## 4 Results: Example Design of Parent-Child Interactive Exercise Bike
### User Satisfaction Survey  
To further verify the feasibility of the design scheme, we invited 12 parents in Wuhan to evaluate it, following the same assessment process as that of the expert panel.  
1. Parents were asked to evaluate the performance of every scheme indicator and acquired the fuzzy comprehensive assessment matrix \(E\) for each indication: \[E_{A}=\begin{bmatrix}7&3&1&1&0\\ 6&3&1&1&1\\ 8&4&0&0&0\\ 7&2&2&1&0\end{bmatrix}\] (26) \[E_{B}=\begin{bmatrix}6&4&0&1&1\\ 7&3&0&2&0\\ 6&5&1&0&0\\ 5&4&2&0&1\\ 8&2&2&0&0\end{bmatrix}\] (27)\[E_{C}=\begin{bmatrix}5&5&0&2&0\\ 8&3&0&1&0\\ 6&4&1&0&1\\ 9&2&1&0&0\\ 5&3&3&0&1\end{bmatrix} \tag{28}\] \[E_{D}=\begin{bmatrix}7&4&1&0&0\\ 6&4&0&1&1\\ 6&3&1&1&1\end{bmatrix} \tag{29}\]
2. The matrices \(E_{A}\), \(E_{B}\), \(E_{C}\), and \(E_{D}\) are obtained by normalizing the matrices, respectively, and then utilizing the weighted average fuzzy operator via the synthesis operation of the index weights in Tables 4-7 and the corresponding evaluation matrix \(E\), the evaluation weight vector \(Z\) of the criterion layer index of the design scheme can be determined. Finally, it is thus possible to create a fuzzy comprehensive evaluation matrix of target layer indicators: \[Z_{P}=\begin{bmatrix}Z_{A}\\ Z_{B}\\ Z_{C}\\ Z_{D}\end{bmatrix}=\begin{bmatrix}0.5871&0.2487&0.0847&0.0656&0.0140\\ 0.5169&0.3012&0.0858&0.0466&0.0495\\ 0.4981&0.3158&0.0848&0.0627&0.0387\\ 0.5311&0.3018&0.0627&0.0521&0.0521\end{bmatrix}\] (30) 3. Likewise, it is possible to compute the comprehensive evaluation vector for the parent-child interactive exercise bike design scheme: \[Q=W_{P}\times Z_{P}=\begin{pmatrix}0.5394&0.2863&0.0816&0.0570&0.0358\end{pmatrix}\] (31) 4. Ultimately, the total assessment score for the scheme is calculated: \[L=Q\times r=82.3742\] (32)  
Based on the corresponding relationship between the assessment levels and assessment scores, the ultimate score of the design scheme falls between very satisfied and satisfied. It indicates that parents are relatively satisfied with the design scheme.  
In addition, we invited 10 parent-child families to conduct satisfaction interviews regarding the design of the parent-child interactive exercise bike, targeting both parents and children separately. By conducting separate interviews with parents and children, we can more accurately obtain the needs and feedback of different user groups. The Informed Consent form can be found in the Supplementary Materials. The User Satisfaction Interview Outline can be found in Tables A1 and A2. The parent version of the outline focuses on functionality, safety, and flow-clutch experience, while the child version places greater emphasis on interestingness and interactivity. This role-based interview approach can provide a more comprehensive basis for optimizing the design scheme. Before interviewing the children, we invited the parents to sign an Informed Consent form. The Informed Consent form can be found in the Supplementary Materials. The interviews with 10 parent-child families revealed high satisfaction with the design, particularly its ability to promote family bonding, engagement, and safety. Parents appreciated features like the foldable design and safety mechanisms, while children enjoyed the interactive games and real-time feedback. However, both groups suggested improvements, such as enhancing durability, adding more games, and incorporating advanced features like AI-based parent-child interaction. These insights will guide future design iterations to better meet user needs and expectations.