State-of-the-Art Methods for Skeletal Muscle Glycogen Analysis in Athletes-The Need for Novel Non-Invasive Techniques

Challenges in Applying Multimodal Imaging Technologies to Quantify In Vivo Glycogen and Intramuscular Fat in Livestock

Predicting meat quality, especially dark, firm and dry meat, as well as muscle fat prior to slaughter, presents a challenge in practice. Medical as well as high-frequency ultrasound applications can be utilized to predict body composition and meat quality aspects. Ultrasounds are non-invasive, rapid-to-operate in vivo and show high correlations to the animal production traits being estimated. Farm animal ultrasounds are used to predict intramuscular fat content in the beef cattle industry. Challenges are identified in applying ultrasound technology to detect glycogen content in farm animals due to a wide range of fat, muscle and water composition. Other technologies and methods are reported in this literature review to overcome issues in the practicability and accuracy of ultrasound technology when estimating muscle glycogen levels in cattle. The discussion of other tools such as hyperspectral imaging, microwave sensor technology and digital infrared thermal imaging were addressed because of their superior accuracy in estimating moisture and fat components.

Implementation of Two-pulse Phase-modulated (TPPM) 1H Decoupling in a Clinical MR Scanner for the Detection of the C1-glycogen Peak in 13C MRS

Two-pulse phase-modulated (TPPM) 1H-decoupling pulse sequence repeats a pair of 180o RF pulses while changing the signs of the RF phase modulation angle and has been widely used for the 13C NMR of organic solids. TPPM was introduced into the 13C MRS pulse sequence on a clinical 3T MR scanner, and the 1H-decoupling performance was compared with conventional 1H-decoupling schemes using aqueous solutions containing glucose and oyster glycogen. The 13C C1-glucose peaks were 1H-decoupled using TPPM with B2 = 500 Hz, and the optimal RF phase modulation angle was up to 30o. Cycling sidebands were not observed when TPPM was used but were observed when WALTZ-16 was used. The 13C C1-glycogen peak was 1H-decoupled even with reducing TPPM duration to 8 ms, which reduced simulated specific absorption rate (SAR) to 39%. In conclusion, the TPPM 1H decoupling is applicable to clinical MR scanners, and the low-SAR sequence may be more valuable at 7T.

Effects of a 10-Week Exercise and Nutritional Intervention with Variable Dietary Carbohydrates and Glycaemic Indices on Substrate Metabolism, Glycogen Storage, and Endurance Performance in Men: A Randomized Controlled Trial

BACKGROUND

Daily nutrition plays an important role in supporting training adaptions and endurance performance. The objective of this 10-week study was to investigate the consequences of varying carbohydrate consumption and the glycaemic index (GI) together with an endurance training regimen on substrate oxidation, muscle energy storage and endurance performance under free-living conditions. Sixty-five moderately trained healthy men (29 ± 4 years; VO2 peak 55 ± 8 mL min-1 kg-1) were randomized to one of three different nutritional regimes (LOW-GI: 50-60% CHO with ≥ 65% of these CHO with GI < 50 per day, n = 24; HIGH-GI: 50-60% CHO with ≥ 65% CHO with GI > 70 per day, n = 20; LCHF: ≤ 50 g CHO daily, n = 21). Metabolic alterations and performance were assessed at baseline (T0) and after 10 weeks (T10) during a graded exercise treadmill test. Additionally, a 5 km time trial on a 400-m outdoor track was performed and muscle glycogen was measured by magnet resonance spectroscopy.

RESULTS

Total fat oxidation expressed as area under the curve (AUC) during the graded exercise test increased in LCHF (1.3 ± 2.4 g min-1 × km h-1, p < 0.001), remained unchanged in LOW-GI (p > 0.05) and decreased in HIGH-GI (- 1.7 ± 1.5 g min-1 × km h-1, p < 0.001). After the intervention, LOW-GI (- 0.4 ± 0.5 mmol L-1 × km h-1, p < 0.001) and LCHF (- 0.8 ± 0.7 mmol L-1 × km h-1, p < 0.001) showed significantly lower AUC of blood lactate concentrations. Peak running speed increased in LOW-GI (T0: 4.3 ± 0.4 vs. T10: 4.5 ± 0.3 m s-1, p < 0.001) and HIGH-GI (T0: 4.4 ± 0.5 vs. T10: 4.6 ± 0.4 m s-1), while no improvement was observed in LCHF. Yet, time trial performance improved significantly in all groups. Muscle glycogen content increased for participants in HIGH-GI (T0: 97.3 ± 18.5 vs. T10: 144.5 ± 39.8 mmol L wet-tissue-1, p = 0.027) and remained unchanged in the LOW-GI and the LCHF group. At the last examination, muscle glycogen concentration was significantly higher in LOW-GI compared to LCHF (p = 0.014).

CONCLUSION

Changes in fat oxidation were only present in LCHF, however, lower lactate concentrations in LOW-GI resulted in changes indicating an improved substrate metabolism. Compared to a LCHF diet, changes in peak running speed, and muscle glycogen stores were superior in LOW- and HIGH-GI diets. The low GI diet seems to have an influence on substrate metabolism without compromising performance at higher intensities, suggesting that a high-carbohydrate diet with a low GI is a viable alternative to a LCHF or a high GI diet.

TRIAL REGISTRATION

Clinical Trials, NCT05241730. https://clinicaltrials.gov/study/NCT05241730 . Registered 25 January 2021.

A Tutorial on Skeletal Muscle Metabolism and the Role of Blood Lactate: Implications for Speech Production

PURPOSE

The purpose of this tutorial is threefold: (a) present relevant exercise science literature on skeletal muscle metabolism and synthesize the limited available research on metabolism of the adult human speech musculature in an effort to elucidate the role of metabolism in speech production; (b) introduce a well-studied metabolic serum biomarker in exercise science, lactate, and the potential usefulness of investigating this metabolite, through a well-established exercise science methodology, to better understand metabolism of the musculature involved in voice production; and (c) discuss exercise physiology considerations for future voice science research that seeks to investigate blood lactate and metabolism in voice physiology in an ecologically valid manner.

METHOD

This tutorial begins with relevant exercise science literature on the basic cellular processes of muscle contraction that require energy and the metabolic mechanisms that regenerate the energy required for task execution. The tutorial next synthesizes the available research investigating metabolism of the adult human speech musculature. This is followed by the authors proposing a hypothesis of speech metabolism based on the voice science literature and the application of well-studied exercise science principles of muscle physiology. The tutorial concludes with a discussion and the potential usefulness of lactate in investigations to better understand the metabolism of the musculature involved in vocal demand tasks.

CONCLUSION

The role of metabolism during speech (respiratory, laryngeal, and articulatory) is an understudied yet critical aspect of speech physiology that warrants further study to better understand the metabolic systems that are used to meet vocal demands.

Food for thought: Physiological considerations for nutritional ergogenic efficacy

Top-class athletes have optimized their athletic performance largely through adequate training, nutrition, recovery, and sleep. A key component of sports nutrition is the utilization of nutritional ergogenic aids, which may provide a small but significant increase in athletic performance. Over the last decade, there has been an exponential increase in the consumption of nutritional ergogenic aids, where over 80% of young athletes report using at least one nutritional ergogenic aid for training and/or competition. Accordingly, due to their extensive use, there is a growing need for strong scientific investigations validating or invalidating the efficacy of novel nutritional ergogenic aids. Notably, an overview of the physiological considerations that play key roles in determining ergogenic efficacy is currently lacking. Therefore, in this brief review, we discuss important physiological considerations that contribute to ergogenic efficacy for nutritional ergogenic aids that are orally ingested including (1) the impact of first pass metabolism, (2) rises in systemic concentrations, and (3) interactions with the target tissue. In addition, we explore mouth rinsing as an alternate route of ergogenic efficacy that bypasses the physiological hurdles of first pass metabolism via direct stimulation of the central nervous system. Moreover, we provide real-world examples and discuss several practical factors that can alter the efficacy of nutritional ergogenic aids including human variability, dosing protocols, training status, sex differences, and the placebo effect. Taking these physiological considerations into account will strengthen the quality and impact of the literature regarding the efficacy of potential ergogenic aids for top-class athletes.

Methodology for studying Relative Energy Deficiency in Sport (REDs): a narrative review by a subgroup of the International Olympic Committee (IOC) consensus on REDs

In the past decade, the study of relationships among nutrition, exercise and the effects on health and athletic performance, has substantially increased. The 2014 introduction of Relative Energy Deficiency in Sport (REDs) prompted sports scientists and clinicians to investigate these relationships in more populations and with more outcomes than had been previously pursued in mostly white, adolescent or young adult, female athletes. Much of the existing physiology and concepts, however, are either based on or extrapolated from limited studies, and the comparison of studies is hindered by the lack of standardised protocols. In this review, we have evaluated and outlined current best practice methodologies to study REDs in an attempt to guide future research.This includes an agreement on the definition of key terms, a summary of study designs with appropriate applications, descriptions of best practices for blood collection and assessment and a description of methods used to assess specific REDs sequelae, stratified as either Preferred, Used and Recommended or Potential Researchers can use the compiled information herein when planning studies to more consistently select the proper tools to investigate their domain of interest. Thus, the goal of this review is to standardise REDs research methods to strengthen future studies and improve REDs prevention, diagnosis and care.

The sonographic quantitative assessment of the deltoid muscle to detect type 2 diabetes mellitus: a potential noninvasive and sensitive screening method?

BACKGROUND

In our previous published study, we demonstrated that a qualitatively assessed elevation in deltoid muscle echogenicity on ultrasound was both sensitive for and a strong predictor of a type 2 diabetes (T2DM) diagnosis. This study aims to evaluate if a sonographic quantitative assessment of the deltoid muscle can be used to detect T2DM.

METHODS

Deltoid muscle ultrasound images from 124 patients were stored: 31 obese T2DM, 31 non-obese T2DM, 31 obese non-T2DM and 31 non-obese non-T2DM. Images were independently reviewed by 3 musculoskeletal radiologists, blinded to the patient's category. Each measured the grayscale pixel intensity of the deltoid muscle and humeral cortex to calculate a muscle/bone ratio for each patient. Following a 3-week delay, the 3 radiologists independently repeated measurements on a randomly selected 40 subjects. Ratios, age, gender, race, body mass index, insulin usage and hemoglobin A_1c were analyzed. The difference among the 4 groups was compared using analysis of variance or chi-square tests. Both univariate and multivariate linear mixed models were performed. Multivariate mixed-effects regression models were used, adjusting for demographic and clinical variables. Post hoc comparisons were done with Bonferroni adjustments to identify any differences between groups. The sample size achieved 90% power. Sensitivity and specificity were calculated based on set threshold ratios. Both intra- and inter-radiologist variability or agreement were assessed.

RESULTS

A statistically significant difference in muscle/bone ratios between the groups was identified with the average ratios as follows: obese T2DM, 0.54 (P < 0.001); non-obese T2DM, 0.48 (P < 0.001); obese non-T2DM, 0.42 (P = 0.03); and non-obese non-T2DM, 0.35. There was excellent inter-observer agreement (intraclass correlation coefficient 0.87) and excellent intra-observer agreements (intraclass correlation coefficient 0.92, 0.95 and 0.94). Using threshold ratios, the sensitivity for detecting T2DM was 80% (95% CI 67% to 88%) with a specificity of 63% (95% CI 50% to 75%).

CONCLUSIONS

The sonographic quantitative assessment of the deltoid muscle by ultrasound is sensitive and accurate for the detection of T2DM. Following further studies, this process could translate into a dedicated, simple and noninvasive screening method to detect T2DM with the prospects of identifying even a fraction of the undiagnosed persons worldwide. This could prove especially beneficial in screening of underserved and underrepresented communities.

Concurrent Validity of a Continuous Glucose-Monitoring System at Rest and During and Following a High-Intensity Interval Training Session

Purpose: To assess the concurrent validity of a continuous blood-glucose-monitoring system (CGM) postbreakfast, preexercise, exercise, and postexercise, while assessing the impact of 2 different breakfasts on the observed level of validity. Methods: Eight nondiabetic recreational athletes (age = 30.8 [9.5] y; height = 173.6 [6.6] cm; body mass = 70.3 [8.1] kg) took part in the study. Blood glucose concentration was monitored every 10 minutes using both a CGM (FreeStyle Libre, Abbott, France) and finger-prick blood glucose measurements (FreeStyle Optimum) over 4 different periods (postbreakfast, preexercise, exercise, and postexercise). Two different breakfasts (carbohydrates [CHO] and protein oriented) over 2 days (2 × 2 d in total) were used. Statistical analyses included the Bland–Altman method, standardized mean bias (expressed in standardized units), median absolute relative difference, and the Clarke error grid analysis. Results: Overall, mean bias was trivial to small at postbreakfast (effect size ± 90% confidence limits: −0.12 ± 0.08), preexercise (−0.08 ± 0.08), and postexercise (0.25 ± 0.14), while moderate during exercise (0.66 ± 0.09). A higher median absolute relative difference was observed during exercise (13.6% vs 7%–9.5% for the other conditions). While there was no effect of the breakfast type on the median absolute relative difference results, error grid analysis revealed a higher value in zone D (ie, clinically unsafe zone) during exercise for CHO (10.5%) compared with protein (1.6%). Conclusion: The CGM device examined in this study can only be validly used at rest, after both a CHO and protein-rich breakfast. Using CGM to monitor blood glucose concentration during exercise is not recommended. Moreover, the accuracy decreased when CHO were consumed before exercise.

Innovation in culture systems to study muscle complexity

Endogenous skeletal muscle development, regeneration, and pathology are extremely complex processes, influenced by local and systemic factors. Unpinning how these mechanisms function is crucial for fundamental biology and to develop therapeutic interventions for genetic disorders, but also conditions like sarcopenia and volumetric muscle loss. Ex vivo skeletal muscle models range from two- and three-dimensional primary cultures of satellite stem cell-derived myoblasts grown alone or in co-culture, to single muscle myofibers, myobundles, and whole tissues. Together, these systems provide the opportunity to gain mechanistic insights of stem cell behavior, cell-cell interactions, and mature muscle function in simplified systems, without confounding variables. Here, we highlight recent advances (published in the last 5 years) using in vitro primary cells and ex vivo skeletal muscle models, and summarize the new insights, tools, datasets, and screening methods they have provided. Finally, we highlight the opportunity for exponential advance of skeletal muscle knowledge, with spatiotemporal resolution, that is offered by guiding the study of muscle biology and physiology with in silico modelling and implementing high-content cell biology systems and ex vivo physiology platforms.

The Validity of Ultrasound Technology in Providing an Indirect Estimate of Muscle Glycogen Concentrations Is Equivocal

Researchers and practitioners in sports nutrition would greatly benefit from a rapid, portable, and non-invasive technique to measure muscle glycogen, both in the laboratory and field. This explains the interest in MuscleSound^®, the first commercial system to use high-frequency ultrasound technology and image analysis from patented cloud-based software to estimate muscle glycogen content from the echogenicity of the ultrasound image. This technique is based largely on muscle water content, which is presumed to act as a proxy for glycogen. Despite the promise of early validation studies, newer studies from independent groups reported discrepant results, with MuscleSound^® scores failing to correlate with the glycogen content of biopsy-derived mixed muscle samples or to show the expected changes in muscle glycogen associated with various diet and exercise strategies. The explanation of issues related to the site of assessment do not account for these discrepancies, and there are substantial problems with the premise that the ratio of glycogen to water in the muscle is constant. Although further studies investigating this technique are warranted, current evidence that MuscleSound^® technology can provide valid and actionable information around muscle glycogen stores is at best equivocal.

Variation of skeletal muscle ultrasound imaging intensity in horses after treadmill exercise: a proof of concept for glycogen content estimation

Background

Glycogen in skeletal muscle is a major source of energy during exercise and an important determinant of endurance capacity, so that its measurement may provide a meaningful marker of athletes’ preparation and a possible predictor of performance, both in humans and in equines. Gold standard of glycogen concentration measurement is the histochemical and biochemical analysis of biopsy-derived muscle tissue, an invasive and potentially injuring procedure. Recently, high-frequency ultrasound (US) technology is being exploited in human sports medicine to estimate muscle glycogen content. Therefore, aim of the present study is to evaluate the feasibility of US assessment of muscle glycogen in equines.

Results

US images of gluteus medius (GL) and semitendinosus (ST) muscles were obtained on eight healthy horses (3–10 years) before and after a steady-state exercise on treadmill (velocity: 4.0–12.5 m/s; duration: 2–20 min; heart rate: 137–218 b/min). Average image greyscale intensity was significantly different between GL and ST, both before and after exercise (p < 0.001). Comparing baseline and post-exercise US images, significant increase in greyscale intensity has been observed in ST (p < 0.001), but not in GL (p = 0.129). The volume of the exercise was significantly correlated with exercise-dependent change in image intensity (R² = 0.891), consistent with a reduction of glycogen muscle stores resulting from aerobic activity.

Conclusions

US technique evidences also in horses muscle changes possibly associated to glycogen utilisation during exercise. Present results on a small sample need to be further confirmed and provide preliminary data warranting future validation by direct glycogen measurement through biopsy technique.

The Effect of Consuming Carbohydrate With and Without Protein on the Rate of Muscle Glycogen Re-synthesis During Short-Term Post-exercise Recovery: a Systematic Review and Meta-analysis

BACKGROUND

Rapid restoration of muscle glycogen stores is imperative for athletes undertaking consecutive strenuous exercise sessions with limited recovery time (e.g. ≤ 8 h). Strategies to optimise muscle glycogen re-synthesis in this situation are essential. This two-part systematic review and meta-analysis investigated the effect of consuming carbohydrate (CHO) with and without protein (PRO) on the rate of muscle glycogen re-synthesis during short-term post-exercise recovery (≤ 8 h).

METHODS

Studies were identified via the online databases Web of Science and Scopus. Investigations that measured muscle glycogen via needle biopsy during recovery (with the first measurement taken ≤ 30 min post-exercise and at least one additional measure taken ≤ 8 h post-exercise) following a standardised exercise bout (any type) under the following control vs. intervention conditions were included in the meta-analysis: part 1, water (or non-nutrient beverage) vs. CHO, and part 2, CHO vs. CHO+PRO. Publications were examined for methodological quality using the Rosendal scale. Random-effects meta-analyses and meta-regression analyses were conducted to evaluate intervention efficacy.

RESULTS

Overall, 29 trials (n = 246 participants) derived from 21 publications were included in this review. The quality assessment yielded a Rosendal score of 61 ± 8% (mean ± standard deviation). Part 1: 10 trials (n = 86) were reviewed. Ingesting CHO during recovery (1.02 ± 0.4 g·kg body mass (BM)-1 h-1) improved the rate of muscle glycogen re-synthesis compared with water; change in muscle glycogen (MGΔ) re-synthesis rate = 23.5 mmol·kg dm-1 h-1, 95% CI 19.0-27.9, p < 0.001; I2 = 66.8%. A significant positive correlation (R2 = 0.44, p = 0.027) was observed between interval of CHO administration (≤ hourly vs. > hourly) and the mean difference in rate of re-synthesis between treatments. Part 2: 19 trials (n = 160) were reviewed. Ingesting CHO+PRO (CHO: 0.86 ± 0.2 g·kg BM-1 h-1; PRO: 0.27 ± 0.1 g·kg BM-1 h-1) did not improve the rate of muscle glycogen re-synthesis compared to CHO alone (0.95 ± 0.3 g·kg BM-1 h-1); MGΔ re-synthesis rate = 0.4 mmol·kg  dm-1 h-1, 95% CI -2.7 to 3.4, p = 0.805; I2 = 56.4%.

CONCLUSIONS

Athletes with limited time for recovery between consecutive exercise sessions should prioritise regular intake of CHO, while co-ingesting PRO with CHO appears unlikely to enhance (or impede) the rate of muscle glycogen re-synthesis.

TRIAL REGISTRATION

Registered at the International Prospective Register of Systematic Reviews (PROSPERO) (identification code CRD42020156841 ).

Markers of muscle damage and strength performance in professional football (soccer) players during the competitive period

Background

The present study investigated the impact of competitive soccer on the short-term changes in isometric strength of the adductor muscle group during the competitive season.

Methods

In this cohort study we evaluated the association between a serum marker of muscle damage [creatine phosphokinase (CPK)] and isometric strength of the adductor muscles of the hip in 30 professional football players (age: 26.7±2.9 years) during two seasons of the national top-level championship. Serum CPK level was determined the day before the match, 12–20, 36–48, 60–72 h after the match. The maximum voluntary isometric contraction force of the adductor muscles complex was determined immediately after having taken blood samples.

Results

There was evidence of a statistically significant positive association between age, body mass index (BMI), percentage of body fat, and muscle strength, and between weight and muscle strength. There was evidence of a statistically significant negative association between the level of CPK and the maximum isometric strength of the adductors of soccer players. Changes in CPK levels were associated with the muscle strength recovery trend (P<0.001). The strength/CPK ratio at different time points had a U-shaped curve.

Conclusions

Exercise induced muscle damage significantly affects the strength of the adductor muscle group of professional soccer players during the competitive period. The lower the CPK level, the greater the athletes' strength at a given time point. Also, the greater the decrease in CPK level, the greater the rate of strength restoration.

The Effects of 10-Day Exogenous Ketone Consumption on Repeated Time Trial Running Performances: A Randomized-Control Trial

INTRODUCTION

The effects of ketone salt supplementation on repeated short-distance running time trial (TT) performance in well-trained subjects remain unknown.

PURPOSE

To determine the effects of 10-day exogenous ketone salt supplementation on two consecutive 800 m running TTs in endurance-trained subjects.

METHODS

Male and female subjects were randomly allocated to one of the following groups: Ketone (KET) (n = 16) or placebo (CON) (n = 16) (8 m, 8f per group). Subjects underwent two consecutive 800 m TTs before and after a 10-day treatment on a self-propelled treadmill. Time-to-completion of the first (TT1) and second (TT2) TT, the average time-to-completion (TT_AVG), and blood lactate response during each TT was measured pre-post-treatment. Changes in blood ketone levels in response to a single dosing were measured pre- and post-treatment. Data was analyzed with a mixed factorial ANOVA with significance set to p < 0.05.

RESULTS

KET demonstrated a faster TT_AVG from pre- to post-treatment (-6.1 ± 8.9 s; p = 0.02) while CON showed no change. At pre- and post-treatment, CON showed no acute changes in blood ketones after a single-dosing while KET demonstrated a significant increases (Pretreatment = +0.4 ± 0.3 mmol/L; p < 0.001; Post-Treatment = +0.4 ± 0.4 mmol/L; p < 0.001). These acute single-dosing responses in blood ketone levels for KET did not change between pre- and post-treatment. There were no interactions for blood lactate response to exercise or fatigue index.

CONCLUSIONS

In trained subjects, 10 days of ketone salt supplementation does not affect performance in an initial bout of short-distance running, such as during TT1. However, ergogenic effects may be observed under fatigue conditions for example during a repeated running bout.

Effects of hydrolyzed cottonseed protein supplementation on performance, blood metabolites, gastrointestinal development, and intestinal microbial colonization in neonatal calves

The objective of this study was to investigate the effects of an enzymatically hydrolyzed cottonseed protein (HCSP) as a peptide source on performance, blood metabolites, gastrointestinal development, and intestinal microbes. Forty-eight newborn Holstein calves were randomly assigned to 1 of the 4 dietary treatments including 0, 2, 4, and 6% of HCSP (dry matter basis). All calves received the same amount of pasteurized whole milk, weaned on d 56 of the experiment, and the study was concluded on d 70. Data were analyzed using PROC MIXED in SAS (SAS Institute Inc., Cary, NC) as a randomized complete block design with linear and quadratic contrasts. Results showed that increased amount of HCSP linearly decreased the starter intake during the postweaning (d 57 to 70) and overall period (d 1 to 70). In addition, when dietary HCSP increased during the overall period, average daily gain tended to linearly decrease. All skeletal growth variables also linearly decreased as dietary HCSP increased at the end of the study, except for body length, which did not differ among the treatments. Serum cortisol concentration was higher in calves supplemented with 6% of HCSP at weaning and at the end of the study. This indicates that these calves may have experienced a stressful condition compared with calves in other treatments. Total antioxidant capacity was quadratically affected by HCSP supplementation; calves fed 2 and 4% of HCSP diets had the highest total antioxidant capacity, whereas calves fed 0 and 6% HCSP diets had lower total antioxidant capacity at weaning and at end of the study. Calves supplemented with 6% HCSP had lower empty reticulo-rumen and omasum weights and rumen wall thickness compared with calves in other treatments at the end of the study. In conclusion, supplementation of HCSP at the rate of 2% of starter diet enhanced antioxidant status without any detrimental effects on the performance and metabolic status of calves, whereas greater inclusion rates impaired starter intake and growth of calves, and exposed them to a stressful status.

Indirect Assessment of Skeletal Muscle Glycogen Content in Professional Soccer Players before and after a Match through a Non-Invasive Ultrasound Technology

Skeletal muscle glycogen (SMG) stores in highly glycolytic activities regulate muscle contraction by controlling calcium release and uptake from sarcoplasmic reticulum, which could affect muscle contraction. Historically, the assessment of SMG was performed through invasive and non-practical muscle biopsies. In this study we have utilized a novel methodology to assess SMG through a non-invasive high-frequency ultrasound. Nine MLS professional soccer players (180.4 ± 5.9 cm; 72.4 ± 9.3 kg; 10.4% ± 0.7% body fat) participated. All followed the nutritional protocol 24 h before the official match as well as performing the same practice program the entire week leading to the match. The SMG decreased from 80 ± 8.6 to 63.9 ± 10.2; p = 0.005 on MuscleSound^® score (0–100) representing a 20% ± 10.4% decrease in muscle glycogen after match. Inter-individual differences in both starting glycogen content (65–90) and in percentage decrease in glycogen after the match (between 6.2% and 44.5%). Some players may not start the match with adequate SMG while others’ SMG decreased significantly throughout the game. Adequate pre-match SMG should be achieved during half-time and game-play in order to mitigate the decrease in glycogen. Further and more ample studies are needed before the application of this technology.

The Hyperechoic Appearance of the Deltoid Muscle on Shoulder Ultrasound Imaging as a Predictor of Diabetes and Prediabetes

OBJECTIVES

To evaluate whether the ultrasound appearance of the deltoid muscle in diabetic patients differs from that in obese nondiabetic patients.

METHODS

Ultrasound images of the deltoid muscle from 137 type 2 diabetic patients (including 13 prediabetic patients) and 49 obese nondiabetic patients were blindly reviewed by 2 musculoskeletal radiologists, and by a third when arbitration was needed, to determine whether the appearance was "normal," "suspected diabetes," or "definite diabetes." Age, sex, race, body mass index (BMI), insulin use, and hemoglobin A_1c were analyzed. This retrospective study included patients presenting between October 2005 and November 2017. Statistical analyses included a 2-sided sample t test or Wilcoxon rank sum test and a χ² or Fisher exact test. Statistical significance was defined as P < .05.

RESULTS

The type 2 diabetic patients included 98 women and 39 men aged 29 to 92 years, and the nondiabetic patients included 19 women and 30 men aged 18 to 75 years. A consensus diagnosis of definite diabetes by the musculoskeletal radiologists based on a hyperechoic deltoid was a powerful predictor of diabetes, with a positive predictive value of 89%. A hyperechoic deltoid was also a powerful predictor of prediabetes. Of the 13 prediabetic patients, all had the same hyperechoic appearance of the diabetic deltoid, regardless of BMI. Although obese diabetic patients more often had a diagnosis of definite diabetes, the BMI alone could not explain the increased echogenicity, as obese nondiabetic patients' deltoid muscles did not appear as hyperechoic and were correctly categorized as not having definite diabetes with 82% specificity.

CONCLUSIONS

The characteristic hyperechoic deltoid appearance is a strong predictor of both diabetes and prediabetes and differs from that of obese nondiabetic patients.

Skeletal Muscle Glycogen Content at Rest and During Endurance Exercise in Humans: A Meta-Analysis

BACKGROUND

Skeletal muscle glycogen is an important energy source for muscle contraction and a key regulator of metabolic responses to exercise. Manipulation of muscle glycogen is therefore a strategy to improve performance in competitions and potentially adaptation to training. However, assessing muscle glycogen in the field is impractical, and there are no normative values for glycogen concentration at rest and during exercise.

OBJECTIVE

The objective of this study was to meta-analyse the effects of fitness, acute dietary carbohydrate (CHO) availability and other factors on muscle glycogen concentration at rest and during exercise of different durations and intensities.

DATA SOURCE AND STUDY SELECTION

PubMed was used to search for original articles in English published up until February 2018. Search terms included muscle glycogen and exercise, filtered for humans. The analysis incorporated 181 studies of continuous or intermittent cycling and running by healthy participants, with muscle glycogen at rest and during exercise determined by biochemical analysis of biopsies.

DATA ANALYSIS

Resting muscle glycogen was determined with a meta-regression mixed model that included fixed effects for fitness status [linear, as maximal oxygen uptake ([Formula: see text]O_2max) in mL·kg^-1·min^-1] and CHO availability (three levels: high, ≥ 6 g·kg^-1 of CHO per day for ≥ 3 days or ≥ 7 g·kg^-1 CHO per day for ≥ 2 days; low, glycogen depletion and low-CHO diet; and normal, neither high nor low, or not specified in study). Muscle glycogen during exercise was determined with a meta-regression mixed model that included fixed effects for fitness status, resting glycogen [linear, in mmol·kg^-1 of dry mass (DM)], exercise duration (five levels, with means of 5, 23, 53 and 116 min, and time to fatigue), and exercise intensity (linear, as percentage of [Formula: see text]O_2max); intensity, fitness and resting glycogen were interacted with duration, and there were also fixed effects for exercise modes, CHO ingestion, sex and muscle type. Random effects in both models accounted for between-study variance and within-study repeated measurement. Inferences about differences and changes in glycogen were based on acceptable uncertainty in standardised magnitudes, with thresholds for small, moderate, large and very large of 25, 75, 150 and 250 mmol·kg^-1 of DM, respectively.

RESULTS

The resting glycogen concentration in the vastus lateralis of males with normal CHO availability and [Formula: see text]O_2max (mean ± standard deviation, 53 ± 8 mL·kg^-1·min^-1) was 462 ± 132 mmol·kg^-1. High CHO availability was associated with a moderate increase in resting glycogen (102, ± 47 mmol·kg^-1; mean ± 90% confidence limits), whereas low availability was associated with a very large decrease (- 253, ± 30 mmol·kg^-1). An increase in [Formula: see text]O_2max of 10 mL·kg^-1·min^-1 had small effects with low and normal CHO availability (29, ± 44 and 67, ± 15 mmol·kg^-1, respectively) and a moderate effect with high CHO availability (80, ± 40 mmol·kg^-1). There were small clear increases in females and the gastrocnemius muscle. Clear modifying effects on glycogen utilisation during exercise were as follows: a 30% [Formula: see text]O_2max increase in intensity, small (41, ± 20 mmol·kg^-1) at 5 min and moderate (87-134 mmol·kg^-1) at all other timepoints; an increase in baseline glycogen of 200 mmol·kg^-1, small at 5-23 min (28-59 mmol·kg^-1), moderate at 116 min (104, ± 15 mmol·kg^-1) and moderate at fatigue (143, ± 33 mmol·kg^-1); an increase in [Formula: see text]O_2max of 10 mL·kg^-1·min^-1, mainly clear trivial effects; exercise mode (intermittent vs. continuous) and CHO ingestion, clear trivial effects. Small decreases in utilisation were observed in females (vs. males: - 30, ± 29 mmol·kg^-1), gastrocnemius muscle (vs. vastus lateralis: - 31, ± 46 mmol·kg^-1) and running (vs. cycling: - 70, ± 32 mmol·kg^-1).

CONCLUSION

Dietary CHO availability and fitness are important factors for resting muscle glycogen. Exercise intensity and baseline muscle glycogen are important factors determining glycogen use during exercise, especially with longer exercise duration. The meta-analysed effects may be useful normative values for prescription of endurance exercise.

Bilateral Asymmetries in Ultrasound Assessments of the Rectus Femoris throughout an NCAA Division I Volleyball Preseason

The purpose of the study was to assess glycogen content of the rectus femoris (RF) muscles utilizing high-frequency ultrasound throughout an intensive, nine-day preseason training period in NCAA division I volleyball athletes. In the morning prior to the beginning of practice, athletes (n = 13) left and right RF muscles were assessed via ultrasound to quantify muscle fuel ratings (0–100 score range). The recommended location of the RF ultrasound scans were based on manufacturer guidelines, and the same technician recorded the daily measurements. To assess daily training load, session ratings of perceived exertion (s-RPE) were utilized. A paired t-test revealed a large significant difference between left (51.7 ± 17.9) and right (32.8 ± 17.4) RF muscle fuel ratings (p < 0.001). There was also a major effect of time on s-RPE (p < 0.001) and left (dominant) RF fuel rating (p = 0.001). s-RPE decreased from the beginning to the end of the training camp. However, left RF fuel ratings increased from the first to the second day, then remained elevated all throughout the preseason. In conclusion, all athletes were left-leg dominant and had a 57.6% bilateral asymmetry between their left and right RF muscle fuel ratings despite changes in training load. High-frequency ultrasounds are a noninvasive assessment tool that can determine glycogen replenishment asymmetries in the RF.