RESEARCH: studies shared from 13 to 19 Mar 23

All the studies I've shared are available on the RESOURCES PAGE.

This week's quick summary:

• Training load metrics and acute performance decrements after training sessions
• Effectiveness of a short-term heat acclimation protocol
• Exogenous ketone supplements in athletic contexts
• Maximal time spent at VO2 Max from sprints to the marathon
• Metabolic adaptations to weight loss

TRAINING: Training load and acute performance decrements following different training sessions

On my resources pages I have a number of studies which have investigated different training load metrics. It is important to quantify the demands of training and there are multiple different tricks that can be used. This study set out "to examine the differences in training load (TL) metrics when quantifying training sessions differing in intensity and duration".

STUDY DETAILS

1. Eleven male recreational cyclists performed 4 training sessions in a random order, immediately followed by a 3-km time trial (TT).
2. The training sessions were quantified using 7 different TL metrics, 4 using heart rate as input, 2 using power output, and 1 using the rating of perceived exertion.
3. The load of the sessions was estimated differently depending on the TL metrics used.
4. TL using the rating of perceived exertion was the only metric showing a response that was consistent with the acute performance decrements found for the different training sessions.
5. The Training Stress Score and the individualized training impulse demonstrated similar patterns but overexpressed the intensity of the training sessions.
6. The load based on TL using the rating of perceived exertion was the only one in line with the acute performance decrements found in this study.

PRACTICAL TAKEAWAY

Training load metrics show different levels of response to the same training session. Therefore it is important to compare the same training load metric over time (don't mix and match different metrics) and to be aware of the biases inherent in each metric. Session rating of perceived exertion (sRPE) appears to be the most consistent and reliable metric so I would recommend always using this first before considering other additional metrics.

HEAT: Effectiveness of short-term isothermic-heat acclimation (4 days) on physical performance in moderately trained males

I've shared heat acclimation (HA) protocols in the past that typically use a period of two weeks (11-day HA protocol, two week phased HA protocol). This study set out to identify "the minimum dose of HA required to elicit a heat adapted phenotype".

STUDY DETAILS

1. Twelve moderately trained males were heat acclimated using controlled hyperthermia (Tre > 38.5°C), with no fluid intake for 90 min on 4 consecutive days, with a heat stress test (HST) being completed one week prior to (HST2), and within one-week post (HST3) HA.
2. Heat stress tests comprised of cycling for 90 min @ 40% Peak Power Output (PPO); 35°C; 60%RH followed by 10 minutes of passive recovery before an incremental test to exhaustion.
3. Physical performance outcomes time to exhaustion (TTE), PPO, end rectal temperature (Tre END), and heart rate (HREND) was measured during the incremental test to exhaustion.
4. Physiological markers indicated no significant changes in the heat; however descriptive statistics indicated mean resting Tre lowered 0.24°C and end-exercise lowered by 0.32°C.
5. There were significant improvements across multiple timepoints following HA in perceptual measures; Rate of perceived exertion (RPE), Thermal Sensation (TS), and Thermal Comfort (TC).
6. Short-term isothermic HA (4 days) was effective in enhancing performance capacity in hot and humid conditions.

PRACTICAL TAKEAWAY

A short heat acclimation protocol appears to help performance through reduction in perception of heat and the sensation of heat while exercising. Even though such a short acclimation protocol is not long enough to result in changes in physiological markers, it appears to be enough to help performance. Therefore, even if an athlete is unable to perform a full heat acclimation protocol before a race in a hot environment, a short period (4 days) at the competition location may still help.

NUTRITION: Exogenous ketone supplements in athletic contexts

Exogenous ketone supplements (EKS) are a topical subject in endurance sports. The research I've seen in the past has not shown a benefit from using them:

• EKS...neither causes muscle glycogen sparing nor improves performance in the final stage of the event.
• Acute ketogenic diet and ketone ester supplementation impairs race walk performance.
• Exogenous ketosis suppresses diuresis and atrial natriuretic peptide during exercise.

This "review explores the rationale and historical development of EKS, the mechanistic basis for their proposed effects, both positive and negative, and evidence to date for their effects on exercise performance and recovery outcomes". A few highlights from the paper are below.

STUDY DETAILS

1. The uptake and utilisation of ketone bodies (KBs) in skeletal muscle is likely to be greatest in those individuals that are highly endurance-trained with a high proportion of type I muscle fibres and a high oxidative capacity in skeletal muscle.
2. It is questionable as to whether a small change in contribution of KBs to energy provision in skeletal muscle during exercise would have a meaningful effect on muscular efficiency.
3. A subsequent study observed no effect of ingestion of R-BD R-βHB KME on muscle glycogen utilisation during 3 h of intermittent-intensity cycling exercise, or during a 15-min cycling time trial (TT) that followed.
4. Two studies have demonstrated impaired performance during high-intensity, short-duration (~ 10 to 30 min) cycling TTs after ingestion of R,S-βHB salts or R-BD R-βHB KME, although the mechanism of impaired performance was not established in either study.
5. There is no clear pattern of supplement type, dosing strategies, and/or exercise type, intensity, or duration that is definitively associated with greater incidence of GI symptoms with acute ingestion of EKS, but a tentative recommendation is that it would be prudent to avoid large doses (> 30 g) in a single bolus in close proximity to high-intensity exercise.
6. Ultimately, there is little evidence overall for ergogenic effects of acute ingestion of KS in the form of R,S-βHB salts, albeit all of the performance outcomes have focussed on short duration, high-intensity exercise performance tests, but the data are also consistent in the finding that increases in circulating [R-βHB] are modest (generally < 1.0 mM) under the dosing strategies employed to date.
7. At present there is a lack of evidence for the ergogenic effect of ketone esters, yet in endurance sports such as professional cycling, the use of ketone esters reportedly remains widespread.
8. Overall, the data on recovery and overreaching are preliminary, but suggest that there may be efficacy for EKS in these contexts.

PRACTICAL TAKEAWAY

This is a very detailed and comprehensive review of the current literature on ketones. I believe the authors' conclusion provides useful advice for athletes:

Despite the mechanistic bases for potential beneficial effects of EKS, the evidence at present is overwhelmingly against EKS being an ergogenic aid for athletic performance.

My recommendation at this point would be that the evidence does not yet suggest there is sufficient benefit to justify the current cost of testing and using exogenous ketones. This may change in the future, but I personally would let researchers and other athletes explore this at their cost (financially and potentially on performance too).

PHYSIOLOGY: Maximal time spent at VO2max from sprint to the marathon

In this study the authors "tested the hypothesis that VO2max can be elicited in both the sprint and marathon distances and that the fraction of time spent at VO2max is not significantly different between distances".

STUDY DETAILS

1. Seventy-eight well-trained males performed the University of Montreal Track Test using a portable respiratory gas sampling system to measure a baseline VO2max.
2. Each participant ran one or two different distances (100 m, 200 m, 800 m, 1500 m, 3000 m, 10 km or marathon) in which they are specialists.
3. VO2max was elicited and sustained in all distances tested.
4. The time limit (Tlim) at VO2max on a relative scale of the total time (Tlim at VO2max%Ttot) during the sprint, middle-distance, and 1500 m was not significantly different.
5. By focusing on the solicitation of VO2max, we demonstrated that the maintenance of VO2max is possible in the sprint, middle, and marathon distances.

PRACTICAL TAKEAWAY

I find this result to be similar to a previous study I shared which showed that even in ultramarathon trail races the athletes spent ~50' above the second ventilatory threshold. This study showed that athletes in all events achieved a certain time at VO2 Max (~10' in a 10000m race and ~8' in a marathon). While the proportion of time at this intensity is relatively lower in the marathon (~5%), the authors note in the discussion that "a high peak oxygen consumption and the ability to run fast over a 1000 m section of the marathon determined the difference between an elite marathon performance (2 h 6 min–2 h 11 min) and a non-elite marathon time (2 h 12 min–2 h 16 min)".

My recommendation based on this research is that there is still an importance for athletes of all distances to perform shorter intervals in the severe intensity domain. For ultramarathon runners, I prefer using a concentrated block of 8-10 sessions (2-3 weeks) of short intervals of ~3' early in the training phase before moving towards more race specific training.

PHYSIOLOGY: Metabolic adaptations to weight loss

Losing weight is challenging and the body's biological drive of "metabolic adaptation" makes it even more difficult to achieve. This study reviewed the various adaptations during weight loss.

STUDY DETAILS

1. As the scientific literature has continuously shown, body mass loss attempts do not always follow a linear fashion nor always go as expected even when the intervention is calculated with precise tools.
2. One of the main reasons why this tends to happen relies on our body's biological drive to regain the body mass we lose to survive. This phenomenon has been referred to as “metabolic adaptation” many times in the literature and plays a very relevant role in the management of obesity and human weight loss.
3. Nutritional strategies and dietetic tools are thus necessary to confront these so-called adaptations to body mass loss:
• Increasing protein intake over usual values might be wise to offset the negatives of dieting over long periods of time.
• It seems that the distribution of carbohydrate and fat is of little relevance when designing a nutritional plan whose aim is to reduce metabolic adaptation and prevent body mass regain.
• High-fiber intakes have been reported to reduce the energy density of the diet as well as allowing for larger volumes of food without drastically increasing calories, fiber could be a useful dietetic tool to attain an energy deficit.
• Athletes might benefit more from intermittent refeeds than overweight subjects because this population has reported favorable results after this protocol.
4. Outside the nutritional aspects, it might be wise to increase the physical activity and thus the energy flux of an individual when possible to maintain diet-induced body mass loss in the long term.

PRACTICAL TAKEAWAY

In order to account for the metabolic adaptations that occur during calorie restriction and to create a sustainable diet that an athlete can adhere to requires consideration of nutritional strategies. As per the study, I would recommend increasing protein and dietary fiber intake during a period of calorie deficit. This may be during a period of deliberate weight loss or perhaps during a heavy training block. Last week I shared a study that reported binging behaviors in the 4 wk leading up to the race for ultramarathon runners which shows a lack of diet adherence and another time where these nutritional strategies may be useful.