RESEARCH: Studies reviewed this week: 29 November 2021 to 5 December 2021

HRV: Training Load, Heart Rate Variability, Direct Current Potential and Elite Long Jump Performance Prior and during the 2016 Olympic Games

The authors explain that the "primary objective of this investigation was to investigate the relationships between training load (TL), heart rate variability (HRV) and direct current potential (DC) with elite long jump performance prior to and during the 2016 Olympics Games". Following the athletes for a 16-week period and during the Olympic Games the authors found that:

Successful compared to unsuccessful intra-athlete performances were characterised by a higher chronic TL.
There were also negative correlations between HRV and performance and HRV was significantly lower for more successful performances.

The authors concluded that:

Monitoring sRPE and HRV measures and manipulating TL prior to competition seems worthwhile for elite long jump athletes.

PRACTICAL TAKEAWAY - monitoring sRPE, HRV and TL are important for elite athletes. However, it's critical to understand how they respond to TL and what HRV profiles to expect for each athlete.

SLEEP: Monitoring Effects of Sleep Extension and Restriction on Endurance Performance Using Heart Rate Indices

I have shared a number of resources on sleep including looking at sleep extension and deprivation (see the resources page). This study set out to quantify this by examining "whether HR indices are sensitive to changes in readiness following sleep restriction (SR) and sleep extension (SE)".

Athletes underwent three interventions: SR = time in bed was reduced by 30%, NS = normal sleep, SE = time in bed extended 30%. The authors looked specifically at exercise intensity ratios incorporating mean HR, mean power (W), and perceived exertion (RPE) were recorded at steady state during constant-load tests (W:HRSS) and during TTs (W:HRTT, RPE:HRTT). They found that:

RPE:HRTT was lower on day 4 of SE when TT performances were faster.
Compared with day 1 of SR, RPE:HRTT was higher on day 3 and day 4 of SR.
Intensity ratios incorporating mean HR seem sensitive to effects of sleep duration on athlete readiness to perform.

PRACTICAL TAKEAWAY - sleep can have an impact on intensity perception and readiness to perform. Carefully consider your sleep strategy leading into races and if necessary try to increase sleep through sleep extension strategies.

HRV: Acute effects of long-distance races on heart rate variability and arterial stiffness

This systematic review "quantified the effects of running a long-distance race (LDR) on heart rate variability (HRV) and arterial stiffness (AS)". The authors looked at a range of metrics in 52 studies pre- and post-event including:

Standardised mean difference pre- and post-race of various time-domain and frequency-domain indices of HRV, mean arterial blood pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP) and carotid-femoral pulse wave velocity (cfPWV) was calculated.

They found that:

Regarding HRV, there was a significant decrease in most of the variables considered as markers of parasympathetic activity, indicating a shift of autonomic balance towards a reduced vagal tone.
Regarding vascular variables, there was a significant drop in blood pressure and reduced AS.

PRACTICAL TAKEAWAY - running a long-distance race has significant acute effects on HRV and vascular properties.

TRAINING LOAD: Monitoring training status with HR measures

This review provides a broad range of insights into monitoring training using heart rate measures. A couple of key points:

Most of the contradictory findings are related to methodological inconsistencies and/or misinterpretation of the data rather than to limitations of heart rate measures to accurately inform on training status.
The decision to use a given measure should be based upon the level of information that is required by the athlete, the marker's sensitivity to changes in training status and the practical constrains required for the measurements.
The data reviewed in the present manuscript suggest that 5 min of resting HR(V) aimed at capturing cardiac parasympathetic activity, together with submaximal exercise HR (last min of a 4–5 min cycling/running bout) are likely the most useful monitoring variables.

PRACTICAL TAKEAWAY - this is a very informative paper with extensive details on how to use and interpret HR and HRV metrics. I highly recommend reading it in detail.

SUPPLEMENTATION: Impact of Magnesium Supplementation in Muscle Damage of Professional Cyclists Competing in a Stage Race

The purpose of this study was to "analyze the effects of magnesium supplementation in preventing muscle damage in professional cyclists taking part in a 21-day cycling stage race". In the intervention group supplementation consisted of an intake of 400 mg/day of magnesium during the 3 weeks of competition. The authors found that:

Serum and erythrocyte magnesium levels decreased during the race. Circulating tissue markers increased at the end of the race in both groups.
However, myoglobin increase was mitigated in the supplemented group compared with the controls.
We conclude that magnesium supplementation seems to exert a protective effect on muscle damage.

PRACTICAL TAKEAWAY - magnesium supplementation during heavy blocks of training may protect against muscle damage. The study used 400mg/day as their dose.

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