Mental load and fatigue are important causes of performance decreases and accidents in different activities. However, a robust systematic review, detailing the instruments used to quantify them, is currently lacking. The purpose of this study was to summarize and classify by derivations the validated instruments used to quantify mental load and fatigue. The most representative electronic databases in the scope of this review, PubMed, WOS, Scopus, SPORTDiscus, and PsycINFO (until September 2020) were searched for studies that included instruments to analyze mental load and fatigue. The quality of the selected studies was scored using a quality assessment checklist. A total of 40 papers were included. Most of the papers used subjective scales (75%) to quantify mental load and fatigue, with a small presence of behavioral (n = 5) and objective techniques (n = 5). Less is known about the analysis of mental load and fatigue using a combination of derivations. Despite the high cost and complexity of objective techniques, research that applies these measures is important for further analysis of brain processes in mental load and fatigue. The design of a battery of tests that include the three types of derivations also seems necessary.

The main purpose was to compare by each training the mental load and fatigue reported by semiprofessional soccer players comparing between regular season phase and the play‐offs. Fifty‐three players (M_age = 24.59 years) for two teams participated during the 2020/21 season. Mental load was measured with a Likert questionnaire. Mental fatigue was quantified with a Visual Analogue Scale. Four trainings were recorded each week (Monday = MD+1, Wednesday = MD‐4, Thursday = MD‐3 and Saturday = MD‐1), with a competitive match on Sunday across 10 weeks (five dates of regular season – five dates of play‐offs). A Linear Mixed Model was performed with R‐studio, using the training days and the competitive phase as independent variables. The influence of time played as co‐variable was also checked. Results showed MD+1 as the more mentally fatiguing day in both phases, although MD‐4 were the training with higher mental load reported (p = 0.001). Comparing phases, mental fatigue was significantly higher during the play‐offs (p = 0.037). With regard time played, players that did not usually play showed a decrease in mental load during the play‐offs. Then, we recommend coaches to use recovery strategies for mental fatigue, avoid mentally fatiguing tasks close to competition and considerer the time played as a factor which may contribute to individual differences in player mental fatigue.

The present study examined the effects of stressful constraints during soccer trainings on psychological skill development and internal load when compared with control (nonstressful) trainings. A total of 51 elite male youth soccer players (27 in the experimental group, M = 16.54 years; 24 in the control group, M = 15.44 years) participated in the study. In a 12-week longitudinal survey, team resilience, using the Spanish version of the Characteristics of Resilience in Sports Teams Inventory, and anxiety, using the Sport Anxiety Scale, were measured at baseline (after 4 weeks of regular trainings), postprotocol (after 4 weeks of control or experimental trainings), and follow-up (after 4 weeks of regular trainings). Results show that, when compared with the control group, a program with stressful constraints helped young soccer players to develop better psychological skills: specifically, increased ability to cope with impairments in resilience (both resilience characteristics and team vulnerability under pressure; p < 0.001). Increases in anxiety (p = 0.06) and decreases in preoccupation (p < 0.001) and lack of concentration (p < 0.001) were also observed. The adaptation of human behavior to specific trainings may explain these results. In conclusion, the regular exposure of young soccer players to stressful situations during trainings shows benefits for their psychological skill development in soccer. Then, benefits on internal load were also observed.

The present study aimed to analyze the influence of the Video Assistant Referee (VAR) on match physical demands in the top Spanish professional football league. Match physical demand data from all the matches for two seasons (2017/2018 and 2018/2019) in the First Spanish Division (n = 1454) were recorded using an optical tracking system (ChyronHego^®). Total distance, relative total distance covered per minute, distance covered between 14–21 km·h⁻¹, distance covered between 21–24 km·h⁻¹, and distance covered at more than 24 km·h⁻¹ were analyzed; also, the number of sprints between 21–24 km·h⁻¹ and more than 24 km·h⁻¹ were taken into consideration. The times the VAR intervened in matches were also taken into account. Results showed that total distance and relative total distance significantly decreased in seasons with VAR compared to seasons without VAR. Finally, distance covered between 21–24 km·h⁻¹, distance covered at more than 24 km·h⁻¹, and the number of high-intensity efforts between 21–24 km·h⁻¹ and more than 24 km·h⁻¹ increased in seasons with VAR compared to seasons without VAR, but the differences were nonsignificant. Thus, these findings help practitioners to better understand the effects of the VAR system on professional football physical performance and to identify strategies to reproduce competition demands.

Constraints are common in soccer training to develop physical, technical-tactical, and mental training concurrently. This study examined how different scoring systems influence physical, tactical, and mental demands during large-sided games in soccer. Eighteen youth-elite male (17.39 ± 1.04 y) soccer players completed three 8 vs. 8 large-sided games where the different score systems were i) official score system (OSS; i.e., 1 goal = 1 goal), ii) double the value of the goal—4 min (DVx4; i.e., 1 goal = 1 goal from 0.00 to 7.59 min, and 1 goal = 2 goals from 8.00 to 12.00 min), and iii) double the value of the goal—8 min (DVx8; i.e., 1 goal = 1 goal from 0.00 to 3.59 min, and 1 goal = 2 goals from 4.00 to 12.00 min). Physical demands and tactical behaviors were recorded during tasks using a global positioning system and video camera. Mental fatigue was recorded pre- and post-task using a visual analogue scale. Also, the ratio of perceived exertion and mental load were recorded after tasks were finished. Results reported the highest values of mental and physical demands in DVx4. Mental fatigue increased during all three large-sided games, although this increase was significantly higher in DVx4 compared with OSS (p = 0.006) and DVx8 (p = 0.027). Tactical behavior showed a trend towards more direct play during DVx4, which was less observed during DVx8, and not at all during OSS. In conclusion, changing the scoring system affects physical, tactical, and mental demands.

Background: Mental fatigue can impair sport, exercise and cognitive performance. Warmup activities can improve performance when the individual is rested. However, their effectiveness when the individual is fatigued has yet to be established. The research objectives were to evaluate the effects of physical and combined physical plus cognitive warmup activities on subsequent sport, exercise, and cognitive performance when rested and fatigued by sleep restriction in athletes (Study 1) and older adults (Study 2). Methods: In Study 1, 31 padel players completed a padel performance test and Stroop task after physical and combined warmups when rested and fatigued by sleep deprivation. In Study 2, 32 older adults completed sit–stand, arm curl, walking, Stroop, and psychomotor vigilance tests after no warmup, physical warmup, and combined warmup when rested and fatigued by sleep deprivation. In both studies, combined warmups intermixed short-, medium-, or long-duration cognitive tasks between physical warmup activities. Mental fatigue was measured using visual analog scale ratings. Results: In both studies, sleep deprivation increased mental fatigue and impaired performance. In Study 1, relative to a physical warmup, padel and Stroop performance were improved by combined warmups (with short-to-medium cognitive tasks) when rested and fatigued. In Study 2, relative to no warmup, sit–stand, arm curl, walking, Stroop, and reaction time performance were improved by physical and combined warmups (with short-to-medium cognitive tasks) when rested and fatigued. Conclusions: The negative effects of sleep deprivation on sport, exercise, and cognitive performance were best mitigated by combined warmups with short-to-medium cognitive tasks. Combined warmups are effective countermeasures against the deleterious effects of mental fatigue on performance.