Elite Cyclists with Type 1 Diabetes Show Acceptable Glycemic Excursions During a Time-Trial Performance Under High-Definition Transcranial Direct Current Stimulation

OBJECTIVE

To evaluate the effects of bilateral dorsolateral prefrontal cortex high-definition transcranial direct current stimulation (HD-tDCS) on glycemic excursions during a time-trial performance in elite cyclists with type 1 diabetes (T1D).

METHODS

In a double-blind, randomized crossover order, 9 elite cyclists with T1D (no complications) underwent either HD-tDCS (F3 and F4) or control (SHAM) and completed a constant-load trial at 75% of the second ventilatory threshold plus a 15-km cycling time trial.

RESULTS

Real-time continuous glucose monitoring revealed similar glycemic variability between the 2 conditions, showing a significant effect of time but no interaction (stimulation × time) or stimulation effect.

CONCLUSION

Because glycemic control is crucial for both health and performance, these findings suggest that HD-tDCS could be safely used to enhance performance in athletes with T1D and potentially in a broader active T1D population.

Effects of In-Exercise Carbohydrate Supplementation on Prolonged High-Intensity Exercise Performance in Oral Contraceptive Users

PURPOSE

To examine the impact of oral contraceptive (OC) phases on performance, physiological, and subjective responses to prolonged, intensive exercise when carbohydrate (CHO) stores are reduced.

METHODS

Ten well-trained female cyclists using monophasic OC completed 4 identical trials (>150 min) under conditions of in-trial 60-g·h-1 CHO supplementation (CHO+) or placebo (CHO-) during the sugar- (SUG) and active-pill (ACT) phases of their OC cycle. Each trial comprised two 400-kcal time trials (TT) separated by 1 hour of submaximal cycling at first ventilatory threshold.

RESULTS

Change in completion time from TT1 to TT2 was minimized in CHO+ compared with CHO- (4.06 [2.55] vs 6.08 [5.33] min; P = .019, effect size = -0.36). An interaction effect of OC and CHO was observed for time to complete TT (P = .006), mean TT power (P = .002), mean TT heart rate (P = .002), and posttrial emotional balance (P = .020) and negative emotional state (P = .033). In ACT, mean TT power and heart rate were higher in CHO+ when compared with CHO-, resulting in faster TTs in CHO+ and improved posttrial emotional well-being. When CHO was not supplemented, TT power and heart rate were higher in SUG when compared with ACT, resulting in faster TTs in SUG and improved posttrial emotional balance.

CONCLUSION

CHO depletion during ACT negatively influenced TT performance and emotional well-being when compared with SUG. Irrespective of OC pill phase, CHO supplementation should be prioritized to sustain performance and improve postexercise recovery-stress balance.

Endurance exercise has a negative impact on the onset of SOD1-G93A ALS in female mice and affects the entire skeletal muscle-motor neuron axis

Background

Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disease characterized by the degeneration of motor neurons that leads to muscle wasting and atrophy. Epidemiological and experimental evidence suggests a causal relationship between ALS and physical activity (PA). However, the impact of PA on motor neuron loss and sarcopenia is still debated, probably because of the heterogeneity and intensities of the proposed exercises. With this study, we aimed to clarify the effect of intense endurance exercise on the onset and progression of ALS in the SOD1-G93A mouse model.

Methods

We randomly selected four groups of twelve 35-day-old female mice. SOD1-G93A and WT mice underwent intense endurance training on a motorized treadmill for 8 weeks, 5 days a week. During the training, we measured muscle strength, weight, and motor skills and compared them with the corresponding sedentary groups to define the disease onset. At the end of the eighth week, we analyzed the skeletal muscle-motor neuron axis by histological and molecular techniques.

Results

Intense endurance exercise anticipates the onset of the disease by 1 week (age of the onset: trained SOD1-G93A = 63.17 ± 2.25 days old; sedentary SOD1-G93A = 70.75 ± 2.45 days old). In SOD1-G93A mice, intense endurance exercise hastens the muscular switch to a more oxidative phenotype and worsens the denervation process by dismantling neuromuscular junctions in the tibialis anterior, enhancing the Wallerian degeneration in the sciatic nerve, and promoting motor neuron loss in the spinal cord. The training exacerbates neuroinflammation, causing immune cell infiltration in the sciatic nerve and a faster activation of astrocytes and microglia in the spinal cord.

Conclusion

Intense endurance exercise, acting on skeletal muscles, worsens the pathological hallmarks of ALS, such as denervation and neuroinflammation, brings the onset forward, and accelerates the progression of the disease. Our findings show the potentiality of skeletal muscle as a target for both prognostic and therapeutic strategies; the preservation of skeletal muscle health by specific intervention could counteract the dying-back process and protect motor neurons from death. The physiological characteristics and accessibility of skeletal muscle further enhance its appeal as a therapeutic target.

Effects of Dityrosine on Lactic Acid Metabolism in Mice Gastrocnemius Muscle During Endurance Exercise via the Oxidative Stress-Induced Mitochondria Damage

Dityrosine (Dityr) has been detected in commercial food as a product of protein oxidation and has been shown to pose a threat to human health. This study aims to investigate whether Dityr causes a decrease in lactic acid metabolism in the gastrocnemius muscle during endurance exercise. C57BL/6 mice were administered Dityr or saline by gavage for 13 weeks and underwent an endurance exercise test on a treadmill. Dityr caused a severe reduction in motion displacement and endurance time, along with a significant increase in lactic acid accumulation in the blood and gastrocnemius muscle in mice after exercise. Dityr induced significant mitochondrial defects in the gastrocnemius muscle of mice. Additionally, Dityr induced serious oxidative stress in the gastrocnemius muscle, accompanied by inflammation, which might be one of the causes of mitochondrial dysfunction. Moreover, significant apoptosis in the gastrocnemius muscle increased after exposure to Dityr. This study confirmed that Dityr induced oxidative stress in the gastrocnemius muscle, which further caused significant mitochondrial damage in the gastrocnemius muscle cell, resulting in decreased capacity of lactic acid metabolism and finally affected performance in endurance exercise. This may be one of the possible mechanisms by which highly oxidized foods cause a decreased muscle energy metabolism.

Wearable near-infrared spectroscopy: reliability and sensitivity among different endurance cycling exercise intensities

The present study investigated the reliability and sensitivity of a wearable near-infrared spectroscopy (wNIRS) device in moderate and heavy exercise intensity domains. On three separate days, eleven males performed an incremental test to exhaustion, and in the following visits, four submaximal constant-load bouts (i.e., test and retest) were performed in the moderate-intensity domain (100 and 130 W) and heavy-intensity domain (160 and 190 W). The local tissue oxygen saturation index (SmO2) and pulmonary oxygen uptake (V̇O2) were measured continuously. The absolute SmO2 and V̇O2 values and the change (Δ) from the 3rd to 6th min of exercise were calculated. There was good reliability for SmO2 measurements, as indicated by the high intraclass correlation coefficient analysis (ICC ≥0.84 for all) and low coefficient of variation between the two trials (CV ≤4.1% for all). Steady-state responses were observed for SmO2 and V̇O2 from the 3rd to the 6th min in the two moderate-intensity bouts (P>0.05), whereas SmO2 decreased and V̇O2 increased from the 3rd to the 6th min in the two heavy-intensity bouts (P<0.05). Together, these findings suggested that the SmO2 measured with a wNIRS device is reliable and sensitive to track local metabolic changes provoked by slight increments in exercise intensity.

Effect of five hours of mixed exercise on urinary nitrogen excretion in healthy moderate-to-well-trained young adults

Introduction

Carbohydrates and fats are the primary energy substrates during exercise, but proteins can also contribute. When proteins are degraded in the body, the amino groups are mainly converted to urea and excreted. Therefore, nitrogen excretion has been used as a marker of protein degradation, but a clear conclusion has yet to be reached on the effect of exercise on nitrogen excretion. Thus, we tested whether exercise increases nitrogen excretion.

Methods

Fifteen young, healthy, moderate-to-well-trained participants (4 females, 11 males, VO2max 54.4 ± 1.7 mL·kg-1·min-1; mean ± SEM) participated in a randomized, balanced cross-over design investigation consisting of 1 day with 5 h of exercise (exercise day, EX) and 1 day with no exercise (control day, CON). The participants recorded their dietary intake the day before from 16:00 and throughout the intervention day. They then repeated these dietary intakes on the second trial day. A standardized lunch was provided on both days. In addition, participants were allowed to consume almost protein-free snacks in EX to ensure the same energy balance during both trial days. Urine was collected throughout the whole testing period, and urinary 3-methylhistidine (3-MH) excretion was measured to examine muscular catabolism. The sweat rate was calculated during the exercise period.

Results and discussion

The urinary nitrogen and 3-MH excretions did not differ significantly between EX and CON (p = 0.764 and p = 0.953). The sweat rate was 2.55 ± 0.25 L in EX and 0.14 ± 0.15 L in CON (p < 0.001), and by estimating sweat nitrogen excretion, total nitrogen excretion was shown to differ with exercise. Our results showed that 5 hours of mixed exercise did not significantly impact urinary nitrogen and 3-MH excretions in healthy moderate-to-well-trained young adults.

Endurance exercise upregulates mtp expression in aged Drosophila to ameliorate age-related diastolic dysfunction and extend lifespan

Diastolic dysfunction is a major cardiac dysfunction, and an important predisposing factor is age. Although exercise training is often used for the prevention and treatment of cardiovascular disease nowadays, little is currently known about whether exercise interventions associated with the slowing of cardiac aging are related to mtp-related pathways. In the present study, the UAS/Tub-Gal4 system was used to knockdown whole-body mtp expression levels in Drosophila, which underwent 2 weeks of endurance training. By conducting different assays and quantifying different indicators, we sought to investigate the relationship between mtp, exercise, and age-related diastolic dysfunction. We found that (1) Drosophila in the mtpRNAi youth group exhibited age-related diastolic dysfunction and had a significantly shorter mean lifespan. (2) Endurance exercise could improve diastolic dysfunction and prolong lifespan in aged Drosophila. (3) Endurance exercise could increase the expression levels of apolpp and Acox3, and decrease the levels of TC, LDL-C, and TG in the aged group. In summary, aging causes age-associated diastolic dysfunction in Drosophila, and systemic knockdown of mtp causes premature age-associated diastolic dysfunction in young Drosophila. Besides, endurance exercise improves age-related diastolic dysfunction and prolongs lifespan.

Physiological assessment of a 16 day, 4385 km ultra-endurance mountain bike race: A case study

The Tour Divide (TD) is a 4385 km ultra-endurance bicycle race that follows the continental divide from Canada to Mexico. In this case study, we performed a comprehensive molecular and physiological profile before and after the completion of the TD. Assessments were performed 35 days before the start (Pre-TD) and ∼36 h after the finish (Post-TD). Total energy expenditure was assessed during the first 9 days by doubly labelled water (2 H2 18 O), abdominal and leg tissue volumes via MRI, and graded exercise tests to quantify fitness and substrate preference. Vastus lateralis muscle biopsies were taken to measure mitochondrial function via respirometry, and vascular function was assessed using Doppler ultrasound. The 47-year-old male subject took 16 days 7 h 45 min to complete the route. He rode an average of 16.8 h/day. Neither maximal O2 uptake nor maximal power output changed pre- to post-TD. Measurement of total energy expenditure and dietary recall records suggested maintenance of energy balance, which was supported by the lack of change in body weight. The subject lost both appendicular and trunk fat mass and gained leg lean mass pre- to post-TD. Skeletal muscle mitochondrial and vascular endothelial function decreased pre- to post-TD. Overall, exercise performance was maintained despite reductions in muscle mitochondrial and vascular endothelial function post-TD, suggesting a metabolic reserve in our highly trained athlete.

The acute effects of pre- and mid-exercise carbohydrate ingestion on the immunoregulatory stress hormone release in experienced endurance athletes-a systematic review

Background

In times of physical stress, the body orchestrates a multisystemic regulatory response. The hormones epinephrine and norepinephrine play a role in the immediate regulation chain, while cortisol is involved in delayed regulation. The release of those stress hormones in response to exercise has previously been reported to elicit diverse immune reactions.

Objective

The aim of this systematic review was to examine and present the acute effects of immediate pre- and mid-exercise carbohydrate ingestion on cortisol, epinephrine and norepinephrine levels in experienced endurance athletes.

Methods

A systematic literature search was conducted using PubMed, Cochrane Library and Web of Science in accordance with PRISMA guidelines up to February 2023. Randomized controlled trials in English or German language were included if baseline and at least two follow-up measures of blood plasma or serum of chosen stress hormones (cortisol, epinephrine, norepinephrine) were collected in response to prolonged continuous endurance activity. Eligibility furthermore required an acute carbohydrate ingestion of at least 30 g of carbohydrates per hour no more than 30 min before start of the exercise, as well as a placebo-controlled study design.

Results

Eleven studies of moderate to high quality were included in this review. Carbohydrate ingestion of at least 30 g per hour was able to attenuate rises in cortisol concentration in majority of the included studies. Epinephrine levels were considerably lower with ingestion of carbohydrates compared to placebo in all studies. Norepinephrine concentrations were largely unaffected by acute carbohydrate feeding.

Conclusion

Pre- and mid-exercise ingestion of carbohydrates seems an effective dietary strategy to attenuate rises in cortisol and epinephrine levels and, thus, an effective countermeasure for endurance exercise-induced increases in stress hormone levels.

Effect of a Conical-PEP Mask on Exercise in Subjects With COPD

BACKGROUND

Dynamic hyperinflation (DH) is a major pathophysiology of COPD that is directly related to dyspnea and exercise intolerance. Positive expiratory pressure (PEP) might reduce DH and dyspnea during exercise, but at present, there is insufficient evidence to conclude whether it is beneficial for DH, dyspnea, and exercise capacity in COPD.

METHODS

A randomized crossover trial with concealed allocation was conducted in 37 moderate to very severe subjects with COPD (34 males, age 66.6 ± 7.4 y, FEV1% of predicted 56.3 ± 13.7). The experimental condition was conical-PEP breathing with a PEP of around 5 cm H2O during a spot marching exercise at a constant speed, inducing 71 ± 9% age-predicted maximum heart rate to symptom limit or 25 min. The control condition was usual breathing. Exercise endurance time and end-exercise symptoms were recorded. Inspiratory capacity (IC) was measured pre-exercise and immediately post exercise. Cardiopulmonary function and breathlessness were monitored throughout the test and after 10 min of recovery.

RESULTS

There were no complications or adverse effects during exercise with a conical-PEP mask. Conical-PEP showed longer exercise times than control (median 11.0 [interquartile range 7.7-17.0] min vs 8 [6.0-11.5] min, respectively, P < .001). Most stopped exercising because of breathlessness and leg fatigue. At the end of exercise, IC and breathlessness showed non-significant differences between the conditions, but breathlessness was significantly lower in conical-PEP (median 4 [1.5-5.0] than control 5 [3-6] on Borg scale at isotime for control [8 min]).

CONCLUSIONS

Breathing with a 5 cm H2O conical-PEP mask improved exercise time (median 27.1% [0.6-52.9]) in subjects with COPD. The improvement in exercise with the conical-PEP mask was associated with slower development of breathlessness, possibly due to delays in DH development.

Effects of acute bouts of evening resistance or endurance exercises on sleep EEG and salivary cortisol

Introduction: Deleterious effects of exercise close to bedtime could be due to increased physiological arousal that can be detected during sleep using sleep spectral analysis. Resistance and endurance exercises have different effects on cortisol release that may lead them to impact sleep spectral signatures differently. The present study aimed to investigate the effects of two types of evening exercise on sleep architecture, sleep spectral parameters and salivary cortisol. Methods: Young healthy participants came to our laboratory to undergo 3 counterbalanced pre-sleep conditions that started 1 h before bedtime (a resistance and an endurance exercise conditions of 30 min duration, identical in terms of workload; and a control condition) followed by polysomnographic recordings. Results were compared between the three conditions for 16 participants. Results: Sleep efficiency was lower after both endurance and resistance exercise than after the control condition. Total sleep time was lower after endurance exercise compared to the control condition. Sleep spectral analyses showed that both endurance and resistance exercises led to greater alpha power during N1 sleep stage and greater theta power during N2 sleep stage compared to the control condition. The endurance exercise led to greater beta power during N2 sleep stage, greater alpha power during REM sleep, and higher cortisol levels compared to the control condition (trend), and compared to the resistance exercise condition (significant). The resistance exercise led to lower beta power during N2 sleep stage than the control condition and lower cortisol levels than the endurance exercise condition. Discussion: This study underlines significant modifications of sleep quality and quantity after both moderate evening endurance and resistance exercises. Still, these effects cannot be considered as deleterious. In contrast to the resistance exercise, endurance exercise led to an increase in sleep EEG activity associated with hyperarousal during sleep and higher cortisol levels, suggesting an hyperarousal effect of endurance exercise performed in the evening. These results align with previous warning about the arousal effects of evening exercise but do not support the notion of deleterious effects on sleep. While these results provide support for the physiological effects of evening exercises on sleep, replication with larger sample size is needed.

Effects of endurance exercise on physiologic complexity of the hemodynamics in prefrontal cortex

Significance

Prefrontal cortex (PFC) hemodynamics are regulated by numerous underlying neurophysiological components over multiple temporal scales. The pattern of output signals, such as functional near-infrared spectroscopy fluctuations (i.e., fNIRS), is thus complex. We demonstrate first-of-its-kind evidence that this fNIRS complexity is a marker that captures the influence of endurance capacity and the effects of hydrogen gas (H 2 ) on PFC regulation.

Aim

We aim to explore the effects of different physical loads of exercise as well as the intaking of hydrogen gas on the fNIRS complexity of the PFC.

Approach

Twenty-four healthy young men completed endurance cycling exercise from 0 (i.e., baseline) to 100% of their physical loads after intaking 20 min of either H 2 or placebo gas (i.e., control) on each of two separate visits. The fNIRS measuring the PFC hemodynamics and heart rate (HR) was continuously recorded throughout the exercise. The fNIRS complexity was quantified using multiscale entropy.

Results

The fNIRS complexity was significantly greater in the conditions from 25% to 100% of the physical load (p < 0.0005 ) compared with the baseline and after intaking H 2 before exercise; this increase of fNIRS complexity was significantly greater compared with the control (p = 0.001 ∼ 0.01 ). At the baseline, participants with a greater fNIRS complexity had a lower HR (β = - 0.35 ∼ - 0.33 , p = 0.008 ∼ 0.02 ). Those with a greater increase of complexity had a lower increase of the HR (β = - 0.30 ∼ - 0.28 , p = 0.001 ∼ 0.002 ) during exercise.

Conclusions

These observations suggest that fNIRS complexity would be a marker that captures the adaptive capacity of PFC to endurance exercise and to the effects of interventions on PFC hemodynamics.

Sedentarism in Recreational Marathon Runners

Aim

Although it has been previously observed that sedentary behavior (SB) was not related to training duration in marathon runners, little information existed about the relationship of SB with training, anthropometric and physiological characteristics in this population. This study aimed to investigate the prevalence of SB and its correlation with performance parameters (such as body fat percentage, maximal oxygen uptake and weekly training volume) as well as its variation by sex and day (ie, weekdays versus weekend) in recreational marathon runners.

Methods

A total of 151 finishers (women, n = 29; men, n = 122; age 43.1 (8.7) years, mean (standard deviation)) in the Athens marathon 2017 performed a series of anthropometric and physiological tests, and completed the Multi-context sitting time questionnaire.

Results

SB did not correlate with anthropometric and physiological characteristics and no difference in these characteristics was shown between low and high sedentary participants (p > 0.05). SB did not differ between women and men (p > 0.05), but differed between working and non-working days (p < 0.05).

Conclusion

In contrast to previous findings on the general population indicating an association of a high SB with a low cardiorespiratory and muscular fitness, our finding of no correlation between SB and physical fitness in marathon runners suggested that endurance exercise might offset the negative effects of SB.

Short-term effects and long-term changes of FUEL-a digital sports nutrition intervention on REDs related symptoms in female athletes

Female endurance athletes are at high risk for developing Relative Energy Deficiency in Sport (REDs), resulting in symptoms such as menstrual dysfunction and gastrointestinal (GI) problems. The primary aim of this study was to investigate effects of the FUEL (Food and nUtrition for Endurance athletes-a Learning program) intervention consisting of weekly online lectures combined with individual athlete-centered nutrition counseling every other week for sixteen weeks on REDs related symptoms in female endurance athletes at risk of low energy availability [Low Energy Availability in Females Questionnaire (LEAF-Q) score ≥8]. Female endurance athletes from Norway (n = 60), Sweden (n = 84), Ireland (n = 17), and Germany (n = 47) were recruited. Fifty athletes with risk of REDs (LEAF-Q score ≥8) and with low risk of eating disorders [Eating Disorder Examination Questionnaire (EDE-Q) global score <2.5], with no use of hormonal contraceptives and no chronic diseases, were allocated to either the FUEL intervention (n = 32) (FUEL) or a sixteen-week control period (n = 18) (CON). All but one completed FUEL and n = 15 completed CON. While no evidence for difference in change in LEAF-Q total or subscale scores between groups was detected post-intervention (BFincl < 1), the 6- and 12-months follow-up revealed strong evidence for improved LEAF-Q total (BFincl = 123) and menstrual score (BFincl = 840) and weak evidence for improved GI-score (BFincl = 2.3) among FUEL athletes. In addition, differences in change between groups was found for EDE-Q global score post-intervention (BFincl = 1.9). The reduction in EDE-Q score remained at 6- and 12- months follow-up among FUEL athletes. Therefore, the FUEL intervention may improve REDs related symptoms in female endurance athletes.

Clinical Trial Registration

www.clinicaltrials.gov (NCT04959565).

Effects of branched chain amino acids, l-citrulline, and alpha-glycerylphosphorylcholine supplementation on exercise performance in trained cyclists: a randomized crossover trial

BACKGROUND

Nutrition plays a key role in training and athletic performance and dietary supplements can make a small, but potentially valuable, contribution to achieving peak athletic performance. This study is the first to investigate the effects of supplementation from the combination of BCAAs, L-citrulline, and A-GPC on exercise performance.

METHODS

In this randomized, double-blind, crossover study 30 male trained cyclists (age: 43.7 ± 8.5 years) completed a 20 km cycling time trial (TT) test and a high intensity endurance cycling (HIEC) test following a 7-day supplementation period with either a supplement containing 8 g BCAAs, 6 g L-citrulline, and 300 mg A-GPC or a placebo (15 g maltodextrin). For each trial, mean values for time to completion, peak and average power output, OMNI rating of perceived exertion, and visual analogue scale (VAS) responses on perceived exertion were computed for the 20 km TT test. Mean values for time to fatigue and VAS responses on perceived exertion were computed for the HIEC test. Procedures for dietary intake and exercise patterns were implemented to achieve consistency throughout the study period.

RESULTS

There was a significant increase (p = .003) in peak power in the 20 km TT (354.27 ± 87.88 and 321.67 ± 63.65, for supplement and placebo trials, respectively) and a significant increase (p = .001) in time to fatigue in the HIEC test (0:19:49 ± 0:11:13 min and 0:14:33 ± 0:09:59 min, for supplement and placebo trials, respectively) with the test supplement compared to the placebo. With the test supplement, there was an average increase in TT peak power of 11% and an average increase in time to fatigue of 36.2% in the HIEC test compared to the placebo. There was no significant improvement in time to completion, average power, OMNI rating of perceived exertion, or VAS responses on perceived exertion in the TT test and no significant improvement in VAS measures of perceived exertion in the HIEC test.

CONCLUSIONS

The combination of BCAAs, L-citrulline, and A-GPC used in this study improves cycling performance and may be useful for individuals seeking to improve athletic performance, particularly in disciplines requiring lower body muscular strength and endurance.

Improved endurance capacity of diabetic mice during SGLT2 inhibition: Role of AICARP, an AMPK activator in the soleus

BACKGROUND

Diabetes is associated with an increased risk of deleterious changes in muscle mass and function or sarcopenia, leading to physical inactivity and worsening glycaemic control. Given the negative energy balance during sodium-glucose cotransporter-2 (SGLT2) inhibition, whether SGLT2 inhibitors affect skeletal muscle mass and function is a matter of concern. However, how SGLT2 inhibition affects the skeletal muscle function in patients with diabetes remains insufficiently explored. We aimed to explore the effects of canagliflozin (CANA), an SGLT2 inhibitor, on skeletal muscles in genetically diabetic db/db mice focusing on the differential responses of oxidative and glycolytic muscles.

METHODS

Db/db mice were treated with CANA for 4 weeks. We measured running distance and handgrip strength to assess skeletal muscle function during CANA treatment. At the end of the experiment, we performed a targeted metabolome analysis of the skeletal muscles.

RESULTS

CANA treatment improved the reduced endurance capacity, as revealed by running distance in db/db mice (414.9 ± 52.8 vs. 88.7 ± 22.7 m, P < 0.05). Targeted metabolome analysis revealed that 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranosyl 5'-monophosphate (AICARP), a naturally occurring AMP-activated protein kinase (AMPK) activator, increased in the oxidative soleus muscle (P < 0.05), but not in the glycolytic extensor digitorum longus muscle (P = 0.4376), with increased levels of AMPK phosphorylation (P < 0.01).

CONCLUSIONS

This study highlights the potential role of the AICARP/AMPK pathway in oxidative rather than glycolytic skeletal muscles during SGLT2 inhibition, providing novel insights into the mechanism by which SGLT2 inhibitors improve endurance capacity in patients with type 2 diabetes.

Correlation properties of heart rate variability to assess the first ventilatory threshold and fatigue in runners

PURPOSE

The short-term scaling exponent alpha1 of detrended fluctuation analysis (DFA-a1) of heart rate variability (HRV) has shown potential to delineate the first ventilatory threshold (VT1). The aims of this study were to investigate the accuracy of this method for VT1 determination in runners using a consumer grade chest belt and to explore the effects of acute fatigue.

METHODS

We compared oxygen uptake (V̇O2) and heart rate (HR) at gas exchange VT1 to V̇O2 and HR at a DFA-a1 value of 0.75. Gas exchange and HRV data were obtained from 14 individuals during a treadmill run involving two incremental ramps. Agreement was assessed using Bland-Altman analysis and linear regression.

RESULTS

Bland-Altman analysis between gas exchange and HRV V̇O2 and HR at VT1 during the first ramp showed a mean (95% limits of agreement) bias of -0.5 (-6.8 to 5.8) ml∙kg-1∙min-1, and -0.9 (-12.2 to 10.5) beats∙min-1, with R2 of 0.83 and 0.56, respectively. During the second ramp, the differences were -7.3 (-18.1 to 3.5) ml∙kg-1∙min-1 and -12.3 (-30.4 to 5.9) beats∙min-1, with R2 of 0.62 and 0.43, respectively.

CONCLUSION

A chest-belt derived DFA-a1 of 0.75 is closely related to gas exchange VT1, with the variability in accuracy at an individual level being similar to gas exchange methods. This suggests this to be a useful method for exercise intensity demarcation. The altered relationship during the second ramp indicates that DFA-a1 is only able to accurately demarcate exercise intensity thresholds in a non-fatigued state, but also opens opportunities for fatigue-based training prescription.

The long noncoding RNA lnc-H19 is important for endurance exercise by maintaining slow muscle fiber types

Skeletal muscle consists of different muscle fiber types whose heterogeneity is characterized by different metabolic patterns and expression of MyHC isomers. The transformation of muscle fiber types is regulated by a complex molecular network in which long noncoding (lnc) RNAs play an important role. In this study, we found that lnc-H19 is more enriched in slow muscle fibers. In vitro, interference of lnc-H19 by siRNA significantly promoted the expression of fast muscle fiber gene MyHC IIB and inhibited the expression of the slow muscle fiber gene MyHC I, thereby leading to a fast muscle fiber phenotype. In addition, interference of lnc-H19 significantly inhibited mRNA expression of the mitochondrial genes, such as COX5A, COX-2, UQCRFSL, FABP3, and CD36. Overexpression of lnc-H19 resulted in an opposite result. In vivo, knockdown of lnc-H19 by AAV-shRNA-H19 suppressed the mRNA expression of the slow muscle fiber gene MyHC I and the protein expression of slow-MyHC. Simultaneously, mitochondria were reduced in number, swollen, and vacuolated. The activities of succinate dehydrogenase, lactic dehydrogenase, and superoxide dismutase were significantly inhibited, and malondialdehyde content was significantly increased, indicating that deficiency of lnc-H19 leads to decreased oxidative metabolism and antioxidant capacity in muscle. Furthermore, inhibition of lnc-H19 decreased the weight-bearing swimming time and limb suspension time of mice. In conclusion, our results revealed the role of lnc-H19 in maintaining slow muscle fiber types and maintaining exercise endurance, which may help to further improve the regulatory network of lnc-H19 in muscle function.

Muscle-specific overexpression of Atg2 gene and endurance exercise delay age-related deteriorations of skeletal muscle and heart function via activating the AMPK/Sirt1/PGC-1α pathway in male Drosophila

Atg2 is a key gene in autophagy formation and plays an important role in regulating aging progress. Exercise is an important tool to resist oxidative stress in cells and delay muscle aging. However, the relationship between exercise and the muscle Atg2 gene in regulating skeletal muscle aging remains unclear. Here, overexpression or knockdown of muscle Atg2 gene was achieved by constructing the AtgUAS/MhcGal4 system in Drosophila, and these flies were also subjected to an exercise intervention for 2 weeks. The results showed that both overexpression of Atg2 and exercise significantly increased the climbing speed, climbing endurance, cardiac function, and lifespan of aging flies. They also significantly up-regulated the expression of muscle Atg2, AMPK, Sirt1, and PGC-1α genes, and they significantly reduced muscle malondialdehyde and triglyceride. These positive benefits were even more pronounced when the two were combined. However, the effects of Atg2 knockdown on skeletal muscle, heart, and lifespan were reversed compared to its overexpression. Importantly, exercise ameliorated age-related changes induced by Atg2 knockdown. Therefore, current results confirmed that both overexpression of muscle Atg2 and exercise delayed age-related deteriorations of skeletal muscle, the heart function, and lifespan, and exercise could also reverse age-related changes induced by Atg2 knockdown. The molecular mechanism is related to the overexpression of the Atg2 gene and exercise, which increase the activity of the AMPK/Sirt1/PGC-1α pathway, oxidation and antioxidant balance, and lipid metabolism in aging muscle.

Effects of the order of endurance and high-intensity interval exercise in combined training on mouse skeletal muscle metabolism

Endurance exercise (EE) mainly improves oxidative capacity, whereas high-intensity interval exercise (HIIE) also improves glycolytic capacity. There is growing evidence that suggests that combining EE with HIIE can lead to improved athletic performance and fitness outcomes compared with either form of exercise alone. This study aimed to elucidate whether the order in which EE and HIIE are performed in combined training affects oxidative metabolism and glycolysis in mouse skeletal muscle. Male ICR mice at 7 wk of age were divided into three groups: control (CON), EE-HIIE, and HIIE-EE. The total training period was 3 wk (3 times/week). Mice performed running on a treadmill as endurance exercise and swimming with a weight load of 10% of body weight as high-intensity interval exercise. EE before HIIE (EE-HIIE) improved running performance in the maximal EE capacity test (all-out test) and partly enhanced the expression levels of molecular signals involved in glycolysis compared with HIIE before EE (HIIE-EE). The order of exercise did not, however, impact the expression of proteins related to mitochondrial dynamics, including those involved in the morphological changes of mitochondria through repeated fusion and fission, as well as oxidative energy metabolism. The findings suggest that the order of exercise has no significant impact on the expression of proteins associated with glycolytic and oxidative energy metabolism. Nevertheless, our results indicate that the order of EE-HIIE may enhance running performance.

Assessment of Intercostal Muscle Near-Infrared Spectroscopy for Estimating Respiratory Compensation Point in Trained Endurance Athletes

This study aimed to assess the reliability and validity of estimating the respiratory compensation point (RCP) in trained endurance athletes by analyzing intercostal muscles' NIRS-derived tissue oxygenation dynamics. Seventeen experienced trail runners underwent an incremental treadmill protocol on two separate occasions, with a 7-day gap between assessments. Gas exchange and muscle oxygenation data were collected, and the oxygen saturation breakpoint (SmO2BP) measured in the intercostal muscles was compared to the RCP, which was identified by the increase in the VE/V.CO2 slope and the point at which the PetCO2 started to decrease. No statistically significant differences were observed between the two methods for any of the variables analyzed. Bland-Altman analysis showed significant agreement between the NIRS and gas analyzer methods for speed (r = 0.96, p < 0.05), HR (r = 0.98, p < 0.05), V.O2 relative to body mass (r = 0.99, p < 0.05), and %SmO2 (r = 0.98, p < 0.05). The interclass correlation coefficient values showed moderate to good reliability (0.60 to 0.86), and test-retest analysis revealed mean differences within the confidence intervals for all variables. These findings suggest that the SmO2BP measured using a portable NIRS device in the intercostal muscles is a reliable and valid tool for estimating the RCP for experienced trail runners and might be useful for coaches and athletes to monitor endurance training.

Octopamine Rescues Endurance and Climbing Speed in Drosophila Clkout Mutants with Circadian Rhythm Disruption

Circadian rhythm disturbances are associated with various negative health outcomes, including an increasing incidence of chronic diseases with high societal costs. While exercise can protect against the negative effects of rhythm disruption, it is not available to all those impacted by sleep disruptions, in part because sleep disruption itself reduces exercise capacity. Thus, there is a need for therapeutics that bring the benefits of exercise to this population. Here, we investigate the relationship between exercise and circadian disturbances using a well-established Drosophila model of circadian rhythm loss, the Clkout mutant. We find that Clkout causes reduced exercise capacity, measured as post-training endurance, flight performance, and climbing speed, and these phenotypes are not rescued by chronic exercise training. However, exogenous administration of a molecule known to mediate the effects of chronic exercise, octopamine (OA), was able to effectively rescue mutant exercise performance, including the upregulation of other known exercise-mediating transcripts, without restoring the circadian rhythms of mutants. This work points the way toward the discovery of novel therapeutics that can restore exercise capacity in patients with rhythm disruption.

Gastrointestinal cell injury and perceived symptoms after running the Boston Marathon

Gastrointestinal (GI) disturbances are a prevalent cause of marathon related complaints, and in extreme cases can promote life-threatening conditions such as exertional heat stroke. Our aim was to study intestinal cell injury [via intestinal fatty acid binding protein (I-FABP)] and perceived GI distress symptoms among marathon runners. We also examined potential risk factors (e.g., inadequate sleep) that could exacerbate GI disturbances in healthy, trained endurance runners. This was a parallel mixed-methods study design. 2019 Boston Marathon participants were recruited via email and subjects completed surveys before the race describing demographics and training history. Participants completed a GI questionnaire to assess presence and severity of symptoms, a survey regarding risk factors (e.g., recent illness, medications) that could promote GI disturbances, and provided a urine sample at three time points (immediately pre-race, post-race, and 24-h post-race). Due to weather, blood samples were only collected immediately and 24-h post-race. A total of 40 runners (males: n = 19, age = 44.9 ± 10.8 years; females: n = 21, age = 44.8 ± 10.6 years) completed this study. I-FABP significantly decreased from post-race (3367.5 ± 2633.5 pg/mL) to 24-h post-race (1657.3 ± 950.7 pg/mL, t (39) = -4.228, p < .001, d = -.669). There was a significant difference in overall GI symptom scores across the three time points (F (2, 39) = 41.37, p < .001). The highest average score occurred post-race (.84 ± .68), compared to pre-race (.09 ± .12) and 24-h post-race (.44 ± .28). Post-race I-FABP (r = .31, p = .048) and post-race urine specific gravity (r = .33, p = .041) were significantly correlated with post-race GI symptom scores. Our study provides further support to the individualized nature of GI disturbances, with participants experiencing a wide range of risk factors that can influence the extent of GI damage and perceived symptoms during and after exercise.

High-fat ketogenic diets and ketone monoester supplements differentially affect substrate metabolism during aerobic exercise

Chronically adhering to high-fat ketogenic diets or consuming ketone monoester supplements elicits ketosis. Resulting changes in substrate metabolism appear to be drastically different between ketogenic diets and ketone supplements. Consuming a ketogenic diet increases fatty acid oxidation with concomitant decreases in endogenous carbohydrate oxidation. Increased fat oxidation eventually results in an accumulation of circulating ketone bodies, which are metabolites of fatty acids that serve as an alternative source of fuel. Conversely, consuming ketone monoester supplements rapidly increases circulating ketone body concentrations that typically exceed those achieved by adhering to ketogenic diets. Rapid increases in ketone body concentrations with ketone monoester supplementation elicit a negative feedback inhibition that reduces fatty acid mobilization during aerobic exercise. Supplement-derived ketosis appears to have minimal impact on sparing of muscle glycogen or minimizing of carbohydrate oxidation during aerobic exercise. This review will discuss the substrate metabolic and associated aerobic performance responses to ketogenic diets and ketone supplements.

Ultra-Endurance triathlon competition shifts fecal metabolome independent of changes to microbiome composition

Understanding changes to gut microbiota composition and metabolic output in response to acute exercise may be necessary for understanding the mechanisms mediating the long-term health and performance benefits of exercise. Our primary objective was to characterize acute changes in the fecal microbiome and metabolome following participation in an ultra-endurance (3.9 km swim, 180.2 km bike, 42.2 km run) triathlon. An exploratory aim was to determine associations between athlete-specific factors [race performance (i.e., completion time) and lifetime years of endurance training] with pre-race gut microbiota and metabolite profiles. Stool samples from 12 triathletes (9 males/3 females; 43 ± 14 yr, 23 ± 2 kg/m2) were collected ≤48 h before and the first bowel movement following race completion. Intra- and inter-individual diversity of bacterial species and individual bacterial taxa were unaltered following race completion (P > 0.05). However, significant reductions (P < 0.05) in free and secondary bile acids [deoxycholic acid (DCA), 12-keto-lithocholic acid (12-ketoLCA)] and short-chain fatty acids (butyric and pivalic acids), and significant increases (P < 0.05) in long-chain fatty acids (oleic and palmitoleic acids) were observed. Exploratory analyses revealed several associations between pre-race bacterial taxa and fecal metabolites with race performance and lifetime history of endurance training (P < 0.05). These findings suggest that 1) acute ultra-endurance exercise shifts microbial metabolism independent of changes to community composition and 2) athlete performance level and training history relate to resting-state gut microbial ecology.NEW & NOTEWORTHY This is the first study to characterize acute changes in gut microbial ecology and metabolism following an ultra-endurance triathlon. We demonstrate changes in gut microbial community function, but not structure, as well as several associations between gut microbiome and fecal metabolome characteristics with race completion time and lifetime history of endurance training. These data add to a small but growing body of literature seeking to characterize the acute and chronic effects of exercise on the gut microbial ecosystem.