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The Endurance Performance Nerd Alert.
Learn to train smart, run fast, and be strong with Thomas Solomon PhD 
January 2025
This page contains the latest research studies on exercise science and sports nutrition.
Use them to help level up your running performance or coaching practice.
The studies are divided into sub-topics:
training methods,
sports supplements,
athlete health (inc. mental health),
injuries and rehab, and
female athlete physiology,
plus my beer of the month to wash it all down.
I’ve provided a deeper insight into my favourite studies of the month. For everything else, you can click on the study title to plunge deep into the full paper and evaluate the authors’ findings. In doing so, aim to be skeptical, not cynical.
My favourite papers this month.
Can transcranial direct current stimulation (tDCS) over the motor cortex increase endurance running performance? a randomized crossover-controlled trial. Martens et al. (2024 ) PLoS One. (click the title to access the full article) 
What type of study is in this article?
- This study is a
Randomised controlled trialThe “gold standard” approach for determining whether a treatment has a causal effect on an outcome of interest. In such a study, a sample of people representing the population of interest is randomised to receive the treatment or a no-treatment placebo (control), and the outcome of interest is measured before and after the exposure to treatment/control.
What is the authors’ hypothesis or research question?
- The authors' research question was whether transcranial direct current stimulation (tDCS) applied over the motor cortex improves endurance running performance in trained athletes.
What did the authors do to test the hypothesis or answer the research question?
- The authors used a randomized, sham-controlled, double-blind crossover trial design and recruited 45 healthy male runners aged 18-32 years (mean VO2max: 46.6 mL/min/kg).
- Participants underwent two treadmill time-to-exhaustion (TTE) tests at 90% of maximal aerobic speed (MAS) following 20 minutes of either active or sham tDCS. Secondary analyses included a control session without tDCS. Physiological measures (e.g., VO2, blood lactate, heart rate) and perceived exertion were recorded every five minutes.
- The double-blind design ensured neither participants nor investigators were aware of the tDCS condition.
- Paired t-tests and ANOVAs were used to compare outcomes between conditions.
What did the authors find?
- For the primary outcome, there was no significant difference in TTE between active tDCS (12.2 minutes) and sham (12.5 minutes; p = 0.96).
- For the secondary outcomes, there were no significant differences in physiological parameters (e.g., VO2, heart rate, lactate levels) or perceived exertion between conditions. Blood lactate levels showed a non-significant trend of being higher following active tDCS. There were no significant differences in TTE among subgroups (amateur vs. competitive runners) or in participants completing the additional control session.
- A trend suggesting a relationship between baseline VO2max and TTE changes following tDCS was observed but not statistically significant (p = 0.058).
- The authors concluded that tDCS over the motor cortex does not improve endurance running performance in trained athletes.
What are the strengths of the study?
- Robust double-blind and sham-controlled design.
- Large sample size compared to previous studies.
- Comprehensive measurement of physiological and psychological parameters.
What are the weaknesses of the study?
- Limited to a single tDCS session; cumulative effects were not explored.
- Results from the additional control session were based on a smaller subsample (n = 21).
- The specific tDCS protocol (cephalic montage) may not be optimal for endurance performance.
- Limited generalizability to untrained or elite athletes due to the sample characteristics.
How was the study funded and are there any conflicts of interest that may influence the findings?
- The study received no specific funding, and the authors declared no conflicts of interest.
Are the findings useful in application to training and/or coaching practice?
- Yes → The findings suggest that tDCS is not a viable ergogenic aid for enhancing endurance running performance, and it does not currently represent a doping threat in sports. However, while the study followed rigorous scientific protocols and addressed a novel question with a robust methodology, the lack of exploration into cumulative tDCS effects and limited subgroup analyses leave some gaps for future research.
What is my Rating of Perceived scientific Enjoyment?
-
RP(s)E = 8 out of 10.
International society of sports nutrition position stand: β-hydroxy-β-methylbutyrate (HMB). Rathmacher et al. (2025 ) J Int Soc Sports Nutr. (click the title to access the full article)
What type of study is in this article?
- This study is a
Position standA position stand is a detailed policy recommendation published by a society that describes a course of action for practice.
What is the authors’ hypothesis or research question?
- The authors’ research question was to evaluate and summarize the scientific literature on the effects, safety, and applications of β-Hydroxy-β-Methylbutyrate (HMB) in human health and sports performance.
What did the authors do to test the hypothesis or answer the research question?
- This study synthesized findings from a scoping review of over 750 articles, including experimental and clinical studies. The literature review covered populations of varying age, sex, and training status, examining outcomes like muscle mass, body composition, and functional recovery.
What did the authors find?
- Safety: HMB (in its calcium and free acid forms) is safe for chronic use (up to one year) and does not adversely affect glucose tolerance or insulin sensitivity in humans.
- Mechanism of Action: HMB enhances muscle protein synthesis and reduces muscle protein breakdown through pathways involving mTORC1 activation and the suppression of the ubiquitin-proteasome pathway.
- Muscle Damage and Recovery: HMB supplementation reduces muscle damage markers (e.g., creatine kinase) and improves recovery post-exercise, particularly in untrained or moderately trained individuals.
- Body Composition: HMB improves lean mass and reduces fat mass, particularly in conjunction with robust resistance training programs.
- Performance Effects: While HMB benefits untrained individuals in strength and aerobic performance, its effects in trained athletes are inconsistent and may depend on study duration (>6 weeks for notable benefits).
- Special Populations: HMB shows promise for combating muscle atrophy in ageing or sedentary populations and during periods of inactivity.
- The authors concluded that HMB is a safe, effective supplement for improving muscle health, body composition, and recovery, especially when combined with structured exercise programs.
What are the strengths of the study?
- Comprehensive literature review covering a wide range of populations and outcomes.
- Clear presentation of HMB’s safety profile and mechanisms of action.
- Detailed exploration of HMB’s applications across different training regimens and populations.
What are the limitations in this field of research?
- Limited data on the direct comparison between HMB forms (calcium vs. free acid).
- Lack of consistent findings in trained athletes and specific populations like women.
- Some studies included in the review were underpowered or lacked robust dietary controls.
How was the study funded and are there any conflicts of interest that may influence the findings?
- Funding and conflicts of interest were not explicitly detailed in the article.
Are the findings useful in application to training and/or coaching practice?
- Yes → The findings are useful as HMB supplementation may enhance recovery and muscle health, which are crucial for endurance training and performance. The study used a comprehensive review methodology and made practical recommendations; however, there is limited heterogeneity and reporting on specific population groups.
What is my Rating of Perceived scientific Enjoyment?
-
RP(s)E = 8 out of 10.
Low energy availability surrogates are associated with Relative Energy Deficiency in Sport outcomes in male athletes. Holtzman et al. (2024 ) Br J Sports Med. (click the title to access the full article)
What type of study is in this article?
- This study is an
Observational studyObservational studies can have different types of study designs, including cross-sectional, case-control, retrospective cohort, and prospective cohort studies. Typically, an observational study examines a specific cohort of people to characterise them and learn about them; there are no intentional interventions (i.e., people are not prescribed a diet, drug, or exercise). Sometimes the cohort of people is followed over time to determine whether there is a relationship between the natural exposure to a specific variable (e.g. exposure to dietary saturated fat intake) and a specific outcome of interest (e.g. cardiovascular disease).
What is the authors’ hypothesis or research question?
- The authors hypothesised that Relative Energy Deficiency in Sport (REDs) outcomes would be more frequent in male athletes with indicators of low energy availability (EA) compared to those with adequate EA.
What did the authors do to test the hypothesis or answer the research question?
- The study included 813 male athletes aged 15–30 years presenting to sports medicine clinics at Boston Children’s Hospital and Stanford Medicine.
- Participants completed a survey assessing energy availability (EA) and health/performance indicators. Low EA was identified using self-reported eating disorders, the Eating Disorder Examination Questionnaire (EDE-Q), or the Eating Disorder Screen for Primary Care (ESP). Health and performance outcomes were compared between groups.
- Data were collected between November 2018–January 2023 (Boston) and September 2021–December 2022 (Stanford).
What did the authors find?
- Health Outcomes: Athletes with low EA showed a higher prevalence of cardiovascular dysfunction (OR 2.87, p < 0.001), psychological illness (OR 3.23, p < 0.001), and metabolic dysfunction (not statistically significant), but a reduced likelihood of gonadal dysfunction (OR 0.49, p = 0.006).
- Performance Outcomes: Low EA associated with a reduced endurance performance (OR 2.26, p = 0.021), decreased training response (OR 2.64, p = 0.003), and increased irritability and depression (not statistically significant).
- The authors concluded that low EA surrogates are linked to multiple adverse health outcomes and performance decrements in male athletes.
What are the strengths of the study?
- Large, diverse cohort from multiple sports and ability levels.
- Use of established screening tools (EDE-Q and ESP) for identifying low EA.
- Comprehensive assessment of both health and performance indicators.
What are the weaknesses of the study?
- Cross-sectional design limits causal inferences.
- Self-reported data introduces potential recall bias.
- Limited inclusion of racial and ethnic diversity (84.4% White).
- Lack of validated low EA thresholds specific to male athletes.
- No control group of healthy athletes not requiring medical care.
How was the study funded and are there any conflicts of interest that may influence the findings?
- No funding information was provided and no conflicts of interest were disclosed.
Are the findings useful in application to training and/or coaching practice?
- Partially → The findings emphasize the importance of screening male athletes for low EA regardless of size, experience, or sport. This is crucial for early identification and management of REDs to optimize health and performance outcomes in endurance coaching and athlete management. The paper highlights the need for addressing a critical gap in REDs research for male athletes, but the lack of a control group, the reliance on self-reported measures, and the lack of diversity in the participant pool limit the utility of the findings.
What is my Rating of Perceived scientific Enjoyment?
-
RP(s)E = 7 out of 10.
Using Self-Reported Training Characteristics to Better Understand Who Is More Likely to Sustain Running-Related Injuries Than Others: The Garmin-RUNSAFE Running Health Study. Abrahamson et al. (2025 ) Scand J Med Sci Sports. (click the title to access the full article)
What type of study is in this article?
- This study is an
observational study (a prospective cohort study)Observational studies can have different types of study designs, including cross-sectional, case-control, retrospective cohort, and prospective cohort studies. Typically, an observational study examines a specific cohort of people to characterise them and learn about them; there are no intentional interventions (i.e., people are not prescribed a diet, drug, or exercise). Sometimes the cohort of people is followed over time to determine whether there is a relationship between the natural exposure to a specific variable (e.g. exposure to dietary saturated fat intake) and a specific outcome of interest (e.g. cardiovascular disease).
What is the authors’ hypothesis or research question?
- The authors hypothesized that runners with shorter running experience, lower and higher running frequencies and distances, and not using structured training programs are more likely to sustain a running-related injury (RRI).
What did the authors do to test the hypothesis or answer the research question?
- The authors used a prospective cohort study of 7,391 adult runners from various countries, with 77.6% male participants.
- Participants were at least 18 years old, used Garmin devices, uploaded training data, and completed weekly questionnaires in English.
- Self-reported baseline data (e.g., running experience, frequency, distance, program use) and weekly injury statuses were collected for 18 months.
- The main outcome was Running-Related Injuries (RRIs), categorized dichotomously as injured or uninjured.
What did the authors find?
- Overall Injury Incidence: The cumulative injury proportion at 1,000 km of running was 57.8%.
- Runners with less than 1 year or more than 40 years of experience had the highest RRI risk. Running 7+ times/week showed the lowest RRIs (24.7% cumulative incidence). Longer weekly running distances (e.g., more than 105 km) were associated with fewer RRIs (Cumulative Risk Difference −31.6%, 95% CI: −40.1, −23.1). Following a structured program slightly reduced injury risk.
- Kaplan-Meier curves highlighted trends across running experience, frequency, distance, and program use.
- The authors concluded that runners with fewer years of experience, lower weekly frequency or distance, and those not following structured programs are at higher risk for RRIs.
What are the strengths of the study?
- Large and diverse sample size.
- Extended follow-up period (18 months).
- Use of robust statistical methods.
- Comprehensive evaluation of training-related variables.
What are the weaknesses of the study?
- Self-reported injuries may introduce recall bias.
- Overrepresentation of male and Western participants limits generalizability.
- Use of ordinal scales for some data may reduce precision.
- Lack of injury history data.
How was the study funded and are there any conflicts of interest that may influence the findings?
- No specific funding was reported but authors declared that they had no conflicts of interest.
Are the findings useful in application to training and/or coaching practice?
- Partially → Findings are applicable for identifying risk factors in endurance training. However, while the study is well-designed and statistically robust, limitations in generalizability and potential bias slightly detract from its overall impact. Furthermore, this type of data identifies risk factors but cannot be used to develop tailored injury-prevention strategies.
What is my Rating of Perceived scientific Enjoyment?
-
RP(s)E = 7 out of 10.
All the other interesting papers I found this month are below.
You can dig in and evaluate the authors’ findings by clicking on the titles to access the full papers.
Learn to critically evaluate each paper using the framework I used for my favourite papers.
General training methods.
Can transcranial direct current stimulation (tDCS) over the motor cortex increase endurance running performance? a randomized crossover-controlled trial. Martens et al. (2024 ) PLoS One. Sports supplements.
International society of sports nutrition position stand: β-hydroxy-β-methylbutyrate (HMB). Rathmacher et al. (2025 ) J Int Soc Sports Nutr. Athlete health (including mental health).
Low energy availability surrogates are associated with Relative Energy Deficiency in Sport outcomes in male athletes. Holtzman et al. (2024 ) Br J Sports Med. Injury and rehab.
Using Self-Reported Training Characteristics to Better Understand Who Is More Likely to Sustain Running-Related Injuries Than Others: The Garmin-RUNSAFE Running Health Study. Abrahamson et al. (2025 ) Scand J Med Sci Sports. Runners with a high body mass index and previous running-related problems is a high-risk population for sustaining a new running-related injury: A 18-month cohort study. Lindman et al. (2025 ) Eur J Sport Sci. Female athlete physiology and sex differences.
Attentional, anticipatory and spatial cognition fluctuate throughout the menstrual cycle: Potential implications for female sport. Ronca et al. (2025 ) Neuropsychologia.
And, to help you wash down the latest evidence, here's a snifter from my recent indulgence...
My beer of the month.
Gilda.
Brewed by Basqueland Brewing (Hernani, Spain).
New England IPA.
6.1% ABV.
What a very interesting beer this is. There’s no description indicating that the initial taste is infused with olives and mild chillis, but that it is! However, perhaps that taste sensation was implanted in my mind by the image of said veg on the can. As I said, how very interesting.
RP(be)E(r)(Rating of Perceived beer Enjoyment)
7 out of 10
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Disclaimer: I occasionally mention brands and products but it is important to know that I am not affiliated with, sponsored by, an ambassador for, or receiving advertisement royalties from any brands. I have conducted biomedical research for which I have received research money from publicly-funded national research councils and medical charities, and also from private companies, including Novo Nordisk Foundation, AstraZeneca, Amylin, A.P. Møller Foundation, and Augustinus Foundation. I’ve also consulted for Boost Treadmills and Gu Energy on their research and innovation grant applications and I’ve provided research and science writing services for Examine — some of my articles contain links to information provided by Examine but I do not receive any royalties or bonuses from those links. These companies had no control over the research design, data analysis, or publication outcomes of my work. Any recommendations I make are, and always will be, based on my own views and opinions shaped by the evidence available. My recommendations have never and will never be influenced by affiliations, sponsorships, advertisement royalties, etc. The information I provide is not medical advice. Before making any changes to your habits of daily living based on any information I provide, always ensure it is safe for you to do so and consult your doctor if you are unsure.