For most people, the aim of endurance training is to have more in reserve than you need. Office workers, for example, need less endurance than gardeners to do their job. A good workout routine shouldn’t push you right to the brink of exhaustion every time, because even with endurance work, form and technique are important. Stay in control, and don't push yourself too far.
Muscle fibres fall into two categories – there are fast twitch muscles, which power fast movements like jumping, or sprinting, and slow twitch muscles which you use constantly and are harder to wear out. The muscles in your lower back, for example, keep you upright, while your pelvic floor helps keep you continent. You can train these slow twitch muscles to keep them in shape and avoid future problems.
Even Mo Farah didn’t start out by running marathons! When building up endurance, try to increase the volume of your training (how long you train for in total) by no more than 10% per week. Top endurance athletes don’t only focus on their long runs either – vary things with shorter sprint sessions.