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We explored the impact of running in the severe intensity domain on running mechanics and muscle oxygenation in competitive runners by investigating the relationship between mechanical deviations from typical stride characteristics and muscle oxygen saturation (SmO2) in the quadriceps muscle. Sixteen youth competitive runners performed an 8-min exhaustive running test on an outdoor track. Running mechanics were continuously monitored using inertial measurement units. Rectus femoris SmO2 and total hemoglobin (a measure of blood volume) were continuously monitored by near-infrared spectroscopy. One-class support vector machine (OCSVM) modeling was employed for subject-specific analysis of the kinematic data. Statistical analysis included principal component analysis, ANOVA, and correlation analysis. Mechanical deviations from typical stride characteristics increased as the running test progressed. Specifically, the percentage of outliers in the OCSVM model rose gradually from 2.2 ± 0.8% at the start to 43.6 ± 28.2% at the end (p < 0.001, mean ± SD throughout). SmO2 dropped from 74.3 ± 8.4% at baseline to 10.1 ± 6.8% at the end (p < 0.001). A moderate negative correlation (r = -0.61, p = 0.013) was found between the average SmO2 and the percentage of outlier strides during the last 15% of the run. During high-intensity running, alterations in running biomechanics may occur, linked to decreased quadriceps muscle oxygenation. These parameters highlight the potential of using running kinematics and muscle oxygenation in training to optimize performance and reduce injury risks. Our research contributes to understanding biomechanical and physiological responses to endurance running and emphasizes the importance of individualized monitoring.

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This study aimed to develop a low-fructose (<3 g/serve) carbohydrate (CHO) gel for athletes. Various prototypes with 30 g CHO/serve and differing water content (12 %, 21 %, 32 %, 39 % w/v) were created and evaluated for sensory attributes. The final gel contained 62.1 ± 0.2 g CHO/100 g with 0.17 % w/w fructose. Endurance athletes (n = 20) underwent a feeding-challenge protocol, ingesting 30 g gel every 20 min during 2 h of running (60 % V ˙ O2max), followed by a 1 h self-paced distance test. Blood glucose increased significantly from baseline (4.0 ± 0.9 vs. 6.6 ± 0.6 mmol/L, p < 0.001) and remained elevated after the distance test (4.9 ± 0.7 mmol/L, p < 0.05). Breath hydrogen levels increased (5 ± 4 ppm, p < 0.05) without substantial CHO malabsorption detected. Gastrointestinal symptoms (GIS) increased during exercise but were mild. The low-fructose CHO gel demonstrated good tolerance, promoting glucose availability without severe GIS or CHO malabsorption.

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Footwear has the potential to reduce soft-tissue vibrations (STV) but responses are highly subject-specific. Recent evidence shows that compressive garments minimizing STV have a beneficial effect on neuromuscular (NM) fatigue. The aim was to determine whether an individualized midsole hardness can minimize STV and NM fatigue during a half marathon. Twenty experienced runners were recruited for three visits: a familiarization session including the identification of midsole minimizing and maximizing STV amplitude (MIN and MAX, respectively), and two half marathon sessions at 95% of speed at the second ventilatory threshold. STV of the gastrocnemius medialis (GM) muscle, running kinetics, foot strike pattern, rating perceived exhaustion (RPE), and midsole liking were recorded every 3 km. NM fatigue was assessed on plantar flexors (PF) before (PRE) and after (POST) the half marathon. At POST, PF central and peripheral alterations and changes in contact time, step frequency, STV median frequency, and impact force frequency as well as foot strike pattern were found in both MIN and MAX. No significant differences in damping, STV main frequency, flight time, duty factor, and loading rate were observed between conditions whatever the time period. During the half marathon, STV amplitude of GM significantly increased over time for the MAX condition (+13.3%) only. Differences between MIN and MAX were identified for RPE and midsole liking. It could be hypothesized that, while significant, the effect of midsole hardness on STV is too low to substantially affect NM fatigue.

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PURPOSE: Delayed structural and functional recovery after a 20 km graded running race was analyzed with respect to the sex effect. METHODS: Thirteen female and 14 male recreational runners completed the race and three test sessions: one before (PRE) and two after, once on Day 1 or 2 (D1-2) and then on Day 3 or 4 (D3-4). Muscle damage was assessed indirectly using ultrasonography to quantify changes in cross-sectional area (CSA) of 10 lower-limb muscles. Delayed onset of muscle soreness (DOMS) was assessed for three muscle groups. Functional recovery was quantified by kinetic analysis of a squat jump (SJ) and a drop jump (DJ) test performed on a sledge ergometer. Linear mixed models were used to assess control group reproducibility and recovery patterns according to sex. RESULTS: Regardless of sex, DOMS peaked at D1-2 for all muscle groups and resolved at D3-4. CSA was increased in each muscle group until D3-4, especially in the semimembranosus muscle. A specific increase was found in the short head of the biceps femoris in women. Regardless of sex, SJ and DJ performances declined up to D3-4. Depending on the muscle, positive and/or negative correlations were found between structural and functional changes. Some of these were sex-specific. CONCLUSION: Structural and functional recovery was incomplete in both sexes up to D3-4, although DOMS had disappeared. More emphasis should be placed on hamstring muscle recovery. Highlighting the intermuscular compensations that can occur during multi-joint testing tasks, the structural-functional relationships were either positive or negative, muscle- and sex-dependent.

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A 36-year-old professional marathon runner reported sudden irregular palpitations occurring during competitions, with heart rates (HR) up to 230 bpm recorded on a sports HR monitor (HRM) over 4 years. These episodes subsided upon the cessation of exercise. Electrocardiograms, echocardiography, and cardiac magnetic resonance imaging results were borderline for athlete's heart. Because an electrophysiology study and standard exercise tests provoked no arrhythmia, doctors suspected Munchausen syndrome. Ultimately, an exercise test that simulated the physical effort of a competition provoked tachyarrhythmia consistent with the HRM readings. This case demonstrates the diagnostic difficulties related to exercise-induced arrhythmia and the diagnostic usefulness of sports HRMs.

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Our purpose is to move beyond the borders of the athlete-centered approach by examining the runners' environment interplay as a key factor for performance. Based on the ecological systems theory, the micro-level (intrapersonal, interpersonal, and training characteristics), meso-level (a direct association with athletes is not observed, but the environment plays an influence on the relationships built at the micro-level), and macro-level (contextual features that influence athletic systems) were theorized and contextualized as important factors for the expression of different outcomes, including performance and participation. We also conceptualized the microtime, mesotime, and macrotime as a constraint. Through this model, we aimed to provide applications and conclusions about how this conceptual model provides advances in the scientific research field. By understanding how environmental factors influence their performance, runners can make informed decisions about where and how to train and compete. Furthermore, by recognizing the role of culture and social context in shaping runners' experiences and outcomes, we can work toward creating a more equitable and supportive running culture for all.

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Neuroimaging studies have identified significant differences in brain structure, function, and connectivity between endurance runners and healthy controls. However, the topological organization of large-scale functional brain networks remains unexplored in endurance runners. Using resting-state functional magnetic resonance imaging data, this study examined the differences in the topological organization of functional networks between endurance runners (n = 22) and healthy controls (n = 20). Endurance runners had significantly higher clustering coefficients in the whole-brain functional network than healthy controls, but the two did not differ regarding the shortest path length or small-world index. Using network-based statistics, we identified one subnetwork in endurance runners with higher functional connectivity than healthy controls, and the mean functional connectivity of the subnetwork significantly correlated with the three aforementioned small-world parameters. In this subnetwork, the mean clustering coefficient of nodes associated with short-range connections was higher in endurance runners than in healthy controls, but the mean clustering coefficient of nodes associated with long-range connections did not differ between the two groups. In conclusion, using graph theoretical approaches, we revealed significant differences in the topological organization of the whole-brain functional network and functional connectivity between endurance runners and healthy controls. The relationship between these two features suggests that a more segregated network may arise from the optimization of the identified subnetwork in endurance runners. These findings are possibly the neural basis underlying the good performance of endurance runners in endurance running.

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We aimed to compare differences in performance and pacing variability indices between 5000 m heats and finals during major championships in men and women. Data with 100 m time resolution were used to compare overall pacing variability (standard deviation of 100 m section times, SD; and coefficient of variation, CV%) and short-term pacing variability (root mean square of successive differences between 100 m section times, RMSSD). The changes in performance and pacing indices differed between races and competitions. For instance, the men's final in Beijing 2008 was quicker than the heat (p < 0.01) while the CV% was reduced (p = 0.03) and RMSSD increased (p < 0.01). For women, the heats and the final exhibited a similar mean time in London 2017 (p = 0.33) but with CV% (p < 0.001) and RMSSD (p < 0.001) showing opposite trends. Individual analyses of men's and women's champions revealed highly individual variability metrics. The use of RMSSD can complement overall variability indices for better characterization of pacing stochasticity.

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Introduction: Extreme endurance events may result in numerous adverse metabolic, immunologic, and physiological perturbations that may diminish athletic performance and adversely affect the overall health status of an athlete, especially in the absence of sufficient recovery. A comprehensive understanding of the post-marathon recovering metabolome, may aid in the identification of new biomarkers associated with marathon-induced stress, recovery, and adaptation, which can facilitate the development of improved training and recovery programs and personalized monitoring of athletic health/recovery/performance. Nevertheless, an untargeted, multi-disciplinary elucidation of the complex underlying biochemical mechanisms involved in recovery after such an endurance event is yet to be demonstrated. Methods: This investigation employed an untargeted proton nuclear magnetic resonance metabolomics approach to characterize the post-marathon recovering metabolome by systematically comparing the pre-, immediately post, 24, and 48 h post-marathon serum metabolite profiles of 15 athletes. Results and Discussion: A total of 26 metabolites were identified to fluctuate significantly among post-marathon and recovery time points and were mainly attributed to the recovery of adenosine triphosphate, redox balance and glycogen stores, amino acid oxidation, changes to gut microbiota, and energy drink consumption during the post-marathon recovery phase. Additionally, metabolites associated with delayed-onset muscle soreness were observed; however, the mechanisms underlying this commonly reported phenomenon remain to be elucidated. Although complete metabolic recovery of the energy-producing pathways and fuel substrate stores was attained within the 48 h recovery period, several metabolites remained perturbed throughout the 48 h recovery period and/or fluctuated again following their initial recovery to pre-marathon-related levels.

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Success in long-distance running relies on multiple factors including oxygen utilisation and lactate metabolism, and genetic associations with athlete status suggest elite competitors are heritably predisposed to superior performance. The Gly allele of the PPARGC1A Gly482Ser rs8192678 polymorphism has been associated with endurance athlete status and favourable aerobic training adaptations. However, the association of this polymorphism with performance amongst long-distance runners remains unclear. Accordingly, this study investigated whether rs8192678 was associated with elite status and competitive performance of long-distance runners. Genomic DNA from 656 Caucasian participants including 288 long-distance runners (201 men, 87 women) and 368 non-athletes (285 men, 83 women) was analysed. Medians of the 10 best UK times (Top10) for 10 km, half-marathon and marathon races were calculated, with all included athletes having personal best (PB) performances within 20% of Top10 (this study's definition of "elite"). Genotype and allele frequencies were compared between athletes and non-athletes, and athlete PB compared between genotypes. There were no differences in genotype frequency between athletes and non-athletes, but athlete Ser allele carriers were 2.5% faster than Gly/Gly homozygotes (p = 0.030). This study demonstrates that performance differences between elite long-distance runners are associated with rs8192678 genotype, with the Ser allele appearing to enhance performance.

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Aim: The research aimed to investigate the effect of endurance running and T. Brumale extract on α-Syn and HSF1 in the brain and serum of healthy and diabetic rats. Methods: A total of 40 Wistar rats were randomly divided into eight groups: Control (C), Exercise (E), Control-Tuber (T), Exercise-Tuber (ET), Control-Diabetes (D), Exercise-Diabetes (ED), Control-Diabetes-Tuber (CDT), and Exercise-Diabetes-Tuber (EDT). The endurance running was carried out five times per week for five weeks. The hippocampus and the serum α-Syn and HSF1 were measured using an enzyme-linked immunosorbent assay method. Results: The brain α-Syn levels were higher in diabetic groups than in the healthy groups, but insignificantly (P ≤ 0.05). The brain α-Syn level significantly increased in the EDT group compared to the T group (P ≤ 0.05). The serum level of α-Syn in the ED group was significantly higher than in the E and D groups (P ≤ 0.05). The brain HSF1 level was significantly higher in the ED group compared to the D group (P ≤ 0.05). The gene expression of hsf1 was significantly reduced in the E group compared to the other groups and the EDT group compared to ED and CDT groups (P ≤ 0.05). Furthermore, the serum HSF1 level significantly increased in the ED group compared to the D group (P ≤ 0.05). Conclusion: The results of this study suggest that progressive endurance running may improve neuroprotective conditions in diabetic patients by increasing HSF1 in the brain.

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ABSTRACTThis study aimed to clarify the contribution of L-menthol administration to endurande exercise capacity. Thirteen male runners (age, 35.8 ± 7.8 years; peak oxygen uptake, 62.7 ± 6.8 mL kg-1 min-1) ran on treadmills at fixed intensities of their anaerobic thresholds to exhaustion. All participants underwent three trials-water ingestion (W-IG), L-menthol mouth rinsing (M-MR), and L-menthol ingestion (M-IG)- in a random order every 5 min while running. Breathing comfort (BC) was measured immediately after fluid intake. Dyspnea threshold against external inspiratory resistance was examined before and after the running test. The running time with M-IG (1683.9 ± 520.3 s) was longer than that with W-IG (1410.2 ± 465.9 s, effect size [ES] = 0.55). BC with M-IG (2.00 ± 0.74) was higher than that with W-IG (0.42 ± 0.79) at exhaustion (ES > 2.00). The dyspnea threshold after running decreased to 19.2 ± 7.6 cm H2O L-1 s-1 with W-IG, whereas that with M-MR (26.2 ± 6.5 cm H2O L-1 s-1) and M-IG (29.2 ± 2.8 cm H2O L-1 s-1) remained high (p for interaction < 0.001). M-IG facilitated BC during running, improved endurance capacity, and prevented decreases in the dyspnea threshold against external inspiratory resistance after exhaustive running.HighlightsL-menthol ingestion facilitated breathing comfort during high intensity endurance running and improved exhaustive endurance running capacity.Even after exhaustion, L-menthol solution relieved dyspnea sensitivity against external inspiratory resistance.L-menthol ingestion might help athletes improve their endurance running capacity.

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BACKGROUND: Several phenomena may point to potentially detrimental cardiac effects of endurance exercise, such as elevated circulating cardiac troponin levels and reductions in systolic and diastolic function directly after marathon completion. Furthermore, while myocardial abnormalities have been reported in patients who recovered from COVID-19, the cardiac impact of extensive endurance exercise in individuals who recovered from COVID-19 remains unknown. We therefore aim to investigate (potentially detrimental) cardiac effects of first-time marathon training and participation, including a subset of participants who recovered from COVID-19, in apparently healthy middle-aged men. STUDY DESIGN: This exploratory prospective cohort study investigates cardiac effects of first-time marathon running in 24 middle-aged (35-50 years) healthy men. Primary outcomes are cardiac morphological changes from pre-training up to 1 month after marathon completion, measured with magnetic resonance imaging (MRI) at 4 time points: 1) baseline (4 months before the marathon), 2) pre-marathon (2 weeks before the marathon), 3) post-marathon (< 24 h post-marathon), and 4) recovery (4 weeks after the marathon). Secondary parameters include other cardiac or non-cardiac changes: 1) quantitative MRI myocardial mapping, including mean diffusivity and extracellular volume fraction, 2) echocardiographic morphology and function changes, 3) VO2max, 4) electrocardiogram changes, and 5) levels of cardiac biomarkers. DISCUSSION: This study will contribute to our understanding of cardiac adaptations and maladaptations to first-time marathon running in middle-aged men, and the interaction between extreme endurance exercise and potential detrimental cardiac effects, also in the context of COVID-19. Results will inform on future research directions while providing new clinical insights for health professionals involved in athlete care.

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The scientific literature lacks consensus on classification of middle- and long-distance runners. This creates situations where the sample studied may not represent the target population and could produce misleading conclusions. Thus, we present an approach for a data-driven classification of middle- and long-distance runners according to their competition results. The best annual results of middle- and long-distance track runners participating at major (Olympics, World and European Championships) and national championships (Denmark, Sweden, Finland, Norway) were gathered for the 2012-2018 period. Overall, 1920 men's and 1808 women's performance results were gathered. The results were grouped accordingly. Quadratic discriminant analysis was applied to define the limits between the groups. Three basic categories could be proposed for classification: world class, international and national. Classification provides a realistic overview of performance standards and the number of athletes for different categories in middle- and long-distance track running in real-world settings. The performance-based classification provides data-driven and unified criteria for reporting standards on athletes' proficiency levels. It allows for more consistent reporting practices on the target population in research. In addition to scientific research, the classification could also be employed for a variety of practical purposes.

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Nowadays, the growing popularity of distance running has been accompanied by the increasing prevalence of vegan and vegetarian diets, especially among endurance athletes. The present study aimed to examine the association between diet type and dietary intake of distance runners competing at distances longer than 10 km. From a total of 317 participants, 211 endurance runners (57% females) were considered the final sample after applying the exclusion criteria. Runners were assigned to three groups based on the self-reported diet types: 95 omnivores, 40 vegetarians, and 76 vegans. Data collection was conducted using an online survey with questions about sociodemographic information, dietary intake, and dietary-associated motives. A comprehensive food frequency questionnaire with 53 food groups (categorized in 14 basic-plus three umbrella-food clusters) was used to assess dietary intake. Vegan runners had a higher intake of "beans and seeds", "fruit and vegetables", and "dairy alternatives", as well as lower intakes of "oils" than other two groups. Vegetarian runners had a lower intake of "dairy products" and "eggs" than omnivores. A greater intake of "alcohol" and a lower intake of "meat alternatives" was observed in omnivorous runners compared to vegans and vegetarians. Despite the existence of a tendency toward the consumption of health-related food clusters by vegan runners, further investigations are needed to verify the predominance of vegans in health-oriented dietary patterns.

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Sport and exercise can be boring. In the general population, thinking of sports as boring has been linked to exercising less. However, less is known about the role of boredom in people who participate in ultra-endurance competitions: Do these athletes also associate their sports with boredom, and does boredom pose a self-regulatory challenge that predicts if they encounter a crisis during an ultra-endurance competition? Here, we investigate these questions with a sample of N = 113 (n = 34 female) competitors of a 24 h hour running competition, aged M = 37.6 ± 13.8 years. In this study, n = 23 very extreme athletes competed as single starters or in a relay team of 2, and n = 84 less extreme athletes competed in relay teams of 4 or 6. Before the run, athletes completed self-report measures on sport-specific trait boredom, as well as the degree to which they expected boredom, pain, effort, and willpower to constitute self-regulatory challenges they would have to cope with. After the run, athletes reported the degree to which they actually had to deal with these self-regulatory challenges and if they had faced an action crisis during the competition. Analyses revealed that very extreme athletes displayed a significantly lower sport-specific trait boredom than less extreme athletes (p = 0.024, d=-0.48). With respect to self-regulatory challenges, willpower, pain, and effort were expected and reported at a much higher rate than boredom. However, only boredom was as a significant predictor of experiencing a crisis during the competition (odds ratio = 12.5, p = 0.02). Our results show that boredom also matters for highly active athletes. The fact that the experience of boredom-and not more prototypical competition-induced challenges, such as pain or effort-were linked to having an action crisis highlights the relevance of incorporating boredom into the preparation for a race and to the performance management during competition.

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The acute and delayed phases of the functional recovery pattern after running exercise have been studied mainly in men. However, it seems that women are less fatigable and/or recover faster than men, at least when tested in isometric condition. After a 20 km graded running race, the influence of sex on the delayed phase of recovery at 2-4 days was studied using a horizontal ballistic force-velocity test. Nine female and height male recreational runners performed maximal concentric push-offs at four load levels a week before the race (PRE), 2 and 4 days (D2 and D4) later. Ground reaction forces and surface electromyographic (EMG) activity from 8 major lower limb muscles were recorded. For each session, the mechanical force-velocity-power profile (i.e. theoretical maximal values of force ( F ¯ 0), velocity ( V ¯ 0), and power ( P ¯ max)) was computed. Mean EMG activity of each recorded muscle and muscle synergies (three for both men and women) were extracted. Independently of the testing sessions, men and women differed regarding the solicitation of the bi-articular thigh muscles (medial hamstring muscles and rectus femoris). At mid-push-off, female made use of more evenly distributed lower limb muscle activities than men. No fatigue effect was found for both sexes when looking at the mean ground reaction forces. However, the force-velocity profile varied by sex throughout the recovery: only men showed a decrease of both V ¯ 0 (p < 0.05) and P ¯ max (p < 0.01) at D2 compared to PRE. Vastus medialis activity was reduced for both men and women up to D4, but only male synergies were impacted at D2: the center of activity of the first and second synergies was reached later. This study suggests that women could recover earlier in a dynamic multi-joint task and that sex-specific organization of muscle synergies may have contributed to their different recovery times after such a race.

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Dietary manipulation with high-protein or high-carbohydrate content are frequently employed during elite athletic training, aiming to enhance athletic performance. Such interventions are likely to impact upon gut microbial content. This study explored the impact of acute high-protein or high-carbohydrate diets on measured endurance performance and associated gut microbial community changes. In a cohort of well-matched, highly trained endurance runners, we measured performance outcomes, as well as gut bacterial, viral (FVP), and bacteriophage (IV) communities in a double-blind, repeated-measures design randomized control trial (RCT) to explore the impact of dietary intervention with either high-protein or high-carbohydrate content. High-dietary carbohydrate improved time-trial performance by +6.5% (P < 0.03) and was associated with expansion of Ruminococcus and Collinsella bacterial spp. Conversely, high dietary protein led to a reduction in performance by -23.3% (P = 0.001). This impact was accompanied by significantly reduced diversity (IV: P = 0.04) and altered composition (IV and FVP: P = 0.02) of the gut phageome as well as enrichment of both free and inducible Sk1virus and Leuconostoc bacterial populations. Greatest performance during dietary modification was observed in participants with less substantial shifts in community composition. Gut microbial stability during acute dietary periodization was associated with greater athletic performance in this highly trained, well-matched cohort. Athletes, and those supporting them, should be mindful of the potential consequences of dietary manipulation on gut flora and implications for performance, and periodize appropriately. IMPORTANCE Dietary periodization is employed to improve endurance exercise performance but may impact on gut microbial communities. Bacteriophage are implicated in bacterial cell homeostasis and have been identified as biomarkers of disequilibrium in the gut ecosystem possibly brought about through dietary periodization. We find high-carbohydrate and high-protein diets to have opposing impacts on endurance performance in highly trained athlete populations. Reduced performance is linked with disturbance of microbial stasis in the gut. We demonstrate bacteriophage communities are the most sensitive component of the gut microbiota to increased gut stress following dietary manipulation. Athletes undertaking dietary periodization should be aware of potential negative impacts of drastic changes to dietary composition on gut microbial stasis and, in turn, endurance performance.

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Although the marathon race has been democratized, it remains complex due to the famous "hitting the wall" phenomenon after the 25th km. To characterize this "wall" from a physiological and Rate of Perceived Exertion (RPE) perspective in recreational marathon runners, we report first continuous breath-by-breath gas exchange measurements during an actual marathon race. In order to test the hypothesis that RPE could be a candidate for controlling the marathon pace, this study examined the relationship between RPE and the physiological variables time course throughout a marathon. Only the respiratory frequency and heart rate increased progressively during the race in all the runners, while the oxygen uptake and ventilatory rate followed different kinetics according the individuals. However, the indexation of the physiological parameters and speed by RPE showed the same decreased tendency for all the runners. In conclusion, these results suggest that running a marathon must be self-paced with the RPE.

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AIM: The specificity of muscle-tendon and foot architecture of elite Kenyan middle- and long-distance runners has been found to contribute to their superior running performance. To investigate the respective influence of genetic endowment and training on these characteristics, we compared leg and foot segmental lengths as well as muscle-tendon architecture of Kenyans and Japanese males (i) from infancy to adulthood and (ii) non-athletes versus elite runners. METHODS: The 676 participants were divided according to their nationality (Kenyans and Japanese), age (nine different age groups for non-athletes) and performance level in middle- and long-distance races (non-athlete, non-elite and elite adult runners). Shank and Achilles tendon (AT) lengths, medial gastrocnemius (MG) fascicle length, pennation angle and muscle thickness, AT moment arm (MAAT ), and foot lever ratio were measured. RESULTS: Above 8 years old, Kenyans had a longer shank and AT, shorter fascicle, greater pennation angle, thinner MG muscle as well as longer MAAT , with lower foot lever ratio than age-matched Japanese. Among adults of different performance levels and independently of the performance level, Kenyans had longer shank, AT and MAAT , thinner MG muscle thickness, and lower foot lever ratio than Japanese. The decrease in MG fascicle length and increase pennation angle observed for the adult Japanese with the increase in performance level resulted in a lack of difference between elite Kenyans and Japanese. CONCLUSION: The specificity of muscle-tendon and foot architecture of elite Kenyan runners could result from genetic endowment and contribute to the dominance of Kenyans in middle- and long-distance races.

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