Key Investor Signals
Three founders led teams at WHOOP before reuniting at Appex.
Ben Katz, Caroline Shoemaker, and Mats Terwiesch led growth, product, and analytics at before reuniting at , where Katz and Shoemaker held VP and General Manager roles.
AI coach users convert and retain at more than 4x the rate.
HYBRD reports that athletes using HYBRD Brain convert to paying customers and retain at more than four times the rate of users who do not use the AI coach.
Selected for Y Combinator's Fall 2024 batch.
HYBRD joined 's Fall 2024 batch.
Other Positive Signals
- Rated 4.8 from 617 ratings in the US App Store.
- Named the preferred tracking app for training plans.
Team
Ben Katz
Co-Founder & CEO
- Vice President and General Manager for the health and fitness portfolio at Appex, a mobile app roll-up.
- Senior Product Manager on the growth team at WHOOP, rising from associate product manager in two years.
- Spent three years at Wayfair across ecommerce strategy and site navigation analytics.
- Studied entrepreneurship at Babson College.
Matt Ruiters
Co-Founder & CTO
- Spent seven years at Amazon Web Services, ending as Senior Software Engineer on Amazon Connect.
- Tech lead for Amazon Connect Global Resiliency, leading a 15-engineer team while building the initial prototype.
- Tech lead for EC2 metering, the system measuring usage behind the largest revenue stream at AWS.
- Earned a computer engineering degree from the University of Virginia in 2017.
Caroline Shoemaker
Co-Founder & COO
- Rose from Senior Manager of Analytics to Vice President and General Manager at Appex.
- Spent nearly three years at WHOOP, rising from Senior Business Intelligence Analyst to Senior Manager.
- Business intelligence analyst on Wayfair's advanced analytics and insights team.
- Mechanical engineering degree with a statistics minor from Virginia, plus the Tuck Business Bridge at Dartmouth.
Mats Terwiesch
Co-Founder & CPO
- Product Manager for Strain, a core WHOOP app metric, after starting in WHOOP Labs.
- Research Associate at Harvard, publishing on how AI is changing health care delivery in NEJM Catalyst.
- Senior Product Manager for health and fitness at Appex.
- Economics degree from Bates College with Phi Beta Kappa, and a prize-winning thesis applying machine learning to hospital discharge prediction.
Product
HYBRD is a subscription coaching app for athletes who combine strength and endurance training. It brings workout data, structured programs and an AI coach into one system that adjusts training around each athlete's goals and schedule.
Combined strength and endurance plans
Users can follow programs pairing strength work with running, or triathlon goals. This creates a single schedule across disciplines that are usually managed through separate apps.
Training data in one place
HYBRD aggregates workout data from 16 connected platforms and can log strength sessions from typed text, whiteboard photos or screenshots. Its HYBRD Score shows strength and cardio performance separately.
AI coach that changes the plan
HYBRD Brain can rewrite the training week when equipment, availability or physical condition changes. Updated workouts can then be sent to connected watches and training devices.
Market Overview
Hybrid training has moved into the mainstream as more athletes combine strength and endurance in the same program. More than half of users track multiple activity types, while users uploaded over 400 million strength workouts in 2025. HYROX adds a fast-growing competitive format, with more than 1.3 million participants expected during its 2025/26 season.
This behaviour supports a large subscription market. The global fitness-app market reached $12.1 billion in 2025 and is projected to reach $33.6 billion by 2033. HYBRD addresses the gap between single-discipline tools by combining strength, endurance and adaptive programming in one product.
Share of Strava users who track more than one activity type.
Strength workouts uploaded to Strava in 2025.
Participants expected worldwide during the 2025/26 season.
Projected growth from 2025 to 2033.
Comparable Outcomes
MapMyFitness
MapMyFitness built GPS-based apps letting people map, record and share workouts with others, integrating with more than 400 devices and sensors. Under Armour acquired MapMyFitness for $150 million in 2013. At the time the platform had over 20 million registered users, roughly 9 million monthly active users, and about 83 million app installs.
MyFitnessPal
MyFitnessPal built a calorie and nutrition logging app with a large free user base and a paid premium tier. Under Armour acquired MyFitnessPal in February 2015 for $475 million, when the app had roughly 80 million users.
Runtastic
Runtastic built more than twenty running, fitness and endurance apps, reaching 140 million downloads and around 70 million registered users. Adidas acquired Runtastic in August 2015 for €220 million.
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Sources
This profile was built from public company materials, ecosystem sources, market references, and professional profiles.