RESEARCH: Studies reviewed this week: 22 March 2021 to 28 March 2021

HYDRATION: Effect of oral rehydration solution versus spring water intake during exercise in the heat on muscle cramp susceptibility of young men

Muscle cramping is a difficult issue to manage and prevent. The "causes of exercise-associated muscle cramp (EAMC) are likely to be multifactorial, but dehydration and electrolytes deficits are considered to be factors". This study set out to determine if "post-exercise muscle cramp susceptibility would be increased with spring water ingestion, but reduced with oral rehydration solution (ORS) ingestion during exercise".

The test conditions were challenging and also useful for trail and ultramarathon runners as the simulated trail running conditions:

Ten men performed downhill running (DHR) in the heat (35–36 °C) for 40–60 min to reduce 1.5–2% of their body mass in two conditions (spring water vs ORS) in a cross-over design. The body mass was measured at 20 min and every 10 min thereafter during DHR, and 30 min post-DHR. The participants ingested either spring water or ORS for the body mass loss in each period.

The authors found that:

These results suggest that ORS intake during exercise decreased muscle cramp susceptibility. It was concluded that ingesting ORS appeared to be effective for preventing EAMC.

PRACTICAL TAKEAWAY - drinking an oral rehydration solution may result in lower cramping susceptability. Make sure to rehydrate after training and to do so with a hydrating solution (this could be particularly important if training multiple times a day or during a stage race).

SLEEP: Short‐term sleep deprivation and human thermoregulatory function during thermal challenges

Last week I shared a couple of studies on the importance of sleep (you can find them here). This paper set out to summarize "the current state of human‐based evidence on the impact of short‐term (i.e., ≤4 nights) sleep deprivation on autonomic and behavioural thermoeffectors during acute exposure to low and high ambient temperatures".

The key point in this narrative review is that:

Limited‐to‐moderate evidence suggest that sleep deprivation per se impairs thermoregulatory defence mechanisms during exposure to thermal extremes.

PRACTICAL TAKEAWAY - this highlights another potential downside to sleep deprivation. As I said last week: get enough sleep!

SLEEP: Patterns of performance degradation and restoration during sleep restriction and subsequent recovery

Following on from the previous studies on sleep, this study set out to determine the amount of degradation of performance due to sleep deprivation and then the rate at which this performance would return after sleep restoration. The protocol of the study was:

Sixty-six normal volunteers spent either 3, 5, 7, or 9h daily time in bed (TIB) for 7 days (restriction/augmentation) followed by 3 days with 8 h daily TIB (recovery).

The authors found that:

  • In the 3-h group, speed (mean and fastest 10% of responses) on the psychomotor vigilance task (PVT) declined, and PVT lapses (reaction times greater than 500 ms) increased steadily across the 7 days of sleep restriction
  • In the 7- and 5-h groups speed initially declined, then appeared to stabilize at a reduced level; lapses were increased only in the 5-h group.
  • In the 9-h group, speed and lapses remained at baseline levels.
  • During recovery, PVT speed in the 7- and 5-h groups (and lapses in the 5-h group) remained at the stable, but reduced levels seen during the last days of the experimental phase, with no evidence of recovery.
  • Speed and lapses in the 3-h group recovered rapidly following the first night of recovery sleep; however, recovery was incomplete with speed and lapses stabilizing at a level comparable with the 7- and 5-h groups.

The authors conclude that:

These results suggest that the brain adapts to chronic sleep restriction. In mild to moderate sleep restriction this adaptation is sufficient to stabilize performance, although at a reduced level.

PRACTICAL TAKEAWAY - sleep deprivation reduces performance and it is slow to recover. Again, get enough sleep and if you are sleep deprived be patient about the rate of return to performance whn you get back to normal sleep patterns.

TRAINING: The Influence of Training Load on Hematological Athlete Biological Passport Variables in Elite Cyclists

This study looked at the impact of training load on the biological passport (ABP). While this is interesting in itself, I'm more interested to learn what the impact of these training loads had on the blood qualities of athletes to understand how to adapt and adjust training. The study investigated:

Total hemoglobin mass (Hbmass) and plasma volume (PV) were measured by carbon monoxide rebreathing. Acute and chronic training loads–respectively 5 and 42 days before sampling–were calculated considering duration and intensity (training stress score, TSSTM).

The results showed that:

Higher acute–but not chronic—training loads were associated with significantly decreased hemoglobin concentration. Our results support that acute training load variations significantly affect (Hb), likely due to short-term PV fluctuations.

PRACTICAL TAKEAWAY - acute training load impacts the blood profile most likely due to plasma volume. This could be related to dehydration so that may be something to be wary of during high acute training loads.

TRAINING: Re-thinking athlete training loads: would you rather have one big rock or lots of little rocks dropped on your foot?

Training load is something that is difficult to manage and to quantify (have a look at all the papers I've already shared on this topic on the resources page). The general principle is that the "total load calculations are the product of exercise intensity and duration". In this paper the authors argue that:

These methods may be limited, however, as they do not account for non-linearities in the biological response to stress, with the end result being that they fail to fully account for the load imposed by high-intensity or interval-based training sessions.

PRACTICAL TAKEAWAY - be cautious when interpreting training load metrics. They may not always reflect the entirety of the load that an athlete is facing.

HEAT: Stability of Heart Rate at Physiological Thresholds Between Temperate and Heat Stress Environments in Endurance-Trained Males

This paper addresses the question of whether or not you should adjust your training heart rate zones when training in a heat stress environment. The protocol the authors used was:

A total of 16 endurance-trained cyclists and triathletes performed incremental exercise assessments in 18°C and 35°C (both 60% relative humidity) to determine heart rates at absolute blood lactate and ventilatory thresholds.

The results showed that:

The coefficient of variation for heart rate at these blood lactate concentrations and ventilatory thresholds between conditions was low, with significant strong positive correlations between measurements in the 2 environments.
These data indicate heart rates measured at physiological thresholds in temperate environments are reflective of measurements taken under moderate environmental heat stress.

PRACTICAL TAKEAWAY - use your normal training zones when going to heat stress environments.

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