By Eoin Flynn, Running Coach Ireland
www.runningcoach.ie | @running_coach_ireland
The Importance of the Long Run - How long should it really be?
As arguably the most exciting day of the Irish running calendar edges closer — now just over 11 weeks away — thousands of runners are focusing each weekend on the most important session in their weekly training cycle: the Long Run. Whether your goal is to simply complete the famous 26 miles or hit a specific time target, the long run holds a special status in marathon preparation for three key reasons: aerobic conditioning, physiological adaptation, and mental resilience.
Why the Long Run Matters So Much
Aerobic Conditioning
The marathon is a test of your aerobic system’s efficiency — your ability to produce energy using oxygen over extended durations. Long runs are the most direct way to increase mitochondrial density (your body’s energy factories), improve fat metabolism, and raise your aerobic threshold — the pace you can sustain without accumulating fatigue-inducing by-products. Simply put: the more aerobic capacity you have, the easier it feels to hold race pace.
Physiological Adaptation
Long runs help develop your muscular durability, glycogen storage, and connective tissue strength. They condition your body to tolerate the pounding of 26.2 miles. But there’s a caveat: longer isn’t always better. There’s a point where benefits plateau and risks rise — especially past 2h30m of running.
One of my core marathon principles for my marathon squad at Running Coach Ireland is that no long run should exceed 2.5 hours — regardless of ability or pace. Maximum return from minimum invest is a phrase I use a lot and thankfully controlling the time of my squad’s long runs has led to a very low injury rate while also being backed up with a very high PB % rate on race day.
Why do I recommend capping the long run at 2.5 hours? Beyond this threshold, the risks of tissue breakdown, chronic fatigue, and injury start to outweigh the physiological rewards. It’s better to be consistently good through July to October than gamble with Long Runs that are too long to handle and result in a niggle or injury and potential knock-out blow ahead of race day.
Mental Rehearsal
The marathon is as much a psychological challenge as a physical one. Long runs teach you to stay calm through fatigue, to manage your thoughts, and to reinforce race-day confidence. Include hills in your Long Runs to replicate the hills of the Dublin Marathon course and work on your mental game as you stay calm and focused moving through each hill, the ups and the downs!
How Long Should the Long Run Be?
From mid-August onward, long runs should fall in the 2 to 2.5 hour range, not going above 2.5 hours as mentioned above. Here’s a suggested timeline:
- Early August: 1h45 – 2h00 (easy Zone 1–2 effort)
- Late August through September to early October: 2h15 – 2h30 (peak build)
