RESEARCH: studies reviewed this week - 14 September 2020 to 20 September 2020

PHYSIOLOGY: The energetics of ultra-endurance running

I've shared a few different studies about ultramarathons and the factors that affect of determine performance in these races. This first study suggested that maximum aerobic speed and leg strength are key to performance. This study suggested certain sacrifices to traditional running economy concepts may be worthwhile because of the differences in marathon races and mountain ultramarathons. This week's study aimed to determine both whether an ultramarathon affects economy and "the role of maximal oxygen uptake (VO(2max)), its fractional utilisation (F) and C(r) in determining the performance".

The authors found that:

(1) the substantial increase of C(r-mean) during the competition yields to marked worsening of the performance;

(2) the three variables F, VO(2max) and C(r-mean) combined as described above explaining 87% of the total competition time variance.

PRACTICAL TAKE AWAY - training to improve running economy, VO2Max and fractional use of VO2Max can improve you ultramarathon performance.

NUTRITION: Glucose–Fructose Enhances Performance versus Isocaloric, but Not Moderate, Glucose

There are a number of studies showing that adding fructose to glucose to create a blended nutrition product can be used to increase the rate of absorbtion of CHO during activity. This study tests the same process and compares a number of different solutions:

  • an artificially sweetened placebo (PL)
  • a moderate-glucose beverage (MG, 1.03 g·min−1)
  • a high-glucose beverage (HG, 1.55 g·min−1)
  • a GF beverage (1.55 g·min−1, 2:1 ratio)

I found the results to be surprising and not what I expected, in comparison with placebo:

  • TT performances were faster with GF (50.4 ± 2.2 min, “very likely” benefit)
  • TT performances were faster with MG (51.1 ± 2.4 min, “likely” benefit)
  • TT performances were faster with HG (52.0 ± 3.7 min, “possible” benefit)

I didn't expect the HG solution to only have a "possible" benefit and also the benefits were relatively small compared to previous CHO studies.

PRACTICAL TAKE AWAY - taking a CHO solution will help performance and it appears that a glucose-fructose blend is the best option.

HYDRATION: Fluid Loss during Exercise-Heat Stress Reduces Cardiac Vagal Autonomic Modulation

This study is particularly interesting me for me because I work with HRV4Training (although the app is designed for daily monitoring rather than in-exercise measurement) and I haven't seen many HRV during exercise studies. Specifically, this study aimed to investigate the effects of "sweat-induced fluid loss during prolonged exercise-heat stress can compromise cardiovascular and thermoregulatory function...on cardiac autonomic modulation". Tha authors found that:

Prolonged exercise heat stress attenuates the vagal influence and complexity of cardiac rhythms, that reduction is further exacerbated by fluid loss, highlighting the importance of fluid replacement in such conditions.

PRACTICAL TAKE AWAY - hydration and fluid replacement during exercise in heat may be an important part of reducing the degradation of performance over the duration of the event.

HYDRATION: Errors in the estimation of hydration status from changes in body mass

I have never tried to weigh myself before and after exercise to determine my hydration status and fluid loss even though I have read about it and heard it suggested as a useful guide to preparing a hydration strategy. This study aimed to quantify the potential errors that may lead to misleading results using this method. The authors found that:

Body mass change is not always a reliable measure of changes in hydration status and substantial loss of mass may occur without an effective net negative fluid balance.

PRACTICAL TAKE AWAY - don't use body mass changes to inform your hydration strategy.

HYDRATION: Effect of high and low rates of fluid intake on post-exercise rehydration

I like this study because it has practical applications to stage races or multi-day events. The authors investigated "the effect of a high (H) and a low (L) rate of post-exercise fluid consumption on plasma volume and fluid balance restoration". Two scenarios were tested on cyclists dehydrated to 3%:

  • they ingested 60%, 40%, and 20% in the 1st, 2nd, and 3rd hours of the recovery period, respectively (H)
  • they ingested 24% x h(-1) during 5 hours (L)

The authors found that:

Plasma volume and fluid balance increased more rapidly in H compared to L. After 6 hours this difference disappeared. It is concluded that H results in a faster rate of plasma volume and fluid balance restoration compared to L, despite a temporary large urine output.

PRACTICAL TAKE AWAY - if you need to hydrate quickly after an event, a strategy of ingesting a CHO-electrolyte solution at 60%, 40% and 20% in the first three hours is more effective than drinking equal amounts over 5 hours.

TRAINING: Effects of Including Sprints in One Weekly Low-Intensity Training Session During the Transition Period of Elite Cyclists

This is a useful study to keep in your notes or records because it becomes relevant each off-season or during periods when decreased training is possible. The authors tested whether including 3 x [3 x 30" sprints] once a week during a low-intensity training period (60% decrease in training volume for 3 weeks) would be better than just cycling at a low intensity during this period. The results showed that:

Including sprints in one weekly LIT-session in the transition period improves sprint performance and maintains 20-min all-out power and fractional utilization of VO2max without compromising mental recovery.

PRACTICAL TAKE AWAY - including sprints once a week during reduced training is an easy and effective way to reduce the loss in performance from usually associated from reduced training.

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