Aerobic endurance is the ability of the heart and lungs to deliver oxygen to the working muscles. To stimulate the physiological adaptations required to become more oxygen proficient requires many hours of training, with top age-groupers ticking off 300-600hrs of annual sessions to hit the top 25% overall. Ultimately, this increases your maximum oxygen uptake or VO2max. Longer, moderate-intensity sessions are a foundation to boost aerobic endurance.
Muscular endurance, on the other hand, is the ability of the muscles – in general, your slow-twitch muscle fibres – to sustain repeated production of force at low to moderate intensities for extended periods of time. In tri terms, there’s no point in having a strong heart and lungs if your musculoskeletal system can’t handle the stress of thousands of repetitions, whether it’s front crawl, pedalling or striding.
Naturally, your muscular endurance is built from consistent, progressive triathlon training. But your swim, bike and run sessions should be complemented with weight or bodyweight training. Press-ups, tricep dips and core training are all ways to boost muscular endurance.