Even though positive effects of being physically active are commonly

known, only a few parts of the world population are sufficiently ac-

tive. The World Health Organization (WHO) states that this problem

affects 31% of the adult’s world population and 80% of the adolescent

population. Appropriate levels of physical activity (PA) are essential

to prevent obesity in childhood and to keep a Quality of Life (QOL)

in old age but are also essential to prevent other Noncommunicable

Diseases (NCDs). Thus, physical inactivity is growing into a severe

problem globally, and there is a growing need to motivate people

to become more physically active during their lifetime. One primary

cause that raises PA levels is having a peer or help from professionals.

However, having assistance is not possible in every situation. It might

be challenging to find and schedule with a partner or to commute to

other places. Roboticist introduced Socially Assistive Robot (SAR) as

an assistive tool for exercising, cognitive or rehabilitation tasks. This

thesis explores SAR in the context of exercising along four features

that have been partly targeted but not yet thoroughly investigated.

These features are a) the social role of the robot, b) encouragement

c) embodiment and d) adaptation. First, this thesis looks at the mo-

tivational effects of exercising with SAR concerning features a) - c).

Second, this thesis questions how a system can adapt to the user, and

whether adaptivity or adaptability is enough to close the gap between

user needs and system behavior. I conducted studies that test the dif-

ferent features by assessing subjective ratings of the robot as well as

measurable motivational variables (e.g., time spent exercising with

the robot) in a bodyweight workout scenario.

The results show that features a) - c) have a positive influence on

user’s exercising time. Additionally, users perceive a robot compan-

ion as more likable than a robot instructor or a human partner. Fur-

thermore, an adaptive robot increases the associated competence and

quality of relationship compared to an adaptable robot. However, the

results also show that the robot does not always have to exercise along

with the user. In situations where it is not possible, the robot could

also only give encouraging feedback. This thesis backs up earlier find-

ings of using SAR by replicating motivational group exercising ef-

fects found in Human-Human Interaction (HHI). Thus, the evidence

that SARs are a suitable tool for rehabilitative interventions increases

which may convince health experts to consider SAR as a useful thera-

peutic tool. Nevertheless, this thesis evaluated the effects only during

short-term interactions. Thus, proving that the found effects are long-

lasting is essential for future studies.