RESEARCH: studies shared from 5 to 11 June 23

Each summary that I prepare adds to my archives and is distributed as a newsletter. If you're interested in either of those you can find them here:

1. All the studies I've shared are available on the RESOURCES PAGE.
2. The weekly summary is distrubted by email through my SUBSTACK NEWSLETTER.

This week's quick summary:

• Training twice every second day vs. training once daily
• Ketone monoester ingestion impairs time trial performance
• Caffeine during exercise in the heat
• Functional overreaching in endurance athletes
• Training intensity distribution among endurance athletes

TRAINING: Skeletal muscle adaptation: training twice every second day vs. training once daily

Deciding how to schedule training sessions over a week is important to optimize performance improvements. I've shared multiple studies on time-intensity distribution which look into these principles and which you can find on my resources page. This study looked to compare training either every day or twice every other day. The authors set up "a study in which seven healthy untrained men performed knee extensor exercise with one leg trained in a low-glycogen (Low) protocol and the other leg trained at a high-glycogen (High) protocol".

STUDY DETAILS

1. The participants trained both legs for one hour on day 1, followed by a two-hour rest in a fasting state. Then, one leg (Low) underwent an additional hour of training, while the other leg (High) rested.
2. On day 2, only the High leg was trained for one hour.
3. This training schedule was repeated for a total of 10 weeks.
4. The increase in maximal workload was found to be the same for both legs, indicating similar improvements in overall fitness.
5. However, the Low leg showed a significantly longer time until exhaustion at 90% compared to the High leg. This suggests that training at a low muscle glycogen content may enhance endurance performance.
6. In conclusion, the present study suggests that training twice every second day may be superior to daily training.

PRACTICAL TAKEAWAY

It is important to note the authors' comments that "coaches and athletes should be careful not to draw practical consequences of the present study with regard to training regimens". Therefore my recommendations are ideas and suggestions about how athletes can think about testing these ideas to see how they apply to training. The main idea to takeaway from this work is that there may be some benefit to training in a glycogen depleted state. This could be achieved by doing two sessions in a day and potentially two hard sessions in a day.

When I share this on Twitter, José Manuel Valverde suggested two options of doing either "2 short HIT sessions a same day" or "weight training (moderate weight high velocity) in the morning [to] potentiate SIT in the evening". Sander Berk suggested that this strategy works well in triathlon training by "concentrating the fast/hard sessions in 1 or 2 days instead of spreading them out over 4-5 days".

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KETONES: Acute ketone monoester supplementation impairs 20-min time-trial performance in trained cyclists

I always try to share new research on ketones because it's an interesting subject and there seems to be many anecdotal reports of athletes using them, but little research to back up the claims of benefits they provide (search for "ketone" on my resources page). In this study the authors tested "the hypothesis that mean power output during a 20-min cycling time trial (TT) would be different after KE ingestion compared to a placebo (PL)".

STUDY DETAILS

1. The study involved 23 trained cyclists (peak oxygen uptake: 65 ± 12 ml·kg-1 min-1) who regularly cycled over five hours per week.
2. Participants underwent a familiarization trial followed by two experimental trials in a randomized, triple-blind, crossover manner.
3. Prior to each trial, participants replicated their diet and exercise routine for approximately 24 hours.
4. In one trial, participants ingested 0.35 g/kg body mass of (R)-3-hydroxybutyl (R)-3-hydroxybutyrate KE, while in the other trial, they consumed a flavor-matched placebo.
5. Results revealed that pre-exercise venous [β-hydroxybutyrate] levels were significantly higher after KE ingestion (2.0 ± 0.6 mM) compared to the placebo (0.2 ± 0.1 mM). Mean TT power output was found to be 2.4% lower after KE ingestion (255 ± 54 W) than after taking the placebo (261 ± 54 W).
6. The mechanistic basis for the impaired TT performance after KE ingestion under the present study conditions remains to be determined.

PRACTICAL TAKEAWAY

The findings of this study are similar to what I've shared in the past so I'm sticking with my previous recommendation:

"My recommendation at this point is that ketones are not beneficial for performance. There is still work to be done to understand ketones better, however, given the cost of these products I would suggest letting others experiment and waiting until the research catches up before trying them."

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CAFFEINE: Caffeine during exercise in the heat

A previous study I shared showed that a "moderate dose of caffeine [5mg/kg] exacerbates hyperthermia-induced hyperventilation and reductions in the cerebral blood flow index during exercise in the heat [37C]". Based on those findings my recommendation at the time was for athletes to test their individual response to using caffeine in the heat. This study is useful as it adds to our understanding of caffeine by testing "the effects of caffeine ingestion on thermoregulation and fluid-electrolyte losses during prolonged exercise in the heat".

STUDY DETAILS

1. Seven endurance-trained cyclists participated in the study.
2. Participants pedaled for 120 minutes at 63% of their maximum oxygen consumption in a hot and dry environment.
3. The experiment included six conditions:
   • No fluid replacement (NF)
   • Rehydration with water (WAT) to compensate for 97% of sweat losses
   • Rehydration with a 6% carbohydrate-electrolyte solution (CES) to compensate for 97% of sweat losses
   • Caffeine ingestion (6 mg/kg body weight) + no fluid replacement (C(AFF) + NF)
   • Caffeine ingestion + rehydration with water (C(AFF) + WAT)
   • Caffeine ingestion + rehydration with a carbohydrate-electrolyte solution (C(AFF) + CES)
4. Without fluid replacement, the participants experienced a significantly higher final rectal temperature (T(REC)) compared to the rehydration conditions.
5. Caffeine did not affect heat production, forearm skin blood flow, or sweat rate. However, when combined with the carbohydrate-electrolyte solution, caffeine tended to increase T(REC) compared to the solution alone.
6. Caffeine intake also led to higher sweat losses of sodium, chloride, and potassium and increased urine flow.

PRACTICAL TAKEAWAY

The authors found that "caffeine ingested alone or in combination with water or a sports drink was not thermogenic or impaired heat dissipation". This is good news and supports the use of caffeine in hot conditions. I suggest using the well-established approach of taking 3-6mg/kg an hour before a race.

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TRAINING: Functional overreaching in endurance athletes

Athletes are always walking a fine line between a training load they can adapt to and doing too much training. The goal is to optimize performance and that means doing as much as possible, while hopefully not going too far and risking overtraining. This review is useful in that it provides an update on "the most recent research on functional overreaching (FOR) in endurance athletes".

STUDY DETAILS

1. Endurance athletes show diverse responses to short-term periods of increased training load, with some improving without negative effects on performance, while others experience diminished exercise performance for days to months.
2. The time course of performance decrement and subsequent restoration, known as super-compensation, distinguishes functional overreaching (FOR), non-functional overreaching (NFOR), and overtraining syndrome.
3. Short-term transient training-induced decrements in performance, such as FOR, are intentionally incorporated into training programs to promote physiological adaptations and performance super-compensation.
4. FOR has been associated with negative cardiovascular, hormonal, and metabolic effects, and recent studies have shown dampened training and performance adaptations in FOR athletes compared to non-overreached athletes.
5. Contextual factors may influence the metabolic consequences of FOR, and classifying this training-induced state of fatigue solely based on performance decrement might oversimplify the situation.
6. Understanding the nuances of FOR in endurance athletes is crucial for optimizing training strategies. While deliberately inducing FOR may be necessary for performance super-compensation, it is important to consider the potential negative cardiovascular, hormonal, and metabolic consequences.

PRACTICAL TAKEAWAY

The authors suggest that "there does not seem to be evidence to suggest that FOR is necessary to induce performance improvements in trained endurance athletes". My recommendation would be to be conservative in training and to back off whenever there are indicators of overreaching. A study I shared before showed that "functional overreaching can be determined effectively by non-invasive means" and I would recommend becoming familiar with those parameters and measuring them consistently.

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TRAINING: The training intensity distribution among well-trained and elite endurance athletes

This review that investigated "the training intensity distribution (TID) of nationally and internationally competitive athletes in different endurance disciplines to determine the optimal volume and intensity for maximal adaptation".

When I shared this on Twitter, Tom Hughes warned me about some issues of the bias and unsubstantiated conclusions the authors arrived at. As a result, I have taken key points from the results and based on the studies that were referenced in this review to highlight here.

STUDY DETAILS

1. Most retrospective studies report a pyramidal TID, with extensive high-volume low-intensity training (HVLIT) (>70%), less time in zone 2, and very little time spent in zone 3, independent of the time of season.
2. Athletes favor HVLIT, since when the training volume is high, low intensity training (< 2 mM or ~55–85% HRmax) is more tolerable.
3. Since the amount of HVLIT has been linked to improved race performance, the necessity of HVLIT in achieving physiological adaptations for gains in performance has been pointed out in longitudinal observations and experimental designs.
4. However, when the amount of HVLIT by elite athletes is doubled, no further improvement in performance is evident, and the athletes mood may be negatively affected.
5. Therefore, for elite endurance athletes with high amounts of HVLIT, the ability to distribute the training intensity optimally may be paramount to both success and counteracting non-functional overreaching.
6. Most retrospective studies on well-trained to elite endurance athletes report a pyramidal TID, with a large proportion of HVLIT. Polarized TID has been proven to be an effective strategy for some elite athletes during certain phases of the season.

Figure 1 from the paper shows the various TID results from a range of source papers across all parts of a training year:

PRACTICAL TAKEAWAY

Most elite athletes are performing a high volume of low-intensity training year round. My recommendation would be to follow this approach and then to use a periodised approach to select what to focus on in the remaining training time. One of the best approaches is to perform high-intensity training that most closely resembles race pace close to events. Then plan each preceding period moving from the most specific to the least specific high-intensity training stimulus. For an ultramarathon runner, this could mean starting the training year with VO2 Max focused intervals (the least specific training), then moving towards threshold focused training, and finally completing a block of steady state (race pace and the most specific training) just before the taper.

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