###### Abstract
Figure 1: Structure of blocks in blockchain. Hashing is a one-way function, meaning that the original data cannot be reconstructed from the hash; it only represents the data. This characteristic enables an alternative storage model called off-chain storage. In this model, the original data is stored in external databases, while the blockchain only stores the hash values of that data. This allows data to be stored privately, with the blockchain serving as a secure reference for verifying the integrity of the data without actually storing it. This approach can be especially useful in physical activity, exercise-based rehabilitation, fitness, sport, and exercise-based therapeutics (PARFSET) cases, where data is collected in various ways, such as through wearable sensors, and stored locally on personal devices. Additionally, private PARFSET data can be stored in publicly available databases in encrypted form. Some meta-data, such as the ownership or timestamps can be public. At the same time, the encrypted data can be easily shared, while the data owner retains control over decryption by choosing who can access the decryption key. Another key feature of blockchain technology is the use of smart contracts. These are self-executing programs stored on the blockchain that automatically enforce the terms of an agreement once specific conditions are met, eliminating the need for intermediaries. For example, in online purchases, a smart contract can hold the buyer's payment until the seller delivers the product or service. Once the conditions are verified, the smart contract releases the payment automatically. This process ensures that both parties fulfill their obligations without needing a third-party mediator. This concept can also be applied to other types of transactions involving different parties or assets, including information exchange. This highlights how smart contracts could be beneficial in PARFSET information cases, where information itself is the asset being managed. In addition to storing PARFSET records, blockchains can also store audit logs. For example, when a user's physical activity record is requested in an off-chain setup, the request time and the identity of the requester can be recorded in the blockchain by the data provider. This adds an additional layer of accountability and traceability to blockchain-based data management. Blockchains can be enhanced by a consensus mechanism. When a new block is created in a blockchain, it must first be validated by the participating nodes in the network through a distributed agreement mechanism. This is particularly important in cryptocurrencies, where consensus among network participants is required to confirm financial transactions. Although we did not find any work using a consensus mechanism for PARFSET, it is conceivable that it could be utilized in innovative ways to both match the nature of data in PARFSET and enhance data integrity, fairness and trust in these applications. The problem we investigate in this study is how blockchain technology influences quality attributes in PARFSET systems. Given the large volume of data in this domain and its distinct challenges compared to medical and health-related information, a focused and systematic approach is essential to assess a blockchain's impact in this area. Therefore, in this study, we review the application of blockchain technology in PARFSET and discuss the quality attributes achieved through these applications. The aim is to contextualize blockchain technology within PARFSET and demonstrate how it can enhance specific quality attributes in this domain. It is important to note that there are several commercial software applications that claim to use blockchain technology in PARFSET but lack peer-reviewed documentation in scientific journals or proceedings. These applications often make unverified claims and were therefore excluded from our review. It should also be noted that the application of blockchain technology to electronic health records (EHRs) may provide similar benefits to its use in PARFSET.