RESEARCH: Studies reviewed this week: 26 July 2021 to 1 August 2021

HEAT: Nutritional considerations to counteract gastrointestinal permeability during exertional heat stress

Gastrointestinal issues are one of the most common issues in ultramarathons and often in hot races these issues are exacerbated. That makes this study particularly important for athletes in these races and for anyone competing in the heat. The authors outline that:

Intestinal barrier integrity and function are compromised during exertional heat stress (EHS) potentially leading to consequences that range from minor gastrointestinal (GI) disturbances to fatal outcomes in exertional heat stroke or septic shock.

A couple of highlights from the review:

For athletes who are frequently exposed to EHS, training with a specific carbohydrate intake strategy (including glucose and fructose) can improve GI comfort, potentially through reduction in GI symptoms
Acute glutamine supplementation (0.9 g/kg FFM, 2 h before exercise) prevented increases in intestinal permeability and lowered the appearance of plasma endotoxin and TNF-α later in recovery.
When endurance runners underwent 2 h of running at 70% V̇o2max (25°C, 46% RH) with fluid restriction and lost 3.1% BM, I-FABP was significantly higher compared with euhydration via water provision, demonstrating fluid intake influences GI permeability even in nonhyperthermic environments.

PRACTICAL TAKEAWAY - stay hydrated in hot conditions, train with your race nutrition plan to prepare for the heat, and consider trying glutamine supplementation.

PHYSIOLOGY: Erythropoiesis with endurance training: dynamics and mechanisms

This study set out to "characterize the progression of red blood cell volume (RBCV) expansion and potential volumetric and endocrine regulators of erythropoiesis during endurance training (ET)". The study used untrained individuals and asked them to cycle for 3-4hrs a week for 8 weeks. While this is a small dose considering how much most endurance athletes train, it can still be instructive to understand the mechanisms and increase in RBCV.

The authors found that:

Increases in RBCV from baseline were manifested at week 4
Overnight fasting plasma EPO concentration increased from baseline at week 2 and returned to baseline concentration at weeks 4 and 8.
ET leads to mild, transient increases in circulating EPO concentration, concurring with early PV expansion and lowered hematocrit, preceding gradual RBCV enhancement.

PRACTICAL TAKEAWAY - endurance training improves red blood cell volume but the improvement is not linear. This could have implications for blood tests at certain times of year when training is increased but RBCV has yet to respond.

HRV: Monitoring and adapting endurance training on the basis of heart rate variability monitored by wearable technologies

This meta analysis investigated "the scientific literature to determine whether the outcomes of endurance training based on HRV are more favourable than those of predefined training". The key findings were that:

The effects of endurance training guided by heart rate variability (HRV) as an indicator of the functioning of the autonomic nervous system on parameters of performance are somewhat, although not statistically significantly better than those of predefined training.
With respect to performance, endurance training guided by HRV is associated with fewer who respond negatively and more who benefit.
In comparison to predefined training, HRV-guided training exerts a significant medium positive impact on submaximal physiological parameters.

PRACTICAL TAKEAWAY - training guided by HRV can be beneficial and most likely will provide a positive impact (also see the case studies below), but it shouldn't be taken as a certainty and it needs to be used intelligently and considering the athletes physiological characteristics.

PSYCHOLOGY: Psychological Resilience in Olympic Medal–Winning Coaches

I haven't shared too many studies on coaches becase there aren't too many (see last week's note about the lack of best practice studies on coaches). It was particularly interesting for me to see this study were a "longitudinal qualitative design was adopted due to the dynamic and temporal nature of resilience". The authors categorized the findings into three general dimensions:

Coach stressors (managing the Olympic environment, preparation for major events, coach personal well-being, directing an organization);
Coach protective factors (progressive coaching, coaching support network, maintaining work/life balance, secure working environment, durable motivation, effective decision making);
Enhancing resilience in athletes (developing a strong coach–athlete relationship, creating a facilitative environment, developing a resilience process, athlete individual factors).

PRACTICAL TAKEAWAY - coaches need resilience too and having a framework of how to think about it is a valuable way to identify how to develop it better.

HRV: Fine-tuning training strategy based on heart rate variability

This case study provides some insight into how to apply HRV guidance to your training. The athlete took daily HRV measurements and adjusted his training based on these values over a 23-week period. The process he followed was:

If HRV decreased significantly then high-intensity training was avoided.
If HRV dropped only a little then the number of intervals was reduced.

The results were that:

The runner improved his 800m and 1500m PBs and ranked 7th in the Japanese University Student Championships [qualifying for the championships for the first time].

PRACTICAL TAKEAWAY - in this case study the athlete improved significantly using HRV-guided training.

HRV: The longitudinal relationship among heart rate variability, training load, psychological state, and race performance in an elite middle-distance runner

This is a follow-on study from the previous study adding another year and a 36-week period of HRV-guided training to the athlete's career. He improved again and set two more PBs. Importantly the study sets out a series of practical applications at the end which can help us to further understand how to apply HRV-guided training principles:

Conditioning based on both training and non-training stressors are important for elite athletes. The athlete adjusted his training when [HRV] was low, but an increase in HRV CV could not be prevented. Thus, the management of factors other than training load may be important for elite athletes.
Increase in HRV CV over a period of several weeks may be a predictor of improvement in middle-distance running performance being inhibited.

PRACTICAL TAKEAWAY - HRV-guided training can be a useful way to improve performance, but there needs to be consideration of the bigger picture and not just use of the daily measurements to adjust training.

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