The longitudinal relationship between muscle strength, dietary intake and physical activity among adolescents is not well understood. We investigated the trend and longitudinal effects of dietary intakes and physical activity scores on muscle strength in this adolescent. This prospective cohort study consisted of 436 adolescents (134 males; 302 females), aged 13 years at baseline (2012) and were followed up at the age of 15 (2014) and 17 (2016) years, respectively. We measured muscle strength using a calibrated hand dynamometer, estimated dietary intake with a seven-day dietary history and physical activity scores with validated PAQ-C questionnaire. A generalised estimating equation (GEE) used to examine the effect of dietary intakes and physical activity on muscle strength changes. The analysis was performed separately by sex. The muscle strength for males and females had increased within the five-year period. The dietary intakes (energy and macronutrients) also increased initially but plateaued after those aged 15 years for both sexes. Females recorded a significant declining trend in physical activity scores compared to male as they grew older. A significant positive longitudinal relationship was found between protein (β=0.035; p=0.016), carbohydrate intake (β=0.002; p=0.013) and muscle strength among males. However, no longitudinal relationship was found between dietary intake, physical activity and muscle strength among females. Higher protein and carbohydrate intake among males were associated with higher muscle strength but was not observed in females. Nutrition and physical activity focusing on strength building are required in early adolescence and need to be tailored to males and females accordingly.