Moving Beyond the Black Box: How I Built a Real-Time Voice Fitness Coach using Next.js 15, Convex, & Vapi.ai

Moving Beyond the Black Box: How I Built a Real-Time Voice Fitness Coach using Next.js 15, Convex, & Vapi.ai I've used a lot of fitness apps. I've followed their calorie numbers, done their workout splits, and trusted their recommendations - all without ever understanding where any of it came from. The number just appeared, authoritative and unexplained, and I was supposed to trust it. Eventually, I stopped. Not because the numbers were wrong. Because I had no reason to believe they were right.