RESEARCH: Studies reviewed this week: 6 June 2021 to 13 June 2021

PHYSIOLOGY: Respiratory frequency is strongly associated with perceived exertion during time trials of different duration

This study provided an insight into a potential sensation for pacing and effort. The authors set out to "provide further insight into the link between respiratory frequency (fR) and the rating of perceived exertion (RPE)". I find this interesting as the frequency of respiration can be used as a cue or means of calibrating effort during a run or cycle.

The authors found that:

Unlike the relationship between RPE and both minute ventilation and HR, the relationship between RPE and frequency of respiration was not affected by exercise duration.
These findings indicate that fR is the best correlate of RPE during self-paced exercise, at least among the parameters and for the range of durations herein investigated.

PRACTICAL TAKEAWAY - learning what the rate of breathing feels like at different effort levels can be used to guide your effort during different training sessions or races.

NUTRITION: Effects of nonnutritive sweeteners on body weight and BMI in diverse clinical contexts

This study set out to understand "the possible influences of nonnutritive sweeteners (NNS) on body weight". Endurance athletes are often concerned with weight as it is an important component of the power-to-weight output that can be a determinant of success. While NNS are not generally recommended, sometimes a broad understanding of the tools or options available can help with weight loss strategies.

In this study the authors found that:

Participants with overweight/obesity and adults showed significant favourable weight/BMI differences with NNS.
Data suggest that replacing sugar with NNS leads to weight reduction, particularly in participants with overweight/obesity under an unrestricted diet.

PRACTICAL TAKEAWAY - nonnutritive sweeteners can be effective at helping with weight loss.

HRV: Cardiac parasympathetic reactivation following exercise

In this review the authors set out to understand the different markers of cardiovascular recovery and parasympathetic reactivation after training. This helps to athletes and coaches to understand the impact of each training session. The authors explain the important and rational for looking at these markers:

As a marker of cardiovascular recovery, cardiac parasympathetic reactivation following a training session is highly individualized. It appears to parallel the acute/intermediate recovery of the thermoregulatory and vascular systems, as described by the supercompensation theory.

The findings of the review showed that:

Our results demonstrate that the time required for complete cardiac autonomic recovery after a single aerobic-based training session is up to 24 h following low-intensity exercise, 24-48 h following threshold-intensity exercise and at least 48 h following high-intensity exercise.
Our data lend support to the concept that in conjunction with daily training logs, data on cardiac parasympathetic activity are useful for individualizing training programmes.

PRACTICAL TAKEAWAY - using HRV along with training logs and a training plan can result in the optimal training programme.

HRV: Autonomic recovery after exercise in trained athletes

Similar to the study mentioned above, this study set out to investigate "the effects of training intensity and duration, through a range representative of training in endurance athletes, on acute recovery of autonomic nervous system (ANS) balance after exercise".

The authors found that:

When highly trained athletes (HT) ran 60 or 120 min below VT1, HRV returned to pretraining values within 5-10 min.
However, training at threshold (2.7 +/- 0.4 mM) or above VT2 (7.1 +/- 0.7 mM) induced a significant, but essentially identical, delay of HRV recovery (return to baseline by approximately 30 min).
The first ventilatory threshold may demarcate a "binary" threshold for ANS/HRV recovery in highly trained athletes, because further delays in HRV recovery with even higher training intensities were not observed.

PRACTICAL TAKEAWAY - exercise intensity impacts the rate of recover of the automomic nervous system so it is important to control your intensity in training (especially with respect to staying below AeT / VT1).

HRV: Post-exercise cardiac autonomic and cardiovascular responses to heart rate-matched and work rate-matched hypoxic exercise

This study is great because it provides some insight into how best to manage intensity in hypoxic exercises. The authors set out to investigate "the effect of performing hypoxic exercise at the same heart rate (HR) or work rate (WR) as normoxic exercise on post-exercise autonomic and cardiovascular responses".

The findings were that"

Moderate HR-matched hypoxic exercise mimicked post-exercise autonomic responses of normoxic exercise without resulting in significant post-exercise hypotension (PEH).
Conversely, WR-matched hypoxic exercise impacted upon post-exercise autonomic and cardiovascular responses, delaying cardiac autonomic recovery, temporarily decreasing cardiac baroreflex sensitivity (cBRS) and evoking prolonged PEH.

PRACTICAL TAKEAWAY - if you're training in an hypoxic environment, use HR matched workload rather than work-rate matched workloads to control your training load.

SLEEP: Associations between sleep and in-race gastrointestinal symptoms

The purpose of this study states that "it remains unstudied whether poor sleep is involved in the etiology of gastrointestinal (GI) problems in athletes". I'm not surprised that it hasn't been studied, but now that the authors have done this work it is interesting to look at GI issues are one of the most common issues for endurance athletes.

The authors found that:

Sleep Problems Index (SPI-I) scores correlated with in-race upper GI symptoms.
Controlling for anxiety attenuated this association, while other control variables had little effect.
Chronic sleep dysfunction is modestly correlated with in-race upper GI symptoms.

PRACTICAL TAKEAWAY - make sure to get enough sleep as even GI issues can result from sleep dysfunction.

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