Physical activity, especially high-intensity training (HIT), leads to physiological and behavioural changes. The objectives of this randomized cross-over study were to investigate i) the effects of physical exercise on weight, behaviours, and head and ear positions on the days after low-intensity training (LIT) or high-intensity training; and ii) to explore if behaviours, and/or physiological parameters (sweat, salivation and blood lactate levels) during training can predict post-training behaviours. A total of nineteen French trotter horses housed in four different training centres were studied the day before (D pre ) and after LIT or HIT (afternoon after training (D training ) and 2 days after training (D1 Post and D2 Post )). The results showed that horses exhibited i) longer durations of resting and head below the withers (HBW) on D training and D1 Post than on D pre and ii) shorter eating durations on D1 Post and D2 Post than on D pre after HIT. This was associated with significant weight loss on D 2 Post . Several behaviours associated with discomfort ( e.g ., head conflict behaviours, nose behind the vertical, and open mouth), as well as amount of sweat, seemed to predict the durations of resting, HBW and eating on D1 Post . Thus, behaviours are impacted by training, and a combination of behaviours and visible physiological parameters exhibited during training have the potential to predict physical tiredness in harness racing horses.