Sunno Fitness: A Fitness Coaching Platform Using Digital Skinfold Caliper Data and Isolation Forest Algorithm for Data-Driven Performance Monitoring

Abstract

The integration of digital tools into fitness coaching has become increasingly important for delivering personalized and data-informed guidance. Despite this need, many practitioners continue to rely on manual tracking or costly body composition devices that lack seamless data integration. This study developed Sunno Fitness, a web-based coaching platform that combines a custom Bluetooth-enabled digital skinfold caliper with the Isolation Forest algorithm to support data-driven performance monitoring. The project employed a Developmental Research Design guided by Agile methodology. The hardware system incorporated an ESP32 microcontroller and an AS5047P magnetic rotary sensor to digitize skinfold measurements, while the software platform automated the Jackson–Pollock 3-site method and analyzed client progress. System validation was conducted through a two-phase testing procedure involving 31 participants. Results showed that the digital skinfold caliper achieved high precision, with a negligible mean difference of –0.01 mm and a percent error of 2.15% relative to a manual caliper. Automated body fat computation demonstrated strong agreement with manual calculations, reflected by a 0.01 percentage point mean difference and a 1.21% error rate. Higher variance observed when compared to Bioelectrical Impedance Analysis (21.87% error) was attributed to inherent methodological differences rather than hardware limitations. The machine learning component, validated using four health-related proxy datasets, effectively detected anomalies and distinguished long-term trends from data noise. Additionally, the web platform demonstrated reliable performance, achieving a 100% notification delivery rate with an average latency of under 1.5 seconds. Overall, Sunno Fitness offers a validated, cost-effective solution that integrates accurate body composition assessment with intelligent, real-time monitoring to enhance modern fitness coaching.