Reduced fat oxidation during high intensity,submaximal exercise: is the availability of carnitine important?

Abstract

The increased energy demand that occurs with incremental exercise intensity is met by increases in the oxidation of both endogenous fat and carbohydrate stores up to an intensity of ~70% V˙O_2max in trained individuals. However, when exercise intensity increases beyond this workload, fat oxidation rates decline, both from a relative and absolute perspective. As endogenous glycogen use is accelerated, glycogen stores can become depleted, ultimately resulting in fatigue and the inability to maintain high intensity, submaximal exercise (>70% V˙O_2max). Despite a considerable accumulation of knowledge that has been gained over the past half century, the precise mechanism(s) regulating muscle fuel selection and underpinning the aforementioned decline in fat oxidation remain largely unclear. A greater understanding would undoubtedly lead to novel strategies to increase fat utilization and, as such, improve exercise capacity. The present review primarily addresses one of the most prominent theories to explain the phenomenon of diminished fat oxidation during high intensity, submaximal exercise; a reduced availability of muscle free carnitine for mitochondrial fat translocation. This is discussed in the light of recent work in this area taking advantage of the discovery that muscle carnitine content can be increased in vivo in humans. Furthermore, the evidence supporting the recently proposed theory that reduced muscle co-enzyme A availability to several key enzymes in the fat oxidation pathway may also exert a degree of control over muscle fuel selection during exercise is also considered. Strong correlational evidence exists that muscle free carnitine availability is likely to be a key limiting factor to fat oxidation during high intensity, submaximal exercise. However, it is concluded that further intervention studies manipulating the muscle carnitine pool in humans are required to establish a direct causal role. In addition, it is concluded that while a depletion of muscle coenzyme A availability during exercise also offers a viable mechanism for impairing fat oxidation, at present, this remains speculative.     

Index for Volume 52 (1981)

Abstract

The purpose of this study was to compare fitness levels of children participating in a movement education (ME) program to Illinois fitness norms (control group). The AAHPERD Health-Related Fitness test was administered to children ages 7 through 12 during May in each of the three years, 1980–83. The skinfold measures showed that the ME children had more skinfold thickness regardless of age and gender. Scores for sit-ups and sit and reach over the three years for ME children showed that the 9- and 11-year-old ME males had more abdominal strength and 11- and 12-year-old ME females, less flexibility. Times in the mile run indicated that ME children were slower than the control group. Reference scores at the 50th and 25th percentile on the Illinois norm tables were located for each fitness measurement. These references were then used to determine the percentage of ME children who fell at or above the 50th percentile and at or below the 25th percentile. Data indicated that ME children need remediation in cardiovascular activity and reduction in subcutaneous fat.     

Gender Differences in Strength

The purpose of this study was to examine gender differences in upper and lower body strength as a function of lean body weight and the distribution of muscle and subcutaneous fat in the upper and lower limbs. The subjects were 103 physically active men (n = 48) and women (n = 55). The peak torques produced during shoulder flexion (SF) and knee extension (KE) were used as measures of upper body and lower body strength, respectively. Flexed arm girth, thigh girth, triceps skinfold, and thigh skinfold were used to estimate the distribution of muscle and subcutaneous fat in the limbs. Results of the MANOVA revealed that the overall strength of men was significantly greater than that of women. Results of MANCOVA indicated that the SF and KE strength of women and men did not differ significantly when differences in lean body weight, arm girth, thigh girth, triceps skinfold and thigh skinfold were statistically controlled. High levels of SF and KE strength were associated with a high lean body weight and a large arm girth. Results of the multiple regression analysis indicated that for men a substantial portion of the variance in both SF and KE strength was explained by lean body weight alone; whereas strength variations in women were explained more adequately by including limb variables along with lean body weight. Within the limitations of this study, it was concluded that gender differences in upper and lower body strength are a function of differences in lean body weight and the distribution of muscle and subcutaneous fat in the body segments. Upper body strength is relatively more important than lower body strength in characterizing the gender difference in strength.     

Effects of Sit up Exercise Training on Adipose Cell Size and Adiposity

Abstract

The present experiment evaluated the effects of a 27-day sit up exercise training program on adipose cell size and adiposity. Fat biopsies were taken from the abdomen, subscapular, and gluteal sites by needle aspiration in 13 experimental and 6 control male subjects before and after a five days/week progressive training regimen. Day 1 consisted of 10 bouts of 10-sec exercise, 7 sit ups/bout, with 10-sec rest intervals; on day 27, 14 bouts of 30-sec exercise were performed, 24 sit ups/bout with 10-sec rest intervals. The total number of sit ups done was 5004. Fat cells were isolated using collagenase and photographed to determine cell diameter. Repeated measures ANOVA revealed significant decreases in cell diameter at the three biopsy sites (p<.01), but no significant differences in the rate of change (pre to post) in cell diameter between sites for the experimental and control groups (p>.05). Body weight, total body fat (underwater weighing), and fatfolds and girths remained unaltered. The results demonstrate that (1) the conventional sit up exercise does not preferentially reduce adipose cell size or subcutaneous fat thickness in the abdominal region to a greater extent compared to other adipose sites, and (2) significant changes in fat cell size may occur in the absence of changes in fatfolds, girths or total body composition.     

A Reply to Karpman

Abstract

College female swimmers (N = 15), mean age 18.6 yr, were assessed for body composition and skinfolds at the beginning and end of 9 wk of competitive training. A significant increase, 1.052 to 1.054 g.cm-3, in body density resulted in significant decreases in absolute body fat, 12.7 to 12.1 kg, and relative fat, 20.4 to 19.6%. Skinfolds of the triceps, suprailiac, and subscapula also decreased significantly, suggesting the fat loss was mainly subcutaneous. The relation of these body composition changes to body insulation and sinking force while swimming are discussed.     

玉林师范学院大学生皮褶厚度与体成分分析

在2005年全国学生体质健康调研工作中对玉林师范学院793名大学生进行皮褶厚度的检测。结果表明:男生的肱三头肌部皮下脂肪厚度低于肩胛下部脂肪厚度,女生在这两个部位的皮下脂肪厚度相近;女生的体脂较多,而男生的瘦体重较高;皮褶厚度与性别相关,存在着非常显著性差异,但与城乡差别无相关影响;因客观因素的影响,玉林师范学院大学生皮褶厚度值与目前的《中国大学生皮褶厚度正常值表》没有可比性,建议尽快建立中国南方大学生皮褶厚度正常值表。     

Assessment of subcutaneous adipose tissue using ultrasound in highly trained junior rowers

Introduction: There is a large variety of body fat (BF) measurements, which differ in validity and reliability. The aim of this study was to measure subcutaneous adipose tissue (SAT) using ultrasound (US) in highly trained junior rowers in a field setting, establish fat patterning profiles, and compare the profiles between male and female athletes. Skinfold thickness (SKF) measurements were also taken and compared to US measurements. Methods: Sixteen athletes participated. US measurements were taken at eight sites and reported as a sum of SAT (D): D_Excl (without embedded structures) and D_Incl (including embedded structures). SKF was measured at three sites and reported as a sum of adipose tissue thickness (SUM_SKF). Results: Mean SAT thickness (D_Incl) was 27.6?±?12.4?mm for males and 65.5?±?11.8?mm for females. Females had significantly more embedded structures than males (P?=?.016). Significant correlations were found (P?<?.001, r?=?0.92) comparing SUM_SKF to D_Incl and between SKF and US measurements at the thigh site (P?<?.001, r?=?0.86). Conclusion: US is a suitable tool to measure BF in the field testing of athletes and enables measurements of SAT with an accuracy and reliability not reached before. The sum of thicknesses (D_Incl or D_Excl) can be used to represent subcutaneous fat based on accurate measurements of uncompressed SAT thicknesses.     

Effects of an 8-weeks erythropoietin treatment on mitochondrial and whole body fat oxidation capacity during exercise in healthy males

The present investigation was performed to elucidate if the non-erythropoietic ergogenic effect of a recombinant erythropoietin treatment results in an impact on skeletal muscle mitochondrial and whole body fatty acid oxidation capacity during exercise, myoglobin concentration and angiogenesis. Recombinant erythropoietin was administered by subcutaneous injections (5000 IU) in six healthy male volunteers (aged 21 ± 2 years; fat mass 18.5 ± 2.3%) over 8 weeks. The participants performed two graded cycle ergometer exercise tests before and after the intervention where VO_2max and maximal fat oxidation were measured. Biopsies of the vastus lateralis muscle were obtained before and after the intervention. Recombinant erythropoietin treatment increased mitochondrial O₂ flux during ADP stimulated state 3 respiration in the presence of complex I and II substrates (malate, glutamate, pyruvate, succinate) with additional electron input from β-oxidation (octanoylcarnitine) (from 60 ± 13 to 87 ± 24 pmol · s^?1 · mg^?1 P < 0.01). β-hydroxy-acyl-CoA-dehydrogenase activity was higher after treatment (P < 0.05), whereas citrate synthase activity also tended to increase (P = 0.06). Total myoglobin increased by 16.5% (P < 0.05). Capillaries per muscle area tended to increase (P = 0.07), whereas capillaries per fibre as well as the total expression of vascular endothelial growth factor remained unchanged. Whole body maximal fat oxidation was not increased after treatment. Eight weeks of recombinant erythropoietin treatment increases mitochondrial fatty acid oxidation capacity and myoglobin concentration without any effect on whole body maximal fat oxidation.     

Changes in Skinfold and Girth Measures of Women Varsity Basketball and Field Hockey Players

Abstract

Pre- and post-season subcutaneous fat, girth and weight measures were made on 12 women varsity field hockey players and 17 women varsity basketball players at The Pennsylvania State University. Each experimental period consisted of eight weeks. Skinfold measures were taken with Lange calipers using the technique suggested by Keys. Girth measurements were made using a Tip Top Whyteface tape with a Gulick handle to aid in exerting equal tension on the tape for each measure. The sites measured were: (1) the right upper arm, (2) above the right iliac crest in the midaxillary line, (3) immediately to the right of and directly opposite the umbilicus, and (4) the anterior upper quarter of the right thigh in the midline. All sites were marked so that the girth measurements could be taken over the same place. Reliability was computed for all measures. Results of a comparison of pre- and post- mean scores indicated that the field hockey players studied showed a decrease in fat at the arm, umbilical, and thigh sites, with a reduction in girth at the umbilical site. Basketball players decreased in fat at the arm, iliac, and umbilical sites, with a reduction in girth of the thighs.     

Exploring overweight and obesity beyond body mass index: A body composition analysis in people with and without patellofemoral pain

BackgroundWe compared body mass index (BMI), body fat, and skeletal muscle mass between (1) a mixed-sex nonathletic cohort of people with patellofemoral pain (PFP) and pain-free people, and (2) a nonathletic cohort of people with PFP and pain-free people subgrouped by sex (i.e., men and women with PFP vs. pain-free men and women).MethodsThis cross-sectional study included 114 people with PFP (71 women, 43 men) and 54 pain-free controls (32 women, 22 men). All participants attended a single testing session to assess body composition measures, which included BMI, percentage of body fat (%BF_Bioimpedance), and skeletal muscle mass (both assessed by bioelectrical impedance analysis), and percentage of body fat (%BF_Skinfold) (assessed by skinfold caliper analysis). A one-way univariate analysis of covariance (age and physical activity levels as covariates) was used to compare body composition measures between groups (i.e., PFP vs. pain-free group; women with PFP vs. pain-free women; men with PFP vs. pain-free men).ResultsWomen with PFP presented significantly higher BMI, %BF_Bioimpedance, and %BF_Skinfold, and lower skeletal muscle mass compared to pain-free women (p ≤ 0.04; effect size : ‒0.47 to 0.85). Men with PFP and men and women combined had no differences in BMI, %BF_Bioimpedance, %BF_Skinfold, and skeletal muscle mass compared to their respective pain-free groups (p > 0.05).ConclusionOur findings indicate that BMI and body composition measures should be considered as part of the evaluation and management of people with PFP, especially in women, who have demonstrated higher BMI and body fat and lower skeletal muscle mass compared to pain-free controls. Future studies should not assess body composition measures in a mixed-sex population without distinguishing men participants from women participants.     

Correlation between architectural variables and torque in the erector spinae muscle during maximal isometric contraction

Abstract

This study analysed whether a significant relationship exists between the torque and muscle thickness and pennation angle of the erector spinae muscle during a maximal isometric lumbar extension with the lumbar spine in neutral position. This was a cross-sectional study in which 46 healthy adults performed three repetitions for 5 s of maximal isometric lumbar extension with rests of 90 s. During the lumbar extensions, bilateral ultrasound images of the erector spinae muscle (to measure pennation angle and muscle thickness) and torque were acquired. Reliability test analysis calculating the internal consistency (Cronbach's alpha) of the measure, correlation between pennation angle, muscle thickness and torque extensions were examined. Through a linear regression the contribution of each independent variable (muscle thickness and pennation angle) to the variation of the dependent variable (torque) was calculated. The results of the reliability test were: 0.976–0.979 (pennation angle), 0.980–0.980 (muscle thickness) and 0.994 (torque). The results show that pennation angle and muscle thickness were significantly related to each other with a range between 0.295 and 0.762. In addition, multiple regression analysis showed that the two variables considered in this study explained 68% of the variance in the torque. Pennation angle and muscle thickness have a moderate impact on the variance exerted on the torque during a maximal isometric lumbar extension with the lumbar spine in neutral position.     

Tracking of gross motor coordination in Portuguese children

The purpose of this study was to investigate the tracking of gross motor coordination (GMC) and to profile children at 6 years of age who consistently showed higher stability patterns in different levels of GMC. The participants were 245 children (123 boys and 122 girls) who were assessed longitudinally from 6 to 9 years of age. GMC was assessed using the Korperkoordinationtest fur Kinder (KTK) test battery. Anthropometry, physical activity, and health- and performance-related physical fitness were also measured. Cohen’s kappa (κ) was used to estimate tracking. Tracking was poor for all GMC tests (0.17 ≤ κ ≤ 0.38) and moderate for the GMC motor quotient (MQ) in both boys and girls (0.44 ≤ κ ≤ 0.45). Instability at the extremes was low in GMC tests and negligible for MQ. Children who consistently showed high GMC levels during the 4 years of follow-up were lighter, had lower body mass index and subcutaneous fat, and showed higher scores in physical fitness tests at 6 years of age than those who consistently had low GMC levels. In conclusion, GMC showed low-to-moderate tracking over time in childhood. However, children who consistently demonstrated high GMC levels over time had healthier profiles at 6 years of age.     

Nutritional intake and body composition changes in a UCI World Tour cycling team during the Tour of Spain

Abstract

The aim of this study was to quantify the food intake of an International Cyclist Union (UCI) World Tour professional cyclist team and to analyse changes in body composition during the Tour of Spain. Nine male professional road cyclists (31.3?±?3.0 years) volunteered to participate in the study. Nutritional data were collected each day throughout the 3-week Tour by two trained investigators who weighed the food ingested by the cyclists. Mean nutritional intake of the cyclists was as follows: carbohydrate, 12.5?±?1.8?g/kg/day of body weight (BW) (65.0?±?5.9%); fat, 1.5?±?0.5 g/kg/day BW (17.9?±?5.6%); and protein, 3.3?±?0.3?g/kg/day BW (17.1?±?1.6%). Intake of all micronutrients, except for folate, vitamin D and potassium (which were 78.7%, 46% and 84% of Recommended Dietary Allowances (RDA), respectively), exceeded the RDA. Height, weight, skinfolds, circumferences and diameters were taken following the guidelines outlined by the International Society for the Advancement of Kinanthropometry. Body density, body fat percentage, muscle mass, total muscle mass and fat mass of the arms and thighs were calculated. Percentage body fat, fat mass and upper arm fat mass significantly decreased (p < .05) after the Tour independent of the equation method used in the calculations. Total muscle mass remained unchanged. Generally, this sample of cyclists consumed more protein and less fat than the recommended amount and had low weight, BMI and fat mass. It is suggested that sports nutritionists design personalised diets in order to maintain a correct proportion of nutrients as well as controlling possible anthropometrical changes that could affect performance.     

Comparison of lower limb muscle architecture and geometry in distance runners with rearfoot and forefoot strike pattern

ABSTRACT

We examined the association between footfall pattern and characteristics of lower limb muscle function and compared lower limb muscle function between forefoot and rearfoot runners. Fifteen rearfoot and 16 forefoot runners were evaluated using ultrasonography of the gastrocnemii and tibialis anterior while strike index and heel strike angle quantified footfall pattern. Higher strike index was associated with lower medial gastrocnemius echo intensity (p = 0.05), lower lateral gastrocnemius echo intensity (p = 0.04), smaller tibialis anterior pennation angle (p = 0.05), and longer lateral gastrocnemius fascicle length (p = 0.04). Larger heel strike angle was associated with smaller medial gastrocnemius cross-sectional area (p = 0.04), shorter lateral gastrocnemius fascicle length (p < 0.01), and lower plantar flexion moment (p < 0.01). Larger plantar flexion moment was associated with lesser medial gastrocnemius echo intensity (p = 0.04), lesser lateral gastrocnemius echo intensity (p = 0.03), and greater lateral gastrocnemius fascicle length (p = 0.02). A smaller plantar flexion moment, larger heel strike angle, lower tibialis anterior echo intensity, larger tibialis anterior pennation angle, and smaller lateral gastrocnemius pennation angle were observed in rearfoot compared to forefoot runners (p < 0.05). Lower limb muscle architecture is associated with footfall pattern and ankle mechanics during running.

Abbreviation: EMG: electromyographic; MG: medial gastrocnemius; LG: lateral gastrocnemius; TA: tibialis anterior; EI: echo intensity; CSA: cross-sectional area; PA: pennation angle; FL: fascicle length; FT: fat thickness     

Physical and Physiological Characteristics of Elite Volleyball Players

Abstract

The purpose of this study was to characterize the body fat, maximum aerobic power and maximum anaerobic power of elite junior wrestlers. The study was conducted in conjunction with an elite wrestler training camp. Wrestlers (n = 39) from ages 14 to 18 qualified for the camp and volunteered as subjects. Measurements were made for body composition (skinfold thickness), maximal aerobic power (treadmill run), and maximal anaerobic power of the arms and legs (Wingate test). Body fat averaged (±SD) 7.2% (±2.4), whereas the means (±SD) for maximal aerobic power, arm power, and leg power were 51.2(±9.3) ml/kg min^-1, 390.7 (±92) watts, and 549.1 ± 101 watts, respectively. Elite junior wrestlers appear to have a similar percentage of body fat, lower maximum aerobic power and higher relative anaerobic power compared to elite collegiate and senior wrestlers.     

Tracking of Gross Motor Coordination From Childhood Into Adolescence

Purpose: The purpose of this study was to analyze tracking and stability of motor coordination in children from age 6 years to ages 9 and 13 years. Method: Data were from the Copenhagen School Child Intervention Study. Motor coordination (MC) was measured using the körperkoordinationstest für Kinder (KTK) test. The crude performance score on every item was converted into a standardized “score” based on the original German reference study, which was used to generate a total standardized motor coordination (MQ) score. The MQ scores, which represented children's level of gross MC, were classified as low (MQ score < 85), normal (MQ score = 85–115), or high (MQ score>115). Pearson correlation was used to calculate the tracking coefficients of each KTK element and MQ score, and weighted kappa was used to analyze maintenance in MC classification groups. Mixed-effects logistic regression analyses were performed to examine the odds of remaining in the low MC group over time based on body mass index (BMI), weight, and height tertiles. Results: Tracking coefficients among the MQ score and each KTK element at different ages were moderate (r>.35). Children in the highest BMI and weight tertiles had a 5.44 and 5.15 times greater chance to be in the lower MC classification group during the 7-year follow-up, respectively, in comparison with children in their lowest tertiles. Conclusion: MC tracked moderately through childhood to early adolescence. Because heavier children had a greater chance to be in the lower MC group at older ages, intervention may be useful at earlier ages for those with lower MC and disadvantageous weight status.     

The skinfold: myth and reality

The interest in skinfolds, given the easy accessibility of the subcutaneous layer and its non-invasive nature, has led to a proliferation of 'skinfold' applications and formulae. To obtain data to investigate body composition methods, particularly the use of skinfolds, two separate cadaver dissection studies were undertaken, allowing for the analysis of data from 32 cadavers with more than 2500 data per cadaver. In addition, 40 elderly 'living' subjects of the same age range were compared with the cadaver population and no significant macro-morphological differences were found. The available data have clearly demonstrated that skinfold compressibility is by no means constant. Adipose tissue patterning by assessment of skinfold thickness using calipers and incision confirms significant sex differences but emphasizes the neglected importance of skin thickness. It appears that the best adipose tissue predictors are different from those used in general. Also the problem of estimating body fat content by skinfold is compounded by the fact that two identical thicknesses of adipose tissue may contain significantly different concentrations of fat. Skinfolds are significantly related to external (subcutaneous) adipose tissue. However, the relation to internal tissue is less evident and the relation with intramuscular adiposity is unknown.     

Neuromuscular Control Mechanisms and Strategy in Arm Movements of Attempted Supranormal Speed

Abstract

Rapid, goal-directed elbow flexion movements were examined under interacting conditions of inertial loading and resistance to movement initiation. The resistance ceased when movement began, resulting in quick release movements. Inertial load slowed the movement and lengthened the agonist and antagonist electromyographic (EMG) burst durations. The quick release resulted in larger accelerations but only minimal changes in peak velocity. Most aspects of the triphasic EMG pattern were little affected by the quick release, but the build up of agonist EMG and the corresponding rate of static force development differed markedly between load and quick release conditions. These and other data suggest that the specific pattern of agonist muscle activation is set according to neuromuscular constraints of the antagonist muscle and the expectation of movement dynamics.     

Childhood single skinfold thickness is a better predictor for adult relative fat mass in females than the body mass index: Data from a 30-year longitudinal growth study

Abstract

Information on the prediction of adult relative fat mass (percent body fat,%BF) using measures from pre-pubertal ages and early childhood is scarce. In the present longitudinal study, we assess the development of different anthropometric indicators of percent body fat during childhood, adolescence, and adulthood in 37½-year-old females stratified for low and high percent body fat. Consequently, we study the predictability of percent body fat based on simple anthropometric measurements during childhood and adolescence.

Anthropometric data from the Belgian longitudinal experimental growth study “LEGS” were used. Beginning in 1969, five yearly cohorts of about 100 individuals each (mean age 6 years) were recruited in public kindergartens. Of the original 515 participants (260 males, 255 females) that were measured annually from age 6 to 18 years, 59 males and 60 females agreed to participate in a follow-up study in 2004. During the follow-up measurements, the participants were invited for a body-composition assessment by bioelectrical impedance analysis (BIA). We stratified the participants into low (%BF-BIA < 35%) and high (%BF-BIA≥35%) relative fat mass samples. Pearson correlations were calculated and used as tracking coefficients. Multiple stepwise linear regression was applied with anthropometric variables at each age separately as predictors for adult percent body fat, expressed as%BF-BIA, %BF-Segal, and %BF-D&W (Durnin & Womersley, 1974).

The results indicate that a single skinfold thickness during adolescence is a better predictor for adult percent body fat than adolescent body mass index. Additionally, our results suggest that this holds during childhood as early as from age 8 onwards. The use of single skinfold measurements as predictors for adult adiposity and obesity is supported by other arguments, including: (1) body mass index as a proxy for overweight does not discriminate between fat mass and fat-free mass, and (2) an excess of adipose tissue is more strongly associated with morbidity than the body mass index.     

The influence of` preseason training phase and training load on body composition and its relationship with physical qualities in professional junior rugby league players

ABSTRACT

This study investigated changes in body composition in relation to training load determined using RPE and duration (sRPE), and its relationship with physical qualities over a preseason period. Sixteen professional academy players (age = 17.2 ± 0.7 years; stature = 179.9 ± 4.9 cm; body mass = 88.5 ± 10.1 kg) participated in the study. Body composition was assessed before and after each training phase and physical qualities assessed at the start and end of preseason. Across the whole preseason period, skinfold thickness, body fat percentage and fat mass were most likely lower (ES = ?0.73 to ?1.00), and fat free mass and lean mass were likely to most likely higher (ES = 0.31 to 0.40). Results indicated that the magnitude of change appeared phase-dependent (ES = ?0.05 to ?0.85) and demonstrated large individual variability. Changes in physical qualities ranged from unclear to most likely (ES = ?0.50 to 0.64). Small to moderate correlations were observed between changes in body composition, and TL with changes in physical qualities. This study suggests training phase and TL can influence a player’s body composition; that large inter-participant variability exists; and that body composition and TL are related to the change in physical qualities.