RESEARCH: Studies reviewed this week: 15 February 2021 to 21 February 2021

NUTRITION: Glycogen resynthesis in human muscle fibre types following exercise-induced glycogen depletion

I recently shared this excellent article on the fundamentals of glycogen meatbolism. In this study the authors looked into the topic in even more detail, investigating "glycogen resynthesis in type I and II fibres using biochemical methods of analysis".

The authors found that:

  • In the initial 3 h of recovery, there was a 25 +/- 8% higher rate of resynthesis in type I compared with type II fibres.
  • Between 3 and 10 h of recovery, resynthesis in type I fibres declined by 60 +/- 13% whilst the rate in type II fibres was maintained.

Leading them to conclude that:

The higher initial glycogen resynthesis rate in type I fibres may be attributable to fibre-type differences in glucose uptake and disposal.

PRACTICAL TAKEAWAY - this may have implications for doing doubles on a training day as it appears that the type II fibres will most likely not have achieved full glycogen resynthesis before the second training session.

TRAINING: Running behaviors, motivations, and injury risk during the COVID-19 pandemic: A survey of 1147 runners

2020 was an unusual for training and racing with many athletes changing their habitual behaviours. This study investigated the "influence of the COVID-19 pandemic on running volume, behaviors, motives, and RRI changes from the year prior to the pandemic to the timeframe during social isolation restrictions".

The key findings were that runners reported:

  • increased runs per week
  • increased mileage and sustained runs
  • less motives to train
  • less workouts
"These results provide insights into how physical activity patterns were influenced by large-scale social isolation directives associated with the pandemic."

PRACTICAL TAKEAWAY - during the pandemic it appears that runners turned to running for more than just performance or training benefits.

TRAINING: More than a Metric: How Training Load is Used in Elite Sport for Athlete Management

I've shared multiple different studies on training load (see the resources page) as it is an important concept to consider. This editorial provides an excellent overview on the topic and some ideas on how best to use training load. A couple of key highlights include:

Currently, athlete monitoring stands between art and science, with practitioners working to contextualise load-related data within the decision-making process.
Both injury and performance are multifactorial and cannot be explained by any risk factor in isolation.
In this vein, while training load management is highly complex and imperfect, it is an important piece of the puzzle to help guide decisions for maximising player performance, welfare, and team success.

PRACTICAL TAKEAWAY - understanding and managing training load is important and cannot be outsourced to single metrics or factors.

HEAT: Heat Reacclimation using Exercise or Hot Water Immersion

Heat reacclimation (HRA) is an important topic for athletes preparing for races in hot environments. Understanding how best to reacclimate after a training camp or competition and the next competition will allow athletes to optimise their performance in hot environments. "The aim of this study was to compare the effectiveness of exercise versus hot water immersion heat re-acclimation (HRA) protocol".

The protocol of the study was as follows:

Heat stress test 1 (HST1) was prior to a 10-day controlled hyperthermia (CH) heat acclimation protocol, and HST2 immediately after. Participants completed HST3 after a 28-day decay period without heat exposure.

The authors found that:

HRA protocol may not be necessary for cardiovascular and thermal adaptations within a 28-day decay period, as long as a 10-day CH-HA protocol has successfully induced these physiological adaptations. For sweat adaptations, a 5-day CH or HWI-HRA protocol can reinstate the lost adaptations.

PRACTICAL TAKEAWAY - a 10-day heat training camp can have adaptations that last for up to a month. This is useful for planning acclimation training camps.

TRAINING: Hepcidin response to three consecutive days of endurance training in hypoxia

An interesting recent addition to altitude training has been the ideas of training in an hypoxic environment. This study set out "to determine the effects of 3 consecutive days of endurance training in hypoxia on hepcidin responses".

The authors found that:

Serum iron, ferritin and ketone body concentrations increased significantly in both trials on days 2-4 compared with day 1, with no significant differences between trials.
Serum hepcidin concentrations also increased significantly on days 2-4 compared with day 1 in both trials, with no significant differences observed between trials.

PRACTICAL TAKEAWAY - it does not appear that three days of training in hypoxic conditions has any additional benefit over normal training protocols.

PHYSIOLOGY: Effect of marathon and ultra‐marathon on inflammation and iron homeostasis

This study set out to compare the differences between "the impact of marathon (M) and ultra‐marathon (UM) on inflammation and iron homeostasis".

The key findings were that:

Biomarkers of inflammation (leucocytes, neutrophil granulocytes, monocytes, and c‐reactive protein [CRP]) increased significantly after both marathon and ultra‐marathon with higher levels of CRP after ultra‐marathon compared with marathon both immediately after the race and at follow‐up.
Concentrations of ferritin also increased significantly after both races and remained high at follow‐up. Higher levels of ferritin immediately after the race and at follow‐up were found in ultra‐marathon finishers. The observed increase of serum iron and transferrin saturation (TSAT) after marathon and the decrease of serum iron and TSAT after ultra‐marathon resulted in a significant absolute difference between the two races.

PRACTICAL TAKEAWAY - the duration of ultramarathon events has significant impacts on both inflammation and iron homeostasis beyond the impacts seen in a marathon alone.

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