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OBJECTIVES: This study was designed to quantify inter- and intra-individual variability in performance, physiological, and perceptual responses to high-intensity interval training prescribed using the percentage of delta (%Δ) method, in which the gas exchange threshold and maximal oxygen uptake (V̇O2max) are taken into account to normalise relative exercise intensity. DESIGN: Repeated-measures, within-subjects design with mixed-effects modelling. METHODS: Eighteen male and four female cyclists (age: 36 ±â€¯12 years, height: 178 ±â€¯10 cm, body mass: 75.2 ±â€¯13.7 kg, V̇O2max: 51.6 ±â€¯5.3 ml·kg-1·min-1) undertook an incremental test to exhaustion to determine the gas exchange threshold and V̇O2max as prescription benchmarks. On separate occasions, participants then completed four high-intensity interval training sessions of identical intensity (70 %Δ) and format (4-min on, 2-min off); all performed to exhaustion. Acute high-intensity interval training responses were modelled with participant as a random effect to provide estimates of inter- and intra-individual variability. RESULTS: Greater variability was generally observed at the between- compared with the within-individual level, ranging from 50 % to 89 % and from 11 % to 50 % of the total variability, respectively. For the group mean time to exhaustion of 20.3 min, inter- and intra-individual standard deviations reached 9.3 min (coefficient of variation = 46 %) and 4.5 min (coefficient of variation = 22 %), respectively. CONCLUSIONS: Due to the high variability observed, the %Δ method does not effectively normalise the relative intensity of exhaustive high-intensity interval training across individuals. The generally larger inter- versus intra-individual variability suggests that day-to-day biological fluctuations and/or measurement errors cannot explain the identified shortcoming of the method.

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Despite its comparatively limited size in humans, spleen has been shown able to expel red-blood cells in the circulation and thus augment blood oxygen-carrying capacity under certain physiologic conditions. In the present state-of-the-art review, the short- and long-term regulation of spleen volume will be discussed. With regards to the physiological mechanism underlying spleen contraction, sympathetic activation stands as the prime contributor to the response. A dose-dependent relationship between specific interventions of apnea, exercise and hypoxia (imposed separately or in combination) and spleen contraction alleges to the trainability of the spleen organ. The trainability of the spleen is further substantiated by virtue of cross-sectional and longitudinal studies reporting robust increases in both organ volume at rest and subsequent spleen contraction. Alternative ways to assess the relationship between hematologic gains and the magnitude of spleen contraction (i.e., the reduction of spleen volume) will be presented herein. In extension of changes in the conventional measures of hemoglobin concentration and hematocrit, assessment of hemoglobin mass and total blood volume using the (safe, low-cost and time-efficient) CO-rebreathing technique could deepen scientific knowledge on the efficiency of human spleen contraction.

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PURPOSE: To investigate the influence of exercise intensity normalisation on intra- and inter-individual acute and adaptive responses to an interval training programme. METHODS: Nineteen cyclists were split in two groups differing (only) in how exercise intensity was normalised: 80% of the maximal work rate achieved in an incremental test (% W ˙ max) vs. maximal sustainable work rate in a self-paced interval training session (% W ˙ max-SP). Testing duplicates were conducted before and after an initial control phase, during the training intervention, and at the end, enabling the estimation of inter-individual variability in adaptive responses devoid of intra-individual variability. RESULTS: Due to premature exhaustion, the median training completion rate was 88.8% for the % W ˙ max group, but 100% for the % W ˙ max-SP the group. Ratings of perceived exertion and heart rates were not sensitive to how intensity was normalised, manifesting similar inter-individual variability, although intra-individual variability was minimised for the % W ˙ max-SP group. Amongst six adaptive response variables, there was evidence of individual response for only maximal oxygen uptake (standard deviation: 0.027 L·min-1·week-1) and self-paced interval training performance (standard deviation: 1.451 W·week-1). However, inter-individual variability magnitudes were similar between groups. Average adaptive responses were also similar between groups across all variables. CONCLUSIONS: To normalise completion rates of interval training, % W ˙ max-SP should be used to prescribe relative intensity. However, the variability in adaptive responses to training may not reflect how exercise intensity is normalised, underlining the complexity of the exercise dose-adaptation relationship. True inter-individual variability in adaptive responses cannot always be identified when intra-individual variability is accounted for.

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INTRODUCTION: Sports medicine, as a classical cross-sectional subject, includes diverse topics which show gender-specific differences and thus require a differentiated consideration. Evidence-based research exists in the field of musculoskeletal medicine, for example, in relation to cruciate ligament injuries or concussions. Marked differences in trainability (both muscular and cardiac or pulmonary) are also emerging. Pregnancy and sport is also a topic of increasing interest. Close interdisciplinary care of female athletes, knowledge of physiological changes during pregnancy and contraindications to sports activity (especially with higher intensity) are essential here. Aspects in the field of internal sports medicine with gender differences are topics like iron deficiency or the relative energy deficit (RED-S). There are also sex and gender differences with implications for preventative aspects such as the annual screening examination (so called 'preparticipation screening').

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This study aimed to clarify whether aerobic exercise training-induced alterations in the gut microbiota affect physiological adaptation with endurance exercise capacity. In study 1, ICR mice were randomly divided into three groups: vehicle intake + sedentary (V+S), vehicle intake + exercise training (V+Ex) and antibiotic intake + exercise training (AB+Ex). In the exercise training groups, treadmill running was performed for 8 weeks. During the exercise training intervention, the antibiotic-intake group freely drank water containing antibiotics. In study 2, ICR mice were randomly divided into three groups: Sham, transplantation of caecum microbiota from sedentary mice (Sed-CMT) and exercise training mice (Ex-CMT). In study 1, the treadmill running time to exhaustion, an index of maximal aerobic capacity, after aerobic exercise training in the V+Ex group was significantly longer than that in the V+S and AB+Ex groups. Gastrocnemius muscle citrate synthase (CS) activity and PGC-1α protein levels in the V+Ex group were significantly higher than in the V+S and AB+Ex groups. The bacterial Erysipelotrichaceae and Alcaligenaceae families were positively correlated with treadmill running time to exhaustion. In study 2, the treadmill running time to exhaustion after transplantation was significantly higher in the Ex-CMT group than in the Sham and Sed-CMT groups. Furthermore, CS activity and PGC-1α protein levels in the gastrocnemius muscle were significantly higher in the Ex-CMT group than in the Sham and Sed-CMT groups. Thus, gut microbiota altered by aerobic exercise training may be involved in the augmentation of endurance capacity and muscle mitochondrial energy metabolism. KEY POINTS: Aerobic exercise training changes gut microbiota composition, and the Erysipelotrichaceae and Alcaligenaceae families were among the altered gut bacteria. The gut microbiota was associated with endurance performance and metabolic regulator levels in skeletal muscle after aerobic exercise training. Continuous antibiotic treatment attenuated the increase in endurance performance, citrate synthase activity and PGC-1α levels in skeletal muscle induced by aerobic exercise training. Gut microbiota transplantation from exercise-trained mice improved endurance performance and metabolic regulator levels in recipient skeletal muscle, despite the absence of aerobic exercise training.

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Dopamine (DA) is a neurotransmitter associated with animal behaviors. Along with other neurotransmitters such as oxytocin (OXT) and serotonin (5-HT), DA is also involved in determining the temperament of animals. However, the involvement of DA in horse temperament has not been well elucidated. Therefore, in this study, we aimed to determine the correlation between plasma DA concentration and OXT and 5-HT concentrations and behavioral temperament (eg, docility and friendliness, fearfulness, dominance, and trainability) of horses. Blood samples were collected from 31 horses and the concentrations of DA, OXT, and 5-HT were measured using enzyme-linked immunosorbent assay. The temperament of horses was assessed and scored by 3 researchers. The correlation between the plasma concentration of DA and OXT or 5-HT was statistically analyzed using SPSS software and linear regression analysis was performed to determine the association between DA concentration and OXT and 5-HT concentrations. Meanwhile, the DA concentration associated with each type of temperament was analyzed via one-way analysis of variance with LSD post hoc analysis as well as Student's t-test (for trainability). Plasma DA concentration was not found to be correlated with either OXT or 5-HT concentrations. Furthermore, we found no correlation between plasma DA concentration and dominance and trainability. However, our results suggest the possibility of predicting the degree of fearfulness of horses using plasma DA concentrations. We conclude that plasma DA concentration has a potentiality to be used as a biomarker to predict the fearfulness of horses.

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PURPOSE: To compare methods of relative intensity prescription for their ability to normalise performance (i.e., time to exhaustion), physiological, and perceptual responses to high-intensity interval training (HIIT) between individuals. METHODS: Sixteen male and two female cyclists (age: 38 ± 11 years, height: 177 ± 7 cm, body mass: 71.6 ± 7.9 kg, maximal oxygen uptake ([Formula: see text]O2max): 54.3 ± 8.9 ml·kg-1 min-1) initially undertook an incremental test to exhaustion, a 3 min all-out test, and a 20 min time-trial to determine prescription benchmarks. Then, four HIIT sessions (4 min on, 2 min off) were each performed to exhaustion at: the work rate associated with the gas exchange threshold ([Formula: see text]GET) plus 70% of the difference between [Formula: see text]GET and the work rate associated with [Formula: see text]O2max; 85% of the maximal work rate of the incremental test (85%[Formula: see text]max); 120% of the mean work rate of the 20 min time-trial (120%TT); and the work rate predicted to expend, in 4 min, 80% of the work capacity above critical power. Acute HIIT responses were modelled with participant as a random effect to provide estimates of inter-individual variability. RESULTS: For all dependent variables, the magnitude of inter-individual variability was high, and confidence intervals overlapped substantially, indicating that the relative intensity normalisation methods were similarly poor. Inter-individual coefficients of variation for time to exhaustion varied from 44.2% (85%[Formula: see text]max) to 59.1% (120%TT), making it difficult to predict acute HIIT responses for an individual. CONCLUSION: The present study suggests that the methods of intensity prescription investigated do not normalise acute responses to HIIT between individuals.

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Background: Cross-sectional studies in children reported better balance performance for girls than for boys. Thus, balance trainability might be different between female and male children. The aim of the present study was to examine the effects of balance training (BT) on dynamic balance performance in girls compared to boys. Methods: Seventeen girls (age: 11.1 ± 0.7 years) and 22 boys (age: 11.1 ± 0.8 years) were assigned to either a BT-group or an active control (CON) group. BT was conducted over eight weeks (two sessions/week) while the CON-groups received their regular physical education lessons during the same period. Before and after treatment, dynamic balance performance was assessed by using the Lower Quarter Y-Balance (YBT-LQ) test. A series of three-way analyses of covariance (ANCOVA) were undertaken to test for within-between effects of Test [×2 (pretest vs. posttest)], Group [×2 (BT-group vs. CON-group)] and Sex [×2 (boys vs. girls)]. Results: The three-way ANCOVA yielded a significant main effect of Test (p = 0.002-0.043, η p 2 = 0.122-0.262) and of Group (all p < 0.001, η p 2 = 0.330-0.651) but not of sex for all YBT-LQ reach directions and the composite score. Further, there were significant Test × Group interactions (all p < 0.001, η p 2 = 0.330-0.651) in favor of both BT-groups but neither Test × Sex nor Test × Group × Sex interactions were detected. Conclusions: We conclude that BT is an effective treatment to improve dynamic balance performance in healthy children regardless of their sex. Consequently, girls and boys can be provided with the same BT regime to enhance their postural control.

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Resilience, a Buzzword? Abstract. There is a growing awareness of the importance of resilience in many areas of our society. Current research largely assumes that resilience can be trained and used to avoid suffering or to better overcome crises. This article deals with the question of what is meant by resilience and how t can be trained.

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BACKGROUND: Endurance exercise training promotes the catabolism of branched-chain amino acids (BCAAs) in skeletal muscles. We have previously shown that mitochondrial DNA (mtDNA) haplogroups J and K are markers of low responders in endurance training. In this paper, we hypothesize that BCAA catabolism is a surrogate marker of lower respiratory chain activity attributed to these haplogroups. We evaluated whether exercise-induced changes in amino acid concentrations differ between subjects harbouring mtDNA haplogroups J or K and those with non-JK haplogroups. METHODS: Finnish male conscripts (N = 633) undertook the 12-min Cooper running test at the beginning and end of their military service. The intervention during the service mainly included endurance aerobic exercise and sports-related muscle training. Concentrations of seven amino acids were analysed in the serum using a high-throughput 1H NMR metabolomics platform. Total DNA was extracted from whole blood, and restriction fragment analysis was used to determine mtDNA haplogroups J and K. RESULTS: The concentrations of the seven amino acids were higher following the intervention, with the exception of phenylalanine; interestingly, the increase in the concentrations of three BCAAs was larger in subjects with haplogroup J or K than in subjects with non-JK haplogroups (p = 0.029). MtDNA haplogroups J and K share two common nonsynonymous variants. Structural analysis based on crystallographic data on bovine complexes I and III revealed that the Leu18 variant in cytochrome b encoded by m.14798T > C may interfere with ubiquinone binding at the Qi site in complex III. CONCLUSIONS: The increase in the concentrations of serum BCAAs following exercise intervention differs between subjects harbouring mtDNA haplogroup J or K and those harbouring non-JK haplogroups. Lower response in endurance training and difference in exercise-induced increase in the concentrations of serum BCAAs suggest decreased respiratory chain activity. Haplogroups J and K share m.14798T > C in MT-CYB, which may hamper the function of complex III.

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BACKGROUND: The gut microbiome has been associated with cardiorespiratory fitness. OBJECTIVES: To assess the effects of oligofructose (FOS)-enriched inulin supplementation on the gut microbiome and the peak oxygen uptake (V̇O2peak) response to high-intensity interval training (HIIT). METHODS: The study was a randomized controlled trial. Forty sedentary and apparently healthy adults [n = 31 women; aged 31.8 ± 9.8 y, BMI (in kg⋅m-2) 25.9 ± 4.3] were randomly allocated to 1) 6 wk of supervised HIIT (4 × 4-min bouts at 85-95% peak heart rate, interspersed with 3 min of active recovery, 3·wk-1) + 12 g·d-1 of FOS-enriched inulin (HIIT-I) or 2) 6 wk of supervised HIIT (3·wk-1, 4 × 4-min bouts) + 12 g·d-1 of maltodextrin/placebo (HIIT-P). Each participant completed an incremental treadmill test to assess V̇O2peak and ventilatory thresholds (VTs), provided a stool and blood sample, and completed a 24-h diet recall questionnaire and FFQ before and after the intervention. Gut microbiome analyses were performed using metagenomic sequencing. Fecal short-chain fatty acids were measured by mass spectrometry. RESULTS: There were no differences in the mean change in V̇O2peak response between groups (P = 0.58). HIIT-I had a greater improvement in VTs than HIIT-P [VT1 (lactate accumulation): mean difference + 4.3% and VT2 (lactate threshold): +4.2%, P < 0.05]. HIIT-I had a greater increase in the abundance of Bifidobacterium taxa [false discovery rate (FDR) < 0.05] and several metabolic processes related to exercise capacity (FDR < 0.05). Exploratory analysis of merged data found participants with a greater response to HIIT (V̇O2peak ≥3.5 mL⋅kg-1⋅min-1) had a 2.2-fold greater mean abundance of gellan degradation pathways (FDR < 0.05) and a greater, but not significant, abundance of Bifidobacterium uniformis species (P < 0.00023, FDR = 0.08). CONCLUSIONS: FOS-enriched inulin supplementation did not potentiate HIIT-induced improvements in V̇O2peak but led to gut microbiome changes possibly associated with greater ventilatory threshold improvements in healthy inactive adults. Gellan degradation pathways and B. uniformis spp. were associated with greater V̇O2peak responses to HIIT.

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Background: Many reports describe statistical approaches for estimating interindividual differences in trainability and classifying individuals as "responders" or "non-responders." The extent to which studies in the exercise training literature have adopted these statistical approaches remains unclear. Objectives: This systematic review primarily sought to determine the extent to which studies in the exercise training literature have adopted sound statistical approaches for examining individual responses to exercise training. We also (1) investigated the existence of interindividual differences in trainability, and (2) tested the hypothesis that less conservative thresholds inflate response rates compared with thresholds that consider error and a smallest worthwhile change (SWC)/minimum clinically important difference (MCID). Methods: We searched six databases: AMED, CINAHL, EMBASE, Medline, PubMed, and SportDiscus. Our search spanned the aerobic, resistance, and clinical or rehabilitation training literature. Studies were included if they used human participants, employed standardized and supervised exercise training, and either: (1) stated that their exercise training intervention resulted in heterogenous responses, (2) statistically estimated interindividual differences in trainability, and/or (3) classified individual responses. We calculated effect sizes (ESIR) to examine the presence of interindividual differences in trainability. We also compared response rates (n = 614) across classification approaches that considered neither, one of, or both errors and an SWC or MCID. We then sorted response rates from studies that also reported mean changes and response thresholds (n = 435 response rates) into four quartiles to confirm our ancillary hypothesis that larger mean changes produce larger response rates. Results: Our search revealed 3,404 studies, and 149 were included in our systematic review. Few studies (n = 9) statistically estimated interindividual differences in trainability. The results from these few studies present a mixture of evidence for the presence of interindividual differences in trainability because several ESIR values lay above, below, or crossed zero. Zero-based thresholds and larger mean changes significantly (both p < 0.01) inflated response rates. Conclusion: Our findings provide evidence demonstrating why future studies should statistically estimate interindividual differences in trainability and consider error and an SWC or MCID when classifying individual responses to exercise training. Systematic Review Registration: [website], identifier [registration number].

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Purpose: High heterogeneity of the response of cardiorespiratory fitness (CRF) to standardized exercise doses has been reported in different training programs, but the associated mechanisms are not widely known. This study investigated whether changes in the metabolic profile and pathways in blood serum and the skeletal muscle are associated with the inter-individual variability of CRF responses to 8-wk of continuous endurance training (ET) or high-intensity interval training (HIIT). Methods: Eighty men, young and sedentary, were randomized into three groups, of which 70 completed 8 wk of intervention (> 90% of sessions): ET, HIIT, or control. Blood and vastus lateralis muscle tissue samples, as well as the measurement of CRF [maximal power output (MPO)] were obtained before and after the intervention. Blood serum and skeletal muscle samples were analyzed by 600 MHz 1H-NMR spectroscopy (metabolomics). Associations between the pretraining to post-training changes in the metabolic profile and MPO gains were explored via three analytical approaches: (1) correlation between pretraining to post-training changes in metabolites' concentration levels and MPO gains; (2) significant differences between low and high MPO responders; and (3) metabolite contribution to significantly altered pathways related to MPO gains. After, metabolites within these three levels of evidence were analyzed by multiple stepwise linear regression. The significance level was set at 1%. Results: The metabolomics profile panel yielded 43 serum and 70 muscle metabolites. From the metabolites within the three levels of evidence (15 serum and 4 muscle metabolites for ET; 5 serum and 1 muscle metabolites for HIIT), the variance in MPO gains was explained: 77.4% by the intervention effects, 6.9, 2.3, 3.2, and 2.2% by changes in skeletal muscle pyruvate and valine, serum glutamine and creatine phosphate, respectively, in ET; and 80.9% by the intervention effects; 7.2, 2.2, and 1.2% by changes in skeletal muscle glycolate, serum creatine and creatine phosphate, respectively, in HIIT. The most changed and impacted pathways by these metabolites were: arginine and proline metabolism, glycine, serine and threonine metabolism, and glyoxylate and dicarboxylate metabolism for both ET and HIIT programs; and additional alanine, aspartate and glutamate metabolism, arginine biosynthesis, glycolysis/gluconeogenesis, and pyruvate metabolism for ET. Conclusion: These results suggest that regulating the metabolism of amino acids and carbohydrates may be a potential mechanism for understanding the inter-individual variability of CRF in responses to ET and HIIT programs.

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[This corrects the article DOI: 10.3389/fnhum.2019.00466.].

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Genome-wide association study (GWAS) using dog breed standard values as phenotypic measurements is an efficient way to identify genes associated with morphological and behavioral traits. As a result of strong human purposeful selections, several specialized behavioral traits such as herding and hunting have been formed in different modern dog breeds. However, genetic analyses on this topic are rather limited due to the accurate phenotyping difficulty for these complex behavioral traits. Here, 268 dog whole-genome sequences from 130 modern breeds were used to investigate candidate genes underlying dog herding, predation, temperament, and trainability by GWAS. Behavioral phenotypes were obtained from the American Kennel Club based on dog breed standard descriptions or groups (conventional categorization of dog historical roles). The GWAS results of herding behavior (without body size as a covariate) revealed 44 significantly associated sites within five chromosomes. Significantly associated sites on CFA7, 9, 10, and 20 were located either in or near neuropathological or neuronal genes including THOC1, ASIC2, MSRB3, LLPH, RFX8, and CHL1. MSRB3 and CHL1 genes were reported to be associated with dog fear. Since herding is a restricted hunting behavior by removing killing instinct, 36 hounds and 55 herding dogs were used to analyze predation behavior. Three neuronal-related genes (JAK2, MEIS1, and LRRTM4) were revealed as candidates for predation behavior. The significantly associated variant of temperament GWAS was located within ACSS3 gene. The highest associated variant in trainability GWAS is located on CFA22, with no variants detected above the Bonferroni threshold. Since dog behaviors are correlated with body size, we next incorporate body mass as covariates into GWAS; and significant signals around THOC1, MSRB3, LLPH, RFX8, CHL1, LRRTM4, and ACSS3 genes were still detected for dog herding, predation, and temperament behaviors. In humans, these candidate genes are either involved in nervous system development or associated with mental disorders. In conclusion, our results imply that these neuronal or psychiatric genes might be involved in biological processes underlying dog herding, predation, and temperament behavioral traits.

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Oxytocin (OXT) and serotonin (5-HT) are essential neurotransmitters associated with the behavior of animals. Recently, we found that the plasma concentration of OXT is positively correlated with horse docility and friendliness toward humans. However, the relationships between the neurotransmitters and other temperaments such as fearfulness, dominance, and trainability are unknown. This study aimed to identify whether the plasma concentration of OXT or 5-HT is correlated with fearfulness, dominance, and trainability of horses. Blood samples of 34 horses were collected at the Horse Industry Complex Center of Jeonju Kijeon College. The concentration of OXT and 5-HT was measured in the plasma samples using enzyme-linked immunosorbent assays. The fearfulness, dominance, and trainability of horses were scored by three professors who were very familiar with the horses. One-way analysis of variance with the least significant difference post-hoc analysis was used to compare the scores for fearfulness and dominance among groups. The trainability of horses was compared using the student t-test. The 5-HT was negatively correlated with dominance, but it had no relation with fearfulness. The OXT appeared to be negatively correlated with fearfulness and dominance in horses. Furthermore, OXT was positively correlated with the trainability of horses. Additionally, 5-HT appeared to enhance trainability. In conclusion, the concentration of OXT or 5-HT in horse blood plasma can be used as a biomarker to monitor the fearfulness, dominance, or trainability of horses.

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We used a within-subject crossover design to examine the impact of exercise modality, i.e., resistance (RT) and endurance (END), on the acute impact of exercise on endothelial function. Then, we examined whether a 4-wk period of chronic exercise training altered the acute exercise-induced change in endothelial function in healthy individuals. Thirty-four healthy, young men (21 ± 2 yr) reported to our laboratory and completed assessment of endothelial function [using the brachial artery flow-mediated dilation test (FMD)] before and immediately after a single bout of RT (leg-extension) or END (cycling). Subsequently, participants completed a 4-wk period of training (12 sessions), followed by evaluation of the FMD before and after a single bout of exercise. Following a 3-wk washout, participants repeated these experiments with the different exercise modality (in a balanced crossover design). An exercise × modality interaction effect was found (P < 0.001). Post hoc pairwise analyses revealed a decrease in FMD after END (P < 0.001) but not after RT (P = 0.06). Four weeks of exercise training improved resting FMD after END and RT (P = 0.04) but did not alter the acute effect of exercise on FMD (exercise × modality × training effect: P = 0.63), an effect independent of the modality of exercise (exercise × training interaction: P = 0.46 and P = 0.11 in RT and END, respectively). These distinct changes in FMD following acute exercise may relate to the different prolonged physiological responses induced by endurance versus resistance exercise. Specifically, endurance exercise, but not resistance exercise, causes a decrease in brachial artery endothelial function, which was unaffected by 4 wk of chronic exercise training.NEW & NOTEWORTHY We found that resistance and endurance exercise modalities lead to different endothelial function responses after a single bout of exercise. Endothelial function increased after an acute bout of resistance exercise, whereas it decreased after an acute bout of endurance exercise. Four weeks of chronic exercise training did not affect the acute endothelial function response.

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We used a within-subject, cross-over design study to compare the impact of 4-weeks' resistance (RT) versus endurance (END) training on vascular function. We subsequently explored the association of intra-individual effects of RT versus END on vascular function with a single nucleotide polymorphism (SNP) of the NOS3 gene. Thirty-five healthy males (21 ± 2 years old) were genotyped for the NOS3 rs2070744 SNP and completed both training modalities. Participants completed 12 sessions over a 4-week period, either RT (leg-extension) or END (cycling) training in a randomized, balanced cross-over design with a 3-week washout period. Participants performed peak oxygen uptake (peak VO2 ) and leg-extension single-repetition maximum (1-RM) testing, and vascular function assessment using flow-mediated dilation (FMD) on 3 separated days pre/post-training. Peak VO2 increased after END (p < 0.001), while 1-RM increased after RT (p < 0.001). FMD improved after 4-weeks' training (time effect: p = 0.006), with no difference between exercise modalities (interaction effect: p = 0.92). No relation was found between individual changes (delta, pre-post) in FMD to both types of training (R2  = 0.06, p = 0.14). Intra-individual changes in FMD following END and RT were associated with the NOS3 SNP, with TT homozygotes significantly favoring only END (p = 0.016) and TC/CC tending to favor RT only (p = 0.056). Although both training modes improved vascular function, significant intra-individual variation in the adaptation of FMD was found. The association with NOS3 genotype suggests a genetic predisposition to FMD adapting to a specific mode of chronic exercise. This study therefore provides novel evidence for personalized exercise training to optimize vascular health.

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BACKGROUND: We have previously suggested that some of the mutations defining mitochondrial DNA (mtDNA) haplogroups J and K produce an uncoupling effect on oxidative phosphorylation and thus are detrimental for elite endurance performance. Here, the association between haplogroups J and K and physical performance was determined in a population-based cohort of 1036 Finnish military conscripts. RESULTS: Following a standard-dose training period, excellence in endurance performance was less frequent among subjects with haplogroups J or K than among subjects with non-JK haplogroups (p = 0.041), and this finding was more apparent among the best-performing subjects (p < 0.001). CONCLUSIONS: These results suggest that mtDNA haplogroups are one of the genetic determinants explaining individual variability in the adaptive response to endurance training, and mtDNA haplogroups J and K are markers of low-responders in exercise training.

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Nonresponse to exercise has been extensively examined in young athletes but is seldom reported in studies of aerobic exercise interventions in older adults. This study examined the prevalence of nonresponse and poor response to exercise in functional and quality of life outcomes and response patterns between and among older adults undergoing 12-weeks of supervised exercise therapy for the management of peripheral artery disease (N = 44, mean age 72.3 years, 47.7% female). The prevalence of nonresponse (no change/decline in performance) in walking distance was 31.8%. The prevalence of poor response (lack of a clinically meaningful improvement) was 43.2%. Similar patterns of response were observed in both objective and patient-reported measures of physical function. All participants improved in at least one outcome; only two participants improved in all measured outcomes. Additional research should examine modifiable predictors of response to inform programming and maximize an individual's potential benefit from exercise therapy.

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