Running science nerd alert.


by Thomas Solomon PhD and Matt Laye PhD
June 2020.

Each month we compile a short-list of our favourite recently-published papers from the world of running science and break them into bite-sized chunks so you can digest them as food for thought during your training sessions. Welcome to this month's installment of our "nerd alert". We hope you enjoy it.
Reading time ~20-mins (3800-words)
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Clicking the title of each article will "drop-down" our summary.

https://pubmed.ncbi.nlm.nih.gov/32505092/
What was the hypothesis or research question?
An exercise bout increases circulating markers of inflammatory cytokines but most prior work has used steady-state moderate-intensity exercise in the fasted state. The authors’ aimed to investigate the immediate effect of an interval-running session on circulating cytokine concentrations (markers of inflammation) in the fed state. No hypothesis was stated.
What did they do to test the hypothesis or answer the research question?
Following 48-hours of rest from prior exercise, 9 young healthy recreational runners (4 women, 5 men) completed an interval-training session in the morning, 45-mins after consuming a small meal. The session included a 10-min jog as warm up followed by 30-minutes of intervals: 200 m at ~70–80% HRmax with 200 m recovery at ~30–40% of HRmax, with a 10-minute cool-down. Venous blood samples were collected before and after the training session. Plasma cytokine concentrations were measured using a multiplex ELISA assay, which detects up to 27 inflammatory molecules.
What did they find?
In the post-exercise blood sample, plasma levels of IL-1ra, IL-6, IL-8, TNF-α, IFN-α,, MCP-1, and GM-CSF were lower (P<0.05) while IP-10 was higher (P<0.05), than in the pre-exercise sample. Effect sizes of the changes ranged from 0.23 (small) to 0.69 (moderate).
What were the strengths?
Subjects were studied in the fed state - many exercise studies in the inflammation and metabolism field have been conducted in the fasted state which is not representative of high intensity training sessions and certainly not representative of races.
Effect sizes were calculated to determine the magnitude of significant effects.
Included men and women.
What were the weaknesses?
No non-exercise control arm to determine the time-course effects of meal ingestion on cytokine responses, independent of exercise.
Very small sample size, which was only justified by power calculation after the study was completed - this is very obscure. The authors write that their sample size was “based on sample sizes of previous researches” - again, very obscure and not good scientific practice.
The pre-training meal was seemingly arbitrary - no caloric load or macronutrient breakdown was stated, nor was prior diet analysed. This is important since pre-exercise muscle glycogen levels and glucose feeding massively influences cytokine responses to acute exercise.
Although the methods say that the interval session was conducted at specific percentages of HRmax, we are not told how HRmax was derived and HR values are not reported. Then the authors state that “training intensity was determined subjectively through RPE scale”. This implies that HR was not measured and that intensity was based on RPE, which is fine but RPE values are not reported so we have no idea about the adherence to the training protocol.
We are never told at what time point the pre- and post-exercise blood samples were taken. This is very important because inflammatory events following exercise occur on a timecourse lasting several hours.
Plasma volume was not reported. A single exercise bout typically increases plasma volume which may explain the apparent decrease of plasma concentrations for most of the cytokines measured (i.e. were cytokines diluted by a large plasma volume? This is not discussed).
The lower limit of detection of many cytokines is 1 pg/ml - many of the relevant cytokines are detected at or below this level - so further validation of their multiplex assay with single antibody assays is required to confirm it is measuring what it is supposed to.
Are the findings useful in application to training/coaching practice?
No. Firstly, it is disappointing that this paper passed through peer-review in its current state - there are many key methodological details missing and the study design lacks a non-exercise control intervention. Secondly, inflammatory events following an exercise bout are not indicative of disease - the acute inflammatory response to an exercise bout is part of the mechanisms that triggers adaptations and tissue repair.

https://pubmed.ncbi.nlm.nih.gov/31652404/
What was the hypothesis or research question?
FODMAPs are fermentable oligo- di- mono- saccharide and polyols (i.e. fermentable carbohydrates) that like to make friends with the “gingerbread man”, a runner’s osmotic nightmare. The authors hypothesised that a 24-h high FODMAP (fermentable oligo- di- mono- saccharide and polyol) diet before exertional-heat stress would worsen exercise-associated gastrointestinal integrity and cause greater gastrointestinal (GI) symptom incidence and severity, compared to a low FODMAP diet.
What did they do to test the hypothesis or answer the research question?
Eighteen (10 men, 8 women) trained but non-heat acclimated endurance and ultra-endurance runners completed a double-blind crossover study in which they consumed either a high or low FODMAP diet for 24-hours prior to a 2 hour run at 60% V̇O2max (easy-effort running) in a 35°C environment. Blood samples were collected pre- and post-exercise to measure plasma cortisol, cytokines, and markers of gut integrity and function. Breath hydrogen (released by fermenting gut bacteria) and GI symptoms were determined before, during, and after running.
What did they find?
The high FODMAP diet for caused greater carbohydrate malabsorption (greater breath hydrogen), compared with low FODMAP. GI symptoms during running in the heat were observed in both the low and high FODMAP trials but greater severity of GI symptoms was observed in the high FODMAP trial. The pre- to post-exercise increase (i.e. heat-induced exercise stress) in plasma cortisol was not different between diets. Unexpectedly, the pre- to post-exercise increase (indicative of heat stress-induced epithelial enterocyte injury) in plasma I-FABP (intestinal fatty acid binding protein) was higher on the low-FODMAP diet, and LBP (lipopolysaccharide binding protein) increased during exercise on the low-FODMAP diet but decreased on the high-FODMAP diet. These findings are remarkable, unexpected and contrary to some of the hypothesis, in that the low-FODMAP diet caused less GI symptoms but greater increased in blood markers of gut cell damage (increased i-FABP and LBP).
What were the strengths?
Double-blind (i.e. neither the subjects nor the investigators knew which diet the subjects were receiving), randomised, crossover design.
Sample size justified using power calculations and effect sizes were calculated to determine the magnitude of the effects.
Builds on prior work, which were mostly case studies.
Diets were provided in an in-patient setting and diet formulation used the FODMAP-specific database developed at the authors institution, Monash University, a world-leading institution for FODMAP research.
Included men and women.
To prevent seasonal heat acclimatisation, participants were unaccustomed to running in hot environments and the trials were conducted in cooler seasonal periods (temperatures ≤20°C).
What were the weaknesses?
The details for the exclusion of some data were not provided - the authors write “prior to data analysis, outlying values were detected through box-plot analysis and appropriately removed.” - such a statement needs more clarity.
Less total calories (absolute kcal and relative kcal/kg) and less total carbohydrates were provided in the low FODMAP diet. These were small but significant differences. That said, fiber was matched, grams/kg carbohydrate were above 5 in both trials (i.e. within a range that should restore/maximise glycogen), and, importantly, FODMAP content were clearly very different.
The findings were not described in the context of the effect sizes measured.
Are the findings useful in application to training/coaching practice?
Yes. Given the high incidence of GI symptoms reported by endurance athletes during training sessions and races, particularly when training in hot weather, dietary strategies to help alleviate symptoms may boost endurance success. This paper adds to the knowledge that restricting FODMAP-containing foods in the 24 hour period prior to a race or a key session may be a useful approach for preventing GI symptoms. This is not to say that an athlete should exclude FODMAPS in their habitual diet every day forever because, in that case, macro- and/or micronutrient deficiencies may arise.
The meaning of higher plasma levels of markers of gut damage (i-FABP and LBP) on the low-FODMAP despite less GI issues needs further exploration - is this a real finding or are plasma markers a valid marker of what is truly happening in the intestinal tissue during exercise in the heat?

https://pubmed.ncbi.nlm.nih.gov/32522222/
What was the hypothesis or research question?
The study was not hypothesis driven but was designed to be a hypothesis-generating observational study. The authors’ aim was to assess voluntary, pre-running food restrictions related to running-induced gastrointestinal (GI) symptoms and to explore differences related to gender, age, performance level, and event.
What did they do to test the hypothesis or answer the research question?
A questionnaire assessing pre-racing dietary restrictions and during-race gastrointestinal symptoms was administered to 388 runners in the southern area of Alberta at race events, race number pick-ups, or running clinics. Within-cohort differences in gender, age, performance level, and race distance were quantified and multivariable logistic regression modeling was used to examine relationships between athletes’ demographic/performance characteristics (gender, age, race distance, performance level) and variables related to dietary habits.
What did they find?
The most commonly avoided foods pre-racing included meat, milk products, fish/seafood, poultry, foods high in fiber, chocolate, legumes, coffee/tea, energy drinks, and starchy vegetables. High-fiber foods were more commonly avoided in the marathon and ultra-marathon distances, while coffee and tea were avoided more often in races that were shorter than 10 km.
Performance level was related to food avoidance. For example, lower recreational-level athletes were less likely to avoid foods, while competitive athletes were less likely to avoid coffee or tea. Athletes with higher performance levels were more likely to avoid meat, chocolate, eggs, and milk-related products.
Age was related to food avoidance - milk products and energy drinks were more commonly avoided in younger athletes.
Gender was related to food avoidance - women running longer distances (>5 km) were more likely to avoid high-fiber foods pre-racing than males running longer distances.
Age, gender and performance level were related to GI issues. For example, young women suffered from exercise-induced GI symptoms more frequently than other groups. The longest distances were associated with a greater likelihood to report diarrhea. Women and athletes of a high performance level were more likely to report the urge to defecate. And, athletes with higher performance levels, more frequently had the urge to defecate during runs.
What were the strengths?
Power calculations were used to determine the sample size.
The questionnaire was validated and its test-retest reliability examined in a subset of participants.
Odds-ratios were used to assess the magnitude (effect size) of the relationships between variables.
What were the weaknesses?
A recall-based assessment of dietary exclusions is open to bias since underreporting or false reporting arises in questionnaires assessing diet and energy intake. Observational cross-sectional studies cannot infer causality. That said, the study was intended to generate future research directions.
The multivariate comparison used a threshold of 5% of significance and was not adjusted for the multiple comparisons being simultaneously made. Therefore, the risk of type 1 errors (i.e. false positive rates) is inflated.
History of training duration and typical training load data were not collected. These would have helped provide insight into the “experience” of the athletes studied.
Are the findings useful in application to training/coaching practice?
Possibly. Since GI issues are commonly reported in endurance athletes and since minimising gut discomfort is a key ingredient for endurance racing success, the study identifies foods of interest that could be experimented with in the pre-race diets of athletes who suffer from GI issues. As the authors indicate, fats, oils, spicy foods, and high FODMAP foods should be added to assessments of pre-race diets.

https://pubmed.ncbi.nlm.nih.gov/31802395/
What was the hypothesis or research question?
This was a systematic review that focused on differences in biomechanics between treadmill running and overground running, which I like to call running outside. Some have reported that less propulsion is necessary for treadmill running, which would alter biomechanics relative to overground running. Some of these differences might be due to the increased air resistance in overground running compared to treadmill running
What did they do to test the hypothesis or answer the research question?
They specifically searched for studies that compared treadmill conditions in which there was no incline, no added cushion, and a constant velocity to overground running in the same subjects. They found 33 studies which met these criteria with nearly 500 total subjects. .
What did they find?
The authors found no differences in stride length, frequency, or ground contact time, although there were significant variations in the studies that they used, with some showing an increase in contact time and others showing a decrease. There were also no differences in the biomechanics related to the frontal and transverse planes of movement. However, the following biomechanics were different on a treadmill versus overground running: less hip flexion, less knee extension, less knee range of motion, less vertical oscillation, lower foot landing angle, increased front and back motion of the ankle, and lower propulsion effects overall. Most of these changes, while statistically significant, represented changes that were probably not clinically important. A number of other changes and others were only found when comparing treadmill running to specific surfaces of overground running. For instance, lower vertical force and lower ankle angle of contact on concrete versus other surfaces. There was also a trend for overall lower muscle activity on the treadmill versus overground running as measured by electromyography.
What were the strengths?
Large number of studies and nearly 500 subjects when all pooled together.
A good cross sectional representation of athletes.
What were the weaknesses?
Each of the 33 different studies used a slightly different speed, a different surface, a different population of subjects, a different amount of time between the treadmill and overground trial, different shoes, and just measured different outcomes related to biomechanics. All of that greatly reduces the conclusions that can be made.
Also all the running was flat at a constant speed, which is not similar to real running and racing.
Are the findings useful in application to training/coaching practice?
These findings suggest that a treadmill will replicate outdoors running fairly well if you want to practice running on a flat surface at a constant speed. Athletes that may need to shift paces or run hilly/mountainous trails may not run the same way on a treadmill trying to replicate those specific conditions, which was not addressed in this review.

https://www.ahajournals.org/doi/10.1161/CIRCIMAGING.120.010567
What was the hypothesis or research question?
To test whether the left ventricular function of the heart maintains the amount of blood it was able to pump out during a beat with adaptations to endurance training.
What did they do to test the hypothesis or answer the research question?
The authors took 5 female individuals and followed them in a longitudinal fashion as they trained for the Boston Marathon. At multiple time points they measured various aspects of left ventricular cardiovascular function using echocardiography every 4 months for 16 months in total.
What did they find?
The authors found that, as expected, resting heart rate dropped after training and VO2max tended to increase, but not significantly. With regards to left ventricular function they found that as expected the left ventricle of the heart was increased in volume. However, accompanying that increase in volume was a reduction in the amount of blood the left ventricle could pump, indicating a mild form of left ventricular dysfunction. Interestingly, the strain on the left ventricle was similar to pre and post training, suggesting that the dysfunction may not be pathological or harmful. One potential reason is that the larger chamber requires a lower relative amount of blood pumped to get the same absolute amount of blood out to the tissues to meet metabolic demand.
What were the strengths?
Longitudinal tracking of the same individuals, which many of the other studies have not done and only looked at cross sectional data.
State of the art measures of cardiac function.
Training did occur and subjects are representative of competitive runners capable of qualifying for the Boston Marathon.
What were the weaknesses?
Only 5 subjects, all female and only 16 months of training, which is not long for a lifetime endurance athlete worried about their heart.
Are the findings useful in application to training/coaching practice?
Somewhat. While a decline in left ventricle function sounds bad, the reality is that the typical pathology that would accommodate such a decline was not found in healthy endurance athletes. This reaffirms that endurance exercise over a 16 month period is not detrimental to health, but it does not help answer the question of whether decades of training may be detrimental to cardiovascular health.

https://doi.org/10.1080/00015385.2020.1778871
What was the hypothesis or research question?
Ultra marathons are stressful on the body and can cause significant amounts of muscle damage and oxidative stress. It is also thought an ultra may lead to changes in heart function and that might be related to the oxidative and inflammatory damage that occurs with ultras. The authors sought to determine the time course of several well known oxidative and inflammation markers in parallel with changes in heart function following a 64.2 km ultra-trail race.
What did they do to test the hypothesis or answer the research question?
They recruited 33 ultra runners (mean age 45.8). The race was 64.2km long with 1400 meters of climbing overall. They performed blood draws before, immediately after, and 3 hours after the end of the race in order to measure inflammatory and oxidative biomarkers in the blood.
What did they find?
The runners ran for between 6:27 and 11:32h. All markers of inflammation, cardiac muscle, and skeletal muscle damage were increased immediately post race and remained elevated 3 hours after finishing the race. Markers of antioxidant capacity were elevated 3 hours after the race, but not immediately after finishing, perhaps as a mechanism to combat the inflammatory response. Electrocardiography revealed normal heart functioning immediately after the race with the exception of diastolic and systolic left ventricular volume and the left ventricular global longitudinal strain, a measure of cardiac stress, which was increased following the ultra marathon. They also found that a hormone marker of cardiac stress was correlated to the left ventricular global strain. For most of the markers of inflammation and oxidative damage most of the runners were well outside of the recommended clinical range expected in healthy, resting, individuals. None of these markers were correlated with training status.
What were the strengths?
A strength of this study is that they measured a lot of different markers of inflammation, oxidative damage, and electrocardiography at the same time.
What were the weaknesses?
They only went out 3 hours post race. The inflammatory cascade is complex and multifaceted and extends out several days to fully capture the peak and return to baseline. This study cannot say anything about the full time course of the damage that occurs with an ultra.
Are the findings useful in application to training/coaching practice?
Yes and no. Many runners will present with clinically abnormal levels of muscle and cardiac damage markers. In general this is not thought to be pathological, however your general practitioner medical doctor may not know this. So if you want to present with a lower level of muscle damage then it is wise to give yourself some time for those levels to return to baseline after a hard exercise bout. While not directly indicated by this study the study reinforces the need for recovery following hard exercise bouts.

https://doi.org/10.1016/j.jsams.2019.12.018
What was the hypothesis or research question?
Most prior studies examining footstrike look at running form when athletes are not fatigued. These authors wanted to look at how foot strike patterns changed during a race and whether those changes were associated with performance differences.
What did they do to test the hypothesis or answer the research question?
They set up cameras at 3 km and 13 km of a 15 km road race in Melbourne to capture the biomechanics of 459 runners who completed the race. Foot strike patterns were broken down into rearfoot or non-rearfoot strikes at each of the points during the race. They then looked to see if people that changed their foot strike pattern were faster or slower than those who did not change their foot strike pattern.
What did they find?
At 3km 76.9% of runners used a rear foot strike pattern and by 13km that increased to 91.0% of the runners. Of those with a non-rear foot strike pattern at 3km 61% of them changed to a rear foot strike pattern by 13km. Non-rear foot strike pattern runners finished the race faster than rear-foot strike pattern runners. Runners that switched from non-rear foot strike patterns to rear foot strike patterns finished at an intermediate time point, not as fast as the always non-rear foot strikers and faster than the always rear foot strikers.
What were the strengths?
They had a large number of subjects with two time points of data collected.
Data was inline with what others have found.
What were the weaknesses?
The camera used was a Go Pro and only recorded at 200 frames per a second, far less than biomechanics research equipment.
The authors only looked at foot strike patterns and not the overall changes in biomechanics.
The foot strike pattern was determined only from one foot strike and may not represent the entirety of the race.
The time point during the race at which a change in foot strike pattern occurred was not determined.
Mid foot and forefoot strike patterns were combined and are related to significantly different overall biomechanics.
Are the findings useful in application to training/coaching practice?
Yes and no. For shorter races, a non-rear foot strike pattern is not detrimental and those who fatigue less or run faster may be better able to maintain that foot strike pattern. However, a lot of other work indicates that foot strike pattern is not related to performance over longer races and that trying to change the way that you naturally foot strike may not lead to more efficient running or faster race performances. As coaches, being aware that athletes may change their foot strike pattern as they fatigue and that the change in foot strike pattern may be representative of larger changes in biomechanics is important. Those changes in biomechanics may be associated with increased injury risk.


That is all for this month's nerd alert. We hope to have succeeded in helping you learn a little more about the developments in the world of running science. Until next month, keep active, stay nerdy, and train smart.

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Dr Thomas Solomon and Dr Matt Laye. Running science nerd alert.
About the authors:
Matt and Thomas are both passionate about making science accessible and helping folks meet their fitness and performance goals. They both have PhDs in exercise science, are widely published, have had their own athletic careers, and are both performance coaches alongside their day jobs. Originally from different sides of the Atlantic, their paths first crossed in Copenhagen in 2010 as research scientists at the Centre for Inflammation and Metabolism at Rigshospitalet (Copenhagen University Hospital). After discussing lots of science, spending many a mile pounding the trails, and frequent micro brew pub drinking sessions, they became firm friends. Thomas even got a "buy one get one free" deal out of the friendship, marrying one of Matt's best friends from home after a chance encounter during a training weekend for the CCC in Schwartzwald. Although they are once again separated by the Atlantic, Matt and Thomas meet up about once a year and have weekly video chats about science, running, and beer. This "nerd alert" was created as an outlet for some of the hundreds of scientific papers they read each month.

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