This paper presents TreeCare, a persuasive mobile game for reducing sedentary behaviour and improving physical activity among adults. The game uses the tree metaphor to create a link between a tree's health and player's physical activity level in the real-world. Each player is initially assigned an empty tree that gradually grows leaves and then fruits as the player becomes physically active (measured using step counts). The tree withers as the player reduces his/her activity level, thereby reinforcing the significance of regular physical activity and the negative effect of sedentary behaviour.
Research has shown that sedentary behaviour poses a cardio-metabolic health risk [
This paper presents a persuasive mobile game, called TreeCare, for promoting
physical activity (such as walking or running) and reducing sedentary behaviour among
adults. The game uses the metaphor of a tree (in a garden) with green leaves and fruits
to represent a player’s physical activity level in the real-world (operationalized using
step counts). The tree’s health deteriorates (reflected by the loss of leaves/fruits) as
player’s activity reduces. TreeCare employs twelve widely used persuasive strategies
in health games design, which are self-monitoring, simulation, reminder, reward,
reduction, praise, suggestion, recognition, competition, cooperation, personalization,
and social comparison. These persuasive strategies are part of the Persuasive Systems
Design (PSD) framework [
In the TreeCare game, a flourishing tree (with green leaves and fruits) represents a player who is consistently physically active in the real-world, but an empty tree with no leaf/fruit represents low or no activity. Each player begins the game with an empty tree which, in turn, gradually grows leaves and fruits as the player becomes physically active (measured using step counts). The tree’s health deteriorates (reflected by the loss of leaves/fruits) as player’s activity reduces, thereby showing the negative effect of a sedentary lifestyle on an individual’s health and the benefit of physical activity. The game has two modes – the “Starter” mode and “Challenger” mode – governed by rules for gaining/losing leaves and fruits.
The Starter mode involves a single player whose initial daily goal is set as 5000 steps. The daily goal can be changed by the player. For every 1000 steps achieved in a day, a green leaf appears on the player’s tree. However, if the player fails to meet his/her daily goal, the tree loses the number of leaves that corresponds to the remaining steps required to meet his/her goal, based on the formula below. ceiling(n) is a function that returns the smallest whole number that is greater than or equal to n where n is a real number. For example, if a player achieves 4200 steps out of 5000 daily goal, he/she will gain 4 leaves but lose 1 leaf.
On the other hand, the Challenger mode is a competitive mode involving multiple players. In other words, individual players compete with one another to achieve (or exceed) the minimum step count goal for a challenge. A player can view active challenges and can join any of them to compete. Also, the player can create a challenge which automatically becomes visible to other players. Every challenge has a minimum step count goal that every player is expected to meet, as well as the expiration date and time. Once a player joins a challenge, he/she will be assigned an empty tree for that challenge. For instance, a player that joins two different challenges is assigned two empty trees – one for each challenge. Thus, as the player becomes physically active (such as running or walking) in the real-world, the health of his/her trees gradually improves. Finally, every challenge has a leaderboard that ranks players in descending order of the total step counts achieved, and the top 3 players are rewarded with a trophy each when the challenge ends.
TreeCare employs twelve widely used PSD strategies in health games design, which are self-monitoring, simulation, reminder, reward, reduction, praise, suggestion, recognition, competition, cooperation, personalization, and social comparison. Table 1 shows the strategies already implemented in the current version of TreeCare, and the corresponding game elements or features.
We implemented TreeCare for Android devices using the Unity framework and Android Studio. Step counts are retrieved in real-time through phone sensors using the Google Fit APIs (i.e., Sensors API, Recording API, and History API). Figure 1 shows sample screens of the TreeCare game. In this paper, we presented a persuasive and fun game, called TreeCare, that motivates its players to be more physically active and less sedentary. The game uses the “tree” metaphor to create a link between a tree’s health and player’s physical activity level in the real-world. The idea is to influence players to increase their physical activity levels (measured using step counts) to make their trees look healthy with green leaves and fruits using various persuasive strategies of the PSD framework. The tree withers as the player reduces his/her activity level, thereby reinforcing the significance of regular physical activity and the negative effect of sedentary behaviour.