Fitness trackers often fail people with obesity by underestimating their energy burn, leading to discouraging results and misguided health data. A scientist's frustrating experience in an exercise class with his mother-in-law where her effort wasn t reflected on the fitness leaderboard sparked a breakthrough. His team at Northwestern developed a new open-source smartwatch algorithm that accurately captures energy expenditure for individuals with obesity, rivaling gold-standard lab equipment and paving the way for more inclusive, empowering health tracking.