Make a fast 5 km part of your marathon training

Focusing on a fast 5 km time can bolster your marathon training. Here are some tips and workouts that helped me speed up over 5000 metres.
Run a fast 5k to improve your marathon time

Want to run a fast 5 km?

Even as a marathoner, the answer should always be yes!

 Let me break a few of the reasons why:

  • It’s short enough to make considerable gains with your speed; 
  • Running 5 km races at significantly faster than marathon pace will eventually make that pace feel easier and more sustainable;
  • It is still far enough to improve your stamina, strength and endurance. (I’ve run a fast 5 km race where I’ve been more perceptibly tired crossing the line than after a marathon);
  • It’s a great distance to get familiarised with both fun runs and competitive racing.
  • It’s a distance that’s likely to get you onto a track.
  • It is a distance that can help you better understand your own physicality and running strengths;
  • It can give you a secondary goal within your marathon training. This can serve as a milestone to track progress and break-up the monotony of the preparation block. 

42.2 is the goal, but 5 will see you thrive

A lot of runners take the view that running a marathon is solely about endurance: keeping the legs steadily ticking over at a tough, but relatively comfortable and sustainable pace.

And that’s a fine view to take! Simply finishing a marathon is a major accomplishment. And if you’ve reached a goal pace you’re totally satisfied with that’s awesome!  

However, if you’re like me and rarely satisfied — if your aim is to start speeding-up over the half and full marathon distances, and to continue striving for ever more personal bests, you can start to make some serious gains by focusing on some fast 5 km efforts. 

If you’re used to logging high mileage, a 5 km effort at marathon pace should feel relatively easy.

Let’s say your marathon pace is 4 minutes per kilometre. That’s solid, and good for a 2:49.00 marathon finishing time (which is a Boston Qualifier).

If we extrapolate, that same pace will have you running 20 minutes for 5 km. If you’re a runner of this calibre, that is likely achieved regularly (and routinely) on tempo runs and in workouts.   

You can (and should) push harder!

If you’re running a marathon that fast, you should be capable of running a 5 km race at around 3:30/km pace. That would mean finishing somewhere between 17 and 18 minutes. (In fact, if you use the race predictor calculator over at Runner’s World you get a 17:31). 

In the book Daniels’ Running Formula, the famous coach Jack Daniels reminds readers that the 5k is a “primarily aerobic” distance but is usually performed (in competitive races) at between 95 and 98 per cent of VO2 Max.

“To be sure,” Daniels writes, “these are not fun intensities to hold for prolonged periods.” 

Thanks Jack! It’s an understatement of epic proportions, but worth acknowledging.

I have finished fast 5 km efforts feeling absolutely cooked, my legs burning and my brain spinning out of control. (And unlike some wiser runners who simply collapse and allow themselves several moments of stillness to recover in the aftermath, I usually stagger and stumble around like someone more than a little inebriated, trying to slap embarrassing high-fives and talking too loudly).  

Embrace the pain and befriend discomfort  

But afterwards, when I’m well and truly recovered, and no longer run-drunk, I can reflect on some important outcomes.

I have run fast (so fast, in fact, that my marathon pace would feel almost like a float or recovery). 

In addition, I have tested my fitness and gained confidence in the process.

And finally, I have entered a state of pain and discomfort that will benefit me in longer distance races if I need to match (or make) a surge, or finish the last stretch of a marathon strong. 

The 5 km distance is about speed and pushing your body to new realms of discomfort. It’s also about familiarising yourself with what that red-line, anaerobic threshold effort feels like.

Why do you need to do that? So when you need to get there again you’re prepared, and it doesn’t hit you like a sucker punch. 

How can you improve and run a fast 5 km time? 

The first common mistake is underestimating the distance. A lot of newcomers thing the 5 km is a nice, relatively easy gateway distance.

Five kilometres seems a lot more manageable than 42.2 km, but it can still be a wrecking-ball of an event, if you’re under prepared.

You still need to have some structured training, and importantly, you should run further than 5 km efforts in your preparation 

For more seasoned distance runners and marathoners, the aerobic and endurance base should already be there, so let’s talk speed. 

There are some great targeted interval workouts that can help get you primed to run a fast 5 km and hit a new PB.

When the muscles are placed under this strain, provided these workouts are integrated into a more holistic training plan, they will adapt and you’ll begin to see your speed improve. 

A few sample workouts

Here are a few sessions that I have integrated into my program, which have helped with my speed. *I’ve shaved about 2 minutes off my 5 km time over the last two years.   

400/800/1 KM reps: Pretty straightforward and self-explanatory. Map out a set distance, run it at race pace or slightly faster. Have a standing or jogging recovery of between one and three minutes then go again. If you want to add a layer of difficulty, get after these reps on a hill. I was working on my speed by doing 800m hill reps! Fast-up, jog-down, repeat.

Deek’s Quarters: This is best performed on a track. The workout was popularised by the great Australian marathon runner (and former world record holder) Rob de Castella; and it will definitely get the blood pumping. PodiumRunner has a good explanation but the basic gist is this: 8 x 400 metre (one lap) efforts. You don’t stop to rest between each set; instead you run a 200 metre (half lap) float. 

The effort should be at or faster than your goal 5 km pace; the float pace can vary. It could be at marathon pace (or slightly slower). The catch is that you’re never fully recovering after each set. It’s meant to simulate (and be an excellent predictor for) a 5 km race. 

Another classic Australian workout

Mona Fartlek: This is a structured fartlek session, named after another Aussie running legend, Steve Monaghetti. It’s a continuous 20 minute workout that can be done on the track, road or trails. It might seem hellish the first time around (and every time afterwards), but it pays off.

  • First: 2 x 90 seconds hard, 90 seconds float (Total 6 mins) 
  • Straight into: 4 x 60 seconds hard, 60 seconds float (Total 8 mins)
  • Followed by: 4 x 30 seconds hard, 30 seconds float (Total 4 mins)
  • Finish with: 4 x 15 seconds sprint, 15 seconds float (Total 2 mins) 

It’s a great workout for practicing surges, and more importantly, working on your recovery and quickening that float pace.

This is actually where I got most confused when I started doing this workout. I foolishly thought the gains would come from hitting the efforts at max capacity, so I was running like a bat of hell. This would leave me completely drained for the floats. They’d turn into a slow jog (verging on a crawl) before the next sudden outburst. By the end, I’d be keeled-over but scratching my head wondering how I hadn’t covered more ground.

Slowly, I began to realise the optimal strategy: run fast but don’t annihilate yourself (especially out of the gate). Focus on quickening the floats, and training to recover at ever faster paces. 

There are no shortages of great 5 km-specific workouts to discover and trial. Check out Sweat Elite, or McMillan Running for some inspiration. Or do some reconnaissance work on Strava.

There’s no need to reinvent the wheel. But then again, the awesome thing about intervals is that you can get creative and make-up your own. 

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