Adrenergic Agents 1 Clarity of task difficulty 1 Effort 1 Explicit achievement motive 1 Humans 1 Motivation 1 Motivational intensity theory 1 Myocardial sympathetic activity 1 Personality 1 Task Performance and Analysis 1 achievement 1 adrenergic activity adrenergic receptor stimulating agent 1 adult 1 article 1 female 1 human 1 human experiment 1 major clinical study 1 male 1 mental arithmetic 1 motivation 1 personality 1 pre-ejection period 1 prediction 1 sympathetic tone 1 task performance 1