Exercise performance is reduced in hot environments due to physiological responses caused by increased body temperature. A proper residential environment is important for improving the performance and maintaining physical condition of soccer players in the summer. The purpose of this study was to determine the effect of indoor temperature of the resting space during the summer on the fitness and condition of soccer players. A total of 12 K-3 League semiprofessional players without serious injuries in the last 3 months voluntarily participated in the study. Participants performed speed (10 m, 20 m, and 30 m), soccer-specific coordination skill (dribbling), agility, repeated sprints, Yo-Yo intermittent level 2, vertical jump, and questionnaire (fatigue, sleep quality, muscle soreness, stress, and mood) after staying indoor temperature at 20°C, 26°C, and 30°C for one night, respectively. There was no difference among groups in physical fitness (speed, agility, jump, coordination, Yo-Yo intermittent level 2, and repeated sprints). The differences in fatigue and sleep quality were not statistically significant among groups, but they tended to be different. Muscle soreness was similar among all groups. Significant differences were observed between the 20°C and 30°C groups in stress and mood levels. The present study concluded that, while the physical fitness did not differ among groups, the 30°C residential environment was shown to have a negative psychological effect. Considering that many diseases associated with hot weather occur in low residential temperatures, a room temperature of 26°C is recommended for elite soccer players in hot summer weather.
Several factors need to be considered to win a soccer match. Continuous error-free accuracy of playing is almost impossible throughout a 90-min soccer match. To maintain clear decision during the match and reduce skill-related errors, the ability to psychologically and physically resist fatigue is essential for the players (
Soccer players often have to play in hot environments for certain periods due to the nature of the tournament venue and the duration of the professional soccer league. Players undergo added physical stress when playing in a hot environment. It is well known that athletic performance is reduced in hot environments due to physiological responses caused by increased body temperature (
A proper resting environment, along with various recovery and nutritional methods, is important for improving the performance and maintaining physical condition of soccer players. In addition, the amount and quality of sleep, which can affect athletes’ performance, depends on the sleep environment. Environmental factors such as the room temperature and humidity in hot summer nights are strongly associated with the amount and quality of sleep (
Despite the fact that the rest environment during summer can have a significant impact on performance and controlling physical condition of soccer players, little research has been conducted on the effects of the room temperature on fitness and condition. The purpose of this study was to determine the effect of indoor temperature of the resting space during the summer on the fitness and condition of soccer players.
A total of 12 K-3 League semiprofessional players without serious injuries in the last 3 months voluntarily participated in the study. Goalkeepers were excluded from the study because of their low physical requirements compared to those needed for other positions. Initially, 16 players participated; four dropped out for personal and injury-related reasons (mean age, 23±2 years; mean height, 175±6 cm; mean body mass, 71±5 kg). All subjects had no history of neurological disease or musculoskeletal abnormality; none of them was undergoing any pharmacological treatment during the course of the study.
To determine whether indoor temperature of the resting space affects the fitness and condition of soccer players during the summer. All procedures performed in the study were approved by the Kangwon National University Ethics Committee (KWNUIRB-2019-05-002-002). During the enrolment process, all players gave written informed consent to participate after details and procedures of the study had been fully explained.
The study was conducted during the summer break of the K-3 League (July–August). A specific order of conditions was set for the players who completed the study participation agreement. Three groups were created on the basis of temperature (30°C, normal room temperature; 26°C, recommended room temperature; and 20°C, preferred room temperature); each athlete selected a random group from several sealed paper envelopes. In the group setting of condition 2, the group was assigned by selecting the envelope in the same manner between the two groups except for the group conducted in condition 1. In condition 3, the other group that was not included in condition 1 and 2 was implemented (
The experimental design is shown in
The sprint tests which consisted of 2 maximal sprints of 30 m with 2-min rest between each sprint were conducted. The sprint times at 10, 20, and 30 m were recorded using the photocell gates (Microgate, Bolzano, Italy). The participants started to run 50 cm before the photocell gate recordings. The fastest times at the distances were recorded for data analysis.
The arrowhead agility tests consisted of 4 sprints (2 right, 2 left), with 2-min rest between each sprint (
The players completed vertical jump twice on a pad with sort of compatible height measurer attached (Nike SPARQ, Nike Inc., Beaverton, OR, USA) (
The players completed soccer-specific coordination skill which consisted of the 44-m slalom dribble twice with 5-min rest between each test (
The Yo-Yo IR2 test was performed on an artificial turf. The Yo-Yo IR2 test consists of 2×20-m shuttle runs at increasing speeds, controlled by audio signals from a compact disk. Between each bout of running, the subjects completed 10 sec of active recovery, consisting of 2×5-m jogging (
The repeated sprint test consisted of seven maximal 34.2-m sprints, interspersed by 25 sec of active recovery (40-m jogging distance) (
The questionnaire to check the condition (well-being) of the players was based on a questionnaire used in a previous study (
Statistical analyses were carried out using IBM SPSS Statistics ver. 23.0 (IBM Co., Armonk, NY, USA). Data are presented as mean values±standard deviation. All variables were approved by Shapiro–Wilk normality test. One-way analysis of variance was performed to analyse the differences in physical fitness and condition among the groups and Bonferroni test was used as the
The results of the players’ fitness tests are shown in
The major finding of the present study was that physical fitness was not affected by the resting environment, but differences were found in psychological variables. In particular, fatigue, sleep quality, stress, and mood levels were negatively affected at 30°C compared to the resting conditions of 26°C and 20°C.
To the best of our knowledge, there is no research on the relationship between resting indoor environment and soccer player performance in summers. Therefore, we hypothesised that players’ physical fitness level was strongly affected by the living and resting environment (i.e., temperature) in the summer. However, we found that the players’ housing environment was not significantly related to their fitness performance. Several previous studies have shown that exercise performance at high temperatures is lower than performance at normal temperatures (
The fitness level of the players participating in this experiment was lower than that of the professional soccer players that were included in a previous study (
Unlike the physical fitness results, the psychological variables of players according to residential environment were found to show statistically significant differences in stress and mood and a tendency to differences in fatigue and sleep quality. The difference in the results of the physical and psychological factors is due to the sensitivity of players’ response. Players might be more sensitive to psychological responses than physical responses. For example, physical fitness of elite players such as total time of repeated sprints, fatigue index, and jump height was not changed in afternoon training compared to morning training, but difference in psychological variables such as rate of perceived exertion, vigour scores, and stress was observed (
Higher than normal fatigue was observed in all groups due to the summer training. Players experienced lower fatigue when they slept and rested at a temperature of 20°C compared to a temperature of 30°C. There may be a variety of reasons for the different levels of fatigue among residential environments, but sleep may be closely related. Sufficient amount of sleep and quality of the sleep are critical to maximizing the training response and maintaining players’ condition (
Muscle soreness was not different among the groups in the current study (2.53–2.83). This result is due to a week of training before the test did not cause injury to the players. While muscle injuries usually occur with repeated unfamiliar eccentric movements, and muscle soreness lasts over a period of 5 to 7 days (
Interestingly, stress and mood scores differed between groups, and players felt the most stress and negative feelings at the 30°C condition. These results were consistent with the results of a previous study, where despite changes in stress and mood scores, no differences in fitness levels were found (
In the current study, we analysed the differences in physical fitness and psychological variables according to summer residential environments (20°C, 26°C, and 30°C). Similar fitness factors were observed among the three conditions, but there were differences in psychological variables. The 30°C residential environment was shown to have a negative psychological effect, while no statistically significant differences were found between the 20°C and 26°C conditions. Considering that many diseases associated with hot weather such as “air-conditioningitis” occur in low residential temperatures, a room temperature of 26°C is recommended for elite soccer players in hot summer weather.
No potential conflict of interest relevant to this article was reported.
Schematic illustration of grouping.
Schematic illustration of the experimental design.
Player condition screening questionnaire
Variable | Score | ||||
---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | |
Fatigue | Always tired | More tired than normal | Normal | Fresh | Very fresh |
Sleep quality | Insomnia | Restless sleep | Difficulty falling asleep | Good | Very restful |
General muscle soreness | Very sore | Increase in soreness/tightness | Normal | Feeling good | Feeling great |
Stress level | Highly stressed | Feeling stressed | Normal | Relaxed | Very relaxed |
Mood | Highly annoyed/irritable down | Aggravated/short tempered | Less interested in others and/or activities than usual | A generally good mood | Very positive mood |
Summary of physical fitness in 20°C, 26°C, and 30°C
Variable | Trial | |||
---|---|---|---|---|
| ||||
20°C | 26°C | 30°C | ||
Speed (sec) | ||||
10 m | 1.75±0.12 | 1.70±0.09 | 1.73±0.11 | 0.779 |
20 m | 3.07±0.19 | 2.99±0.14 | 3.02±0.19 | 0.628 |
30 m | 4.36±0.32 | 4.21±0.20 | 4.26±0.26 | 0.991 |
| ||||
Agility (sec) | ||||
Right | 8.55±0.32 | 8.53±0.33 | 8.51±0.25 | 0.041 |
Left | 8.63±0.41 | 8.58±0.33 | 8.57±0.27 | 0.097 |
| ||||
Jump (cm) | 57.17±4.75 | 56.25±6.09 | 56.92±5.23 | 0.093 |
| ||||
Coordination (sec) | 14.10±0.71 | 13.80±0.89 | 14.43±1.46 | 1.063 |
| ||||
Yo-Yo intermittent level 2 (m) | 831.67±179.56 | 873.33±141.51 | 836.67±202.86 | 0.199 |
| ||||
Repeated sprint test | ||||
Total time (sec) | 48.84±2.37 | 48.34±1.84 | 48.03±1.23 | 0.576 |
Fatigue index (%) | 5.53±3.26 | 5.46±1.87 | 6.71±4.01 | 0.585 |
Values are presented as mean±standard deviation (n=12).
Summary of psychological variables in 20°C, 26°C, and 30°C
Variable | Trial | ||||
---|---|---|---|---|---|
20°C (a) | 26°C | 30°C (c) | |||
Fatigue (a.u.) | 3.08±0.90 | 2.33±0.89 | 2.25±0.87 | 3.229 | - |
Sleep quality (a.u.) | 3.67±0.89 | 4.00±0.60 | 3.17±1.03 | 2.863 | - |
Muscle soreness (a.u.) | 2.83±0.58 | 2.83±0.84 | 2.58±0.52 | 0.579 | - |
Stress (a.u.) | 3.58±0.10 | 3.00±0.60 | 2.67±0.49 | 4.848 |
a>c |
Mood (a.u.) | 3.58±0.52 | 3.33±.078 | 2.75±0.72 | 5.235 |
a>c |
Values are presented as mean±standard deviation (n=12).
a.u., arbitrary unit.
Significant difference among conditions (