RESEARCH: Studies reviewed this week: 11 October 2021 to 17 October 2021

NUTRITION: SUPPLEMENT - Sodium bicarbonate ingestion mitigates the heat-induced hyperventilation and reduction in cerebral blood velocity during exercise in the heat

In this study the authors combined two previous sets of knowledge about exercising in the heat and sodium bicarnonate to test "whether sodium bicarbonate ingestion suppresses heat-induced hyperventilation and the resultant hypocapnia and cerebral hypoperfusion during prolonged exercise in the heat". The doses used were:

0.3 g/kg body weight of sodium bicarbonate ingested 90' before exercise in a heat of 35C.

The results showed that:

Minute ventilation (VE) gradually increased with exercise duration in the NaCl trial, but the increases in VE were attenuated in the NaHCO3 trial. Correspondingly, estimated PaCO2 and middle cerebral artery blood velocity (an index of anterior cerebral blood flow) were higher in the NaHCO3 than the NaCl trial.
Ratings of perceived exertion were lower in the NaHCO3 than the NaCl trial.

PRACTICAL TAKEAWAY - sodium bicarbonate may enhance performance in hot environments.

PHYSIOLOGY: Analysis of Fractal Correlation Properties of Heart Rate Variability during an Initial Session of Eccentric Cycling

This study investigated the behavior of DFA1a during eccentric exercise. While the study was aimed at understanding an intensity metric that could be used to prescribe eccentric training to patients with cardiovascular disease, it elucidates the relationship between DFA1a and HR during eccentric training. The authors explain why this is an interesting area to research:

Eccentric cycling (ECC) has garnered interest as an exercise modality to promote locomotor muscle improvements at reduced cardiovascular demands compared to conventional concentric cycling. ECC can be performed at much higher power levels, resulting in enhancement of muscular size, strength, and oxidative properties. However, it appears that ECC cycling offers no benefit for peak aerobic training over CON methods. Therefore, this modality is particularly suited for rehabilitation purposes in patients with cardiovascular or pulmonary disease who are unable to mount sufficient muscular pedaling force due to inherent limitations.

Some highlights from the results are that:

As expected, the power output was higher during ECC than CON and remained stable throughout the 45 min of exercise. VO2 remained stable and similar in both CON and ECC at T10 and T45. However, the results indicate a heterogenous response in HR and DFA a1 at ECC T45, despite a cycling intensity well below the first ventilatory threshold.
Of interest, the difference in DFA a1 between ECC vs. CON was correlated with that of the HR, meaning that the more the HR increased during ECC vs. CON, the more DFA a1 decreased.

PRACTICAL TAKEAWAY - the behavior of DFA1a during eccentric exercise is different to that during concentric exercise.

NUTRITION: SUPPLEMENT - Blueberry supplementation reduces the blood lactate response to running in normobaric hypoxia but has no effect on performance in recreational runners

I've never heard of blueberries being used as a supplement before, however, the authors of this study explained that:

Blueberries are concentrated with anthocyanins possessing antioxidant properties. As these properties counter fatigue, blueberry supplementation may improve performance and recovery, particularly in hypoxia, where oxidative stress is elevated.

The authors tested the "effects of blueberry supplementation on running performance, physiological responses, and recovery in normobaric hypoxia" through a time trial performance. They found that:

No significant differences were observed in the distance run during the TT, HR, SaO2, and RPE.
The post-TT increase in blood lactate was significantly lower in BLU than PLA.

PRACTICAL TAKEAWAY - there is no ergogenic benefit to blueberries in hypoxic conditions.

HEAT: Effects of heat acclimation and acclimatisation on maximal aerobic capacity compared to exercise alone in both thermoneutral and hot environments

I'm always interested to learn more about adaptations to heat acclimation (HA) (see all the studies already available on the resources page) so a meta-anaysis of the previous work that has been done is very useful to provide a recap and context. The authors of this paper found that:

HA can enhance VO2Max adaptation in thermoneutral or hot environments by at least a small and up to a moderate-large amount.

The key variables to consider when designing a HA protocol were:

Longer (>7 days) and hotter (up to 40C) HA programmes appear to confer the greatest benefits on hot VO2 Max when compared to controls.
Planned performance too close to the final day of HA if complete hot VO2 Max adaptation is to be realised. Extending this up to 7 days appears to be optimal.

PRACTICAL TAKEAWAY - optimal performance in hot environments requires heat adaptation and a programme of greater than 7 days at up to 40C at least 7 days before competition appears to be the best protocol.

NUTRITION: SUPPLEMENTS - Dietary Nitrate Intake Is Positively Associated with Muscle Function in Men and Women Independent of Physical Activity Levels

Nitrate supplementation has been studied for it's performance benefits, however, "whether higher habitual dietary nitrate is associated with better muscle function remains underexplored". This study set out to understand this by looking at data over a 12 year period and testing muscle function and physical activity. The findings were that:

Individuals in the highest tertile of nitrate intake (median intake: 91 mg/d) had 2.6 kg stronger knee-extension strength (KES) (11%) and 0.24 s faster 8ft-TUG (4%) compared with individuals in the lowest tertile of nitrate intake.
∼81% [of nitrate intake was] derived from vegetables.

PRACTICAL TAKEAWAY - make sure you're eating enough nitrate-rich vegetables!

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