabolism and body composition, emphasizing action mechanisms.

Conjugated Linoleic Acid Supplementation has no Impact on Aerobic Capacity of Healthy Young Men

This study investigated the effect of conjugated linoleic acid (CLA) on the aerobic capacity and anthropometric measurements of humans. Although this effect has been shown in animal studies, human studies have reported controversial results. In this double-blind, placebo-controlled, randomized clinical trial, 80 non-trained healthy young men received a 50:50 mixture of cis-9,trans-11 and trans-10 cis-12 CLA (CLA 4 × 0.8 g day(-1)) ora placebo (PLA; soybean oil) in an 8-week intervention. Maximal oxygen consumption (VO2 max), time to exhaustion, weight, body mass index (BMI) and waist circumference (WC) were measured. CLA had no effect on VO2 max (p = 0.5) also no change was seen in time to exhaustion (p = 0.51), weight (p = 0.7), BMI (p = 0.7) and WC (p = 0.8) vs PLA. Our results suggest that CLA has no significant effect on VO2 max, time to exhaustion and anthropometric measurements in untrained healthy young male students.

Pros and cons of CLA consumption: an insight from clinical evidences

This comprehensive review critically evaluates whether supposed health benefits propounded upon human consumption of conjugated linoleic acids (CLAs) are clinically proven or not. With a general introduction on the chemistry of CLA, major clinical evidences pertaining to intervention strategies, body composition, cardio-vascular health, immunity, asthma, cancer and diabetes are evaluated. Supposed adverse effects such as oxidative stress, insulin resistance, irritation of intestinal tract and milk fat depression are also examined. It seems that no consistent result was observed even in similar studies conducted at different laboratories, this may be due to variations in age, gender, racial and geographical disparities, coupled with type and dose of CLA supplemented. Thus, supposed promising results reported in mechanistic and pre-clinical studies cannot be extrapolated with humans, mainly due to the lack of inconsistency in analyses, prolonged intervention studies, follow-up studies and international co-ordination of concerted studies. Briefly, clinical evidences accumulated thus far show that CLA is not eliciting significantly promising and consistent health effects so as to uphold it as neither a functional nor a medical food.