The Importance of Work to Rest Ratio in Endurance Sport Training

Time trial type racing such as triathlon and marathon running has a very different physical demand than races such as road cycling where race dynamics play a big role in determining success.

Triathlon and marathon running generally require athletes to maintain their highest sustainable effort for as long as possible with very little fluctuation in intensity.

As a result, training is able to be very controlled where the training purely aims to:

  1. Build aerobic capacity: “the size of the athlete’s engine”
  2. Increase the athlete’s ability to maintain a higher steady state intensity:  “increase the strength of the athlete’s engine”

A common issue with training programs is being able to identify what physiological adaptation the training program is trying to achieve.

Work to Rest Ratio

An example of this is the common prescription of interval training based off distance (eg. 1km efforts with a standardised rest period).

What is the issue with 1km efforts? Nothing, as long as you understand the purpose of the 1km effort. Interval training is the manipulation of work time and rest time. Changes in work to rest ratio changes the purpose of the session.

Example. “4 x 1km efforts with 4mins passive rest”

Athlete A runs 1km in 4 mins. Therefore, the session is 1:1 work to rest. On the other hand, Athlete B runs 1km in 6 mins resulting in a 2:3 work to rest ratio.

As a result, interval training based on distance only works when distances are calculated based on the required work time. 

What Is the Ideal Work to Rest Ratio?

Base Training

1:0 (Continuous effort)

Zone 2 intensity

Aims to increase aerobic capacity by improving mitochondria function, strength of the heart and slow twitch muscular endurance. In order to run a marathon, the body needs to be able to perform for 42.2km.

This training looks to accumulate time at a low intensity to build the size of the athlete’s engine and build muscular strength.

Aerobic Capacity/ VO2 Development


90-95% VO2max

Aims to improve aerobic capacity by increasing the athlete’s ability to increase oxygen uptake and utilisation. Eg. 2 mins at 90-95% cycling at max aerobic capacity followed by 2 mins of complete rest.

By improving top end cycling power and running speed, we get a trickle down effect to overall aerobic performance.

Threshold (2-3:1)


100-110% lactate threshold

Aims to improve maximal lactate steady state (the highest sustainable intensity before blood lactate begins accumulating faster than it is being removed). As mentioned earlier, triathlon and marathon running generally require athletes to maintain their highest sustainable effort for as long as possible with very little fluctuation in intensity.

Racing is not performed at zone 2 nor high zone 5-6. Threshold training is specific training for time trial efforts. Eg. 6mins at 110% lactate threshold running pace followed by 3 mins active recovery. During the 6 mins, blood lactate concentration increases, comes down slightly during the 3 mins active recovery, then increases further as the athlete completes each set.

Anaerobic Capacity (1:2)


> VO2 max

Aims to increase the body’s ability to store glucose, strengthen fast twitch muscle fibres and increase top speed repeatability. Classic speed work or Sprint Interval Training to improve top end performance.

This is less applicable for time trial style racing but may still be effective to improve speed and power. 


Fundamentally, manipulating work to rest ratio dictates what adaptation is achieved with each training session. In a very controlled sport such as triathlon and marathon running, structuring and planning training correctly is the most effective way to ensure athletes peak at the right time during their race season.

If this topic interests you and you’d like to know more about the work we do with endurance sports, please contact our Exercise Physiologist Justin Trang.

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