It is clear that the cause of fatigue is complex, infuenced by both events occurring in the periphery and the central nervous system (CNS). It has been suggested that exercise-induced changes in serotonin (5-HT), dopamine (DA), and noradrenaline (NA) concentrations contribute to the onset of fatigue during prolonged exercise. Serotonin has been linked to fatigue because of its documented role in sleep, feelings of lethargy and drowsiness, and loss of motivation, whereas increased DA and NA neurotransmission favors feelings of motivation, arousal, and reward. 5-HT has been shown to increase during acute exercise in running rats and to remain high at the point of fatigue. DA release is also elevated during exercise but appears to fall at exhaustion, a response that may be important in the fatigue process. The rates of 5-HT and DA/NA synthesis largely depend on the peripheral availability of the amino acids tryptophan (TRP) and tyrosine (TYR), with increased brain delivery increasing serotonergic and DA/NA activity, respectively. TRP, TYR, and the branched-chained amino acids (BCAAs) use the same transporter to pass through the blood-brain barrier, meaning that the plasma concentration ratio of these amino acids is thought to be a very important marker of neurotransmitter synthesis. Pharmacological manipulation of these neurotransmitter systems has provided support for an important role of the CNS in the development of fatigue. Work conducted over the last 20 y has focused on the possibility that manipulation of neurotransmitter precursors may delay the onset of fatigue. Although there is evidence that BCAA (to limit 5-HT synthesis) and TYR (to elevate brain DA/NA) ingestion can influence perceived exertion and some measures of mental performance, the results of several apparently well-controlled laboratory studies have yet to demonstrate a clear positive effect on exercise capacity or performance. There is good evidence that brain neurotransmitters can play a role in the development of fatigue during prolonged exercise, but nutritional manipulation of these systems through the provision of amino acids has proven largely unsuccessful.
Romain Meeusen and Phil Watson
Romain Meeusen and Lieselot Decroix
Cognitive function plays an important role in athletic performance, and it seems that brain functioning can be influenced by nutrition and dietary components. Thus, the central nervous system might be manipulated through changes in diet or supplementation with specific nutrients including branched-chain amino acids, tyrosine, carbohydrates, and caffeine. Despite some evidence that branched-chained amino acids can influence ratings of perceived exertion and mental performance, several well-controlled studies have failed to demonstrate a positive effect on exercise performance. Evidence of an ergogenic benefit of tyrosine supplementation during prolonged exercise is limited. There is evidence that mild dehydration can impair cognitive performance and mood. The beneficial effect of carbohydrate supplementation during prolonged exercise could relate to increased substrate delivery for the brain, with numerous studies indicating that hypoglycemia affects brain function and cognitive performance. Caffeine can enhance performance and reduce perception of effort during prolonged exercise and will influence specific reward centers of the brain. Plant products and herbal extracts such as polyphenols, ginseng, ginkgo biloba, etc. are marketed as supplements to enhance performance. In several animal studies, positive effects of these products were shown, however the literature on their effects on sports performance is scarce. Polyphenols have the potential to protect neurons against injury induced by neurotoxins, suppress neuroinflammation, and to promote memory, learning, and cognitive function. In general, there remains a need for controlled randomized studies with a strong design, sufficient statistical power, and well-defined outcome measures before “claims” on its beneficial effects on brain functioning can be established.
Maria Francesca Piacentini and Romain Meeusen
This longitudinal case study evaluated the effectiveness of an online training-monitoring system to prevent nonfunctional overreaching (NFOR).
A female master track and field athlete was followed by means of a daily online training diary (www.spartanova.com) and a weekly profile of mood state (POMS). The online diary consists of objective training data and subjective feelings reported on a 10-cm visual analog scale. Furthermore, parameters that quantify and summarize training and adaptation to training were calculated. The novelty consists in the inclusion of a specific measuring parameter tested to detect NFOR (OR score).
During track-season preparation, the athlete was facing some major personal changes, and extratraining stress factors increased. Despite the fact that training load (TL) did not increase, the or score showed a 222% and then a 997% increase compared with baseline. POMS showed a 167% increase in fatigue, a 38% decrease in vigor, a 32% increase in depression scores, and a total mood increase of 22%, with a 1-wk shift compared with the OR score. A 41% decrease in TL restored the OR score and POMS to baseline values within 10 d.
The results demonstrate that immediate feedback obtained by “warning signals” to both athletes and coaches, based on individual baseline data, seems an optimal predictor of FOR/NFOR.
Lieselot Decroix, Robert P. Lamberts and Romain Meeusen
Context: The Lamberts and Lambert Submaximal Cycle Test (LSCT) consists of 3 stages during which cyclists cycle for 6 min at 60%, 6 min at 80%, and 3 min at 90% of their maximal heart rate, followed by 1-min recovery. Purpose: To determine if the LSCT is able to reflect a state of functional overreaching in professional female cyclists during an 8-d training camp and the following recovery days. Methods: Six professional female cyclists performed an LSCT on days 1, 5, and 8 of the training camp and 3 d after the training camp. During each stage of the LSCT, power output and rating of perceived exertion (RPE) were determined. Training diaries and Profile of Mood States (POMS) were also completed. Results: At the middle and the end of the training camp, increased power output during the 2nd and 3rd stages of the LSCT was accompanied with increased RPE during these stages and/or the inability to reach 90% of maximal heart rate. All athletes reported increased feelings of fatigue and muscle soreness, while changes in energy balance, calculated from the POMS, were less indicative of a state of overreaching. After 3 d of recovery, all parameters of the LSCT returned to baseline, indicating a state of functional overreaching during the training camp. Conclusion: The LSCT is able to reflect a state of overreaching in elite professional female cyclists during an 8-d training camp and the following recovery days.
Lieselot Decroix, Kevin De Pauw, Carl Foster and Romain Meeusen
To review current cycling-related sport-science literature to formulate guidelines to classify female subject groups and to compare this classification system for female subject groups with the classification system for male subject groups.
A database of 82 papers that described female subject groups containing information on preexperimental maximal cycle-protocol designs, terminology, biometrical and physiological parameters, and cycling experience was analyzed. Subject groups were divided into performance levels (PLs), according to the nomenclature. Body mass, body-mass index, maximal oxygen consumption (VO2max), peak power output (PPO), and training status were compared between PLs and between female and male PLs.
Five female PLs were defined, representing untrained, active, trained, well-trained, and professional female subjects. VO2max and PPO significantly increased with PL, except for PL3 and PL4 (P < .01). For each PL, significant differences were observed in absolute and relative VO2max and PPO between male and female subject groups. Relative VO2max is the most cited parameter for female subject groups and is proposed as the principal parameter to classify the groups.
This systematic review shows the large variety in the description of female subject groups in the existing literature. The authors propose a standardized preexperimental testing protocol and guidelines to classify female subject groups into 5 PLs based on relative VO2max, relative PPO, training status, absolute VO2max, and absolute PPO.
Carlo Minganti, Laura Capranica, Romain Meeusen and Maria Francesca Piacentini
The aim of the present study was to assess the effectiveness of perceived exertion (session-RPE) in quantifying internal training load in divers.
Six elite divers, three males (age, 25.7 ± 6.1 y; stature, 1.71 ± 0.06 m; body mass, 66.7 ± 1.2 kg) and three females (age, 25.3 ± 0.6 y; stature, 1.63 ± 0.05 m; body mass, 58.3 ± 4.0 kg) were monitored during six training sessions within a week, which included 1 m and 3 m springboard dives. The Edwards summated heart rate zone method was used as a reference measure; the session-RPE rating was obtained using the CR-10 Borg scale modified by Foster and the 100 mm visual analog scale (VAS).
Significant correlations were found between CR-10 and VAS session-RPE and the Edwards summated heart rate zone method for training sessions (r range: 0.71–0.96; R 2 range: 0.50–0.92; P < 0.01) and for divers (r range: 0.67–0.96; R 2 range: 0.44–0.92; P < 0.01).
These findings suggest that session-RPE can be useful for monitoring internal training load in divers.
Kevin De Pauw, Bart Roelands, Jef Vanparijs and Romain Meeusen
To determine the effect of active recovery (AR), passive rest (PR), and cold-water immersion (CWI) after 90 min of intensive cycling on a subsequent 12-min time trial (TT2) and the applied pacing strategy in TT2.
After a maximal test and familiarization trial, 9 trained male subjects (age 22 ± 3 y, VO2max 62.1 ± 5.3 mL · min−1 · kg−1) performed 3 experimental trials in the heat (30°C). Each trial consisted of 2 exercise tasks separated by 1 h. The first was a 60-min constant-load trial at 55% of the maximal power output followed by a 30-min time trial (TT1). The second comprised a 12-min simulated time trial (TT2). After TT1, AR, PR, or CWI was applied for 15 min.
No significant TT2 performance differences were observed, but a 1-sample t test (within each condition) revealed different pacing strategies during TT2. CWI resulted in an even pacing strategy, while AR and PR resulted in a gradual decline of power output after the onset of TT2 (P ≤ .046). During recovery, AR and CWI showed a trend toward faster blood lactate ([BLa]) removal, but during TT2 significantly higher [BLa] was only observed after CWI compared with PR (P = .011).
The pacing strategy during subsequent cycling performance in the heat is influenced by the application of different postexercise recovery interventions. Although power was not significantly altered between groups, CWI enabled a differently shaped power profile, likely due to decreased thermal strain.
Roberto Baldassarre, Marco Bonifazi, Romain Meeusen and Maria Francesca Piacentini
Purpose: The 10-km open-water swimming race is an endurance event that takes place in lakes, rivers, or sea and has been an Olympic event since 2008. The aim of the present brief report is to describe training volume and intensity distribution of elite open-water swimmers during the 2016 Olympic season, verifying if, in order to maximize performance, most of the training would be performed at low intensities. Methods: Eight elite Italian open-water swimmers (3 male and 5 female; 25  y, 1.74 [0.05] m, 68.26 [8.17] kg) specialized in distances between 5 and 25 km participated in the study. Training load was determined using an online training diary. Training intensity was categorized according to the 3-zone model: Z1, light intensity; Z2, moderate intensity; and Z3, high intensity. Session rating of perceived exertion was used to quantify training-intensity distribution. This method assigns the entire session into a single intensity zone based on the rating of perceived exertion recorded 30 min posttraining. Results: Total yearly training volume was 3576.93 (272.390) km (3220.80–4041.97), distributed across 446 (37) (397–484) sessions monitored during the 2016 Olympic season. Training-intensity distribution in each zone was 76.83% (8.11%) in Z1, 17.70% (6.79%) in Z2, and 5.47% (5.93%) in Z3. Conclusions: High volumes in Z1 appear to be an important training method used by elite open-water swimmers. However, future research is necessary to study the effects of different training-intensity distribution on open-water swimming performances.
Lieselot Decroix, Maria Francesca Piacentini, Gerard Rietjens and Romain Meeusen
High training loads combined with other stressors can lead to performance decrements. The time needed to recover determines the diagnosis of (non)-functional overreaching or the overtraining syndrome. The aim of this study was to describe the effects of an 8-day (intensified) training camp of professional female cyclists on physical and cognitive performance.
Nine subjects performed a 30-min time trial (TT), cognitive test, and Profile of Mood States questionnaire before, during, and after a training camp (49% increased training volume). On data collection, cyclists were classified as “overreached” (OR) or “adapted” (A) based on TT performance. Two-way repeated-measures analysis of variance was used to detect changes in physical and cognitive parameters.
Five cyclists were described as OR based on decreased mean power output (MPO) (–7.03%) on day 8. Four cyclists were classified as A (increased MPO: +1.72%). MPO and maximal heart rate were significantly different between A and OR groups. A significant slower reaction time (RT) (+3.35%) was found in OR subjects, whereas RT decreased (–4.59%) in A subjects. The change in MPO was negatively correlated with change in RT in the cognitive test (R 2 = .52).
This study showed that the use of objective, inexpensive, and easy-to-interpret physical and cognitive tests can facilitate the monitoring of training adaptations in professional female athletes.
Sabrina Skorski, Iñigo Mujika, Laurent Bosquet, Romain Meeusen, Aaron J. Coutts and Tim Meyer
Physiological and psychological demands during training and competition generate fatigue and reduce an athlete’s sport-specific performance capacity. The magnitude of this decrement depends on several characteristics of the exercise stimulus (eg, type, duration, and intensity), as well as on individual characteristics (eg, fitness, profile, and fatigue resistance). As such, the time required to fully recover is proportional to the level of fatigue, and the consequences of exercise-induced fatigue are manifold. Whatever the purpose of the ensuing exercise session (ie, training or competition), it is crucial to understand the importance of optimizing the period between exercise bouts in order to speed up the regenerative processes and facilitate recovery or set the next stimulus at the optimal time point. This implies having a fairly precise understanding of the fatigue mechanisms that contribute to the performance decrement. Failing to respect an athlete’s recovery needs may lead to an excessive accumulation of fatigue and potentially “nonfunctional overreaching” or to maladaptive training. Although research in this area recently increased, considerations regarding the specific time frames for different physiological mechanisms in relation to exercise-induced fatigue are still missing. Furthermore, recommendations on the timing and dosing of recovery based on these time frames are limited. Therefore, the aim of this article is to describe time courses of recovery in relation to the exercise type and on different physiological levels. This summary supports coaches, athletes, and scientists in their decision-making process by considering the relationship of exercise type, physiology, and recovery.