Japanese Version of Single-Item Fatigue Scale Proves Valid in Student and Athlete Testing

Fatigue is one of the most universal experiences in human life, yet measuring it quickly and reliably remains a stubborn challenge for scientists. A research team at Tohoku University in Japan has now taken a significant step toward solving that problem for Japanese speakers by translating and validating the Rating of Fatigue scale, a single-item instrument originally developed in English, into Japanese. The resulting Japanese version, known as the ROF-J, was evaluated across three carefully staged studies involving university students and varsity athletes, and the evidence indicates that this compact tool captures subjective fatigue with acceptable validity. The work, published in Sports Medicine – Open, arrives at a moment when fatigue has become a pressing social issue in Japan, where overwork-related deaths and chronic sleep shortfalls continue to draw national attention.

The scientific rationale for a brief fatigue measure is rooted in how fatigue itself is understood. Researchers define fatigue as an overwhelming sense of tiredness, lack of energy, and a feeling of exhaustion associated with impaired physical or cognitive functioning. Its functional purpose is to suppress or terminate activity, and it operates through two complementary pathways. Peripheral mechanisms involve biochemical changes within working muscles that reduce activity independently of the central nervous system, while central mechanisms involve neurochemical changes that generate subjective sensations of tiredness and reduced motivation, prompting individuals to voluntarily stop what they are doing. Both pathways are considered essential to fatigue’s protective role in maintaining whole-body homeostasis, and the new study deliberately focused on the subjective experience, treating fatigue as a unidimensional and simple construct.

That conceptual choice matters because it justifies the use of a single-item scale. Although some scholars have argued that single-item measures are inferior to multi-item scales in reliability and validity, single-item instruments can perform equally well, or even better, when the construct being measured is simple and unitary. Long multi-item questionnaires administered to highly fatigued respondents can feel repetitive and redundant, evoking discomfort or disengagement and thereby degrading data quality. Existing Japanese fatigue scales, including a 24-item adolescent subjective fatigue measure, the 25-item Jikaku-sho shirabe developed for occupational settings, and the 20-item Japanese version of the Multidimensional Fatigue Inventory, are valuable but impractical when participants must respond during ongoing physical activity or work. A one-item rating scale sidesteps that burden entirely, requiring no specialized equipment or technical expertise, unlike physiological indicators such as electroencephalography or heart rate variability.

The validation process unfolded in three phases between July and November 2024. In the first phase, two native Japanese-speaking graduate students in psychology independently translated the original Rating of Fatigue scale into Japanese, one of them blind to the study’s purpose. Three native speakers then consolidated the translations into a single version, and three native English speakers proficient in Japanese, all unaware of the study’s aims, translated the Japanese version back into English following Brislin’s classic back-translation method. Four English speakers subsequently rated the comparability of language and the similarity of interpretability between each back-translated passage and the original on seven-point scales, adapting methodology from Sperber and colleagues. Items scoring above the threshold of 3 on either dimension are considered problematic, and only a single sentence describing the level moderately fatigued required revision, a mismatch traced to differences in the intensity of fatigue conveyed by the corresponding adjectives in the two languages.

The second phase tested face validity and concurrent validity in a questionnaire survey of 85 Tohoku University students, 36 men and 49 women with a mean age of 20.27 years, recruited in October 2024. Participants rated their agreement with six face-validity items drawn from the original scale’s development, both before and after receiving instructional text accompanying the ROF-J, and completed a battery including the Jikaku-sho shirabe, an established Japanese fatigue questionnaire covering five symptom domains: drowsiness, instability, uneasiness, dullness, and eyestrain. Statistical analyses, powered a priori using G*Power and conducted in jamovi with a two-tailed significance level of 0.05, compared responses between the instructed and uninstructed conditions and correlated ROF-J scores with each subscale of the occupational fatigue questionnaire.

The results broadly supported the instrument. Participants generally agreed that the ROF-J measured fatigue, and the score on the item asking whether the instructions were helpful in understanding the scale rose significantly above the midpoint of the rating range, indicating that instructional text improved comprehensibility. Descriptive components and overall understandability did not differ between conditions, echoing patterns seen in the original English scale and its validated French counterpart. One result diverged from the earlier studies: rather than strengthening the perception that the scale measures fatigue while weakening the perception that it measures exertion, the instructions in this sample significantly reduced agreement that the scale represents exertion without significantly changing agreement that it represents fatigue. The authors suggest that because high-exertion tasks frequently produce fatigue, a strict subjective separation of the two experiences may be difficult, and future users should apply the scale with that caveat in mind.

Concurrent validity emerged clearly in the correlation analyses. ROF-J scores showed significant positive correlations with all five subscales of the Jikaku-sho shirabe, meaning that students who reported greater overall fatigue also reported more drowsiness, instability, uneasiness, dullness, and eyestrain. This covariation with an established, widely used Japanese fatigue instrument provides reassurance that the translated scale is tapping the same underlying phenomenon rather than an idiosyncratic construct. An independent-samples t-test also found no significant gender difference in ROF-J scores, with men averaging 3.89 and women 4.57 on the rating scale, supporting the instrument’s comparability across respondent groups at least within this sample.

The third phase examined convergent validity in a real-world athletic setting. Thirty-five members of Tohoku University varsity teams, 18 players from a men’s volleyball team and 17 from a women’s lacrosse team, rated their fatigue on paper immediately before and after regular practice sessions in November 2024. The volleyball squad trained in a gymnasium from seven to nine in the evening, progressing from serving and receiving drills to small-sided match play, while the lacrosse squad practiced at an athletic stadium from early morning, combining passing and shooting drills with sub-team matches. A repeated-measures mixed analysis of variance revealed a significant main effect of measurement time, with a large effect size, no significant effect of team affiliation, and no interaction between the two. Bonferroni-corrected post hoc testing confirmed that ROF-J scores rose significantly after exercise, exactly as observed in the original English validation and the French translation.

Together, the three lines of evidence, translational equivalence, agreement that the scale measures what it claims, correlation with an established domestic questionnaire, and sensitivity to the fatigue induced by physical exercise, indicate that the ROF-J possesses adequate validity for research and applied use. The authors acknowledge important limitations that shape the roadmap ahead. Convergent validity was tested only against physical exercise, leaving open whether the scale is equally sensitive to mental fatigue produced by cognitive tasks, desk work, or other low-intensity repetitive activities. The samples consisted exclusively of university students, so generalization to workers, children, older adults, and clinical populations remains untested. Concurrent validity was established against another self-report measure rather than objective fatigue indices such as performance decrements or physiological markers, a gap that future studies should close.

Even so, the practical significance of the work is considerable. Japan faces a documented fatigue burden: epidemiological survey data indicate that 17.2 percent of Japanese adults consider themselves easily fatigued and 13.2 percent experience residual fatigue that persists without signs of recovery, while national nutrition survey figures show that roughly 38.5 percent of men and 43.6 percent of women sleep fewer than six hours per night, with the burden concentrated among middle-aged adults. Overwork-related deaths from cardiovascular disease and suicides tied to overwork-related mental disorders have risen in recent administrative data, and industries such as road freight transport and care services figure prominently in recognized fatal cases. A brief, validated, single-item Japanese fatigue scale offers occupational health practitioners, sports scientists, and researchers an accessible quantitative tool that can be deployed repeatedly during ongoing activity, supporting intervention design, monitoring, and the broader advancement of fatigue science in Japan and beyond.

Subject of Research: Validation of a Japanese-language, single-item subjective fatigue rating scale for use during ongoing activity

Article Title: Validation of the Japanese Version of the Rating of Fatigue Scale

Article References: Suzuki, K., & Arai, T. (2026). Validation of the Japanese Version of the Rating of Fatigue Scale. Sports Medicine – Open, 12(1), Article 134. https://doi.org/10.1186/s40798-026-01108-8

Image Credits: AI Generated

DOI: 10.1186/s40798-026-01108-8

Keywords: fatigue, Rating of Fatigue scale, ROF-J, scale validation, psychometrics, cross-cultural translation, Japan, exercise, sports science, occupational health, sleep deprivation, karoshi