Out and back (sub-threshold run)

The “out and back” workout is the fastest aerobic workout you will do during the aerobic phase. It teaches you to run at the fastest pace you can sustain aerobically, that is, burning mainly fat and oxygen for fuel and incurring little or no oxygen debt. This workout will allow you to run faster before you fatigue because oxygen-independent metabolism (anaerobic) sets in later. Scientifically, this pace is run at the intensities below the  “lactate threshold” or “maximal steady state” our preferred term used by Arthur Lydiard.

“We call the limit the maximum steady state; the level at which you are working to the limit of your ability to breathe in, transport and use oxygen. When you exercise beyond that maximum steady state, your running becomes anaerobic. Chemical changes occur in your body’s metabolism to supply the oxygen you need to supplement what you can breathe in, transport and use.” – Arthur Lydiard, Running with Lydiard

This workout is particularly crucial for half-marathon, marathon and ultra-marathon runners.


High-end aerobic run.

  1. Choose an out and back course of similar difficulty each way or slightly faster on the home journey.
  2. Warm-up briefly.
  3. Run at a comfortably fast pace.
  4. Take your split at half way and the final time at the finish.
  5. Compare the times for each half.

This is one of the most difficult exercises for runners to pace correctly initially: take your time and treat each “out and back” as an opportunity to improve your pacing rather than just increasing pace blindly.

Important points:

  • Attempt to run even pace or negative splits (second half faster).

“Get yourself running fit so that you are capable of running long distances continuously. Do this by running on out and back courses. By running out, say 10 minutes and turning around and running back in nearly the same time. If it takes longer to return, then you should realize that you went too fast on the outward journey and so are forced to slow down upon the return journey. You will soon learn about your present capabilities and fitness and so adjust your running efforts accordingly.” – Arthur Lydiard, Arthur Lydiard’s Athletic Training

Rate of perceived effort:

4-7 (75%-85% VOmax)

Experienced competitors/elites:

The value of this workout increases for experienced competitors and elites. The ability to increase VO2 max (maximum oxygen uptake) decreases over time whereas the lactate threshold remains very trainable and will allow experienced athletes to run at increasingly higher percentages of their VO2 max for longer periods of time. Even for an elite athlete the reduced fatigued from running more at sub-threshold than threshold benefits the overall weekly training effort and general health and well-being.

Lactate threshold pace will generally be around 10-15 seconds per mile slower than 5k race pace for elites whereas it is closer to 10k pace for less trained runners and slower than 10k pace for runners with 50-minute and slower 10k times. Go by intensity first and pace second.


  • Fastest aerobic

“When the maximum steady state, the aerobic exercise upper level, is low, you can be running anaerobically at a comparatively low speed; as the maximum steady state is pushed upwards, the slower anaerobic speeds become aerobic (and economical). And, if training progresses on this principle – that aerobic exercise is 19 times more economical than anaerobic – then the possibilities of running farther and faster aerobically (and with economy) must increase.” – Arthur Lydiard, Running with Lydiard


  • Pacing
  • Rhythm
  • Knowing your recovery pace

Biggest mistakes:

  • Starting out too fast and having to slow down.
  • Maintaining too high a heart rate to sustain your pace and becoming anaerobic
  • Running too slowly at the beginning so that the split for the second half of the run is more than 10% faster than the first.


Even courses will provide the most reliable splits but you do not have to restrict yourself to this. In preparation for mountain races, some of our runners have employed a course with gentle uphill on the way out and gentle downhill on the way back, mirroring to an extent the up and down mountain races of these athletes. This does not have to be a problem for the workout:

” If it’s windy or there’s a slight elevation change between the start/finish and the halfway point, try to arrange it so that the more difficult direction is negotiated first. This will reinforce negative splits and you’ll walk away from the workout in a more positive frame of mind.” – Lorraine Moller, Running Times, Nov 2010


Circuit runs: This variation of the “Out and Back” is another trademark Lydiard-workout which we recommend in the earlier parts of the base (aerobic) phase. More information on it in the dedicated entry on “Circuit Run”.

Lactate (aerobic) intervals and repetitions: similar in principle to standard intervals/repetitions, these are workouts where the fast repetitions are run at lactate threshold pace. For maximum effect, these repetitions should be slightly longer (1 mile or upwards for experienced athletes, approx. 5-7 minute running time for less experienced runners). As you are not incurring oxygen debt in this type of interval training, you should keep your rests brief such as one minute easy jogging. Sample workouts include: 3-5 mile repetitions with 1 minute easy jog recovery or 2×2 miles with 2 minute easy jog recovery.

Super-threshold intervals and repetitions: as above, but your repetitions are slightly faster than your lactate threshold (you are “dipping your toes into anaerobic waters”) with slightly shorter recovery. Sample workouts include: 2 sets of 3x1km repetitions with 45 seconds recovery between repetitions and 2 minute recovery between sets. Recovery can be easy jogging, walking or total rest.

These two variations are useful for runners who are comfortable with their own pacing but wish to mix-up their training or maintain lactate threshold speed more consistently than they are currently able to do through continuous running.

Progression runs: This type of sub-lactate threshold runs are similar to normal aerobic runs where portions are run at lactate threshold pace. A “progression run” simply means that you increase your pace throughout your workout until you are running at your maximal steady state or just beyond it. Several examples of this workout are given in “Advanced Marathoning” (Pete Pfitzinger/Scott Douglas) such as:
  • 10 miles (16km) aerobic with 4 miles (6km) at maximum steady state
  • 12 miles (19km) aerobic with 7 miles (11km) at maximum steady state

Both the above workouts are for highly trained marathoners running 85 miles or more per week but serve as an example of the proportion of aerobic to steady state running you could choose to do. You could be more pragmatic: if you want to practice a fast last 5km of your next half-marathon, why not run a 15km run with the last 5km at maximal steady state pace. Use your imagination.

Progression runs are particularly useful for experienced half-marathon and marathon runners who need the ability to sustain faster aerobic paces against mounting fatigue.

Cruise-intervals: similar to progression runs but you can intersperse your maximal steady state running at any point of the workout depending on what you are trying to simulate. Do you expect to need a fast start and finish? In that case perhaps a session such as the following would be appropriate:

  • 3km @ max. steady state pace + 5km aerobic running + 3km @ max steady state pace.

The term cruise-interval denotes any type of aerobic workout with maximal steady state repetitions inserted. An extreme example could be 20km run with every second kilometre being at maximal steady state. This may be a useful simulation for off-road runners and others who need to be able to handle undulating terrain and regular changes in intensity.

“One of the major advantages to lactate threshold training is that the intensity represents the fastest pace at which your athletes can train without excessive fatigue. That’s because the workouts remain aerobic. Lactate threshold training is the best aerobic bang for your buck.” – Dr Jason Karp, The Three Players of Distance Running

Parts of the workout descriptions are adapted from BreakThrough Running with permission.

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