the short answer
A fitness lead magnet is a free, specific resource a coach gives away in exchange for an email - a calculator, a checklist, a sample week, a short challenge. The ones that convert solve a single problem your ideal client has today, match the paid offer they would buy next, and end with one clear invitation to talk. Most fail because they are too broad, too long, or never followed up. Pick one narrow promise, deliver a real win, then put a discovery call in front of the people who raised their hand.