32Seeking reward is a powerful tool for shaping human behaviour. While it has been 33 demonstrated that reward invigorates performance of simple movements, its effect on more 34 complex sequential actions is less clear. In addition, it is unknown why reward-based 35 improvements for discrete actions are transient, i.e. performance gains are lost once reward 36 is removed, but appear long lasting for sequential actions. We show across three experiments 37 that reward invigorates sequential reaching performance. Driven by a reward-based increase 38 in speed, movements also exhibited greater coarticulation, smoothness and a closer 39 alignment to a minimum jerk trajectory. Critically, these performance gains were maintained 40 across multiple days even after the removal of reward. We propose that coarticulation, the 41 blending together of sub-movements into a single continuous action, provides a mechanism 42 by which reward can invigorate sequential performance whilst also increasing efficiency. This 43 change in efficiency appears essential for the retention of reward-based improvements in 44 motor behaviour.From drinking a cup of coffee to cleaning your teeth, sequential actions form a 64 fundamental component of our daily life activities. When first encountered, these actions are 65 often executed as a series of distinct sub-movements with pronounced stop periods between 66 them 1-8 . However, with learning these discrete sub-movements are gradually blended 67 together to form a continuous action that is executed with increased speed, smoothness and 68 energetic-efficiency 9-12 . This process, known as coarticulation, is an essential mechanism for 69 understanding skilled sequential performance acquisition as it reflects the evolution of 70 behaviour, both temporally and spatially, towards increased efficiency 7-12 . Coarticulation is 71 observed across many motor behaviours such as speech production 13,14 , sign language 15 , 72 piano playing 16 , typing [17][18][19] and various other upper limb actions 20-25 . Within sequential 73 reaching, the coarticulation of sub-movements leads to the gradual development of a new 74 motor primitive that is globally planned and, once initiated, must run to completion 10 . 75 Although this process can take weeks of practise, these newly formed motor primitives are 76 highly generalizable and are not simply the result of increased movement speed 10 . 77 It is important to emphasize that coarticulation represents a fundamentally different 78 process from chunking which appears to feature similar characteristics. Chunking refers to 79 the production of a series of discrete movements (i.e. button presses) that are temporally 80 aligned 21,22,[26][27][28] . This is represented at a behavioural level through shorter reaction times 81 between actions 7,29 , however each action is still performed discretely with a pronounced stop 82 period between them 21,30 . In contrast, coarticulation reflects the merging of neighbouring 83 movements into a continuous and kinema...