RESEARCH: Studies from 23 to 29 Dec 24
Sharing research and insights from coaches, scientists and athletes to help us improve endurance performance.
This week’s quick summary:
The relationship between training load and injury in competitive swimming
Effect of high-dose β-Alanine supplementation on uphill cycling performance
Carbohydrate ingestion during short-duration high-intensity intermittent exercise
Increased footwear comfort is associated with improved running economy
Fluid loss during exercise-heat stress reduces cardiac vagal autonomic modulation
TRAINING: The relationship between training load and injury in competitive swimming: A two-year longitudinal study
Managing training load is important to optimise athletes’ rates of adaptation and improvement while controlling the potential risk of over-training and injury. In this study, the authors aimed to “explore the relationship between training load and injury in competitive swimmers using the session rate of perceived exertion (sRPE) method”.
STUDY DETAILS
34 athletes from two Swim Ireland National Centres participated in the study over 104 weeks.
Data collection involved a prospective, longitudinal study design using the sRPE method.
The average weekly swim volume was 33.5 ± 12.9 km, with a weekly total training load of 3838 ± 1616.1 arbitrary units (AU).
A total of 58 medical attention injury events were recorded during the study period.
Bayesian mixed effects logistic regression models showed a 70% to 98% probability of association between training load and injury, but evidence was deemed weak or highly uncertain.
PRACTICAL TAKEAWAY
The result of this study shows that coaches and athletes should not rely on a single training load metric to predict injuries. This may seem obvious (not relying on a single metric) but measuring training load reliably and effectively is a challenge and there is often a significant difference between different metrics. My recommendation is to use multiple metrics (a more subjective one like sRPE and an objective one TSS or RE) in conjunction with subjective, mood-based assessments from the athlete. This should be combined with a relatively conservative approach to increasing training volume and stimulus to mitigate injury risk effectively.
RELATED RESEARCH
SUPPLEMENT: Effect of high-dose β-Alanine supplementation on uphill cycling performance in World Tour cyclists
β-Alanine supplementation has gained popularity among cyclists for its potential to enhance performance and recovery. However, the effects of high-dose β-Alanine during short-term training camps for elite cyclists remained unexplored. In this study, the authors aimed to “analyse the effect of a high dose of β-alanine in World Tour cyclist during a 7-day camp”.
STUDY DETAILS
11 World Tour cyclists participated in the study, with five receiving β-Alanine supplementation and six receiving a placebo.
The supplementation protocol lasted seven days, with four daily intakes of 5g β-Alanine, totalling 155g over the study period.
Cyclists performed uphill time trials before and after the supplementation period to assess performance changes.
Measurements included relative mean power, time to complete the trial, blood lactate, heart rate, and rating of perceived exertion.
The β-Alanine group showed improvements in relative mean power and time to complete the trial compared to the placebo group, with no significant changes in physiological variables.
PRACTICAL TAKEAWAY
For the World Tour cyclists participating in this short-term training camp, a one-week high-dose β-Alanine supplementation protocol (20g daily) improved uphill time-trial performance. In general, β-Alanine supplementation appears to improve short-duration efforts, however, this study may suggest that it could also be beneficial during periods of high intensity training. My recommendation for athletes who compete in sports where short, high-intensity efforts are required is to try this protocol of 20g β-Alanine supplementation per day during training camps to see if it works for them.
RELATED RESEARCH
NUTRITION: No effects of carbohydrate ingestion on muscle metabolism or performance during short-duration high-intensity intermittent exercise
Carbohydrate ingestion has been shown to improve performance during endurance training. However, shorter sessions (which are often at high intensity) may seem like they would not necessarily need extra carbohydrate ingestion. In this study, the authors set out to assess “the effects of carbohydrate supplementation on muscle metabolism and performance during short-duration high-intensity intermittent exercise”.
STUDY DETAILS
11 moderately-to-well-trained males participated in the study, performing high-intensity intermittent cycling while receiving either carbohydrate or placebo fluid supplementation.
The exercise protocol consisted of three periods, each comprising 10 repetitions of 45-second cycling at approximately 105% of maximum wattage, with rest intervals between bouts and periods.
Repeated sprint ability was assessed at baseline and after each exercise period using five 6-second sprints with 24-second recovery intervals.
Muscle biopsies were taken to determine whole-muscle and fiber-type-specific glycogen depletion at baseline and before and after the third exercise period.
Blood glucose and insulin levels were measured throughout the exercise, showing higher concentrations in the carbohydrate group compared to the placebo group.
PRACTICAL TAKEAWAY
Based on this study, carbohydrate supplementation during short-duration high-intensity intermittent exercise may not provide significant benefits for muscle glycogen preservation or sprint performance. My recommendation is that for short sessions, it is not necessary to take on extra carbohydrates during the session. However, I would also note that this assumes glycogen stores are already high before the session (not starting in a fasted state), and that one of the reasons for taking carbs during a session is for the recovery afterwards so make sure to eat enough post training when following this approach.
RELATED RESEARCH
EQUIPMENT: Increased footwear comfort is associated with improved running economy
Previous research I have shared has explored the potential of footwear and custom orthotics to enhance comfort and performance in running. This systematic review aimed to “investigate the relationship between footwear comfort and running economy in recreational runners”.
REVIEW DETAILS
9 electronic databases were searched from inception to March 2020 for eligible studies.
Studies included direct measures of running performance or physiological measures like running economy (RE) alongside comfort ratings for each footwear condition.
RE during submaximal running was the most common physiological outcome, reported in 4 of 6 eligible studies.
Meta-analysis showed that the most comfortable footwear was associated with reduced oxygen consumption while running at a set submaximal speed.
The Effective Public Health Practice Project (EPHPP) quality assessment indicated weak study quality due to reporting bias and undisclosed psychometric properties of outcome measures.
PRACTICAL TAKEAWAY
This review suggests that choosing more comfortable shoes is likely to result in greater running economy. This study was from 2021 which was at the beginning on the supershoe revolution and now there is plenty of evidence that supershoes improve performance. My recommendation is not to force the use of a supershoe based on what is reported to be the fastest even if it is uncomfortable. Rather find the supershoe that is comfortable for the athlete as that is most likely to result in an improved performance.
RELATED RESEARCH
Does orthotics use improve comfort, speed and injury rate during running?
Effects of highly cushioned and resilient racing shoes on running economy at slower running speeds
HYDRATION: Fluid loss during exercise-heat stress reduces cardiac vagal autonomic modulation
Prolonged exercise in hot conditions can lead to significant fluid loss through sweating, potentially compromising cardiovascular and thermoregulatory functions. In this study, the authors "examined heart rate variability (HRV) and recovery (HRRec), as surrogates of cardiac autonomic modulation, during and after prolonged exercise in the heat with and without fluid replacement”.
STUDY DETAILS
11 young, healthy men participated in the study, performing 90 minutes of semi-recumbent cycling in dry heat (40°C, 20% relative humidity) at a fixed rate of metabolic heat production.
Participants completed two separate trials: one without fluid replacement (No-FR) resulting in ~3.4% body mass reduction, and another with fluid replacement (FR) to offset sweat losses.
Esophageal temperature and ECG were recorded throughout the exercise and 40-minute recovery period, with measurements analysed over 10-minute averaged epochs.
HRV indices reflecting vagal influence, including the cardiac vagal index and root-mean-square of successive differences, were attenuated during exercise in both conditions, with a greater reduction in the No-FR condition.
Sample entropy, indicating cardiac rhythm complexity, was reduced throughout exercise in the No-FR condition compared to the FR condition.
PRACTICAL TAKEAWAY
For the participants in this study, maintaining proper hydration during prolonged exercise in hot conditions made a significant difference. Fluid replacement helped preserve cardiac autonomic modulation, which was important for maintaining cardiovascular function. My recommendation is for athletes and coaches to prioritise fluid intake strategies during extended exercise in hot environments. These strategies should consider the volume of fluid ingested, the amount of sodium included in that fluid, and the temperature of the fluid, and will need to be personalised for each athlete.
RELATED RESEARCH
Effects of dehydration and rehydration on cognitive performance
Muscle blood flow is reduced with dehydration during prolonged exercise in humans
Quick summary from last week’s paid newsletter
Paid subscribers receive a newsletter every week and have full access to all newsletters listed in the archives (535 studies and practical takeaways). Last week, the newsletter covered studies on the following topics:
Reductions in pre-season training loads reduce injury rates in rugby players
Are 72 hours sufficient for hamstring recovery after a soccer match?
The interactive effect of sustained sleep restriction and resistance exercise
Dietary fat restriction affects brain reward regions
Assessing leg blood flow and cardiac output during running using thermodilution
