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The Endurance Performance Nerd Alert.
Learn to train smart, run fast, and be strong with Thomas Solomon PhD 
April 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 nutrition and hydration,
recovery (inc. sleep), and
female athlete physiology,
plus my beer of the month to wash it all down.
I’ve also provided a deeper insight into my four 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.
Isoenergetic Pre-Exercise Meals Varying in Carbohydrate Similarly Affect Resistance Training Volume Performance Compared to Placebo: A Crossover Trial. King et al. (2025) Eur J Sport Sci. (click the title to access the full article)
What type of study is this?
- 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. with crossover.Crossover means that all subjects completed all interventions (control and treatment) usually with a wash-out period in between.
What is the authors’ hypothesis or research question?
- The authors hypothesised that ingesting a high-carbohydrate pre‐exercise meal (HCHO) would improve resistance training volume performance compared to both a low-carbohydrate meal (LCHO) and a low‐calorie placebo (PLA), and that the low-carbohydrate meal would improve performance compared to the placebo only.
What did the authors do to test the hypothesis or answer the research question?
- The investigation recruited 16 resistance-trained participants (13 males and 3 females) who completed a series of familiarisation sessions, a 1‐repetition maximum testing session, and three experimental sessions. In a randomised and double-blind manner, each participant consumed one of three pre‐exercise liquid breakfasts—either high carbohydrate (1.2 g/kg body mass), low carbohydrate (0.3 g/kg body mass), or a nearly calorie-free placebo—two hours before performing a high-volume resistance training session. The training session consisted of three sets of back squats, bench press, prone row, and shoulder press at 80% of 1RM, with repetitions performed to fatigue. Various outcomes were measured, including total repetitions completed, subjective appetite ratings, and metabolic markers such as blood glucose and lactate.
What did the authors find?
- There was no significant difference in the total number of repetitions completed per session or per exercise between the three pre-exercise meal conditions. While participants reported greater satiety and fullness after the high- and low-carbohydrate meals compared to the placebo, subjective hunger ratings did not differ significantly. Metabolic analysis showed that blood glucose levels were significantly higher 30 and 60 minutes after breakfast in the high-carbohydrate condition compared to the other groups, although post-exercise glucose levels were similar across conditions. Blood lactate levels increased during and after the training session, with no differences between the meal conditions. Overall, the expected ergogenic effect of a higher carbohydrate dose on upper-body dominant resistance training performance was not observed.
- The authors concluded that for primarily upper-body resistance training volume performance, a higher or lower carbohydrate pre-exercise meal produces comparable results to a low-calorie placebo, suggesting that the perceived energy intake rather than the macronutrient composition may be sufficient to maintain performance.
What are the strengths of the study?
- The study has a rigorous randomised, double-blind crossover design with appropriate counterbalancing and concealed allocation. The inclusion and exclusion criteria were clearly defined, and the sample size was determined using power calculations. The study provided detailed descriptions of the exercise protocols, standardized pretrial nutritional guidelines, and thorough statistical reporting, including P-values, effect sizes, and the use of linear mixed models. Additionally, the blinding procedures and the use of taste- and texture-matched meals helped minimize bias, thereby enhancing the internal validity of the study.
What are the weaknesses of the study?
- Some limitations include the relatively small sample size, particularly with only three female participants, which may affect the generalizability of the findings. The trial was not prospectively registered, which could have further strengthened the methodological rigor. Moreover, the study did not measure muscle glycogen levels directly, limiting insight into the metabolic mechanisms underlying the observed performance outcomes. The possibility that habitual pre-exercise supplementation by half of the participants may have masked potential effects of the pre-exercise meal is also a noted weakness.
How was the study funded, and are there any conflicts of interest that may influence the findings?
- The authors received no specific funding for this work. They also declared that there were no conflicts of interest.
How do the findings apply to training/coaching practice?
- The findings suggest that, at least for upper-body dominant resistance training sessions, the macronutrient composition of a pre-exercise meal may not critically influence performance when total caloric intake is matched. This could be useful for endurance coaches and athletes by indicating that the perception of having ingested energy may be as important as the actual carbohydrate dose. However, coaches should be cautious in generalizing these results to lower-body training or different exercise protocols where carbohydrate intake might play a more pronounced role.
What is my Rating of Perceived scientific Enjoyment?
-
RP(s)E = 8 out of 10. My Rating of Perceived Scientific Enjoyment was high because the paper utilized a robust randomized, double-blind design with a clearly defined protocol and thorough statistical analysis. The strengths include detailed methodological descriptions, proper counterbalancing, and the use of validated measures for both performance and metabolic markers. Although the study was not prospectively registered, these limitations were relatively minor in the context of the study’s overall rigor.
Important: Don’t make any major changes to your habits based on the findings of one study, especially if the study is small (e.g., less than 30 participants in a randomised controlled trial or less than 5 studies in a meta-analysis) or poor quality (e.g., high risk of bias or low certainty of evidence in a meta-analysis). What do other trials in this field show? (Follow the link to explore those trials.) Do they confirm the findings of this study or have mixed outcomes? Is there a high-quality systematic review and meta-analysis evaluating the entirety of the evidence in this field? (Follow the link to explore those reviews.) If so, what does the analysis show? What is the risk of bias or certainty of evidence of the included studies?
Exploring the impact of high altitude on physiological parameters and training characteristics of endurance runners. Codella et al. (2025 ) J Sports Med Phys Fitness. (click the title to access the full article)
What type of study is this?
- This study is an editorial.An editorial is a summary of an important or interesting paper or a summary of a body of work published in an issue of a journal.
What is the authors’ hypothesis or research question?
- The authors aimed to provide an overview of the benefits and challenges of altitude training, emphasising how high-altitude environments can affect the physiological responses and training characteristics of endurance runners.
What did the authors do to test the hypothesis or answer the research question?
- Because this article is an editorial, it does not describe any original data collection or specific participant recruitment. Instead, it draws upon and discusses existing scientific studies of altitude training. It mentions topics such as the “live high, train low” method, red blood cell and erythropoietin responses, possible reductions in training volume and intensity due to hypoxia, and strategies to mitigate risks like altitude sickness.
What did the authors find?
- The editorial outlines that altitude training can increase red blood cell mass and improve oxygen-carrying capacity, potentially enhancing endurance performance upon returning to lower elevations. It also describes that athletes may experience challenges such as altitude sickness and a reduction in training intensity due to lower oxygen availability. No original data or effect sizes (e.g., mean differences, confidence intervals, or P-values) are reported, as the article relies on summaries of previously published literature. Overall, it highlights individual variability in adaptation, acknowledging that some athletes may see substantial gains, while others do not adapt as well.
- The authors concluded that altitude training remains a powerful and potentially beneficial strategy for endurance athletes seeking performance improvements, but it must be carefully planned and managed to avoid risks and maximise gains.
What are the strengths of the study?
- A major strength is that the editorial draws on multiple prior studies to offer a concise synthesis of current knowledge regarding altitude training for endurance athletes. It describes both the physiological basis for how altitude training might improve performance and practical considerations such as acclimatisation periods. By referencing numerous publications, it provides a broad view of the benefits and complexities, which can guide readers toward further reading.
What are the weaknesses of the study?
- As an editorial, it does not present new experimental data or a formal analysis of existing data, thereby limiting detailed evidence on within-group or between-group comparisons. Readers seeking specific measurements (e.g., effect sizes, standard deviations, or exact P-values) will not find them here. There are no participant numbers or outcomes reported directly in this piece, which constrains the depth of its empirical insights.
How was the study funded, and are there any conflicts of interest that may influence the findings?
- No specific funding details are provided. The authors state there is no conflict of interest.
How do the findings apply to training/coaching practice?
- These insights may be useful for endurance athletes and coaches looking to understand the potential benefits of altitude training, its physiological basis, and the importance of balancing training loads in a hypoxic environment. While it does not offer definitive guidelines, the editorial can help in making informed decisions about how and when to incorporate altitude exposure into a training regimen.
What is my Rating of Perceived scientific Enjoyment?
-
RP(s)E = 6 out of 10. This is a fairly brief but interesting summary of a complex topic; however, since there is no original data or meta-analysis, I am not jumping over the moon with excitement.
Important: Don’t make any major changes to your habits based on the findings of one study, especially if the study is small (e.g., less than 30 participants in a randomised controlled trial or less than 5 studies in a meta-analysis) or poor quality (e.g., high risk of bias or low certainty of evidence in a meta-analysis). What do other trials in this field show? (Follow the link to explore those trials.) Do they confirm the findings of this study or have mixed outcomes? Is there a high-quality systematic review and meta-analysis evaluating the entirety of the evidence in this field? (Follow the link to explore those reviews.) If so, what does the analysis show? What is the risk of bias or certainty of evidence of the included studies?
Durability in recreational runners: effects of 90-min low-intensity exercise on the running speed at the lactate threshold. Nuuttila et al. (2025) Eur J Appl Physiol. (click the title to access the full article)
What type of study is this?
- This study is a
non-randomised non-controlled trial (a pre-post study).A trial where the outcome of interest is measured before and after exposure to a treatment, but there is no control group or control intervention. Instead, the participants' baseline measurement is used as the control. This type of study design has a high risk of bias and is prone to producing unreliable findings.
What is the authors’ hypothesis or research question?
- The authors aimed to investigate whether a prolonged 90-min low-intensity run would induce shifts in the running speed at the first lactate threshold and whether these changes would differ between males and females.
What did the authors do to test the hypothesis or answer the research question?
- A total of 31 recreational runners (15 females, 16 males) completed two laboratory sessions. First, they performed an incremental treadmill test to assess maximum oxygen uptake and to identify the first lactate threshold. On another day, participants completed a 90-minute low-intensity run at 90% of their threshold speed. Immediately before and after this run, they performed a 5-stage submaximal threshold test (3 min per stage) to measure changes in lactate threshold speed, heart rate, oxygen consumption, ventilation, and blood lactate at the threshold. Throughout the 90-minute run, participants’ heart rate, oxygen uptake, and respiratory exchange ratio were measured periodically. A reactivity jump test was also performed before and after the run. The primary outcome was the change in the speed at the lactate threshold, with additional monitoring of energy expenditure and heart rate variability (via detrended fluctuation analysis alpha 1).
What did the authors find?
- Following the 90-minute run, the speed at the first lactate threshold decreased in both females (approximately −5.8% ± 4.4%, p<0.01) and males (approximately −5.3% ± 6.4%, p<0.01). Heart rate measured at the threshold increased significantly in both groups (p<0.001), while blood lactate at the threshold and threshold-level energy expenditure decreased (p<0.05). Over the 90 minutes of low-intensity running, heart rate drifted upward in both sexes by around 5–6%, oxygen uptake rose slightly over time, whereas the respiratory exchange ratio decreased. An increase in energy expenditure from the start to the end of the run was noted in females but not in males. Reactivity jump performance did not change significantly. Of the in-session physiological variables, only changes in detrended fluctuation analysis alpha 1 (a measure of heart rate variability) correlated significantly (r=0.463, p=0.013) with the magnitude of the threshold-speed decline, suggesting its potential as a marker of within-session fatigue.
- The authors concluded that prolonged low-intensity running induced a significant reduction in the running speed at the lactate threshold and that this effect was similar between males and females. They also concluded that non-linear heart rate variability measures might be useful for monitoring this fatigue-related phenomenon (referred to as “durability”).
What are the strengths of the study?
- A primary strength is the comprehensive, repeated-measures approach: each participant completed both an incremental treadmill test to determine baseline values and a subsequent 90-min run with a closely monitored submaximal threshold test before and after. The researchers measured a range of physiological markers (lactate, oxygen uptake, heart rate, and heart rate variability) and used standardised laboratory protocols to assess changes in threshold performance.
What are the weaknesses of the study?
- No randomised or controlled design was used, and there was no mention of blinding or allocation concealment. A formal sample-size calculation or pre-registration of the study protocol was not reported. Although p-values were presented, confidence intervals and effect size estimates were not explicitly provided. Finally, the study focused on recreational runners in a single-group design, which may limit the direct application of findings to more highly trained or elite populations.
How was the study funded, and are there any conflicts of interest that may influence the findings?
- The study was supported by the Faculty of Sport and Health Sciences at the University of Jyväskylä. The article does not report any external grants beyond institutional funding. The authors stated that they had no conflicts of interest.
How do the findings apply to training/coaching practice?
- These findings suggest that even moderate-intensity prolonged runs can reduce a runner’s lactate threshold speed. Awareness of this “durability” effect may help endurance athletes and coaches refine pacing and training plans, especially in longer sessions or races where maintaining threshold performance is key. Monitoring heart rate variability (particularly non-linear measures) may be a practical way to detect fatigue in real time, thereby informing better in-session intensity adjustments.
What is my Rating of Perceived scientific Enjoyment?
-
RP(s)E = 4 out of 10. This study did not include key features of a randomized clinical trial, such as random allocation, a control group, or double-blinding, and it did not report a registered protocol, power calculation, or full effect-size estimates. Nonetheless, it did clearly specify inclusion criteria, obtained informed consent, used appropriate outcome measures (lactate threshold, oxygen uptake, heart rate, etc.), reported p-values, and disclosed conflicts of interest. These factors strengthen the internal consistency but my enjoyment is hampered by the limitations described above.
Important: Don’t make any major changes to your habits based on the findings of one study, especially if the study is small (e.g., less than 30 participants in a randomised controlled trial or less than 5 studies in a meta-analysis) or poor quality (e.g., high risk of bias or low certainty of evidence in a meta-analysis). What do other trials in this field show? (Follow the link to explore those trials.) Do they confirm the findings of this study or have mixed outcomes? Is there a high-quality systematic review and meta-analysis evaluating the entirety of the evidence in this field? If so, what does the analysis show? What is the risk of bias or certainty of evidence of the included studies?
Impact of different doses of cold water immersion (duration and temperature variations) on recovery from acute exercise-induced muscle damage: a network meta-analysis. Wang et al. (2025) Front Physiol. (click the title to access the full article)
What type of study is this?
- This study is a systematic reviewA systematic review answers a specific research question by systematically collating all known experimental evidence, which is collected according to pre-specified eligibility criteria. A systematic review helps inform decisions, guidelines, and policy. with meta-analysis.A meta-analysis quantifies the overall effect size of a treatment by compiling effect sizes from all studies of that treatment.
What is the authors’ hypothesis or research question?
- The authors aimed to evaluate how different durations and temperatures of cold water immersion might influence recovery from acute exercise-induced muscle damage.
What did the authors do to test the hypothesis or answer the research question?
- The authors searched multiple electronic databases (including PubMed, Cochrane Library, Web of Science, Embase, and CNKI) for randomised controlled trials conducted between January 2000 and September 2024. They included 55 randomised controlled trials investigating cold water immersion protocols with different immersion temperatures (5–10°C, 11–15°C, or 16–20°C) and different immersion durations (<10 min, 10-15 or>15 min). The main outcomes measured were delayed onset muscle soreness, jump performance, and creatine kinase levels. All participants were healthy individuals without chronic diseases. The authors used a network meta-analysis approach, calculated standardised mean differences in outcome changes, and assessed risk of bias using the Cochrane tool.
What did the authors find?
- The authors found that medium-duration cold water immersion (10–15 min) combined with lower temperatures (5–10°C) was most effective for improving jump performance (used to reflect neuromuscular function) and reducing creatine kinase levels (a biochemical marker of muscle damage). Meanwhile, medium-duration cold water immersion (10–15 min) at slightly warmer temperatures (11–15°C) was most effective for alleviating delayed onset muscle soreness. Statistical analysis indicated that, compared with controls, these cold water immersion protocols significantly reduced muscle soreness and creatine kinase levels and enhanced jump performance. The standardised mean differences favoured cold water immersion over control for all three main outcomes, with P-values generally below 0.05. The authors report that the interventions showed no major signs of publication bias on funnel plot inspection, although they noted some methodological limitations among the included studies.
- The authors concluded that medium-duration cold water immersion (10–15 min) at lower or moderate temperatures (5–10°C or 11–15°C) is likely to be the most effective intervention for promoting recovery from acute exercise-induced muscle damage.
What are the strengths of the study?
- The authors named five databases used in their literature search (PubMed, Cochrane Library, Web of Science, Embase, and CNKI), the protocol was registered in PROSPERO, and the authors appear to have adhered to PRISMA guidelines for systematic reviews. A large number of studies (55 in total) were included, increasing the reliability of the pooled results. They used the Cochrane Risk of Bias tool to assess the quality of included studies, conducted a network meta-analysis to compare multiple protocols, and used funnel plots to check for publication bias. Standardised mean differences, confidence intervals, and P-values were consistently reported.
What are the weaknesses of the study?
- The authors did not evaluate the overall certainty of evidence using the GRADE approach, or similar. The authors also noted limited clarity regarding participants’ blinding in many trials (which is often difficult for cold water interventions). The included studies had predominantly male participants, limiting generalizability for female athletes. Additionally, some studies lacked detailed reporting of exercise protocols or randomisation methods, and the authors acknowledged that this variability might constrain definitive conclusions.
How was the study funded, and are there any conflicts of interest that may influence the findings?
- The article states that the authors received no financial support for this work and that they conducted the research in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. No other funding or conflicts of interest are provided.
How do the findings apply to training/coaching practice?
- This meta-analysis may be useful for endurance athletes and coaches seeking practical strategies to reduce muscle soreness, lower muscle damage markers, and restore neuromuscular performance more quickly after intense exercise. By identifying the durations and temperatures most likely to optimise different recovery outcomes, the findings can guide individualised cold water immersion protocols for enhanced athletic training and competition recovery.
What is my Rating of Perceived scientific Enjoyment?
-
RP(s)E = 8 out of 10. My Rating of Perceived Scientific Enjoyment was high because the paper clearly described its systematic methods, specified the databases searched, registered its protocol, assessed risk of bias, and conducted publication bias analysis. The paper included a substantial number of studies, which bolsters its conclusions, although it lacked a formal GRADE evaluation and had limited female samples.
Important: Don’t make any major changes to your habits based on the findings of one study, especially if the study is small (e.g., less than 30 participants in a randomised controlled trial or less than 5 studies in a meta-analysis) or poor quality (e.g., high risk of bias or low certainty of evidence in a meta-analysis). What do other trials in this field show? (Follow the link to explore those trials.) Do they confirm the findings of this study or have mixed outcomes? Is there a high-quality systematic review and meta-analysis evaluating the entirety of the evidence in this field? (Follow the link to explore those reviews.) If so, what does the analysis show? What is the risk of bias or certainty of evidence of the included studies?Important: I’ve written a deep-dive article on this topic; check it out here.
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. 
Training methods.
Effects of hybrid custom foot orthoses on running economy, running mechanics and comfort: A double-blinded randomized crossover study. Alsenoy et al. (2025) Gait Posture. Pacing Strategy and Resulting Performance of Elite Trail Runners: Insights From the 2023 World Mountain and Trail Running Championships. Jaén-Carrillo et al. (2025) Int J Sports Physiol Perform. Effects of Vegan and Omnivore Diet on Post-Downhill Running Economy and Muscle Function. Vasenina et al. (2025) J Am Nutr Assoc. Exploring the impact of high altitude on physiological parameters and training characteristics of endurance runners. Codella et al. (2025 ) J Sports Med Phys Fitness. Effect of condensed heat acclimation on thermophysiological adaptations, hypoxic cross-tolerance, exercise performance, and deacclimation. Stevens et al. (2025 ) J Appl Physiol (1985). Pacing in ultra-marathon running: the Western States 100-mile endurance run 2006-2023. Markovic et al. (2025) Sci Rep. Durability in recreational runners: effects of 90-min low-intensity exercise on the running speed at the lactate threshold. Nuuttila et al. (2025) Eur J Appl Physiol. Sports nutrition and hydration.
Isoenergetic Pre-Exercise Meals Varying in Carbohydrate Similarly Affect Resistance Training Volume Performance Compared to Placebo: A Crossover Trial. King et al. (2025) Eur J Sport Sci. Recovery.
Impact of different doses of cold water immersion (duration and temperature variations) on recovery from acute exercise-induced muscle damage: a network meta-analysis. Wang et al. (2025) Front Physiol. Female athlete physiology and sex differences.
No sex differences in performance and perceived fatigability during a self-paced endurance exercise performed under moderate hypoxia. Hasegawa et al. (2025) Am J Physiol Regul Integr Comp Physiol. Sex differences in absolute and relative changes in muscle size following resistance training in healthy adults: a systematic review with Bayesian meta-analysis. Refalo et al. (2025) PeerJ.
And, to help you wash down the latest evidence, here's a snifter from my recent indulgence...
My beer of the month.
Ianus Insanus.
Brewed by Pulfer Brewery (Zagreb, Croatia).
Imperial Double Pastry Stout.
10.6% ABV.
A black and purple hue to the eye, vanilla and mild coffee to the nose, slightly foamy and bubbly on the tongue, with a chocolatey and liquoricey flavour, and smooth, vanillary and slightly boozy aftertaste. Insanus to the maxus!
RP(be)E(r)(Rating of Perceived beer Enjoyment)
8 out of 10
Access to education is a right, not a privilege:
Equality in education, health, and sustainability is important to me. I was lucky to be born into a social welfare system where higher education was free. Sadly, that is no longer true. Consequently, to provide access to exercise science and sports nutrition education to folks from all walks of life, I publish freely accessible high-quality exercise science and nutritional science content. This nerd alert newsletter is part of that offering. You can find more free educational resources from me, Thomas Solomon PhD, at veohtu.com.
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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.