Aims: Our aim is to investigate whether fatigue in 18 year-old children in the ALSPAC cohort is predicted by a range of factors, including fatigue at younger ages, exercise, and obesity. We also aim to investigate the relationship between fatigue, pain and depression in young adulthood, to explore groups of symptoms in fatigued children, and to investigate the relationship between fatigue and disability.

Hypotheses: Childhood fatigue and lifestyle factors may be associated with chronic disabling fatigue at age 18-19 years.

Exposure variables: body mass index; physical activity (questionnaire and accelerometer data); chronic fatigue at at 13-14 years (defined as fatigue that had prevented school attendance or participation in activities and that was not due to sport, possible sleep apnoea or probable depression [Crawley E, Hughes R, Northstone K, Tilling K, Emond A, Sterne JA. Pediatrics. 2012;130(1):e71-9]) and 15-16 years (defined using an appropriate threshold on the Chalder Fatigue Scale).

Outcome variables: We will identify ALSPAC 18 year-olds with high levels of fatigue using responses to fatigue and energy levels questions asked in the CIS-R questionnaire which was included in TF4. We will investigate the relationship between fatigue and disability (physical function) using responses to the SF-36 inventory which formed part of the "Your Changing Life" questionnaire and between fatigue, disability and depression (using responses to the MFQ questionnaire).

Confounding variables: family adversity.