RESEARCH: Studies reviewed this week: 24 May 2021 to 30 May 2021

NUTRITION: Non-invasive and minimally invasive glucose monitoring devices: a systematic review and meta-analysis on diagnostic accuracy of hypoglycaemia detection

Continuous blood glucose monitors (CGM) are becoming available for consumers and have become quite popular for endurance athletes. This review set out to "the diagnostic accuracy of minimally and non-invasive hypoglycaemia detection in comparison to capillary or venous blood glucose". The authors concluded that:

Overall, the present data suggest that minimally and non-invasive monitoring systems are not sufficiently accurate for detecting hypoglycaemia in routine use.

PRACTICAL TAKEAWAY - while CGM data may be interesting and may prove to be useful, it's worth noting that the current level of accuracy for these devices is not very high.

TRAINING: Retrospective Analysis of Training and Its Response in Marathon Finishers Based on Fitness App Data

I find analysis of actual training to be a useful way to understand what type of training is effective. This type of review can help to inform training and provide evidence for the efficacy of training theories. In this study the authors set out to conduct "a retrospective analysis of training responses during a 16 weeks training period prior to an absolved marathon".

The authors found that:

Subjects allocated in the faster marathon performance group showed systematically higher training volume and higher shares of training at low intensities.

Only subjects in the moderate and high response group increased their training velocity continuously along the 16 weeks of training.

Maximized training volumes at low intensities, a continuous increase in average running speed up to the aimed marathon velocity and high intensity runs ≤ 5 % of the overall training volume was accompanied by an improved 10 km performance which likely benefited the marathon performance as well.

PRACTICAL TAKEAWAY - training volume and intensity control within that training (easy low-intensity days) are critical to marathon performance.

PHYSIOLOGY: Extreme events reveal an alimentary limit on sustained maximal human energy expenditure

This study is quite interesting and perhaps an unusual concept to explore. The idea is that there are limits to how much energy can be sustainable used by athletes on a continuous basis. This type of study has implications for long multi-stage races and expeditions. The authors explain that "the limits on maximum sustained energy expenditure are unclear but are of interest because they constrain reproduction, thermoregulation, and physical activity".

The authors looked at a range of sports and endeavors from Tour de France cyclists and nordic skiers to Race Across America cyclists and polar explorers. This allowed for comparisons across events and also in a range of environment conditions. The conclusion of the study was that:

Whatever the physiological mechanism, the strong relationship between sustained metabolic scope (SusMS) and duration reveals a common underlying framework uniting the full range of protracted endurance endeavors among humans, from exploration to sport and reproduction.

The relationship between SusMS and duration flattens out at ~2.5× basal metabolic rate (BMR), suggesting a metabolic ceiling for habitual metabolic scope (often termed “physical activity level”) in humans.

Prolonged expenditure above this metabolic ceiling (~2.5× BMR) requires consuming energy reserves and is not sustainable indefinitely.

PRACTICAL TAKEAWAY - there are upper limits to sustained metabolic expenditure and it is at roughly 2.5 x BMR. This has implications for big training weeks and training camps and of course long races.

RECOVERY: Supplemental O2 During Recovery Does Not Improve Repeated Maximal Concentric-Eccentric Strength-Endurance Performance in Hypoxia

This study set out to determine if there is an effective method using supplemental O2 to improve recovery in hypoxia. The authors wanted to test if "hyperoxic recovery between 5 sets of high-intensity strength-endurance exercises, which resembled ski racing activity and were performed in hypoxia, has beneficial effects on performance and acid-base status".

The authors concluded that:

Positive effects on arterial oxygen content and cellular metabolism, as indicated by reduced blood lactate levels during recovery in the hyperoxic setting, seem to be insufficient to generate a direct effect on performance.

Hyperoxic recovery has no impact on performance in a setting resembling alpine ski racing training.

PRACTICAL TAKEAWAY - hyperoxic recovery does not seem to help in hypoxia conditions.

HRV: Heart-rate variability: a biomarker to study the influence of nutrition on physiological and psychological health?

I've shared some good studies on HRV and using it to guide training (see resources page). This study looked at health and tried to identify biomarkers that could help understand the "influence of diet on health". The authors point out that:

Reduced HRV is associated with the development of numerous conditions for example, diabetes, cardiovascular disease, inflammation, obesity and psychiatric disorders.

Various aspects of diet have been shown to benefit HRV acutely and in the longer term. Examples include a Mediterranean diet, omega-3 fatty acids, B-vitamins, probiotics, polyphenols and weight loss. Aspects of diet that are viewed as undesirable, for example high intakes of saturated or trans-fat and high glycaemic carbohydrates, have been found to reduce HRV.

They conclude that:

HRV has the potential to become a widely used biomarker when considering the influence of diet on mental and physical health.

PRACTICAL TAKEAWAY - track your HRV!

PSYCHOLOGY: Psychological components of effort sense

Training load and using sensations are something that I believe are important for optimally managing training. However, perception or effort (or RPE) "is governed by many physiological, psychological, and experiential factors". The authors explain a number of factors that influence perception of effort:

It has been shown that anxiety, somatic perception, depression, and neuroticism are associated with perceived exertion

Extroversion has been found to be inversely correlated with perceived exertion, and positively correlated with preferred exercise intensity.

The important point here is that"

It has also been found that perception of effort can be increased and decreased in a systematic manner with various psychological interventions such as hypnotic suggestion, dissociative cognitive strategies, and imagery.

PRACTICAL TAKEAWAY - perception of effort is a useful means of measuring intensity, but it can be influenced by multiple outside psychobiological factors which can be either utilised to improve performance or which need to be limited to reduce negative impact on performance.