These Are 7 Ways to Boost Your Endurance, According to Personal Trainers Marissa Miller Whether you want to PR that 5K, train up for a half marathon, or just make it through your next HIIT workout without feeling like a puddle of mush after those first few reps, there’s one aspect of fitness you’ll want to focus on: building endurance. Though you might associate endurance with running, biking, or swimming mile after mile, there are actually two types of endurance training. Cardiorespiratory endurance refers to your ability to perform sustained cardio-intensive activities (think a marathon, not a sprint), says trainer Ashley Verma, founder of Define London Barre. Muscular endurance, meanwhile, refers to your muscles’ ability to exert force repeatedly or for extended periods of time (think long planks or multiple squat reps).